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This manual is last updated 28 January 2025 for version 3.8.9 of GnuTLS.

Permission is granted to copy, distribute and/or modify this
     document under the terms of the GNU Free Documentation License,
     Version 1.3 or any later version published by the Free Software
     Foundation; with no Invariant Sections, no Front-Cover Texts, and
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INFO-DIR-SECTION Software libraries
START-INFO-DIR-ENTRY
* GnuTLS: (gnutls).		GNU Transport Layer Security Library.
END-INFO-DIR-ENTRY

INFO-DIR-SECTION System Administration
START-INFO-DIR-ENTRY
* certtool: (gnutls)certtool Invocation.	Manipulate certificates and keys.
* gnutls-serv: (gnutls)gnutls-serv Invocation.	GnuTLS test server.
* gnutls-cli: (gnutls)gnutls-cli Invocation.	GnuTLS test client.
* gnutls-cli-debug: (gnutls)gnutls-cli-debug Invocation.	GnuTLS debug client.
* psktool: (gnutls)psktool Invocation.	Simple TLS-Pre-Shared-Keys manager.
* srptool: (gnutls)srptool Invocation.	Simple SRP password tool.
END-INFO-DIR-ENTRY

File: gnutls.info,  Node: Top,  Next: Preface,  Up: (dir)

GnuTLS
******

This manual is last updated 28 January 2025 for version 3.8.9 of GnuTLS.

* Menu:

* Preface::
* Introduction to GnuTLS::
* Introduction to TLS::
* Authentication methods::
* Hardware security modules and abstract key types::
* How to use GnuTLS in applications::
* GnuTLS application examples::
* System-wide configuration of the library::
* Using GnuTLS as a cryptographic library::
* Other included programs::
* Internal architecture of GnuTLS::
* Upgrading from previous versions::
* Support::
* Error codes::
* Supported ciphersuites::
* API reference::
* Copying Information::
* Bibliography::
* Function and Data Index::
* Concept Index::

File: gnutls.info,  Node: Preface,  Next: Introduction to GnuTLS,  Prev: Top,  Up: Top

1 Preface
*********

This document demonstrates and explains the GnuTLS library API. A brief
introduction to the protocols and the technology involved is also
included so that an application programmer can better understand the
GnuTLS purpose and actual offerings.  Even if GnuTLS is a typical
library software, it operates over several security and cryptographic
protocols which require the programmer to make careful and correct usage
of them.  Otherwise it is likely to only obtain a false sense of
security.  The term of security is very broad even if restricted to
computer software, and cannot be confined to a single cryptographic
library.  For that reason, do not consider any program secure just
because it uses GnuTLS; there are several ways to compromise a program
or a communication line and GnuTLS only helps with some of them.

Although this document tries to be self contained, basic network
programming and public key infrastructure (PKI) knowledge is assumed in
most of it.  A good introduction to networking can be found in [*note
STEVENS::], to public key infrastructure in [*note GUTPKI::] and to
security engineering in [*note ANDERSON::].

Updated versions of the GnuTLS software and this document will be
available from <https://www.gnutls.org/>.

File: gnutls.info,  Node: Introduction to GnuTLS,  Next: Introduction to TLS,  Prev: Preface,  Up: Top

2 Introduction to GnuTLS
************************

In brief GnuTLS can be described as a library which offers an API to
access secure communication protocols.  These protocols provide privacy
over insecure lines, and were designed to prevent eavesdropping,
tampering, or message forgery.

Technically GnuTLS is a portable ANSI C based library which implements
the protocols ranging from SSL 3.0 to TLS 1.3 (see *note Introduction to
TLS::, for a detailed description of the protocols), accompanied with
the required framework for authentication and public key infrastructure.
Important features of the GnuTLS library include:

• Support for TLS 1.3, TLS 1.2, TLS 1.1, TLS 1.0 and optionally SSL
     3.0 protocols.

• Support for Datagram TLS 1.0 and 1.2.

• Support for handling and verification of X.509 certificates.

• Support for password authentication using TLS-SRP.

• Support for keyed authentication using TLS-PSK.

• Support for TPM, PKCS #11 tokens and smart-cards.

The GnuTLS library consists of three independent parts, namely the "TLS
protocol part", the "Certificate part", and the "Cryptographic back-end"
part.  The "TLS protocol part" is the actual protocol implementation,
and is entirely implemented within the GnuTLS library.  The "Certificate
part" consists of the certificate parsing, and verification functions
and it uses functionality from the libtasn1 library.  The "Cryptographic
back-end" is provided by the nettle and gmplib libraries.

* Menu:

* Downloading and installing::
* Installing for a software distribution::
* Document overview::

File: gnutls.info,  Node: Downloading and installing,  Next: Installing for a software distribution,  Up: Introduction to GnuTLS

2.1 Downloading and installing
==============================

GnuTLS is available for download at:
<https://www.gnutls.org/download.html>

GnuTLS uses a development cycle where even minor version numbers
indicate a stable release and a odd minor version number indicate a
development release.  For example, GnuTLS 1.6.3 denote a stable release
since 6 is even, and GnuTLS 1.7.11 denote a development release since 7
is odd.

GnuTLS depends on ‘nettle’ and ‘gmplib’, and you will need to install it
before installing GnuTLS. The ‘nettle’ library is available from
<https://www.lysator.liu.se/~nisse/nettle/>, while ‘gmplib’ is available
from <https://www.gmplib.org/>.  Don't forget to verify the
cryptographic signature after downloading source code packages.

The package is then extracted, configured and built like many other
packages that use Autoconf.  For detailed information on configuring and
building it, refer to the ‘INSTALL’ file that is part of the
distribution archive.  Typically you invoke ‘./configure’ and then ‘make
check install’.  There are a number of compile-time parameters, as
discussed below.

Several parts of GnuTLS require ASN.1 functionality, which is provided
by a library called libtasn1.  A copy of libtasn1 is included in GnuTLS.
If you want to install it separately (e.g., to make it possibly to use
libtasn1 in other programs), you can get it from
<https://www.gnu.org/software/libtasn1/>.

The compression library, ‘libz’, the PKCS #11 helper library ‘p11-kit’,
the TPM library ‘trousers’, as well as the IDN library ‘libidn’(1) are
optional dependencies.  Check the README file in the distribution on how
to obtain these libraries.

A few ‘configure’ options may be relevant, summarized below.  They
disable or enable particular features, to create a smaller library with
only the required features.  Note however, that although a smaller
library is generated, the included programs are not guaranteed to
compile if some of these options are given.

--disable-srp-authentication
--disable-psk-authentication
--disable-anon-authentication
--disable-dhe
--disable-ecdhe
--disable-openssl-compatibility
--disable-dtls-srtp-support
--disable-alpn-support
--disable-heartbeat-support
--disable-libdane
--without-p11-kit
--without-tpm
--without-zlib

For the complete list, refer to the output from ‘configure --help’.

---------- Footnotes ----------

(1) Needed to use RFC6125 name comparison in internationalized
domains.

File: gnutls.info,  Node: Installing for a software distribution,  Next: Document overview,  Prev: Downloading and installing,  Up: Introduction to GnuTLS

2.2 Installing for a software distribution
==========================================

When installing for a software distribution, it is often desirable to
preconfigure GnuTLS with the system-wide paths and files.  There two
important configuration options, one sets the trust store in system,
which are the CA certificates to be used by programs by default (if they
don't override it), and the other sets to DNSSEC root key file used by
unbound for DNSSEC verification.

For the latter the following configuration option is available, and if
not specified GnuTLS will try to auto-detect the location of that file.
--with-unbound-root-key-file

To set the trust store the following options are available.
--with-default-trust-store-file
--with-default-trust-store-dir
--with-default-trust-store-pkcs11

The first option is used to set a PEM file which contains a list of
trusted certificates, while the second will read all certificates in the
given path.  The recommended option is the last, which allows to use a
PKCS #11 trust policy module.  That module not only provides the trusted
certificates, but allows the categorization of them using purpose, e.g.,
CAs can be restricted for e-mail usage only, or administrative
restrictions of CAs, for examples by restricting a CA to only issue
certificates for a given DNS domain using NameConstraints.  A publicly
available PKCS #11 trust module is p11-kit's trust module(1).

---------- Footnotes ----------

(1) <https://p11-glue.github.io/p11-glue/trust-module.html>

File: gnutls.info,  Node: Document overview,  Prev: Installing for a software distribution,  Up: Introduction to GnuTLS

2.3 Overview
============

In this document we present an overview of the supported security
protocols in *note Introduction to TLS::, and continue by providing more
information on the certificate authentication in *note Certificate
authentication::, and shared-key as well anonymous authentication in
*note Shared-key and anonymous authentication::.  We elaborate on
certificate authentication by demonstrating advanced usage of the API in
*note More on certificate authentication::.  The core of the TLS library
is presented in *note How to use GnuTLS in applications:: and example
applications are listed in *note GnuTLS application examples::.  In
*note Other included programs:: the usage of few included programs that
may assist debugging is presented.  The last chapter is *note Internal
architecture of GnuTLS:: that provides a short introduction to GnuTLS'
internal architecture.

File: gnutls.info,  Node: Introduction to TLS,  Next: Authentication methods,  Prev: Introduction to GnuTLS,  Up: Top

3 Introduction to TLS and DTLS
******************************

TLS stands for "Transport Layer Security" and is the successor of SSL,
the Secure Sockets Layer protocol [*note SSL3::] designed by Netscape.
TLS is an Internet protocol, defined by IETF(1), described in [*note
RFC5246::].  The protocol provides confidentiality, and authentication
layers over any reliable transport layer.  The description, above,
refers to TLS 1.0 but applies to all other TLS versions as the
differences between the protocols are not major.

The DTLS protocol, or "Datagram TLS" [*note RFC4347::] is a protocol
with identical goals as TLS, but can operate under unreliable transport
layers such as UDP.  The discussions below apply to this protocol as
well, except when noted otherwise.

* Menu:

* TLS layers::
* The transport layer::
* The TLS record protocol::
* The TLS Alert Protocol::
* The TLS Handshake Protocol::
* TLS Extensions::
* How to use TLS in application protocols::
* On SSL 2 and older protocols::

---------- Footnotes ----------

(1) IETF, or Internet Engineering Task Force, is a large open
international community of network designers, operators, vendors, and
researchers concerned with the evolution of the Internet architecture
and the smooth operation of the Internet.  It is open to any interested
individual.

File: gnutls.info,  Node: TLS layers,  Next: The transport layer,  Up: Introduction to TLS

3.1 TLS Layers
==============

TLS is a layered protocol, and consists of the record protocol, the
handshake protocol and the alert protocol.  The record protocol is to
serve all other protocols and is above the transport layer.  The record
protocol offers symmetric encryption, and data authenticity(1).  The
alert protocol offers some signaling to the other protocols.  It can
help informing the peer for the cause of failures and other error
conditions.  *Note The Alert Protocol::, for more information.  The
alert protocol is above the record protocol.

The handshake protocol is responsible for the security parameters'
negotiation, the initial key exchange and authentication.  *Note The
Handshake Protocol::, for more information about the handshake protocol.
The protocol layering in TLS is shown in *note Figure 3.1:
fig-tls-layers.

�[image src="gnutls-layers.png"�]

Figure 3.1: The TLS protocol layers.

---------- Footnotes ----------

(1) In early versions of TLS compression was optionally available as
well.  This is no longer the case in recent versions of the protocol.

File: gnutls.info,  Node: The transport layer,  Next: The TLS record protocol,  Prev: TLS layers,  Up: Introduction to TLS

3.2 The Transport Layer
=======================

TLS is not limited to any transport layer and can be used above any
transport layer, as long as it is a reliable one.  DTLS can be used over
reliable and unreliable transport layers.  GnuTLS supports TCP and UDP
layers transparently using the Berkeley sockets API. However, any
transport layer can be used by providing callbacks for GnuTLS to access
the transport layer (for details see *note Setting up the transport
layer::).

File: gnutls.info,  Node: The TLS record protocol,  Next: The TLS Alert Protocol,  Prev: The transport layer,  Up: Introduction to TLS

3.3 The TLS record protocol
===========================

The record protocol is the secure communications provider.  Its purpose
is to encrypt, and authenticate packets.  The record layer functions can
be called at any time after the handshake process is finished, when
there is need to receive or send data.  In DTLS however, due to
re-transmission timers used in the handshake out-of-order handshake data
might be received for some time (maximum 60 seconds) after the handshake
process is finished.

The functions to access the record protocol are limited to send and
receive functions, which might, given the importance of this protocol in
TLS, seem awkward.  This is because the record protocol's parameters are
all set by the handshake protocol.  The record protocol initially starts
with NULL parameters, which means no encryption, and no MAC is used.
Encryption and authentication begin just after the handshake protocol
has finished.

* Menu:

* Encryption algorithms used in the record layer::
* Compression algorithms and the record layer::
* On Record Padding::

File: gnutls.info,  Node: Encryption algorithms used in the record layer,  Next: Compression algorithms and the record layer,  Up: The TLS record protocol

3.3.1 Encryption algorithms used in the record layer
----------------------------------------------------

Confidentiality in the record layer is achieved by using symmetric
ciphers like ‘AES’ or ‘CHACHA20’.  Ciphers are encryption algorithms
that use a single, secret, key to encrypt and decrypt data.  Early
versions of TLS separated between block and stream ciphers and had
message authentication plugged in to them by the protocol, though later
versions switched to using authenticated-encryption (AEAD) ciphers.  The
AEAD ciphers are defined to combine encryption and authentication, and
as such they are not only more efficient, as the primitives used are
designed to interoperate nicely, but they are also known to interoperate
in a secure way.

The supported in GnuTLS ciphers and MAC algorithms are shown in *note
Table 3.1: tab:ciphers. and *note Table 3.2: tab:macs.

Algorithm      Type    Applicable  Description
                       Protocols
----------------------------------------------------------------------------
AES-128-GCM,   AEAD    TLS 1.2,    This is the AES algorithm in the
AES-256-GCM            TLS 1.3     authenticated encryption GCM mode.
                                   This mode combines message
                                   authentication and encryption and can
                                   be extremely fast on CPUs that support
                                   hardware acceleration.
                                   
AES-128-CCM,   AEAD    TLS 1.2,    This is the AES algorithm in the
AES-256-CCM            TLS 1.3     authenticated encryption CCM mode.
                                   This mode combines message
                                   authentication and encryption and is
                                   often used by systems without AES or
                                   GCM acceleration support.
                                   
CHACHA20-POLY1305AEAD  TLS 1.2,    CHACHA20-POLY1305 is an authenticated
                       TLS 1.3     encryption algorithm based on CHACHA20
                                   cipher and POLY1305 MAC. CHACHA20 is a
                                   refinement of SALSA20 algorithm, an
                                   approved cipher by the European
                                   ESTREAM project.  POLY1305 is
                                   Wegman-Carter, one-time authenticator.
                                   The combination provides a fast stream
                                   cipher suitable for systems where a
                                   hardware AES accelerator is not
                                   available.
                                   
AES-128-CCM-8, AEAD    TLS 1.2,    This is the AES algorithm in the
AES-256-CCM-8          TLS 1.3     authenticated encryption CCM mode with
                                   a truncated to 64-bit authentication
                                   tag.  This mode is for communication
                                   with restricted systems.
                                   
CAMELLIA-128-GCM,AEAD  TLS 1.2     This is the CAMELLIA algorithm in the
CAMELLIA-256-GCM                   authenticated encryption GCM mode.
                                   
AES-128-CBC,   Legacy  TLS 1.0,    AES or RIJNDAEL is the block cipher
AES-256-CBC    (block) TLS 1.1,    algorithm that replaces the old DES
                       TLS 1.2     algorithm.  It has 128 bits block size
                                   and is used in CBC mode.
                                   
CAMELLIA-128-CBC,LegacyTLS 1.0,    This is an 128-bit block cipher
CAMELLIA-256-CBC(block)TLS 1.1,    developed by Mitsubishi and NTT. It is
                       TLS 1.2     one of the approved ciphers of the
                                   European NESSIE and Japanese CRYPTREC
                                   projects.
                                   
3DES-CBC       Legacy  TLS 1.0,    This is the DES block cipher algorithm
               (block) TLS 1.1,    used with triple encryption (EDE). Has
                       TLS 1.2     64 bits block size and is used in CBC
                                   mode.
                                   
ARCFOUR-128    Legacy  TLS 1.0,    ARCFOUR-128 is a compatible algorithm
               (stream)TLS 1.1,    with RSA's RC4 algorithm, which is
                       TLS 1.2     considered to be a trade secret.  It
                                   is a considered to be broken, and is
                                   only used for compatibility purposed.
                                   For this reason it is not enabled by
                                   default.
                                   
GOST28147-TC26Z-CNTLegacyTLS 1.2   This is a 64-bit block cipher GOST
               (stream)            28147-89 with TC26Z S-Box working in
                                   CNT mode.  It is one of the approved
                                   ciphers in Russia.  It is not enabled
                                   by default.
                                   
NULL           Legacy  TLS 1.0,    NULL is the empty/identity cipher
               (stream)TLS 1.1,    which doesn't encrypt any data.  It
                       TLS 1.2     can be combined with data
                                   authentication under TLS 1.2 or
                                   earlier, but is only used transiently
                                   under TLS 1.3 until encryption starts.
                                   This cipher cannot be negotiated by
                                   default (need to be explicitly
                                   enabled) under TLS 1.2, and cannot be
                                   negotiated at all under TLS 1.3.  When
                                   enabled, TLS 1.3 (or later) support
                                   will be implicitly disabled.

Table 3.1: Supported ciphers in TLS.

Algorithm      Description
------------------------------------------------------------------
MAC-MD5        This is an HMAC based on MD5 a cryptographic
               hash algorithm designed by Ron Rivest.  Outputs
               128 bits of data.
               
MAC-SHA1       An HMAC based on the SHA1 cryptographic hash
               algorithm designed by NSA. Outputs 160 bits of
               data.
               
MAC-SHA256     An HMAC based on SHA2-256.  Outputs 256 bits of
               data.
               
MAC-SHA384     An HMAC based on SHA2-384.  Outputs 384 bits of
               data.
               
GOST28147-TC26Z-IMITThis is a 64-bit block cipher GOST 28147-89 with
               TC26Z S-Box working in special MAC mode called
               Imitovstavks.  It is one of the approved MAC
               algorithms in Russia.  Outputs 32 bits of data.
               It is not enabled by default.
               
MAC-AEAD       This indicates that an authenticated encryption
               algorithm, such as GCM, is in use.

Table 3.2: Supported MAC algorithms in TLS.

File: gnutls.info,  Node: Compression algorithms and the record layer,  Next: On Record Padding,  Prev: Encryption algorithms used in the record layer,  Up: The TLS record protocol

3.3.2 Compression algorithms and the record layer
-------------------------------------------------

In early versions of TLS the record layer supported compression.
However, that proved to be problematic in many ways, and enabled several
attacks based on traffic analysis on the transported data.  For that
newer versions of the protocol no longer offer compression, and GnuTLS
since 3.6.0 no longer implements any support for compression.

File: gnutls.info,  Node: On Record Padding,  Prev: Compression algorithms and the record layer,  Up: The TLS record protocol

3.3.3 On record padding
-----------------------

The TLS 1.3 protocol allows for extra padding of records to prevent
statistical analysis based on the length of exchanged messages.  GnuTLS
takes advantage of this feature, by allowing the user to specify the
amount of padding for a particular message.  The simplest interface is
provided by *note gnutls_record_send2::, and is made available when
under TLS1.3; alternatively *note gnutls_record_can_use_length_hiding::
can be queried.

Note that this interface is not sufficient to completely hide the length
of the data.  The application code may reveal the data transferred by
leaking its data processing time, or by leaking the TLS1.3 record
processing time by GnuTLS. That is because under TLS1.3 the padding
removal time depends on the padding data for an efficient
implementation.  To make that processing constant time the *note
gnutls_init:: function must be called with the flag
‘GNUTLS_SAFE_PADDING_CHECK’.

-- Function: ssize_t gnutls_record_send2 (gnutls_session_t SESSION,
          const void * DATA, size_t DATA_SIZE, size_t PAD, unsigned
          FLAGS)
     SESSION: is a ‘gnutls_session_t’ type.

DATA: contains the data to send

DATA_SIZE: is the length of the data

PAD: padding to be added to the record

FLAGS: must be zero

This function is identical to ‘gnutls_record_send()’ except that it
     takes an extra argument to specify padding to be added the record.
     To determine the maximum size of padding, use
     ‘gnutls_record_get_max_size()’ and ‘gnutls_record_overhead_size()’
     .

Note that in order for GnuTLS to provide constant time processing
     of padding and data in TLS1.3, the flag ‘GNUTLS_SAFE_PADDING_CHECK’
     must be used in ‘gnutls_init()’ .

*Returns:* The number of bytes sent, or a negative error code.  The
     number of bytes sent might be less than ‘data_size’ .  The maximum
     number of bytes this function can send in a single call depends on
     the negotiated maximum record size.

*Since:* 3.6.3

Older GnuTLS versions provided an API suitable for cases where the
sender sends data that are always within a given range.  That API is
still available, and consists of the following functions.

‘UNSIGNED *note gnutls_record_can_use_length_hiding:: (gnutls_session_t SESSION)’
‘SSIZE_T *note gnutls_record_send_range:: (gnutls_session_t SESSION, const void * DATA, size_t DATA_SIZE, const gnutls_range_st * RANGE)’

File: gnutls.info,  Node: The TLS Alert Protocol,  Next: The TLS Handshake Protocol,  Prev: The TLS record protocol,  Up: Introduction to TLS

3.4 The TLS alert protocol
==========================

The alert protocol is there to allow signals to be sent between peers.
These signals are mostly used to inform the peer about the cause of a
protocol failure.  Some of these signals are used internally by the
protocol and the application protocol does not have to cope with them
(e.g.  ‘GNUTLS_A_CLOSE_NOTIFY’), and others refer to the application
protocol solely (e.g.  ‘GNUTLS_A_USER_CANCELLED’).  An alert signal
includes a level indication which may be either fatal or warning (under
TLS1.3 all alerts are fatal).  Fatal alerts always terminate the current
connection, and prevent future re-negotiations using the current session
ID. All supported alert messages are summarized in the table below.

The alert messages are protected by the record protocol, thus the
information that is included does not leak.  You must take extreme care
for the alert information not to leak to a possible attacker, via public
log files etc.

Alert                                    ID      Description
------------------------------------------------------------------------
GNUTLS_A_CLOSE_NOTIFY                    0       Close notify
GNUTLS_A_UNEXPECTED_MESSAGE              10      Unexpected message
GNUTLS_A_BAD_RECORD_MAC                  20      Bad record MAC
GNUTLS_A_DECRYPTION_FAILED               21      Decryption failed
GNUTLS_A_RECORD_OVERFLOW                 22      Record overflow
GNUTLS_A_DECOMPRESSION_FAILURE           30      Decompression failed
GNUTLS_A_HANDSHAKE_FAILURE               40      Handshake failed
GNUTLS_A_SSL3_NO_CERTIFICATE             41      No certificate (SSL
                                                 3.0)
GNUTLS_A_BAD_CERTIFICATE                 42      Certificate is bad
GNUTLS_A_UNSUPPORTED_CERTIFICATE         43      Certificate is not
                                                 supported
GNUTLS_A_CERTIFICATE_REVOKED             44      Certificate was
                                                 revoked
GNUTLS_A_CERTIFICATE_EXPIRED             45      Certificate is
                                                 expired
GNUTLS_A_CERTIFICATE_UNKNOWN             46      Unknown certificate
GNUTLS_A_ILLEGAL_PARAMETER               47      Illegal parameter
GNUTLS_A_UNKNOWN_CA                      48      CA is unknown
GNUTLS_A_ACCESS_DENIED                   49      Access was denied
GNUTLS_A_DECODE_ERROR                    50      Decode error
GNUTLS_A_DECRYPT_ERROR                   51      Decrypt error
GNUTLS_A_EXPORT_RESTRICTION              60      Export restriction
GNUTLS_A_PROTOCOL_VERSION                70      Error in protocol
                                                 version
GNUTLS_A_INSUFFICIENT_SECURITY           71      Insufficient
                                                 security
GNUTLS_A_INTERNAL_ERROR                  80      Internal error
GNUTLS_A_INAPPROPRIATE_FALLBACK          86      Inappropriate
                                                 fallback
GNUTLS_A_USER_CANCELED                   90      User canceled
GNUTLS_A_NO_RENEGOTIATION                100     No renegotiation is
                                                 allowed
GNUTLS_A_MISSING_EXTENSION               109     An extension was
                                                 expected but was not
                                                 seen
GNUTLS_A_UNSUPPORTED_EXTENSION           110     An unsupported
                                                 extension was sent
GNUTLS_A_CERTIFICATE_UNOBTAINABLE        111     Could not retrieve
                                                 the specified
                                                 certificate
GNUTLS_A_UNRECOGNIZED_NAME               112     The server name sent
                                                 was not recognized
GNUTLS_A_UNKNOWN_PSK_IDENTITY            115     The SRP/PSK username
                                                 is missing or not
                                                 known
GNUTLS_A_CERTIFICATE_REQUIRED            116     Certificate is
                                                 required
GNUTLS_A_NO_APPLICATION_PROTOCOL         120     No supported
                                                 application protocol
                                                 could be negotiated

File: gnutls.info,  Node: The TLS Handshake Protocol,  Next: TLS Extensions,  Prev: The TLS Alert Protocol,  Up: Introduction to TLS

3.5 The TLS handshake protocol
==============================

The handshake protocol is responsible for the ciphersuite negotiation,
the initial key exchange, and the authentication of the two peers.  This
is fully controlled by the application layer, thus your program has to
set up the required parameters.  The main handshake function is *note
gnutls_handshake::.  In the next paragraphs we elaborate on the
handshake protocol, i.e., the ciphersuite negotiation.

* Menu:

* TLS Cipher Suites::           TLS session parameters.
* Authentication::              TLS authentication.
* Client Authentication::       Requesting a certificate from the client.
* Resuming Sessions::           Reusing previously established keys.

File: gnutls.info,  Node: TLS Cipher Suites,  Next: Authentication,  Up: The TLS Handshake Protocol

3.5.1 TLS ciphersuites
----------------------

The TLS cipher suites have slightly different meaning under different
protocols.  Under TLS 1.3, a cipher suite indicates the symmetric
encryption algorithm in use, as well as the pseudo-random function (PRF)
used in the TLS session.

Under TLS 1.2 or early the handshake protocol negotiates cipher suites
of a special form illustrated by the ‘TLS_DHE_RSA_WITH_3DES_CBC_SHA’
cipher suite name.  A typical cipher suite contains these parameters:

• The key exchange algorithm.  ‘DHE_RSA’ in the example.

• The Symmetric encryption algorithm and mode ‘3DES_CBC’ in this
     example.

• The MAC(1) algorithm used for authentication.  ‘MAC_SHA’ is used in
     the above example.

The cipher suite negotiated in the handshake protocol will affect the
record protocol, by enabling encryption and data authentication.  Note
that you should not over rely on TLS to negotiate the strongest
available cipher suite.  Do not enable ciphers and algorithms that you
consider weak.

All the supported ciphersuites are listed in *note ciphersuites::.

---------- Footnotes ----------

(1) MAC stands for Message Authentication Code.  It can be described
as a keyed hash algorithm.  See RFC2104.

File: gnutls.info,  Node: Authentication,  Next: Client Authentication,  Prev: TLS Cipher Suites,  Up: The TLS Handshake Protocol

3.5.2 Authentication
--------------------

The key exchange algorithms of the TLS protocol offer authentication,
which is a prerequisite for a secure connection.  The available
authentication methods in GnuTLS, under TLS 1.3 or earlier versions,
follow.

• Certificate authentication: Authenticated key exchange using public
     key infrastructure and X.509 certificates.
   • PSK authentication: Authenticated key exchange using a pre-shared
     key.

Under TLS 1.2 or earlier versions, the following authentication methods
are also available.

• SRP authentication: Authenticated key exchange using a password.
   • Anonymous authentication: Key exchange without peer authentication.

File: gnutls.info,  Node: Client Authentication,  Next: Resuming Sessions,  Prev: Authentication,  Up: The TLS Handshake Protocol

3.5.3 Client authentication
---------------------------

In the case of ciphersuites that use certificate authentication, the
authentication of the client is optional in TLS.  A server may request a
certificate from the client using the *note
gnutls_certificate_server_set_request:: function.  We elaborate in *note
Certificate credentials::.

File: gnutls.info,  Node: Resuming Sessions,  Prev: Client Authentication,  Up: The TLS Handshake Protocol

3.5.4 Resuming sessions
-----------------------

The TLS handshake process performs expensive calculations and a busy
server might easily be put under load.  To reduce the load, session
resumption may be used.  This is a feature of the TLS protocol which
allows a client to connect to a server after a successful handshake,
without the expensive calculations.  This is achieved by re-using the
previously established keys, meaning the server needs to store the state
of established connections (unless session tickets are used - *note
Session tickets::).

Session resumption is an integral part of GnuTLS, and *note Session
resumption::, *note ex-resume-client:: illustrate typical uses of it.

File: gnutls.info,  Node: TLS Extensions,  Next: How to use TLS in application protocols,  Prev: The TLS Handshake Protocol,  Up: Introduction to TLS

3.6 TLS extensions
==================

A number of extensions to the TLS protocol have been proposed mainly in
[*note TLSEXT::].  The extensions supported in GnuTLS are discussed in
the subsections that follow.

* Menu:

* Maximum fragment length negotiation::
* Server name indication::
* Session tickets::
* HeartBeat::
* Safe renegotiation::
* OCSP status request::
* SRTP::
* False Start::
* Application Layer Protocol Negotiation (ALPN)::
* Extensions and Supplemental Data::

File: gnutls.info,  Node: Maximum fragment length negotiation,  Next: Server name indication,  Up: TLS Extensions

3.6.1 Maximum fragment length negotiation
-----------------------------------------

This extension allows a TLS implementation to negotiate a smaller value
for record packet maximum length.  This extension may be useful to
clients with constrained capabilities.  The functions shown below can be
used to control this extension.

‘SIZE_T *note gnutls_record_get_max_size:: (gnutls_session_t SESSION)’
‘SSIZE_T *note gnutls_record_set_max_size:: (gnutls_session_t SESSION, size_t SIZE)’

File: gnutls.info,  Node: Server name indication,  Next: Session tickets,  Prev: Maximum fragment length negotiation,  Up: TLS Extensions

3.6.2 Server name indication
----------------------------

A common problem in HTTPS servers is the fact that the TLS protocol is
not aware of the hostname that a client connects to, when the handshake
procedure begins.  For that reason the TLS server has no way to know
which certificate to send.

This extension solves that problem within the TLS protocol, and allows a
client to send the HTTP hostname before the handshake begins within the
first handshake packet.  The functions *note gnutls_server_name_set::
and *note gnutls_server_name_get:: can be used to enable this extension,
or to retrieve the name sent by a client.

‘INT *note gnutls_server_name_set:: (gnutls_session_t SESSION, gnutls_server_name_type_t TYPE, const void * NAME, size_t NAME_LENGTH)’
‘INT *note gnutls_server_name_get:: (gnutls_session_t SESSION, void * DATA, size_t * DATA_LENGTH, unsigned int * TYPE, unsigned int INDX)’

File: gnutls.info,  Node: Session tickets,  Next: HeartBeat,  Prev: Server name indication,  Up: TLS Extensions

3.6.3 Session tickets
---------------------

To resume a TLS session, the server normally stores session parameters.
This complicates deployment, and can be avoided by delegating the
storage to the client.  Because session parameters are sensitive they
are encrypted and authenticated with a key only known to the server and
then sent to the client.  The Session Tickets extension is described in
RFC 5077 [*note TLSTKT::].

A disadvantage of session tickets is that they eliminate the effects of
forward secrecy when a server uses the same key for long time.  That is,
the secrecy of all sessions on a server using tickets depends on the
ticket key being kept secret.  For that reason server keys should be
rotated and discarded regularly.

Since version 3.1.3 GnuTLS clients transparently support session
tickets, unless forward secrecy is explicitly requested (with the PFS
priority string).

Under TLS 1.3 session tickets are mandatory for session resumption, and
they do not share the forward secrecy concerns as with TLS 1.2 or
earlier.

File: gnutls.info,  Node: HeartBeat,  Next: Safe renegotiation,  Prev: Session tickets,  Up: TLS Extensions

3.6.4 HeartBeat
---------------

This is a TLS extension that allows to ping and receive confirmation
from the peer, and is described in [*note RFC6520::].  The extension is
disabled by default and *note gnutls_heartbeat_enable:: can be used to
enable it.  A policy may be negotiated to only allow sending heartbeat
messages or sending and receiving.  The current session policy can be
checked with *note gnutls_heartbeat_allowed::.  The requests coming from
the peer result to ‘GNUTLS_E_HEARTBEAT_PING_RECEIVED’ being returned
from the receive function.  Ping requests to peer can be send via *note
gnutls_heartbeat_ping::.

‘UNSIGNED *note gnutls_heartbeat_allowed:: (gnutls_session_t SESSION, unsigned int TYPE)’
‘VOID *note gnutls_heartbeat_enable:: (gnutls_session_t SESSION, unsigned int TYPE)’

‘INT *note gnutls_heartbeat_ping:: (gnutls_session_t SESSION, size_t DATA_SIZE, unsigned int MAX_TRIES, unsigned int FLAGS)’
‘INT *note gnutls_heartbeat_pong:: (gnutls_session_t SESSION, unsigned int FLAGS)’
‘VOID *note gnutls_heartbeat_set_timeouts:: (gnutls_session_t SESSION, unsigned int RETRANS_TIMEOUT, unsigned int TOTAL_TIMEOUT)’
‘UNSIGNED INT *note gnutls_heartbeat_get_timeout:: (gnutls_session_t SESSION)’

File: gnutls.info,  Node: Safe renegotiation,  Next: OCSP status request,  Prev: HeartBeat,  Up: TLS Extensions

3.6.5 Safe renegotiation
------------------------

TLS gives the option to two communicating parties to renegotiate and
update their security parameters.  One useful example of this feature
was for a client to initially connect using anonymous negotiation to a
server, and the renegotiate using some authenticated ciphersuite.  This
occurred to avoid having the client sending its credentials in the
clear.

However this renegotiation, as initially designed would not ensure that
the party one is renegotiating is the same as the one in the initial
negotiation.  For example one server could forward all renegotiation
traffic to an other server who will see this traffic as an initial
negotiation attempt.

This might be seen as a valid design decision, but it seems it was not
widely known or understood, thus today some application protocols use
the TLS renegotiation feature in a manner that enables a malicious
server to insert content of his choice in the beginning of a TLS
session.

The most prominent vulnerability was with HTTPS. There servers request a
renegotiation to enforce an anonymous user to use a certificate in order
to access certain parts of a web site.  The attack works by having the
attacker simulate a client and connect to a server, with server-only
authentication, and send some data intended to cause harm.  The server
will then require renegotiation from him in order to perform the
request.  When the proper client attempts to contact the server, the
attacker hijacks that connection and forwards traffic to the initial
server that requested renegotiation.  The attacker will not be able to
read the data exchanged between the client and the server.  However, the
server will (incorrectly) assume that the initial request sent by the
attacker was sent by the now authenticated client.  The result is a
prefix plain-text injection attack.

The above is just one example.  Other vulnerabilities exists that do not
rely on the TLS renegotiation to change the client's authenticated
status (either TLS or application layer).

While fixing these application protocols and implementations would be
one natural reaction, an extension to TLS has been designed that
cryptographically binds together any renegotiated handshakes with the
initial negotiation.  When the extension is used, the attack is detected
and the session can be terminated.  The extension is specified in [*note
RFC5746::].

GnuTLS supports the safe renegotiation extension.  The default behavior
is as follows.  Clients will attempt to negotiate the safe renegotiation
extension when talking to servers.  Servers will accept the extension
when presented by clients.  Clients and servers will permit an initial
handshake to complete even when the other side does not support the safe
renegotiation extension.  Clients and servers will refuse renegotiation
attempts when the extension has not been negotiated.

Note that permitting clients to connect to servers when the safe
renegotiation extension is not enabled, is open up for attacks.
Changing this default behavior would prevent interoperability against
the majority of deployed servers out there.  We will reconsider this
default behavior in the future when more servers have been upgraded.
Note that it is easy to configure clients to always require the safe
renegotiation extension from servers.

To modify the default behavior, we have introduced some new priority
strings (see *note Priority Strings::).  The ‘%UNSAFE_RENEGOTIATION’
priority string permits (re-)handshakes even when the safe renegotiation
extension was not negotiated.  The default behavior is
‘%PARTIAL_RENEGOTIATION’ that will prevent renegotiation with clients
and servers not supporting the extension.  This is secure for servers
but leaves clients vulnerable to some attacks, but this is a trade-off
between security and compatibility with old servers.  The
‘%SAFE_RENEGOTIATION’ priority string makes clients and servers require
the extension for every handshake.  The latter is the most secure option
for clients, at the cost of not being able to connect to legacy servers.
Servers will also deny clients that do not support the extension from
connecting.

It is possible to disable use of the extension completely, in both
clients and servers, by using the ‘%DISABLE_SAFE_RENEGOTIATION’ priority
string however we strongly recommend you to only do this for debugging
and test purposes.

The default values if the flags above are not specified are:

‘Server:’
     %PARTIAL_RENEGOTIATION

‘Client:’
     %PARTIAL_RENEGOTIATION

For applications we have introduced a new API related to safe
renegotiation.  The *note gnutls_safe_renegotiation_status:: function is
used to check if the extension has been negotiated on a session, and can
be used both by clients and servers.

File: gnutls.info,  Node: OCSP status request,  Next: SRTP,  Prev: Safe renegotiation,  Up: TLS Extensions

3.6.6 OCSP status request
-------------------------

The Online Certificate Status Protocol (OCSP) is a protocol that allows
the client to verify the server certificate for revocation without
messing with certificate revocation lists.  Its drawback is that it
requires the client to connect to the server's CA OCSP server and
request the status of the certificate.  This extension however, enables
a TLS server to include its CA OCSP server response in the handshake.
That is an HTTPS server may periodically run ‘ocsptool’ (see *note
ocsptool Invocation::) to obtain its certificate revocation status and
serve it to the clients.  That way a client avoids an additional
connection to the OCSP server.

See *note OCSP stapling:: for further information.

Since version 3.1.3 GnuTLS clients transparently support the certificate
status request.

File: gnutls.info,  Node: SRTP,  Next: False Start,  Prev: OCSP status request,  Up: TLS Extensions

3.6.7 SRTP
----------

The TLS protocol was extended in [*note RFC5764::] to provide keying
material to the Secure RTP (SRTP) protocol.  The SRTP protocol provides
an encapsulation of encrypted data that is optimized for voice data.
With the SRTP TLS extension two peers can negotiate keys using TLS or
DTLS and obtain keying material for use with SRTP. The available SRTP
profiles are listed below.

‘GNUTLS_SRTP_AES128_CM_HMAC_SHA1_80’
     128 bit AES with a 80 bit HMAC-SHA1
‘GNUTLS_SRTP_AES128_CM_HMAC_SHA1_32’
     128 bit AES with a 32 bit HMAC-SHA1
‘GNUTLS_SRTP_NULL_HMAC_SHA1_80’
     NULL cipher with a 80 bit HMAC-SHA1
‘GNUTLS_SRTP_NULL_HMAC_SHA1_32’
     NULL cipher with a 32 bit HMAC-SHA1
‘GNUTLS_SRTP_AEAD_AES_128_GCM’
     128 bit AES with GCM
‘GNUTLS_SRTP_AEAD_AES_256_GCM’
     256 bit AES with GCM

Figure 3.2: Supported SRTP profiles

To enable use the following functions.

‘INT *note gnutls_srtp_set_profile:: (gnutls_session_t SESSION, gnutls_srtp_profile_t PROFILE)’
‘INT *note gnutls_srtp_set_profile_direct:: (gnutls_session_t SESSION, const char * PROFILES, const char ** ERR_POS)’

To obtain the negotiated keys use the function below.

-- Function: int gnutls_srtp_get_keys (gnutls_session_t SESSION, void *
          KEY_MATERIAL, unsigned int KEY_MATERIAL_SIZE, gnutls_datum_t *
          CLIENT_KEY, gnutls_datum_t * CLIENT_SALT, gnutls_datum_t *
          SERVER_KEY, gnutls_datum_t * SERVER_SALT)
     SESSION: is a ‘gnutls_session_t’ type.

KEY_MATERIAL: Space to hold the generated key material

KEY_MATERIAL_SIZE: The maximum size of the key material

CLIENT_KEY: The master client write key, pointing inside the key
     material

CLIENT_SALT: The master client write salt, pointing inside the key
     material

SERVER_KEY: The master server write key, pointing inside the key
     material

SERVER_SALT: The master server write salt, pointing inside the key
     material

This is a helper function to generate the keying material for SRTP.
     It requires the space of the key material to be pre-allocated
     (should be at least 2x the maximum key size and salt size).  The
     ‘client_key’ , ‘client_salt’ , ‘server_key’ and ‘server_salt’ are
     convenience datums that point inside the key material.  They may be
     ‘NULL’ .

*Returns:* On success the size of the key material is returned,
     otherwise, ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ if the buffer given is
     not sufficient, or a negative error code.

Since 3.1.4

Other helper functions are listed below.

‘INT *note gnutls_srtp_get_selected_profile:: (gnutls_session_t SESSION, gnutls_srtp_profile_t * PROFILE)’
‘CONST CHAR * *note gnutls_srtp_get_profile_name:: (gnutls_srtp_profile_t PROFILE)’
‘INT *note gnutls_srtp_get_profile_id:: (const char * NAME, gnutls_srtp_profile_t * PROFILE)’

File: gnutls.info,  Node: False Start,  Next: Application Layer Protocol Negotiation (ALPN),  Prev: SRTP,  Up: TLS Extensions

3.6.8 False Start
-----------------

The TLS protocol was extended in [*note RFC7918::] to allow the client
to send data to server in a single round trip.  This change however
operates on the borderline of the TLS protocol security guarantees and
should be used for the cases where the reduced latency outperforms the
risk of an adversary intercepting the transferred data.  In GnuTLS
applications can use the GNUTLS_ENABLE_FALSE_START as option to *note
gnutls_init:: to request an early return of the *note gnutls_handshake::
function.  After that early return the application is expected to
transfer any data to be piggybacked on the last handshake message.

After handshake's early termination, the application is expected to
transmit data using *note gnutls_record_send::, and call *note
gnutls_record_recv:: on any received data as soon, to ensure that
handshake completes timely.  That is, especially relevant for
applications which set an explicit time limit for the handshake process
via *note gnutls_handshake_set_timeout::.

Note however, that the API ensures that the early return will not happen
if the false start requirements are not satisfied.  That is, on
ciphersuites which are not enabled for false start or on insufficient
key sizes, the handshake process will complete properly (i.e., no early
return).  To verify that false start was used you may use *note
gnutls_session_get_flags:: and check for the GNUTLS_SFLAGS_FALSE_START
flag.  For GnuTLS the false start is enabled for the following key
exchange methods (see [*note RFC7918::] for rationale)
   • DHE
   • ECDHE
but only when the negotiated parameters exceed ‘GNUTLS_SEC_PARAM_HIGH’
-see *note Table 6.7: tab:key-sizes, and when under (D)TLS 1.2 or later.

File: gnutls.info,  Node: Application Layer Protocol Negotiation (ALPN),  Next: Extensions and Supplemental Data,  Prev: False Start,  Up: TLS Extensions

3.6.9 Application Layer Protocol Negotiation (ALPN)
---------------------------------------------------

The TLS protocol was extended in ‘RFC7301’ to provide the application
layer a method of negotiating the application protocol version.  This
allows for negotiation of the application protocol during the TLS
handshake, thus reducing round-trips.  The application protocol is
described by an opaque string.  To enable, use the following functions.

‘INT *note gnutls_alpn_set_protocols:: (gnutls_session_t SESSION, const gnutls_datum_t * PROTOCOLS, unsigned PROTOCOLS_SIZE, unsigned int FLAGS)’
‘INT *note gnutls_alpn_get_selected_protocol:: (gnutls_session_t SESSION, gnutls_datum_t * PROTOCOL)’

Note that these functions are intended to be used with protocols that
are registered in the Application Layer Protocol Negotiation IANA
registry.  While you can use them for other protocols (at the risk of
collisions), it is preferable to register them.

File: gnutls.info,  Node: Extensions and Supplemental Data,  Prev: Application Layer Protocol Negotiation (ALPN),  Up: TLS Extensions

3.6.10 Extensions and Supplemental Data
---------------------------------------

It is possible to transfer supplemental data during the TLS handshake,
following [*note RFC4680::].  This is for "custom" protocol
modifications for applications which may want to transfer additional
data (e.g.  additional authentication messages).  Such an exchange
requires a custom extension to be registered.  The provided API for this
functionality is low-level and described in *note TLS Hello Extension
Handling::.

File: gnutls.info,  Node: How to use TLS in application protocols,  Next: On SSL 2 and older protocols,  Prev: TLS Extensions,  Up: Introduction to TLS

3.7 How to use TLS in application protocols
===========================================

This chapter is intended to provide some hints on how to use TLS over
simple custom made application protocols.  The discussion below mainly
refers to the TCP/IP transport layer but may be extended to other ones
too.

* Menu:

* Separate ports::
* Upward negotiation::

File: gnutls.info,  Node: Separate ports,  Next: Upward negotiation,  Up: How to use TLS in application protocols

3.7.1 Separate ports
--------------------

Traditionally SSL was used in application protocols by assigning a new
port number for the secure services.  By doing this two separate ports
were assigned, one for the non-secure sessions, and one for the secure
sessions.  This method ensures that if a user requests a secure session
then the client will attempt to connect to the secure port and fail
otherwise.  The only possible attack with this method is to perform a
denial of service attack.  The most famous example of this method is
"HTTP over TLS" or HTTPS protocol [*note RFC2818::].

Despite its wide use, this method has several issues.  This approach
starts the TLS Handshake procedure just after the client connects on the
--so called-- secure port.  That way the TLS protocol does not know
anything about the client, and popular methods like the host advertising
in HTTP do not work(1).  There is no way for the client to say "I
connected to YYY server" before the Handshake starts, so the server
cannot possibly know which certificate to use.

Other than that it requires two separate ports to run a single service,
which is unnecessary complication.  Due to the fact that there is a
limitation on the available privileged ports, this approach was soon
deprecated in favor of upward negotiation.

---------- Footnotes ----------

(1) See also the Server Name Indication extension on *note
serverind::.

File: gnutls.info,  Node: Upward negotiation,  Prev: Separate ports,  Up: How to use TLS in application protocols

3.7.2 Upward negotiation
------------------------

Other application protocols(1) use a different approach to enable the
secure layer.  They use something often called as the "TLS upgrade"
method.  This method is quite tricky but it is more flexible.  The idea
is to extend the application protocol to have a "STARTTLS" request,
whose purpose it to start the TLS protocols just after the client
requests it.  This approach does not require any extra port to be
reserved.  There is even an extension to HTTP protocol to support this
method [*note RFC2817::].

The tricky part, in this method, is that the "STARTTLS" request is sent
in the clear, thus is vulnerable to modifications.  A typical attack is
to modify the messages in a way that the client is fooled and thinks
that the server does not have the "STARTTLS" capability.  See a typical
conversation of a hypothetical protocol:

(client connects to the server)

CLIENT: HELLO I'M MR. XXX

SERVER: NICE TO MEET YOU XXX

CLIENT: PLEASE START TLS

SERVER: OK

*** TLS STARTS

CLIENT: HERE ARE SOME CONFIDENTIAL DATA

And an example of a conversation where someone is acting in between:

(client connects to the server)

CLIENT: HELLO I'M MR. XXX

SERVER: NICE TO MEET YOU XXX

CLIENT: PLEASE START TLS

(here someone inserts this message)

SERVER: SORRY I DON'T HAVE THIS CAPABILITY

CLIENT: HERE ARE SOME CONFIDENTIAL DATA

As you can see above the client was fooled, and was naïve enough to send
the confidential data in the clear, despite the server telling the
client that it does not support "STARTTLS".

How do we avoid the above attack?  As you may have already noticed this
situation is easy to avoid.  The client has to ask the user before it
connects whether the user requests TLS or not.  If the user answered
that he certainly wants the secure layer the last conversation should
be:

(client connects to the server)

CLIENT: HELLO I'M MR. XXX

SERVER: NICE TO MEET YOU XXX

CLIENT: PLEASE START TLS

(here someone inserts this message)

SERVER: SORRY I DON'T HAVE THIS CAPABILITY

CLIENT: BYE

(the client notifies the user that the secure connection was not
     possible)

This method, if implemented properly, is far better than the traditional
method, and the security properties remain the same, since only denial
of service is possible.  The benefit is that the server may request
additional data before the TLS Handshake protocol starts, in order to
send the correct certificate, use the correct password file, or anything
else!

---------- Footnotes ----------

(1) See LDAP, IMAP etc.

File: gnutls.info,  Node: On SSL 2 and older protocols,  Prev: How to use TLS in application protocols,  Up: Introduction to TLS

3.8 On SSL 2 and older protocols
================================

One of the initial decisions in the GnuTLS development was to implement
the known security protocols for the transport layer.  Initially TLS 1.0
was implemented since it was the latest at that time, and was considered
to be the most advanced in security properties.  Later the SSL 3.0
protocol was implemented since it is still the only protocol supported
by several servers and there are no serious security vulnerabilities
known.

One question that may arise is why we didn't implement SSL 2.0 in the
library.  There are several reasons, most important being that it has
serious security flaws, unacceptable for a modern security library.
Other than that, this protocol is barely used by anyone these days since
it has been deprecated since 1996.  The security problems in SSL 2.0
include:

• Message integrity compromised.  The SSLv2 message authentication
     uses the MD5 function, and is insecure.

• Man-in-the-middle attack.  There is no protection of the handshake
     in SSLv2, which permits a man-in-the-middle attack.

• Truncation attack.  SSLv2 relies on TCP FIN to close the session,
     so the attacker can forge a TCP FIN, and the peer cannot tell if it
     was a legitimate end of data or not.

• Weak message integrity for export ciphers.  The cryptographic keys
     in SSLv2 are used for both message authentication and encryption,
     so if weak encryption schemes are negotiated (say 40-bit keys) the
     message authentication code uses the same weak key, which isn't
     necessary.

Other protocols such as Microsoft's PCT 1 and PCT 2 were not implemented
because they were also abandoned and deprecated by SSL 3.0 and later TLS
1.0.

File: gnutls.info,  Node: Authentication methods,  Next: Hardware security modules and abstract key types,  Prev: Introduction to TLS,  Up: Top

4 Authentication methods
************************

The initial key exchange of the TLS protocol performs authentication of
the peers.  In typical scenarios the server is authenticated to the
client, and optionally the client to the server.

While many associate TLS with X.509 certificates and public key
authentication, the protocol supports various authentication methods,
including pre-shared keys, and passwords.  In this chapter a description
of the existing authentication methods is provided, as well as some
guidance on which use-cases each method can be used at.

* Menu:

* Certificate authentication::
* More on certificate authentication::
* Shared-key and anonymous authentication::
* Selecting an appropriate authentication method::

File: gnutls.info,  Node: Certificate authentication,  Next: More on certificate authentication,  Up: Authentication methods

4.1 Certificate authentication
==============================

The most known authentication method of TLS are certificates.  The PKIX
[*note PKIX::] public key infrastructure is daily used by anyone using a
browser today.  GnuTLS provides a simple API to verify the X.509
certificates as in [*note PKIX::].

The key exchange algorithms supported by certificate authentication are
shown in *note Table 4.1: tab:key-exchange.

Key exchange   Description
               
------------------------------------------------------------------
RSA            The RSA algorithm is used to encrypt a key and
               send it to the peer.  The certificate must allow
               the key to be used for encryption.
               
DHE_RSA        The RSA algorithm is used to sign ephemeral
               Diffie-Hellman parameters which are sent to the
               peer.  The key in the certificate must allow the
               key to be used for signing.  Note that key
               exchange algorithms which use ephemeral
               Diffie-Hellman parameters, offer perfect forward
               secrecy.  That means that even if the private
               key used for signing is compromised, it cannot
               be used to reveal past session data.
               
ECDHE_RSA      The RSA algorithm is used to sign ephemeral
               elliptic curve Diffie-Hellman parameters which
               are sent to the peer.  The key in the
               certificate must allow the key to be used for
               signing.  It also offers perfect forward
               secrecy.  That means that even if the private
               key used for signing is compromised, it cannot
               be used to reveal past session data.
               
DHE_DSS        The DSA algorithm is used to sign ephemeral
               Diffie-Hellman parameters which are sent to the
               peer.  The certificate must contain DSA
               parameters to use this key exchange algorithm.
               DSA is the algorithm of the Digital Signature
               Standard (DSS).
               
ECDHE_ECDSA    The Elliptic curve DSA algorithm is used to sign
               ephemeral elliptic curve Diffie-Hellman
               parameters which are sent to the peer.  The
               certificate must contain ECDSA parameters (i.e.,
               EC and marked for signing) to use this key
               exchange algorithm.

Table 4.1: Supported key exchange algorithms.

* Menu:

* X.509 certificates::
* OpenPGP certificates::
* Raw public-keys::
* Advanced certificate verification::
* Digital signatures::

File: gnutls.info,  Node: X.509 certificates,  Next: OpenPGP certificates,  Up: Certificate authentication

4.1.1 X.509 certificates
------------------------

The X.509 protocols rely on a hierarchical trust model.  In this trust
model Certification Authorities (CAs) are used to certify entities.
Usually more than one certification authorities exist, and certification
authorities may certify other authorities to issue certificates as well,
following a hierarchical model.

�[image src="gnutls-x509.png"�]

Figure 4.1: An example of the X.509 hierarchical trust model.

One needs to trust one or more CAs for his secure communications.  In
that case only the certificates issued by the trusted authorities are
acceptable.  The framework is illustrated on *note Figure 4.1: fig-x509.

* Menu:

* X.509 certificate structure::
* Importing an X.509 certificate::
* X.509 certificate names::
* X.509 distinguished names::
* X.509 extensions::
* X.509 public and private keys::
* Verifying X.509 certificate paths::
* Verifying a certificate in the context of TLS session::
* Verification using PKCS11::

File: gnutls.info,  Node: X.509 certificate structure,  Next: Importing an X.509 certificate,  Up: X.509 certificates

4.1.1.1 X.509 certificate structure
...................................

An X.509 certificate usually contains information about the certificate
holder, the signer, a unique serial number, expiration dates and some
other fields [*note PKIX::] as shown in *note Table 4.2: tab:x509.

Field          Description
               
------------------------------------------------------------------
version        The field that indicates the version of the
               certificate.
               
serialNumber   This field holds a unique serial number per
               certificate.
               
signature      The issuing authority's signature.
               
issuer         Holds the issuer's distinguished name.
               
validity       The activation and expiration dates.
               
subject        The subject's distinguished name of the
               certificate.
               
extensions     The extensions are fields only present in
               version 3 certificates.

Table 4.2: X.509 certificate fields.

The certificate's _subject or issuer name_ is not just a single string.
It is a Distinguished name and in the ASN.1 notation is a sequence of
several object identifiers with their corresponding values.  Some of
available OIDs to be used in an X.509 distinguished name are defined in
‘gnutls/x509.h’.

The _Version_ field in a certificate has values either 1 or 3 for
version 3 certificates.  Version 1 certificates do not support the
extensions field so it is not possible to distinguish a CA from a
person, thus their usage should be avoided.

The _validity_ dates are there to indicate the date that the specific
certificate was activated and the date the certificate's key would be
considered invalid.

In GnuTLS the X.509 certificate structures are handled using the
‘gnutls_x509_crt_t’ type and the corresponding private keys with the
‘gnutls_x509_privkey_t’ type.  All the available functions for X.509
certificate handling have their prototypes in ‘gnutls/x509.h’.  An
example program to demonstrate the X.509 parsing capabilities can be
found in *note ex-x509-info::.

File: gnutls.info,  Node: Importing an X.509 certificate,  Next: X.509 certificate names,  Prev: X.509 certificate structure,  Up: X.509 certificates

4.1.1.2 Importing an X.509 certificate
......................................

The certificate structure should be initialized using *note
gnutls_x509_crt_init::, and a certificate structure can be imported
using *note gnutls_x509_crt_import::.

‘INT *note gnutls_x509_crt_init:: (gnutls_x509_crt_t * CERT)’
‘INT *note gnutls_x509_crt_import:: (gnutls_x509_crt_t CERT, const gnutls_datum_t * DATA, gnutls_x509_crt_fmt_t FORMAT)’
‘VOID *note gnutls_x509_crt_deinit:: (gnutls_x509_crt_t CERT)’

In several functions an array of certificates is required.  To assist in
initialization and import the following two functions are provided.

‘INT *note gnutls_x509_crt_list_import:: (gnutls_x509_crt_t * CERTS, unsigned int * CERT_MAX, const gnutls_datum_t * DATA, gnutls_x509_crt_fmt_t FORMAT, unsigned int FLAGS)’
‘INT *note gnutls_x509_crt_list_import2:: (gnutls_x509_crt_t ** CERTS, unsigned int * SIZE, const gnutls_datum_t * DATA, gnutls_x509_crt_fmt_t FORMAT, unsigned int FLAGS)’

In all cases after use a certificate must be deinitialized using *note
gnutls_x509_crt_deinit::.  Note that although the functions above apply
to ‘gnutls_x509_crt_t’ structure, similar functions exist for the CRL
structure ‘gnutls_x509_crl_t’.

File: gnutls.info,  Node: X.509 certificate names,  Next: X.509 distinguished names,  Prev: Importing an X.509 certificate,  Up: X.509 certificates

4.1.1.3 X.509 certificate names
...............................

X.509 certificates allow for multiple names and types of names to be
specified.  CA certificates often rely on X.509 distinguished names (see
*note X.509 distinguished names::) for unique identification, while
end-user and server certificates rely on the 'subject alternative
names'.  The subject alternative names provide a typed name, e.g., a DNS
name, or an email address, which identifies the owner of the
certificate.  The following functions provide access to that names.

‘INT *note gnutls_x509_crt_get_subject_alt_name2:: (gnutls_x509_crt_t CERT, unsigned int SEQ, void * SAN, size_t * SAN_SIZE, unsigned int * SAN_TYPE, unsigned int * CRITICAL)’
‘INT *note gnutls_x509_crt_set_subject_alt_name:: (gnutls_x509_crt_t CRT, gnutls_x509_subject_alt_name_t TYPE, const void * DATA, unsigned int DATA_SIZE, unsigned int FLAGS)’
‘INT *note gnutls_subject_alt_names_init:: (gnutls_subject_alt_names_t * SANS)’
‘INT *note gnutls_subject_alt_names_get:: (gnutls_subject_alt_names_t SANS, unsigned int SEQ, unsigned int * SAN_TYPE, gnutls_datum_t * SAN, gnutls_datum_t * OTHERNAME_OID)’
‘INT *note gnutls_subject_alt_names_set:: (gnutls_subject_alt_names_t SANS, unsigned int SAN_TYPE, const gnutls_datum_t * SAN, const char * OTHERNAME_OID)’

Note however, that server certificates often used the Common Name (CN),
part of the certificate DistinguishedName to place a single DNS address.
That practice is discouraged (see [*note RFC6125::]), because only a
single address can be specified, and the CN field is free-form making
matching ambiguous.

File: gnutls.info,  Node: X.509 distinguished names,  Next: X.509 extensions,  Prev: X.509 certificate names,  Up: X.509 certificates

4.1.1.4 X.509 distinguished names
.................................

The "subject" of an X.509 certificate is not described by a single name,
but rather with a distinguished name.  This in X.509 terminology is a
list of strings each associated an object identifier.  To make things
simple GnuTLS provides *note gnutls_x509_crt_get_dn2:: which follows the
rules in [*note RFC4514::] and returns a single string.  Access to each
string by individual object identifiers can be accessed using *note
gnutls_x509_crt_get_dn_by_oid::.

-- Function: int gnutls_x509_crt_get_dn2 (gnutls_x509_crt_t CERT,
          gnutls_datum_t * DN)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

DN: a pointer to a structure to hold the name; must be freed using
     ‘gnutls_free()’

This function will allocate buffer and copy the name of the
     Certificate.  The name will be in the form "C=xxxx,O=yyyy,CN=zzzz"
     as described in RFC4514.  The output string will be ASCII or UTF-8
     encoded, depending on the certificate data.

This function does not output a fully RFC4514 compliant string, if
     that is required see ‘gnutls_x509_crt_get_dn3()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.1.10
‘INT *note gnutls_x509_crt_get_dn:: (gnutls_x509_crt_t CERT, char * BUF, size_t * BUF_SIZE)’
‘INT *note gnutls_x509_crt_get_dn_by_oid:: (gnutls_x509_crt_t CERT, const char * OID, unsigned INDX, unsigned int RAW_FLAG, void * BUF, size_t * BUF_SIZE)’
‘INT *note gnutls_x509_crt_get_dn_oid:: (gnutls_x509_crt_t CERT, unsigned INDX, void * OID, size_t * OID_SIZE)’

Similar functions exist to access the distinguished name of the issuer
of the certificate.

‘INT *note gnutls_x509_crt_get_issuer_dn:: (gnutls_x509_crt_t CERT, char * BUF, size_t * BUF_SIZE)’
‘INT *note gnutls_x509_crt_get_issuer_dn2:: (gnutls_x509_crt_t CERT, gnutls_datum_t * DN)’
‘INT *note gnutls_x509_crt_get_issuer_dn_by_oid:: (gnutls_x509_crt_t CERT, const char * OID, unsigned INDX, unsigned int RAW_FLAG, void * BUF, size_t * BUF_SIZE)’
‘INT *note gnutls_x509_crt_get_issuer_dn_oid:: (gnutls_x509_crt_t CERT, unsigned INDX, void * OID, size_t * OID_SIZE)’
‘INT *note gnutls_x509_crt_get_issuer:: (gnutls_x509_crt_t CERT, gnutls_x509_dn_t * DN)’

The more powerful *note gnutls_x509_crt_get_subject:: and *note
gnutls_x509_dn_get_rdn_ava:: provide efficient but low-level access to
the contents of the distinguished name structure.

‘INT *note gnutls_x509_crt_get_subject:: (gnutls_x509_crt_t CERT, gnutls_x509_dn_t * DN)’
‘INT *note gnutls_x509_crt_get_issuer:: (gnutls_x509_crt_t CERT, gnutls_x509_dn_t * DN)’

-- Function: int gnutls_x509_dn_get_rdn_ava (gnutls_x509_dn_t DN, int
          IRDN, int IAVA, gnutls_x509_ava_st * AVA)
     DN: a pointer to DN

IRDN: index of RDN

IAVA: index of AVA.

AVA: Pointer to structure which will hold output information.

Get pointers to data within the DN. The format of the ‘ava’
     structure is shown below.

struct gnutls_x509_ava_st { gnutls_datum_t oid; gnutls_datum_t
     value; unsigned long value_tag; };

The X.509 distinguished name is a sequence of sequences of strings
     and this is what the ‘irdn’ and ‘iava’ indexes model.

Note that ‘ava’ will contain pointers into the ‘dn’ structure which
     in turns points to the original certificate.  Thus you should not
     modify any data or deallocate any of those.

This is a low-level function that requires the caller to do the
     value conversions when necessary (e.g.  from UCS-2).

*Returns:* Returns 0 on success, or an error code.

File: gnutls.info,  Node: X.509 extensions,  Next: X.509 public and private keys,  Prev: X.509 distinguished names,  Up: X.509 certificates

4.1.1.5 X.509 extensions
........................

X.509 version 3 certificates include a list of extensions that can be
used to obtain additional information on the subject or the issuer of
the certificate.  Those may be e-mail addresses, flags that indicate
whether the belongs to a CA etc.  All the supported X.509 version 3
extensions are shown in *note Table 4.3: tab:x509-ext.

The certificate extensions access is split into two parts.  The first
requires to retrieve the extension, and the second is the parsing part.

To enumerate and retrieve the DER-encoded extension data available in a
certificate the following two functions are available.
‘INT *note gnutls_x509_crt_get_extension_info:: (gnutls_x509_crt_t CERT, unsigned INDX, void * OID, size_t * OID_SIZE, unsigned int * CRITICAL)’
‘INT *note gnutls_x509_crt_get_extension_data2:: (gnutls_x509_crt_t CERT, unsigned INDX, gnutls_datum_t * DATA)’
‘INT *note gnutls_x509_crt_get_extension_by_oid2:: (gnutls_x509_crt_t CERT, const char * OID, unsigned INDX, gnutls_datum_t * OUTPUT, unsigned int * CRITICAL)’

After a supported DER-encoded extension is retrieved it can be parsed
using the APIs in ‘x509-ext.h’.  Complex extensions may require
initializing an intermediate structure that holds the parsed extension
data.  Examples of simple parsing functions are shown below.
‘INT *note gnutls_x509_ext_import_basic_constraints:: (const gnutls_datum_t * EXT, unsigned int * CA, int * PATHLEN)’
‘INT *note gnutls_x509_ext_export_basic_constraints:: (unsigned int CA, int PATHLEN, gnutls_datum_t * EXT)’
‘INT *note gnutls_x509_ext_import_key_usage:: (const gnutls_datum_t * EXT, unsigned int * KEY_USAGE)’
‘INT *note gnutls_x509_ext_export_key_usage:: (unsigned int USAGE, gnutls_datum_t * EXT)’

More complex extensions, such as Name Constraints, require an
intermediate structure, in that case ‘gnutls_x509_name_constraints_t’ to
be initialized in order to store the parsed extension data.
‘INT *note gnutls_x509_ext_import_name_constraints:: (const gnutls_datum_t * EXT, gnutls_x509_name_constraints_t NC, unsigned int FLAGS)’
‘INT *note gnutls_x509_ext_export_name_constraints:: (gnutls_x509_name_constraints_t NC, gnutls_datum_t * EXT)’

After the name constraints are extracted in the structure, the following
functions can be used to access them.

‘INT *note gnutls_x509_name_constraints_get_permitted:: (gnutls_x509_name_constraints_t NC, unsigned IDX, unsigned * TYPE, gnutls_datum_t * NAME)’
‘INT *note gnutls_x509_name_constraints_get_excluded:: (gnutls_x509_name_constraints_t NC, unsigned IDX, unsigned * TYPE, gnutls_datum_t * NAME)’
‘INT *note gnutls_x509_name_constraints_add_permitted:: (gnutls_x509_name_constraints_t NC, gnutls_x509_subject_alt_name_t TYPE, const gnutls_datum_t * NAME)’
‘INT *note gnutls_x509_name_constraints_add_excluded:: (gnutls_x509_name_constraints_t NC, gnutls_x509_subject_alt_name_t TYPE, const gnutls_datum_t * NAME)’
‘UNSIGNED *note gnutls_x509_name_constraints_check:: (gnutls_x509_name_constraints_t NC, gnutls_x509_subject_alt_name_t TYPE, const gnutls_datum_t * NAME)’
‘UNSIGNED *note gnutls_x509_name_constraints_check_crt:: (gnutls_x509_name_constraints_t NC, gnutls_x509_subject_alt_name_t TYPE, gnutls_x509_crt_t CERT)’

Other utility functions are listed below.
‘INT *note gnutls_x509_name_constraints_init:: (gnutls_x509_name_constraints_t * NC)’
‘VOID *note gnutls_x509_name_constraints_deinit:: (gnutls_x509_name_constraints_t NC)’

Similar functions exist for all of the other supported extensions,
listed in *note Table 4.3: tab:x509-ext.

Extension              OID            Description
                                      
--------------------------------------------------------------------
Subject key id         2.5.29.14      An identifier of the key of
                                      the subject.
                                      
Key usage              2.5.29.15      Constraints the key's usage
                                      of the certificate.
                                      
Private key usage      2.5.29.16      Constraints the validity
period                                time of the private key.
                                      
Subject alternative    2.5.29.17      Alternative names to
name                                  subject's distinguished
                                      name.
                                      
Issuer alternative     2.5.29.18      Alternative names to the
name                                  issuer's distinguished
                                      name.
                                      
Basic constraints      2.5.29.19      Indicates whether this is a
                                      CA certificate or not, and
                                      specify the maximum path
                                      lengths of certificate
                                      chains.
                                      
Name constraints       2.5.29.30      A field in CA certificates
                                      that restricts the scope of
                                      the name of issued
                                      certificates.
                                      
CRL distribution       2.5.29.31      This extension is set by
points                                the CA, in order to inform
                                      about the location of
                                      issued Certificate
                                      Revocation Lists.
                                      
Certificate policy     2.5.29.32      This extension is set to
                                      indicate the certificate
                                      policy as object identifier
                                      and may contain a
                                      descriptive string or URL.
                                      
Extended key usage     2.5.29.54      Inhibit any policy
                                      extension.  Constraints the
                                      any policy OID
                                      (‘GNUTLS_X509_OID_POLICY_ANY’)
                                      use in the policy
                                      extension.
                                      
Authority key          2.5.29.35      An identifier of the key of
identifier                            the issuer of the
                                      certificate.  That is used
                                      to distinguish between
                                      different keys of the same
                                      issuer.
                                      
Extended key usage     2.5.29.37      Constraints the purpose of
                                      the certificate.
                                      
Authority              1.3.6.1.5.5.7.1.1Information on services by
information access                    the issuer of the
                                      certificate.
                                      
Proxy Certification    1.3.6.1.5.5.7.1.14Proxy Certificates includes
Information                           this extension that
                                      contains the OID of the
                                      proxy policy language used,
                                      and can specify limits on
                                      the maximum lengths of
                                      proxy chains.  Proxy
                                      Certificates are specified
                                      in [*note RFC3820::].

Table 4.3: Supported X.509 certificate extensions.

Note, that there are also direct APIs to access extensions that may be
simpler to use for non-complex extensions.  They are available in
‘x509.h’ and some examples are listed below.
‘INT *note gnutls_x509_crt_get_basic_constraints:: (gnutls_x509_crt_t CERT, unsigned int * CRITICAL, unsigned int * CA, int * PATHLEN)’
‘INT *note gnutls_x509_crt_set_basic_constraints:: (gnutls_x509_crt_t CRT, unsigned int CA, int PATHLENCONSTRAINT)’
‘INT *note gnutls_x509_crt_get_key_usage:: (gnutls_x509_crt_t CERT, unsigned int * KEY_USAGE, unsigned int * CRITICAL)’
‘INT *note gnutls_x509_crt_set_key_usage:: (gnutls_x509_crt_t CRT, unsigned int USAGE)’

File: gnutls.info,  Node: X.509 public and private keys,  Next: Verifying X.509 certificate paths,  Prev: X.509 extensions,  Up: X.509 certificates

4.1.1.6 Accessing public and private keys
.........................................

Each X.509 certificate contains a public key that corresponds to a
private key.  To get a unique identifier of the public key the *note
gnutls_x509_crt_get_key_id:: function is provided.  To export the public
key or its parameters you may need to convert the X.509 structure to a
‘gnutls_pubkey_t’.  See *note Abstract public keys:: for more
information.

-- Function: int gnutls_x509_crt_get_key_id (gnutls_x509_crt_t CRT,
          unsigned int FLAGS, unsigned char * OUTPUT_DATA, size_t *
          OUTPUT_DATA_SIZE)
     CRT: Holds the certificate

FLAGS: should be one of the flags from ‘gnutls_keyid_flags_t’

OUTPUT_DATA: will contain the key ID

OUTPUT_DATA_SIZE: holds the size of output_data (and will be
     replaced by the actual size of parameters)

This function will return a unique ID that depends on the public
     key parameters.  This ID can be used in checking whether a
     certificate corresponds to the given private key.

If the buffer provided is not long enough to hold the output, then
     *output_data_size is updated and GNUTLS_E_SHORT_MEMORY_BUFFER will
     be returned.  The output will normally be a SHA-1 hash output,
     which is 20 bytes.

*Returns:* In case of failure a negative error code will be
     returned, and 0 on success.

The private key parameters may be directly accessed by using one of the
following functions.

‘INT *note gnutls_x509_privkey_get_pk_algorithm2:: (gnutls_x509_privkey_t KEY, unsigned int * BITS)’
‘INT *note gnutls_x509_privkey_export_rsa_raw2:: (gnutls_x509_privkey_t KEY, gnutls_datum_t * M, gnutls_datum_t * E, gnutls_datum_t * D, gnutls_datum_t * P, gnutls_datum_t * Q, gnutls_datum_t * U, gnutls_datum_t * E1, gnutls_datum_t * E2)’
‘INT *note gnutls_x509_privkey_export_ecc_raw:: (gnutls_x509_privkey_t KEY, gnutls_ecc_curve_t * CURVE, gnutls_datum_t * X, gnutls_datum_t * Y, gnutls_datum_t * K)’
‘INT *note gnutls_x509_privkey_export_dsa_raw:: (gnutls_x509_privkey_t KEY, gnutls_datum_t * P, gnutls_datum_t * Q, gnutls_datum_t * G, gnutls_datum_t * Y, gnutls_datum_t * X)’
‘INT *note gnutls_x509_privkey_get_key_id:: (gnutls_x509_privkey_t KEY, unsigned int FLAGS, unsigned char * OUTPUT_DATA, size_t * OUTPUT_DATA_SIZE)’

File: gnutls.info,  Node: Verifying X.509 certificate paths,  Next: Verifying a certificate in the context of TLS session,  Prev: X.509 public and private keys,  Up: X.509 certificates

4.1.1.7 Verifying X.509 certificate paths
.........................................

Verifying certificate paths is important in X.509 authentication.  For
this purpose the following functions are provided.

-- Function: int gnutls_x509_trust_list_add_cas
          (gnutls_x509_trust_list_t LIST, const gnutls_x509_crt_t *
          CLIST, unsigned CLIST_SIZE, unsigned int FLAGS)
     LIST: The list

CLIST: A list of CAs

CLIST_SIZE: The length of the CA list

FLAGS: flags from ‘gnutls_trust_list_flags_t’

This function will add the given certificate authorities to the
     trusted list.  The CAs in ‘clist’ must not be deinitialized during
     the lifetime of ‘list’ .

If the flag ‘GNUTLS_TL_NO_DUPLICATES’ is specified, then this
     function will ensure that no duplicates will be present in the
     final trust list.

If the flag ‘GNUTLS_TL_NO_DUPLICATE_KEY’ is specified, then this
     function will ensure that no certificates with the same key are
     present in the final trust list.

If either ‘GNUTLS_TL_NO_DUPLICATE_KEY’ or ‘GNUTLS_TL_NO_DUPLICATES’
     are given, ‘gnutls_x509_trust_list_deinit()’ must be called with
     parameter ‘all’ being 1.

*Returns:* The number of added elements is returned; that includes
     duplicate entries.

*Since:* 3.0.0

-- Function: int gnutls_x509_trust_list_add_named_crt
          (gnutls_x509_trust_list_t LIST, gnutls_x509_crt_t CERT, const
          void * NAME, size_t NAME_SIZE, unsigned int FLAGS)
     LIST: The list

CERT: A certificate

NAME: An identifier for the certificate

NAME_SIZE: The size of the identifier

FLAGS: should be 0.

This function will add the given certificate to the trusted list
     and associate it with a name.  The certificate will not be be used
     for verification with ‘gnutls_x509_trust_list_verify_crt()’ but
     with ‘gnutls_x509_trust_list_verify_named_crt()’ or
     ‘gnutls_x509_trust_list_verify_crt2()’ - the latter only since
     GnuTLS 3.4.0 and if a hostname is provided.

In principle this function can be used to set individual "server"
     certificates that are trusted by the user for that specific server
     but for no other purposes.

The certificate ‘cert’ must not be deinitialized during the
     lifetime of the ‘list’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.0.0

-- Function: int gnutls_x509_trust_list_add_crls
          (gnutls_x509_trust_list_t LIST, const gnutls_x509_crl_t *
          CRL_LIST, unsigned CRL_SIZE, unsigned int FLAGS, unsigned int
          VERIFICATION_FLAGS)
     LIST: The list

CRL_LIST: A list of CRLs

CRL_SIZE: The length of the CRL list

FLAGS: flags from ‘gnutls_trust_list_flags_t’

VERIFICATION_FLAGS: gnutls_certificate_verify_flags if flags
     specifies GNUTLS_TL_VERIFY_CRL

This function will add the given certificate revocation lists to
     the trusted list.  The CRLs in ‘crl_list’ must not be deinitialized
     during the lifetime of ‘list’ .

This function must be called after
     ‘gnutls_x509_trust_list_add_cas()’ to allow verifying the CRLs for
     validity.  If the flag ‘GNUTLS_TL_NO_DUPLICATES’ is given, then the
     final CRL list will not contain duplicate entries.

If the flag ‘GNUTLS_TL_NO_DUPLICATES’ is given,
     ‘gnutls_x509_trust_list_deinit()’ must be called with parameter
     ‘all’ being 1.

If flag ‘GNUTLS_TL_VERIFY_CRL’ is given the CRLs will be verified
     before being added, and if verification fails, they will be
     skipped.

*Returns:* The number of added elements is returned; that includes
     duplicate entries.

*Since:* 3.0

-- Function: int gnutls_x509_trust_list_verify_crt
          (gnutls_x509_trust_list_t LIST, gnutls_x509_crt_t * CERT_LIST,
          unsigned int CERT_LIST_SIZE, unsigned int FLAGS, unsigned int
          * VOUTPUT, gnutls_verify_output_function FUNC)
     LIST: The list

CERT_LIST: is the certificate list to be verified

CERT_LIST_SIZE: is the certificate list size

FLAGS: Flags that may be used to change the verification algorithm.
     Use OR of the gnutls_certificate_verify_flags enumerations.

VOUTPUT: will hold the certificate verification output.

FUNC: If non-null will be called on each chain element verification
     with the output.

This function will try to verify the given certificate and return
     its status.  The ‘voutput’ parameter will hold an OR'ed sequence of
     ‘gnutls_certificate_status_t’ flags.

The details of the verification are the same as in
     ‘gnutls_x509_trust_list_verify_crt2()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.0

-- Function: int gnutls_x509_trust_list_verify_crt2
          (gnutls_x509_trust_list_t LIST, gnutls_x509_crt_t * CERT_LIST,
          unsigned int CERT_LIST_SIZE, gnutls_typed_vdata_st * DATA,
          unsigned int ELEMENTS, unsigned int FLAGS, unsigned int *
          VOUTPUT, gnutls_verify_output_function FUNC)
     LIST: The list

CERT_LIST: is the certificate list to be verified

CERT_LIST_SIZE: is the certificate list size

DATA: an array of typed data

ELEMENTS: the number of data elements

FLAGS: Flags that may be used to change the verification algorithm.
     Use OR of the gnutls_certificate_verify_flags enumerations.

VOUTPUT: will hold the certificate verification output.

FUNC: If non-null will be called on each chain element verification
     with the output.

This function will attempt to verify the given certificate chain
     and return its status.  The ‘voutput’ parameter will hold an OR'ed
     sequence of ‘gnutls_certificate_status_t’ flags.

When a certificate chain of ‘cert_list_size’ with more than one
     certificates is provided, the verification status will apply to the
     first certificate in the chain that failed verification.  The
     verification process starts from the end of the chain (from CA to
     end certificate).  The first certificate in the chain must be the
     end-certificate while the rest of the members may be sorted or not.

Additionally a certificate verification profile can be specified
     from the ones in ‘gnutls_certificate_verification_profiles_t’ by
     ORing the result of ‘GNUTLS_PROFILE_TO_VFLAGS()’ to the
     verification flags.

Additional verification parameters are possible via the ‘data’
     types; the acceptable types are ‘GNUTLS_DT_DNS_HOSTNAME’ ,
     ‘GNUTLS_DT_IP_ADDRESS’ and ‘GNUTLS_DT_KEY_PURPOSE_OID’ .  The
     former accepts as data a null-terminated hostname, and the latter a
     null-terminated object identifier (e.g., ‘GNUTLS_KP_TLS_WWW_SERVER’
     ).  If a DNS hostname is provided then this function will compare
     the hostname in the end certificate against the given.  If names do
     not match the ‘GNUTLS_CERT_UNEXPECTED_OWNER’ status flag will be
     set.  In addition it will consider certificates provided with
     ‘gnutls_x509_trust_list_add_named_crt()’ .

If a key purpose OID is provided and the end-certificate contains
     the extended key usage PKIX extension, it will be required to match
     the provided OID or be marked for any purpose, otherwise
     verification will fail with ‘GNUTLS_CERT_PURPOSE_MISMATCH’ status.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.  Note that verification failure
     will not result to an error code, only ‘voutput’ will be updated.

*Since:* 3.3.8

-- Function: int gnutls_x509_trust_list_verify_named_crt
          (gnutls_x509_trust_list_t LIST, gnutls_x509_crt_t CERT, const
          void * NAME, size_t NAME_SIZE, unsigned int FLAGS, unsigned
          int * VOUTPUT, gnutls_verify_output_function FUNC)
     LIST: The list

CERT: is the certificate to be verified

NAME: is the certificate's name

NAME_SIZE: is the certificate's name size

FLAGS: Flags that may be used to change the verification algorithm.
     Use OR of the gnutls_certificate_verify_flags enumerations.

VOUTPUT: will hold the certificate verification output.

FUNC: If non-null will be called on each chain element verification
     with the output.

This function will try to find a certificate that is associated
     with the provided name -see
     ‘gnutls_x509_trust_list_add_named_crt()’ .  If a match is found the
     certificate is considered valid.  In addition to that this function
     will also check CRLs.  The ‘voutput’ parameter will hold an OR'ed
     sequence of ‘gnutls_certificate_status_t’ flags.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.0.0

-- Function: int gnutls_x509_trust_list_add_trust_file
          (gnutls_x509_trust_list_t LIST, const char * CA_FILE, const
          char * CRL_FILE, gnutls_x509_crt_fmt_t TYPE, unsigned int
          TL_FLAGS, unsigned int TL_VFLAGS)
     LIST: The list

CA_FILE: A file containing a list of CAs (optional)

CRL_FILE: A file containing a list of CRLs (optional)

TYPE: The format of the certificates

TL_FLAGS: flags from ‘gnutls_trust_list_flags_t’

TL_VFLAGS: gnutls_certificate_verify_flags if flags specifies
     GNUTLS_TL_VERIFY_CRL

This function will add the given certificate authorities to the
     trusted list.  PKCS ‘11’ URLs are also accepted, instead of files,
     by this function.  A PKCS ‘11’ URL implies a trust database (a
     specially marked module in p11-kit); the URL "pkcs11:" implies all
     trust databases in the system.  Only a single URL specifying trust
     databases can be set; they cannot be stacked with multiple calls.

*Returns:* The number of added elements is returned.

*Since:* 3.1

-- Function: int gnutls_x509_trust_list_add_trust_mem
          (gnutls_x509_trust_list_t LIST, const gnutls_datum_t * CAS,
          const gnutls_datum_t * CRLS, gnutls_x509_crt_fmt_t TYPE,
          unsigned int TL_FLAGS, unsigned int TL_VFLAGS)
     LIST: The list

CAS: A buffer containing a list of CAs (optional)

CRLS: A buffer containing a list of CRLs (optional)

TYPE: The format of the certificates

TL_FLAGS: flags from ‘gnutls_trust_list_flags_t’

TL_VFLAGS: gnutls_certificate_verify_flags if flags specifies
     GNUTLS_TL_VERIFY_CRL

This function will add the given certificate authorities to the
     trusted list.

If this function is used ‘gnutls_x509_trust_list_deinit()’ must be
     called with parameter ‘all’ being 1.

*Returns:* The number of added elements is returned.

*Since:* 3.1

-- Function: int gnutls_x509_trust_list_add_system_trust
          (gnutls_x509_trust_list_t LIST, unsigned int TL_FLAGS,
          unsigned int TL_VFLAGS)
     LIST: The structure of the list

TL_FLAGS: GNUTLS_TL_*

TL_VFLAGS: gnutls_certificate_verify_flags if flags specifies
     GNUTLS_TL_VERIFY_CRL

This function adds the system's default trusted certificate
     authorities to the trusted list.  Note that on unsupported systems
     this function returns ‘GNUTLS_E_UNIMPLEMENTED_FEATURE’ .

This function implies the flag ‘GNUTLS_TL_NO_DUPLICATES’ .

*Returns:* The number of added elements or a negative error code on
     error.

*Since:* 3.1

The verification function will verify a given certificate chain against
a list of certificate authorities and certificate revocation lists, and
output a bit-wise OR of elements of the ‘gnutls_certificate_status_t’
enumeration shown in *note Figure 4.2: gnutls_certificate_status_t.  The
‘GNUTLS_CERT_INVALID’ flag is always set on a verification error and
more detailed flags will also be set when appropriate.

‘GNUTLS_CERT_INVALID’
     The certificate is not signed by one of the known authorities or
     the signature is invalid (deprecated by the flags
     ‘GNUTLS_CERT_SIGNATURE_FAILURE’ and ‘GNUTLS_CERT_SIGNER_NOT_FOUND’
     ).
‘GNUTLS_CERT_REVOKED’
     Certificate is revoked by its authority.  In X.509 this will be set
     only if CRLs are checked.
‘GNUTLS_CERT_SIGNER_NOT_FOUND’
     The certificate's issuer is not known.  This is the case if the
     issuer is not included in the trusted certificate list.
‘GNUTLS_CERT_SIGNER_NOT_CA’
     The certificate's signer was not a CA. This may happen if this was
     a version 1 certificate, which is common with some CAs, or a
     version 3 certificate without the basic constrains extension.
‘GNUTLS_CERT_INSECURE_ALGORITHM’
     The certificate was signed using an insecure algorithm such as MD2
     or MD5.  These algorithms have been broken and should not be
     trusted.
‘GNUTLS_CERT_NOT_ACTIVATED’
     The certificate is not yet activated.
‘GNUTLS_CERT_EXPIRED’
     The certificate has expired.
‘GNUTLS_CERT_SIGNATURE_FAILURE’
     The signature verification failed.
‘GNUTLS_CERT_REVOCATION_DATA_SUPERSEDED’
     The revocation data are old and have been superseded.
‘GNUTLS_CERT_UNEXPECTED_OWNER’
     The owner is not the expected one.
‘GNUTLS_CERT_REVOCATION_DATA_ISSUED_IN_FUTURE’
     The revocation data have a future issue date.
‘GNUTLS_CERT_SIGNER_CONSTRAINTS_FAILURE’
     The certificate's signer constraints were violated.
‘GNUTLS_CERT_MISMATCH’
     The certificate presented isn't the expected one (TOFU)
‘GNUTLS_CERT_PURPOSE_MISMATCH’
     The certificate or an intermediate does not match the intended
     purpose (extended key usage).
‘GNUTLS_CERT_MISSING_OCSP_STATUS’
     The certificate requires the server to send the certificate status,
     but no status was received.
‘GNUTLS_CERT_INVALID_OCSP_STATUS’
     The received OCSP status response is invalid.
‘GNUTLS_CERT_UNKNOWN_CRIT_EXTENSIONS’
     The certificate has extensions marked as critical which are not
     supported.

Figure 4.2: The ‘gnutls_certificate_status_t’ enumeration.

An example of certificate verification is shown in *note ex-verify2::.
It is also possible to have a set of certificates that are trusted for a
particular server but not to authorize other certificates.  This purpose
is served by the functions *note gnutls_x509_trust_list_add_named_crt::
and *note gnutls_x509_trust_list_verify_named_crt::.

File: gnutls.info,  Node: Verifying a certificate in the context of TLS session,  Next: Verification using PKCS11,  Prev: Verifying X.509 certificate paths,  Up: X.509 certificates

4.1.1.8 Verifying a certificate in the context of TLS session
.............................................................

When operating in the context of a TLS session, the trusted certificate
authority list may also be set using:
‘INT *note gnutls_certificate_set_x509_trust_file:: (gnutls_certificate_credentials_t CRED, const char * CAFILE, gnutls_x509_crt_fmt_t TYPE)’
‘INT *note gnutls_certificate_set_x509_trust_dir:: (gnutls_certificate_credentials_t CRED, const char * CA_DIR, gnutls_x509_crt_fmt_t TYPE)’
‘INT *note gnutls_certificate_set_x509_crl_file:: (gnutls_certificate_credentials_t RES, const char * CRLFILE, gnutls_x509_crt_fmt_t TYPE)’
‘INT *note gnutls_certificate_set_x509_system_trust:: (gnutls_certificate_credentials_t CRED)’

These functions allow the specification of the trusted certificate
authorities, either via a file, a directory or use the system-specified
certificate authorities.  Unless the authorities are application
specific, it is generally recommended to use the system trust storage
(see *note gnutls_certificate_set_x509_system_trust::).

Unlike the previous section it is not required to setup a trusted list,
and there are two approaches to verify the peer's certificate and
identity.  The recommended in GnuTLS 3.5.0 and later is via the *note
gnutls_session_set_verify_cert::, but for older GnuTLS versions you may
use an explicit callback set via *note
gnutls_certificate_set_verify_function:: and then utilize *note
gnutls_certificate_verify_peers3:: for verification.  The reported
verification status is identical to the verification functions described
in the previous section.

Note that in certain cases it is required to check the marked purpose of
the end certificate (e.g.  ‘GNUTLS_KP_TLS_WWW_SERVER’); in these cases
the more advanced *note gnutls_session_set_verify_cert2:: and *note
gnutls_certificate_verify_peers:: should be used instead.

There is also the possibility to pass some input to the verification
functions in the form of flags.  For *note
gnutls_x509_trust_list_verify_crt2:: the flags are passed directly, but
for *note gnutls_certificate_verify_peers3::, the flags are set using
*note gnutls_certificate_set_verify_flags::.  All the available flags
are part of the enumeration ‘gnutls_certificate_verify_flags’ shown in
*note Figure 4.3: gnutls_certificate_verify_flags.

‘GNUTLS_VERIFY_DISABLE_CA_SIGN’
     If set a signer does not have to be a certificate authority.  This
     flag should normally be disabled, unless you know what this means.
‘GNUTLS_VERIFY_DO_NOT_ALLOW_IP_MATCHES’
     When verifying a hostname prevent textual IP addresses from
     matching IP addresses in the certificate.  Treat the input only as
     a DNS name.
‘GNUTLS_VERIFY_DO_NOT_ALLOW_SAME’
     If a certificate is not signed by anyone trusted but exists in the
     trusted CA list do not treat it as trusted.
‘GNUTLS_VERIFY_ALLOW_ANY_X509_V1_CA_CRT’
     Allow CA certificates that have version 1 (both root and
     intermediate).  This might be dangerous since those haven't the
     basicConstraints extension.
‘GNUTLS_VERIFY_ALLOW_SIGN_RSA_MD2’
     Allow certificates to be signed using the broken MD2 algorithm.
‘GNUTLS_VERIFY_ALLOW_SIGN_RSA_MD5’
     Allow certificates to be signed using the broken MD5 algorithm.
‘GNUTLS_VERIFY_DISABLE_TIME_CHECKS’
     Disable checking of activation and expiration validity periods of
     certificate chains.  Don't set this unless you understand the
     security implications.
‘GNUTLS_VERIFY_DISABLE_TRUSTED_TIME_CHECKS’
     If set a signer in the trusted list is never checked for expiration
     or activation.
‘GNUTLS_VERIFY_DO_NOT_ALLOW_X509_V1_CA_CRT’
     Do not allow trusted CA certificates that have version 1.  This
     option is to be used to deprecate all certificates of version 1.
‘GNUTLS_VERIFY_DISABLE_CRL_CHECKS’
     Disable checking for validity using certificate revocation lists or
     the available OCSP data.
‘GNUTLS_VERIFY_ALLOW_UNSORTED_CHAIN’
     A certificate chain is tolerated if unsorted (the case with many
     TLS servers out there).  This is the default since GnuTLS 3.1.4.
‘GNUTLS_VERIFY_DO_NOT_ALLOW_UNSORTED_CHAIN’
     Do not tolerate an unsorted certificate chain.
‘GNUTLS_VERIFY_DO_NOT_ALLOW_WILDCARDS’
     When including a hostname check in the verification, do not
     consider any wildcards.
‘GNUTLS_VERIFY_USE_TLS1_RSA’
     This indicates that a (raw) RSA signature is provided as in the TLS
     1.0 protocol.  Not all functions accept this flag.
‘GNUTLS_VERIFY_IGNORE_UNKNOWN_CRIT_EXTENSIONS’
     This signals the verification process, not to fail on unknown
     critical extensions.
‘GNUTLS_VERIFY_ALLOW_SIGN_WITH_SHA1’
     Allow certificates to be signed using the broken SHA1 hash
     algorithm.
‘GNUTLS_VERIFY_RSA_PSS_FIXED_SALT_LENGTH’
     Disallow RSA-PSS signatures made with mismatching salt length with
     digest length, as mandated in RFC 8446 4.2.3.

Figure 4.3: The ‘gnutls_certificate_verify_flags’ enumeration.

File: gnutls.info,  Node: Verification using PKCS11,  Prev: Verifying a certificate in the context of TLS session,  Up: X.509 certificates

4.1.1.9 Verifying a certificate using PKCS #11
..............................................

Some systems provide a system wide trusted certificate storage
accessible using the PKCS #11 API. That is, the trusted certificates are
queried and accessed using the PKCS #11 API, and trusted certificate
properties, such as purpose, are marked using attached extensions.  One
example is the p11-kit trust module(1).

These special PKCS #11 modules can be used for GnuTLS certificate
verification if marked as trust policy modules, i.e., with
‘trust-policy: yes’ in the p11-kit module file.  The way to use them is
by specifying to the file verification function (e.g., *note
gnutls_certificate_set_x509_trust_file::), a pkcs11 URL, or simply
‘pkcs11:’ to use all the marked with trust policy modules.

The trust modules of p11-kit assign a purpose to trusted authorities
using the extended key usage object identifiers.  The common purposes
are shown in *note Table 4.4: tab:purposes.  Note that typically
according to [*note RFC5280::] the extended key usage object identifiers
apply to end certificates.  Their application to CA certificates is an
extension used by the trust modules.

Purpose        OID            Description
                              
--------------------------------------------------------------------------
GNUTLS_KP_TLS_WWW_SERVER1.3.6.1.5.5.7.3.1The certificate is to be used for TLS WWW
                              authentication.  When in a CA
                              certificate, it indicates that the CA is
                              allowed to sign certificates for TLS WWW
                              authentication.
                              
GNUTLS_KP_TLS_WWW_CLIENT1.3.6.1.5.5.7.3.2The certificate is to be used for TLS WWW
                              client authentication.  When in a CA
                              certificate, it indicates that the CA is
                              allowed to sign certificates for TLS WWW
                              client authentication.
                              
GNUTLS_KP_CODE_SIGNING1.3.6.1.5.5.7.3.3The certificate is to be used for code
                              signing.  When in a CA certificate, it
                              indicates that the CA is allowed to sign
                              certificates for code signing.
                              
GNUTLS_KP_EMAIL_PROTECTION1.3.6.1.5.5.7.3.4The certificate is to be used for email
                              protection.  When in a CA certificate, it
                              indicates that the CA is allowed to sign
                              certificates for email users.
                              
GNUTLS_KP_OCSP_SIGNING1.3.6.1.5.5.7.3.9The certificate is to be used for signing
                              OCSP responses.  When in a CA
                              certificate, it indicates that the CA is
                              allowed to sign certificates which sign
                              OCSP responses.
                              
GNUTLS_KP_ANY  2.5.29.37.0    The certificate is to be used for any
                              purpose.  When in a CA certificate, it
                              indicates that the CA is allowed to sign
                              any kind of certificates.

Table 4.4: Key purpose object identifiers.

With such modules, it is recommended to use the verification functions
*note gnutls_x509_trust_list_verify_crt2::, or *note
gnutls_certificate_verify_peers::, which allow to explicitly specify the
key purpose.  The other verification functions which do not allow
setting a purpose, would operate as if ‘GNUTLS_KP_TLS_WWW_SERVER’ was
requested from the trusted authorities.

---------- Footnotes ----------

(1) see <https://p11-glue.github.io/p11-glue/trust-module.html>.

File: gnutls.info,  Node: OpenPGP certificates,  Next: Raw public-keys,  Prev: X.509 certificates,  Up: Certificate authentication

4.1.2 OpenPGP certificates
--------------------------

Previous versions of GnuTLS supported limited OpenPGP key
authentication.  That functionality has been deprecated and is no longer
made available.  The reason is that, supporting alternative
authentication methods, when X.509 and PKIX were new on the Internet and
not well established, seemed like a good idea, in today's Internet X.509
is unquestionably the main container for certificates.  As such
supporting more options with no clear use-cases, is a distraction that
consumes considerable resources for improving and testing the library.
For that we have decided to drop this functionality completely in 3.6.0.

File: gnutls.info,  Node: Raw public-keys,  Next: Advanced certificate verification,  Prev: OpenPGP certificates,  Up: Certificate authentication

4.1.3 Raw public-keys
---------------------

There are situations in which a rather large certificate / certificate
chain is undesirable or impractical.  An example could be a resource
constrained sensor network in which you do want to use authentication of
and encryption between your devices but where your devices lack loads of
memory or processing power.  Furthermore, there are situations in which
you don't want to or can't rely on a PKIX. TLS is, next to a PKIX
environment, also commonly used with self-signed certificates in smaller
deployments where the self-signed certificates are distributed to all
involved protocol endpoints out-of-band.  This practice does, however,
still require the overhead of the certificate generation even though
none of the information found in the certificate is actually used.

With raw public-keys, only a subset of the information found in typical
certificates is utilized: namely, the SubjectPublicKeyInfo structure (in
ASN.1 format) of a PKIX certificate that carries the parameters
necessary to describe the public-key.  Other parameters found in PKIX
certificates are omitted.  By omitting various certificate-related
structures, the resulting raw public-key is kept fairly small in
comparison to the original certificate, and the code to process the keys
can be simpler.

It should be noted however, that the authenticity of these raw keys must
be verified by an out-of-band mechanism or something like TOFU.

* Menu:

* Importing raw public-keys::

File: gnutls.info,  Node: Importing raw public-keys,  Up: Raw public-keys

4.1.3.1 Importing raw public-keys
.................................

Raw public-keys and their private counterparts can best be handled by
using the abstract types ‘gnutls_pubkey_t’ and ‘gnutls_privkey_t’
respectively.  To learn how to use these see *note Abstract key types::.

File: gnutls.info,  Node: Advanced certificate verification,  Next: Digital signatures,  Prev: Raw public-keys,  Up: Certificate authentication

4.1.4 Advanced certificate verification
---------------------------------------

The verification of X.509 certificates in the HTTPS and other Internet
protocols is typically done by loading a trusted list of commercial
Certificate Authorities (see *note
gnutls_certificate_set_x509_system_trust::), and using them as trusted
anchors.  However, there are several examples (eg.  the Diginotar
incident) where one of these authorities was compromised.  This risk can
be mitigated by using in addition to CA certificate verification, other
verification methods.  In this section we list the available in GnuTLS
methods.

* Menu:

* Verifying a certificate using trust on first use authentication::
* Verifying a certificate using DANE::

File: gnutls.info,  Node: Verifying a certificate using trust on first use authentication,  Next: Verifying a certificate using DANE,  Up: Advanced certificate verification

4.1.4.1 Verifying a certificate using trust on first use authentication
.......................................................................

It is possible to use a trust on first use (TOFU) authentication method
in GnuTLS. That is the concept used by the SSH programs, where the
public key of the peer is not verified, or verified in an out-of-bound
way, but subsequent connections to the same peer require the public key
to remain the same.  Such a system in combination with the typical CA
verification of a certificate, and OCSP revocation checks, can help to
provide multiple factor verification, where a single point of failure is
not enough to compromise the system.  For example a server compromise
may be detected using OCSP, and a CA compromise can be detected using
the trust on first use method.  Such a hybrid system with X.509 and
trust on first use authentication is shown in *note Client example with
SSH-style certificate verification::.

See *note Certificate verification:: on how to use the available
functionality.

File: gnutls.info,  Node: Verifying a certificate using DANE,  Prev: Verifying a certificate using trust on first use authentication,  Up: Advanced certificate verification

4.1.4.2 Verifying a certificate using DANE (DNSSEC)
...................................................

The DANE protocol is a protocol that can be used to verify TLS
certificates using the DNS (or better DNSSEC) protocols.  The DNS
security extensions (DNSSEC) provide an alternative public key
infrastructure to the commercial CAs that are typically used to sign TLS
certificates.  The DANE protocol takes advantage of the DNSSEC
infrastructure to verify TLS certificates.  This can be in addition to
the verification by CA infrastructure or may even replace it where
DNSSEC is fully deployed.  Note however, that DNSSEC deployment is
fairly new and it would be better to use it as an additional
verification method rather than the only one.

The DANE functionality is provided by the ‘libgnutls-dane’ library that
is shipped with GnuTLS and the function prototypes are in
‘gnutls/dane.h’.  See *note Certificate verification:: for information
on how to use the library.

Note however, that the DANE RFC mandates the verification methods one
should use in addition to the validation via DNSSEC TLSA entries.
GnuTLS doesn't follow that RFC requirement, and the term DANE
verification in this manual refers to the TLSA entry verification.  In
GnuTLS any other verification methods can be used (e.g., PKIX or TOFU)
on top of DANE.

File: gnutls.info,  Node: Digital signatures,  Prev: Advanced certificate verification,  Up: Certificate authentication

4.1.5 Digital signatures
------------------------

In this section we will provide some information about digital
signatures, how they work, and give the rationale for disabling some of
the algorithms used.

Digital signatures work by using somebody's secret key to sign some
arbitrary data.  Then anybody else could use the public key of that
person to verify the signature.  Since the data may be arbitrary it is
not suitable input to a cryptographic digital signature algorithm.  For
this reason and also for performance cryptographic hash algorithms are
used to preprocess the input to the signature algorithm.  This works as
long as it is difficult enough to generate two different messages with
the same hash algorithm output.  In that case the same signature could
be used as a proof for both messages.  Nobody wants to sign an innocent
message of donating 1 euro to Greenpeace and find out that they donated
1.000.000 euros to Bad Inc.

For a hash algorithm to be called cryptographic the following three
requirements must hold:

1. Preimage resistance.  That means the algorithm must be one way and
     given the output of the hash function H(x), it is impossible to
     calculate x.

2. 2nd preimage resistance.  That means that given a pair x,y with
     y=H(x) it is impossible to calculate an x' such that y=H(x').

3. Collision resistance.  That means that it is impossible to
     calculate random x and x' such H(x')=H(x).

The last two requirements in the list are the most important in digital
signatures.  These protect against somebody who would like to generate
two messages with the same hash output.  When an algorithm is considered
broken usually it means that the Collision resistance of the algorithm
is less than brute force.  Using the birthday paradox the brute force
attack takes 2^{((hash size) / 2)} operations.  Today colliding
certificates using the MD5 hash algorithm have been generated as shown
in [*note WEGER::].

There has been cryptographic results for the SHA-1 hash algorithms as
well, although they are not yet critical.  Before 2004, MD5 had a
presumed collision strength of 2^{64}, but it has been showed to have a
collision strength well under 2^{50}.  As of November 2005, it is
believed that SHA-1's collision strength is around 2^{63}.  We consider
this sufficiently hard so that we still support SHA-1.  We anticipate
that SHA-256/386/512 will be used in publicly-distributed certificates
in the future.  When 2^{63} can be considered too weak compared to the
computer power available sometime in the future, SHA-1 will be disabled
as well.  The collision attacks on SHA-1 may also get better, given the
new interest in tools for creating them.

4.1.5.1 Trading security for interoperability
.............................................

If you connect to a server and use GnuTLS' functions to verify the
certificate chain, and get a ‘GNUTLS_CERT_INSECURE_ALGORITHM’ validation
error (see *note Verifying X.509 certificate paths::), it means that
somewhere in the certificate chain there is a certificate signed using
‘RSA-MD2’ or ‘RSA-MD5’.  These two digital signature algorithms are
considered broken, so GnuTLS fails verifying the certificate.  In some
situations, it may be useful to be able to verify the certificate chain
anyway, assuming an attacker did not utilize the fact that these
signatures algorithms are broken.  This section will give help on how to
achieve that.

It is important to know that you do not have to enable any of the flags
discussed here to be able to use trusted root CA certificates
self-signed using ‘RSA-MD2’ or ‘RSA-MD5’.  The certificates in the
trusted list are considered trusted irrespective of the signature.

If you are using *note gnutls_certificate_verify_peers3:: to verify the
certificate chain, you can call *note
gnutls_certificate_set_verify_flags:: with the flags:
   • ‘GNUTLS_VERIFY_ALLOW_SIGN_RSA_MD2’
   • ‘GNUTLS_VERIFY_ALLOW_SIGN_RSA_MD5’
   • ‘GNUTLS_VERIFY_ALLOW_SIGN_WITH_SHA1’
   • ‘GNUTLS_VERIFY_ALLOW_BROKEN’
as in the following example:

gnutls_certificate_set_verify_flags (x509cred,
                                            GNUTLS_VERIFY_ALLOW_SIGN_RSA_MD5);

This will signal the verifier algorithm to enable ‘RSA-MD5’ when
verifying the certificates.

If you are using *note gnutls_x509_crt_verify:: or *note
gnutls_x509_crt_list_verify::, you can pass the
‘GNUTLS_VERIFY_ALLOW_SIGN_RSA_MD5’ parameter directly in the ‘flags’
parameter.

If you are using these flags, it may also be a good idea to warn the
user when verification failure occur for this reason.  The simplest is
to not use the flags by default, and only fall back to using them after
warning the user.  If you wish to inspect the certificate chain
yourself, you can use *note gnutls_certificate_get_peers:: to extract
the raw server's certificate chain, *note gnutls_x509_crt_list_import::
to parse each of the certificates, and then *note
gnutls_x509_crt_get_signature_algorithm:: to find out the signing
algorithm used for each certificate.  If any of the intermediary
certificates are using ‘GNUTLS_SIGN_RSA_MD2’ or ‘GNUTLS_SIGN_RSA_MD5’,
you could present a warning.

File: gnutls.info,  Node: More on certificate authentication,  Next: Shared-key and anonymous authentication,  Prev: Certificate authentication,  Up: Authentication methods

4.2 More on certificate authentication
======================================

Certificates are not the only structures involved in a public key
infrastructure.  Several other structures that are used for certificate
requests, encrypted private keys, revocation lists, GnuTLS abstract key
structures, etc., are discussed in this chapter.

* Menu:

* PKCS 10 certificate requests::
* PKIX certificate revocation lists::
* OCSP certificate status checking::
* OCSP stapling::
* Managing encrypted keys::
* certtool Invocation::            Invoking certtool
* ocsptool Invocation::            Invoking ocsptool
* danetool Invocation::            Invoking danetool

File: gnutls.info,  Node: PKCS 10 certificate requests,  Next: PKIX certificate revocation lists,  Up: More on certificate authentication

4.2.1 PKCS #10 certificate requests
-----------------------------------

A certificate request is a structure, which contain information about an
applicant of a certificate service.  It typically contains a public key,
a distinguished name and secondary data such as a challenge password.
GnuTLS supports the requests defined in PKCS #10 [*note RFC2986::].
Other formats of certificate requests are not currently supported by
GnuTLS.

A certificate request can be generated by associating it with a private
key, setting the subject's information and finally self signing it.  The
last step ensures that the requester is in possession of the private
key.

‘INT *note gnutls_x509_crq_set_version:: (gnutls_x509_crq_t CRQ, unsigned int VERSION)’
‘INT *note gnutls_x509_crq_set_dn:: (gnutls_x509_crq_t CRQ, const char * DN, const char ** ERR)’
‘INT *note gnutls_x509_crq_set_dn_by_oid:: (gnutls_x509_crq_t CRQ, const char * OID, unsigned int RAW_FLAG, const void * DATA, unsigned int SIZEOF_DATA)’
‘INT *note gnutls_x509_crq_set_key_usage:: (gnutls_x509_crq_t CRQ, unsigned int USAGE)’
‘INT *note gnutls_x509_crq_set_key_purpose_oid:: (gnutls_x509_crq_t CRQ, const void * OID, unsigned int CRITICAL)’
‘INT *note gnutls_x509_crq_set_basic_constraints:: (gnutls_x509_crq_t CRQ, unsigned int CA, int PATHLENCONSTRAINT)’

The *note gnutls_x509_crq_set_key:: and *note gnutls_x509_crq_sign2::
functions associate the request with a private key and sign it.  If a
request is to be signed with a key residing in a PKCS #11 token it is
recommended to use the signing functions shown in *note Abstract key
types::.

-- Function: int gnutls_x509_crq_set_key (gnutls_x509_crq_t CRQ,
          gnutls_x509_privkey_t KEY)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

KEY: holds a private key

This function will set the public parameters from the given private
     key to the request.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

-- Function: int gnutls_x509_crq_sign2 (gnutls_x509_crq_t CRQ,
          gnutls_x509_privkey_t KEY, gnutls_digest_algorithm_t DIG,
          unsigned int FLAGS)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

KEY: holds a private key

DIG: The message digest to use, i.e., ‘GNUTLS_DIG_SHA256’

FLAGS: must be 0

This function will sign the certificate request with a private key.
     This must be the same key as the one used in
     ‘gnutls_x509_crt_set_key()’ since a certificate request is self
     signed.

This must be the last step in a certificate request generation
     since all the previously set parameters are now signed.

A known limitation of this function is, that a newly-signed request
     will not be fully functional (e.g., for signature verification),
     until it is exported an re-imported.

After GnuTLS 3.6.1 the value of ‘dig’ may be ‘GNUTLS_DIG_UNKNOWN’ ,
     and in that case, a suitable but reasonable for the key algorithm
     will be selected.

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, otherwise a negative
     error code.  ‘GNUTLS_E_ASN1_VALUE_NOT_FOUND’ is returned if you
     didn't set all information in the certificate request (e.g., the
     version using ‘gnutls_x509_crq_set_version()’ ).

The following example is about generating a certificate request, and a
private key.  A certificate request can be later be processed by a CA
which should return a signed certificate.

/* This example code is placed in the public domain. */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <gnutls/gnutls.h>
#include <gnutls/x509.h>
#include <gnutls/abstract.h>
#include <time.h>

/* This example will generate a private key and a certificate
 * request.
 */

int main(void)
{
	gnutls_x509_crq_t crq;
	gnutls_x509_privkey_t key;
	unsigned char buffer[10 * 1024];
	size_t buffer_size = sizeof(buffer);
	unsigned int bits;

gnutls_global_init();

/* Initialize an empty certificate request, and
	 * an empty private key.
	 */
	gnutls_x509_crq_init(&crq);

gnutls_x509_privkey_init(&key);

/* Generate an RSA key of moderate security.
	 */
	bits = gnutls_sec_param_to_pk_bits(GNUTLS_PK_RSA,
					   GNUTLS_SEC_PARAM_MEDIUM);
	gnutls_x509_privkey_generate(key, GNUTLS_PK_RSA, bits, 0);

/* Add stuff to the distinguished name
	 */
	gnutls_x509_crq_set_dn_by_oid(crq, GNUTLS_OID_X520_COUNTRY_NAME, 0,
				      "GR", 2);

gnutls_x509_crq_set_dn_by_oid(crq, GNUTLS_OID_X520_COMMON_NAME, 0,
				      "Nikos", strlen("Nikos"));

/* Set the request version.
	 */
	gnutls_x509_crq_set_version(crq, 1);

/* Set a challenge password.
	 */
	gnutls_x509_crq_set_challenge_password(crq,
					       "something to remember here");

/* Associate the request with the private key
	 */
	gnutls_x509_crq_set_key(crq, key);

/* Self sign the certificate request.
	 */
	gnutls_x509_crq_sign2(crq, key, GNUTLS_DIG_SHA1, 0);

/* Export the PEM encoded certificate request, and
	 * display it.
	 */
	gnutls_x509_crq_export(crq, GNUTLS_X509_FMT_PEM, buffer, &buffer_size);

printf("Certificate Request: \n%s", buffer);

/* Export the PEM encoded private key, and
	 * display it.
	 */
	buffer_size = sizeof(buffer);
	gnutls_x509_privkey_export(key, GNUTLS_X509_FMT_PEM, buffer,
				   &buffer_size);

printf("\n\nPrivate key: \n%s", buffer);

gnutls_x509_crq_deinit(crq);
	gnutls_x509_privkey_deinit(key);

return 0;
}

File: gnutls.info,  Node: PKIX certificate revocation lists,  Next: OCSP certificate status checking,  Prev: PKCS 10 certificate requests,  Up: More on certificate authentication

4.2.2 PKIX certificate revocation lists
---------------------------------------

A certificate revocation list (CRL) is a structure issued by an
authority periodically containing a list of revoked certificates serial
numbers.  The CRL structure is signed with the issuing authorities'
keys.  A typical CRL contains the fields as shown in *note Table 4.5:
tab:crl.  Certificate revocation lists are used to complement the
expiration date of a certificate, in order to account for other reasons
of revocation, such as compromised keys, etc.

Each CRL is valid for limited amount of time and is required to provide,
except for the current issuing time, also the issuing time of the next
update.

Field          Description
               
------------------------------------------------------------------
version        The field that indicates the version of the CRL
               structure.
               
signature      A signature by the issuing authority.
               
issuer         Holds the issuer's distinguished name.
               
thisUpdate     The issuing time of the revocation list.
               
nextUpdate     The issuing time of the revocation list that
               will update that one.
               
revokedCertificatesList of revoked certificates serial numbers.
               
extensions     Optional CRL structure extensions.

Table 4.5: Certificate revocation list fields.

The basic CRL structure functions follow.

‘INT *note gnutls_x509_crl_init:: (gnutls_x509_crl_t * CRL)’
‘INT *note gnutls_x509_crl_import:: (gnutls_x509_crl_t CRL, const gnutls_datum_t * DATA, gnutls_x509_crt_fmt_t FORMAT)’
‘INT *note gnutls_x509_crl_export:: (gnutls_x509_crl_t CRL, gnutls_x509_crt_fmt_t FORMAT, void * OUTPUT_DATA, size_t * OUTPUT_DATA_SIZE)’
‘INT *note gnutls_x509_crl_export:: (gnutls_x509_crl_t CRL, gnutls_x509_crt_fmt_t FORMAT, void * OUTPUT_DATA, size_t * OUTPUT_DATA_SIZE)’

Reading a CRL
.............

The most important function that extracts the certificate revocation
information from a CRL is *note gnutls_x509_crl_get_crt_serial::.  Other
functions that return other fields of the CRL structure are also
provided.

-- Function: int gnutls_x509_crl_get_crt_serial (gnutls_x509_crl_t CRL,
          unsigned INDX, unsigned char * SERIAL, size_t * SERIAL_SIZE,
          time_t * T)
     CRL: should contain a ‘gnutls_x509_crl_t’ type

INDX: the index of the certificate to extract (starting from 0)

SERIAL: where the serial number will be copied

SERIAL_SIZE: initially holds the size of serial

T: if non null, will hold the time this certificate was revoked

This function will retrieve the serial number of the specified, by
     the index, revoked certificate.

Note that this function will have performance issues in large
     sequences of revoked certificates.  In that case use
     ‘gnutls_x509_crl_iter_crt_serial()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

‘INT *note gnutls_x509_crl_get_version:: (gnutls_x509_crl_t CRL)’
‘INT *note gnutls_x509_crl_get_issuer_dn:: (gnutls_x509_crl_t CRL, char * BUF, size_t * SIZEOF_BUF)’
‘INT *note gnutls_x509_crl_get_issuer_dn2:: (gnutls_x509_crl_t CRL, gnutls_datum_t * DN)’
‘TIME_T *note gnutls_x509_crl_get_this_update:: (gnutls_x509_crl_t CRL)’
‘TIME_T *note gnutls_x509_crl_get_next_update:: (gnutls_x509_crl_t CRL)’
‘INT *note gnutls_x509_crl_get_crt_count:: (gnutls_x509_crl_t CRL)’

Generation of a CRL
...................

The following functions can be used to generate a CRL.

‘INT *note gnutls_x509_crl_set_version:: (gnutls_x509_crl_t CRL, unsigned int VERSION)’
‘INT *note gnutls_x509_crl_set_crt_serial:: (gnutls_x509_crl_t CRL, const void * SERIAL, size_t SERIAL_SIZE, time_t REVOCATION_TIME)’
‘INT *note gnutls_x509_crl_set_crt:: (gnutls_x509_crl_t CRL, gnutls_x509_crt_t CRT, time_t REVOCATION_TIME)’
‘INT *note gnutls_x509_crl_set_next_update:: (gnutls_x509_crl_t CRL, time_t EXP_TIME)’
‘INT *note gnutls_x509_crl_set_this_update:: (gnutls_x509_crl_t CRL, time_t ACT_TIME)’

The *note gnutls_x509_crl_sign2:: and *note
gnutls_x509_crl_privkey_sign:: functions sign the revocation list with a
private key.  The latter function can be used to sign with a key
residing in a PKCS #11 token.

-- Function: int gnutls_x509_crl_sign2 (gnutls_x509_crl_t CRL,
          gnutls_x509_crt_t ISSUER, gnutls_x509_privkey_t ISSUER_KEY,
          gnutls_digest_algorithm_t DIG, unsigned int FLAGS)
     CRL: should contain a gnutls_x509_crl_t type

ISSUER: is the certificate of the certificate issuer

ISSUER_KEY: holds the issuer's private key

DIG: The message digest to use.  GNUTLS_DIG_SHA256 is the safe
     choice unless you know what you're doing.

FLAGS: must be 0

This function will sign the CRL with the issuer's private key, and
     will copy the issuer's information into the CRL.

This must be the last step in a certificate CRL since all the
     previously set parameters are now signed.

A known limitation of this function is, that a newly-signed CRL
     will not be fully functional (e.g., for signature verification),
     until it is exported an re-imported.

After GnuTLS 3.6.1 the value of ‘dig’ may be ‘GNUTLS_DIG_UNKNOWN’ ,
     and in that case, a suitable but reasonable for the key algorithm
     will be selected.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

-- Function: int gnutls_x509_crl_privkey_sign (gnutls_x509_crl_t CRL,
          gnutls_x509_crt_t ISSUER, gnutls_privkey_t ISSUER_KEY,
          gnutls_digest_algorithm_t DIG, unsigned int FLAGS)
     CRL: should contain a gnutls_x509_crl_t type

ISSUER: is the certificate of the certificate issuer

ISSUER_KEY: holds the issuer's private key

DIG: The message digest to use.  GNUTLS_DIG_SHA256 is the safe
     choice unless you know what you're doing.

FLAGS: must be 0

This function will sign the CRL with the issuer's private key, and
     will copy the issuer's information into the CRL.

This must be the last step in a certificate CRL since all the
     previously set parameters are now signed.

A known limitation of this function is, that a newly-signed CRL
     will not be fully functional (e.g., for signature verification),
     until it is exported an re-imported.

After GnuTLS 3.6.1 the value of ‘dig’ may be ‘GNUTLS_DIG_UNKNOWN’ ,
     and in that case, a suitable but reasonable for the key algorithm
     will be selected.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

Since 2.12.0

Few extensions on the CRL structure are supported, including the CRL
number extension and the authority key identifier.

‘INT *note gnutls_x509_crl_set_number:: (gnutls_x509_crl_t CRL, const void * NR, size_t NR_SIZE)’
‘INT *note gnutls_x509_crl_set_authority_key_id:: (gnutls_x509_crl_t CRL, const void * ID, size_t ID_SIZE)’

File: gnutls.info,  Node: OCSP certificate status checking,  Next: OCSP stapling,  Prev: PKIX certificate revocation lists,  Up: More on certificate authentication

4.2.3 OCSP certificate status checking
--------------------------------------

Certificates may be revoked before their expiration time has been
reached.  There are several reasons for revoking certificates, but a
typical situation is when the private key associated with a certificate
has been compromised.  Traditionally, Certificate Revocation Lists
(CRLs) have been used by application to implement revocation checking,
however, several problems with CRLs have been identified [*note
RIVESTCRL::].

The Online Certificate Status Protocol, or OCSP [*note RFC2560::], is a
widely implemented protocol which performs certificate revocation status
checking.  An application that wish to verify the identity of a peer
will verify the certificate against a set of trusted certificates and
then check whether the certificate is listed in a CRL and/or perform an
OCSP check for the certificate.

Applications are typically expected to contact the OCSP server in order
to request the certificate validity status.  The OCSP server replies
with an OCSP response.  This section describes this online communication
(which can be avoided when using OCSP stapled responses, for that, see
*note OCSP stapling::).

Before performing the OCSP query, the application will need to figure
out the address of the OCSP server.  The OCSP server address can be
provided by the local user in manual configuration or may be stored in
the certificate that is being checked.  When stored in a certificate the
OCSP server is in the extension field called the Authority Information
Access (AIA). The following function extracts this information from a
certificate.

‘INT *note gnutls_x509_crt_get_authority_info_access:: (gnutls_x509_crt_t CRT, unsigned int SEQ, int WHAT, gnutls_datum_t * DATA, unsigned int * CRITICAL)’

There are several functions in GnuTLS for creating and manipulating OCSP
requests and responses.  The general idea is that a client application
creates an OCSP request object, stores some information about the
certificate to check in the request, and then exports the request in DER
format.  The request will then need to be sent to the OCSP responder,
which needs to be done by the application (GnuTLS does not send and
receive OCSP packets).  Normally an OCSP response is received that the
application will need to import into an OCSP response object.  The
digital signature in the OCSP response needs to be verified against a
set of trust anchors before the information in the response can be
trusted.

The ASN.1 structure of OCSP requests are briefly as follows.  It is
useful to review the structures to get an understanding of which fields
are modified by GnuTLS functions.

OCSPRequest     ::=     SEQUENCE {
         tbsRequest                  TBSRequest,
         optionalSignature   [0]     EXPLICIT Signature OPTIONAL }

TBSRequest      ::=     SEQUENCE {
         version             [0]     EXPLICIT Version DEFAULT v1,
         requestorName       [1]     EXPLICIT GeneralName OPTIONAL,
         requestList                 SEQUENCE OF Request,
         requestExtensions   [2]     EXPLICIT Extensions OPTIONAL }

Request         ::=     SEQUENCE {
         reqCert                     CertID,
         singleRequestExtensions     [0] EXPLICIT Extensions OPTIONAL }

CertID          ::=     SEQUENCE {
         hashAlgorithm       AlgorithmIdentifier,
         issuerNameHash      OCTET STRING, -- Hash of Issuer's DN
         issuerKeyHash       OCTET STRING, -- Hash of Issuers public key
         serialNumber        CertificateSerialNumber }

The basic functions to initialize, import, export and deallocate OCSP
requests are the following.

‘INT *note gnutls_ocsp_req_init:: (gnutls_ocsp_req_t * REQ)’
‘VOID *note gnutls_ocsp_req_deinit:: (gnutls_ocsp_req_t REQ)’
‘INT *note gnutls_ocsp_req_import:: (gnutls_ocsp_req_t REQ, const gnutls_datum_t * DATA)’
‘INT *note gnutls_ocsp_req_export:: (gnutls_ocsp_req_const_t REQ, gnutls_datum_t * DATA)’
‘INT *note gnutls_ocsp_req_print:: (gnutls_ocsp_req_const_t REQ, gnutls_ocsp_print_formats_t FORMAT, gnutls_datum_t * OUT)’

To generate an OCSP request the issuer name hash, issuer key hash, and
the checked certificate's serial number are required.  There are two
interfaces available for setting those in an OCSP request.  The is a
low-level function when you have the issuer name hash, issuer key hash,
and certificate serial number in binary form.  The second is more useful
if you have the certificate (and its issuer) in a ‘gnutls_x509_crt_t’
type.  There is also a function to extract this information from
existing an OCSP request.

‘INT *note gnutls_ocsp_req_add_cert_id:: (gnutls_ocsp_req_t REQ, gnutls_digest_algorithm_t DIGEST, const gnutls_datum_t * ISSUER_NAME_HASH, const gnutls_datum_t * ISSUER_KEY_HASH, const gnutls_datum_t * SERIAL_NUMBER)’
‘INT *note gnutls_ocsp_req_add_cert:: (gnutls_ocsp_req_t REQ, gnutls_digest_algorithm_t DIGEST, gnutls_x509_crt_t ISSUER, gnutls_x509_crt_t CERT)’
‘INT *note gnutls_ocsp_req_get_cert_id:: (gnutls_ocsp_req_const_t REQ, unsigned INDX, gnutls_digest_algorithm_t * DIGEST, gnutls_datum_t * ISSUER_NAME_HASH, gnutls_datum_t * ISSUER_KEY_HASH, gnutls_datum_t * SERIAL_NUMBER)’

Each OCSP request may contain a number of extensions.  Extensions are
identified by an Object Identifier (OID) and an opaque data buffer whose
syntax and semantics is implied by the OID. You can extract or set those
extensions using the following functions.

‘INT *note gnutls_ocsp_req_get_extension:: (gnutls_ocsp_req_const_t REQ, unsigned INDX, gnutls_datum_t * OID, unsigned int * CRITICAL, gnutls_datum_t * DATA)’
‘INT *note gnutls_ocsp_req_set_extension:: (gnutls_ocsp_req_t REQ, const char * OID, unsigned int CRITICAL, const gnutls_datum_t * DATA)’

A common OCSP Request extension is the nonce extension (OID
1.3.6.1.5.5.7.48.1.2), which is used to avoid replay attacks of earlier
recorded OCSP responses.  The nonce extension carries a value that is
intended to be sufficiently random and unique so that an attacker will
not be able to give a stale response for the same nonce.

‘INT *note gnutls_ocsp_req_get_nonce:: (gnutls_ocsp_req_const_t REQ, unsigned int * CRITICAL, gnutls_datum_t * NONCE)’
‘INT *note gnutls_ocsp_req_set_nonce:: (gnutls_ocsp_req_t REQ, unsigned int CRITICAL, const gnutls_datum_t * NONCE)’
‘INT *note gnutls_ocsp_req_randomize_nonce:: (gnutls_ocsp_req_t REQ)’

The OCSP response structures is a complex structure.  A simplified
overview of it is in *note Table 4.6: tab:ocsp-response.  Note that a
response may contain information on multiple certificates.

Field          Description
               
------------------------------------------------------------------
version        The OCSP response version number (typically 1).
               
responder ID   An identifier of the responder (DN name or a
               hash of its key).
               
issue time     The time the response was generated.
               
thisUpdate     The issuing time of the revocation information.
               
nextUpdate     The issuing time of the revocation information
               that will update that one.
               
               Revoked certificates
               
certificate    The status of the certificate.
status         
certificate    The certificate's serial number.
serial         
revocationTime The time the certificate was revoked.
               
revocationReasonThe reason the certificate was revoked.

Table 4.6: The most important OCSP response fields.

We provide basic functions for initialization, importing, exporting and
deallocating OCSP responses.

‘INT *note gnutls_ocsp_resp_init:: (gnutls_ocsp_resp_t * RESP)’
‘VOID *note gnutls_ocsp_resp_deinit:: (gnutls_ocsp_resp_t RESP)’
‘INT *note gnutls_ocsp_resp_import:: (gnutls_ocsp_resp_t RESP, const gnutls_datum_t * DATA)’
‘INT *note gnutls_ocsp_resp_export:: (gnutls_ocsp_resp_const_t RESP, gnutls_datum_t * DATA)’
‘INT *note gnutls_ocsp_resp_print:: (gnutls_ocsp_resp_const_t RESP, gnutls_ocsp_print_formats_t FORMAT, gnutls_datum_t * OUT)’

The utility function that extracts the revocation as well as other
information from a response is shown below.

-- Function: int gnutls_ocsp_resp_get_single (gnutls_ocsp_resp_const_t
          RESP, unsigned INDX, gnutls_digest_algorithm_t * DIGEST,
          gnutls_datum_t * ISSUER_NAME_HASH, gnutls_datum_t *
          ISSUER_KEY_HASH, gnutls_datum_t * SERIAL_NUMBER, unsigned int
          * CERT_STATUS, time_t * THIS_UPDATE, time_t * NEXT_UPDATE,
          time_t * REVOCATION_TIME, unsigned int * REVOCATION_REASON)
     RESP: should contain a ‘gnutls_ocsp_resp_t’ type

INDX: Specifies response number to get.  Use (0) to get the first
     one.

DIGEST: output variable with ‘gnutls_digest_algorithm_t’ hash
     algorithm

ISSUER_NAME_HASH: output buffer with hash of issuer's DN

ISSUER_KEY_HASH: output buffer with hash of issuer's public key

SERIAL_NUMBER: output buffer with serial number of certificate to
     check

CERT_STATUS: a certificate status, a ‘gnutls_ocsp_cert_status_t’
     enum.

THIS_UPDATE: time at which the status is known to be correct.

NEXT_UPDATE: when newer information will be available, or
     (time_t)-1 if unspecified

REVOCATION_TIME: when ‘cert_status’ is ‘GNUTLS_OCSP_CERT_REVOKED’ ,
     holds time of revocation.

REVOCATION_REASON: revocation reason, a ‘gnutls_x509_crl_reason_t’
     enum.

This function will return the certificate information of the ‘indx’
     'ed response in the Basic OCSP Response ‘resp’ .  The information
     returned corresponds to the OCSP SingleResponse structure except
     the final singleExtensions.

Each of the pointers to output variables may be NULL to indicate
     that the caller is not interested in that value.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.  If you have reached
     the last CertID available ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’
     will be returned.

The possible revocation reasons available in an OCSP response are shown
below.

‘GNUTLS_X509_CRLREASON_UNSPECIFIED’
     Unspecified reason.
‘GNUTLS_X509_CRLREASON_KEYCOMPROMISE’
     Private key compromised.
‘GNUTLS_X509_CRLREASON_CACOMPROMISE’
     CA compromised.
‘GNUTLS_X509_CRLREASON_AFFILIATIONCHANGED’
     Affiliation has changed.
‘GNUTLS_X509_CRLREASON_SUPERSEDED’
     Certificate superseded.
‘GNUTLS_X509_CRLREASON_CESSATIONOFOPERATION’
     Operation has ceased.
‘GNUTLS_X509_CRLREASON_CERTIFICATEHOLD’
     Certificate is on hold.
‘GNUTLS_X509_CRLREASON_REMOVEFROMCRL’
     Will be removed from delta CRL.
‘GNUTLS_X509_CRLREASON_PRIVILEGEWITHDRAWN’
     Privilege withdrawn.
‘GNUTLS_X509_CRLREASON_AACOMPROMISE’
     AA compromised.

Figure 4.4: The revocation reasons

Note, that the OCSP response needs to be verified against some set of
trust anchors before it can be relied upon.  It is also important to
check whether the received OCSP response corresponds to the certificate
being checked.

‘INT *note gnutls_ocsp_resp_verify:: (gnutls_ocsp_resp_const_t RESP, gnutls_x509_trust_list_t TRUSTLIST, unsigned int * VERIFY, unsigned int FLAGS)’
‘INT *note gnutls_ocsp_resp_verify_direct:: (gnutls_ocsp_resp_const_t RESP, gnutls_x509_crt_t ISSUER, unsigned int * VERIFY, unsigned int FLAGS)’
‘INT *note gnutls_ocsp_resp_check_crt:: (gnutls_ocsp_resp_const_t RESP, unsigned int INDX, gnutls_x509_crt_t CRT)’

File: gnutls.info,  Node: OCSP stapling,  Next: Managing encrypted keys,  Prev: OCSP certificate status checking,  Up: More on certificate authentication

4.2.4 OCSP stapling
-------------------

To avoid applications contacting the OCSP server directly, TLS servers
can provide a "stapled" OCSP response in the TLS handshake.  That way
the client application needs to do nothing more.  GnuTLS will
automatically consider the stapled OCSP response during the TLS
certificate verification (see *note gnutls_certificate_verify_peers2::).
To disable the automatic OCSP verification the flag
‘GNUTLS_VERIFY_DISABLE_CRL_CHECKS’ should be specified to *note
gnutls_certificate_set_verify_flags::.

Since GnuTLS 3.5.1 the client certificate verification will consider the
[*note RFC7633::] OCSP-Must-staple certificate extension, and will
consider it while checking for stapled OCSP responses.  If the extension
is present and no OCSP staple is found, the certificate verification
will fail and the status code ‘GNUTLS_CERT_MISSING_OCSP_STATUS’ will
returned from the verification function.

Under TLS 1.2 only one stapled response can be sent by a server, the
OCSP response associated with the end-certificate.  Under TLS 1.3 a
server can send multiple OCSP responses, typically one for each
certificate in the certificate chain.  The following functions can be
used by a client application to retrieve the OCSP responses as sent by
the server.

‘INT *note gnutls_ocsp_status_request_get:: (gnutls_session_t SESSION, gnutls_datum_t * RESPONSE)’
‘INT *note gnutls_ocsp_status_request_get2:: (gnutls_session_t SESSION, unsigned IDX, gnutls_datum_t * RESPONSE)’

GnuTLS servers can provide OCSP responses to their clients using the
following functions.

‘VOID *note gnutls_certificate_set_retrieve_function3:: (gnutls_certificate_credentials_t CRED, gnutls_certificate_retrieve_function3 * FUNC)’
‘INT *note gnutls_certificate_set_ocsp_status_request_file2:: (gnutls_certificate_credentials_t SC, const char * RESPONSE_FILE, unsigned IDX, gnutls_x509_crt_fmt_t FMT)’
‘UNSIGNED *note gnutls_ocsp_status_request_is_checked:: (gnutls_session_t SESSION, unsigned int FLAGS)’

A server is expected to provide the relevant certificate's OCSP
responses using *note
gnutls_certificate_set_ocsp_status_request_file2::, and ensure a
periodic reload/renew of the credentials.  An estimation of the OCSP
responses expiration can be obtained using the *note
gnutls_certificate_get_ocsp_expiration:: function.

-- Function: time_t gnutls_certificate_get_ocsp_expiration
          (gnutls_certificate_credentials_t SC, unsigned IDX, int OIDX,
          unsigned FLAGS)
     SC: is a credentials structure.

IDX: is a certificate chain index as returned by
     ‘gnutls_certificate_set_key()’ and friends

OIDX: is an OCSP response index

FLAGS: should be zero

This function returns the validity of the loaded OCSP responses, to
     provide information on when to reload/refresh them.

Note that the credentials structure should be read-only when in
     use, thus when reloading, either the credentials structure must not
     be in use by any sessions, or a new credentials structure should be
     allocated for new sessions.

When ‘oidx’ is (-1) then the minimum refresh time for all responses
     is returned.  Otherwise the index specifies the response
     corresponding to the ‘odix’ certificate in the certificate chain.

*Returns:* On success, the expiration time of the OCSP response.
     Otherwise (time_t)(-1) on error, or (time_t)-2 on out of bounds.

*Since:* 3.6.3

Prior to GnuTLS 3.6.4, the functions *note
gnutls_certificate_set_ocsp_status_request_function2:: *note
gnutls_certificate_set_ocsp_status_request_file:: were provided to set
OCSP responses.  These functions are still functional, but cannot be
used to set multiple OCSP responses as allowed by TLS1.3.

The responses can be updated periodically using the 'ocsptool' command
(see also *note ocsptool Invocation::).

ocsptool --ask --load-cert server_cert.pem --load-issuer the_issuer.pem
              --load-signer the_issuer.pem --outfile ocsp.resp

In order to allow multiple OCSP responses to be concatenated, GnuTLS
supports PEM-encoded OCSP responses.  These can be generated using
'ocsptool' with the '-no-outder' parameter.

File: gnutls.info,  Node: Managing encrypted keys,  Next: certtool Invocation,  Prev: OCSP stapling,  Up: More on certificate authentication

4.2.5 Managing encrypted keys
-----------------------------

Transferring or storing private keys in plain may not be a good idea,
since any compromise is irreparable.  Storing the keys in hardware
security modules (see *note Smart cards and HSMs::) could solve the
storage problem but it is not always practical or efficient enough.
This section describes ways to store and transfer encrypted private
keys.

There are methods for key encryption, namely the PKCS #8, PKCS #12 and
OpenSSL's custom encrypted private key formats.  The PKCS #8 and the
OpenSSL's method allow encryption of the private key, while the PKCS #12
method allows, in addition, the bundling of accompanying data into the
structure.  That is typically the corresponding certificate, as well as
a trusted CA certificate.

High level functionality
........................

Generic and higher level private key import functions are available,
that import plain or encrypted keys and will auto-detect the encrypted
key format.

-- Function: int gnutls_privkey_import_x509_raw (gnutls_privkey_t PKEY,
          const gnutls_datum_t * DATA, gnutls_x509_crt_fmt_t FORMAT,
          const char * PASSWORD, unsigned int FLAGS)
     PKEY: The private key

DATA: The private key data to be imported

FORMAT: The format of the private key

PASSWORD: A password (optional)

FLAGS: an ORed sequence of gnutls_pkcs_encrypt_flags_t

This function will import the given private key to the abstract
     ‘gnutls_privkey_t’ type.

The supported formats are basic unencrypted key, PKCS8, PKCS12,
     TSS2, and the openssl format.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.1.0

-- Function: int gnutls_x509_privkey_import2 (gnutls_x509_privkey_t
          KEY, const gnutls_datum_t * DATA, gnutls_x509_crt_fmt_t
          FORMAT, const char * PASSWORD, unsigned int FLAGS)
     KEY: The data to store the parsed key

DATA: The DER or PEM encoded key.

FORMAT: One of DER or PEM

PASSWORD: A password (optional)

FLAGS: an ORed sequence of gnutls_pkcs_encrypt_flags_t

This function will import the given DER or PEM encoded key, to the
     native ‘gnutls_x509_privkey_t’ format, irrespective of the input
     format.  The input format is auto-detected.

The supported formats are basic unencrypted key, PKCS8, PKCS12, and
     the openssl format.

If the provided key is encrypted but no password was given, then
     ‘GNUTLS_E_DECRYPTION_FAILED’ is returned.  Since GnuTLS 3.4.0 this
     function will utilize the PIN callbacks if any.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

Any keys imported using those functions can be imported to a certificate
credentials structure using *note gnutls_certificate_set_key::, or
alternatively they can be directly imported using *note
gnutls_certificate_set_x509_key_file2::.

PKCS #8 structures
..................

PKCS #8 keys can be imported and exported as normal private keys using
the functions below.  An addition to the normal import functions, are a
password and a flags argument.  The flags can be any element of the
‘gnutls_pkcs_encrypt_flags_t’ enumeration.  Note however, that GnuTLS
only supports the PKCS #5 PBES2 encryption scheme.  Keys encrypted with
the obsolete PBES1 scheme cannot be decrypted.

‘INT *note gnutls_x509_privkey_import_pkcs8:: (gnutls_x509_privkey_t KEY, const gnutls_datum_t * DATA, gnutls_x509_crt_fmt_t FORMAT, const char * PASSWORD, unsigned int FLAGS)’
‘INT *note gnutls_x509_privkey_export_pkcs8:: (gnutls_x509_privkey_t KEY, gnutls_x509_crt_fmt_t FORMAT, const char * PASSWORD, unsigned int FLAGS, void * OUTPUT_DATA, size_t * OUTPUT_DATA_SIZE)’
‘INT *note gnutls_x509_privkey_export2_pkcs8:: (gnutls_x509_privkey_t KEY, gnutls_x509_crt_fmt_t FORMAT, const char * PASSWORD, unsigned int FLAGS, gnutls_datum_t * OUT)’

‘GNUTLS_PKCS_PLAIN’
     Unencrypted private key.
‘GNUTLS_PKCS_PKCS12_3DES’
     PKCS-12 3DES.
‘GNUTLS_PKCS_PKCS12_ARCFOUR’
     PKCS-12 ARCFOUR.
‘GNUTLS_PKCS_PKCS12_RC2_40’
     PKCS-12 RC2-40.
‘GNUTLS_PKCS_PBES2_3DES’
     PBES2 3DES.
‘GNUTLS_PKCS_PBES2_AES_128’
     PBES2 AES-128.
‘GNUTLS_PKCS_PBES2_AES_192’
     PBES2 AES-192.
‘GNUTLS_PKCS_PBES2_AES_256’
     PBES2 AES-256.
‘GNUTLS_PKCS_NULL_PASSWORD’
     Some schemas distinguish between an empty and a NULL password.
‘GNUTLS_PKCS_PBES2_DES’
     PBES2 single DES.
‘GNUTLS_PKCS_PBES1_DES_MD5’
     PBES1 with single DES; for compatibility with openssl only.
‘GNUTLS_PKCS_PBES2_GOST_TC26Z’
     PBES2 GOST 28147-89 CFB with TC26-Z S-box.
‘GNUTLS_PKCS_PBES2_GOST_CPA’
     PBES2 GOST 28147-89 CFB with CryptoPro-A S-box.
‘GNUTLS_PKCS_PBES2_GOST_CPB’
     PBES2 GOST 28147-89 CFB with CryptoPro-B S-box.
‘GNUTLS_PKCS_PBES2_GOST_CPC’
     PBES2 GOST 28147-89 CFB with CryptoPro-C S-box.
‘GNUTLS_PKCS_PBES2_GOST_CPD’
     PBES2 GOST 28147-89 CFB with CryptoPro-D S-box.
‘GNUTLS_PKCS_PBES1_DES_SHA1’
     PBES1 with single DES; for compatibility purposes only.

Figure 4.5: Encryption flags

PKCS #12 structures
...................

A PKCS #12 structure [*note PKCS12::] usually contains a user's private
keys and certificates.  It is commonly used in browsers to export and
import the user's identities.  A file containing such a key can be
directly imported to a certificate credentials structure by using *note
gnutls_certificate_set_x509_simple_pkcs12_file::.

In GnuTLS the PKCS #12 structures are handled using the
‘gnutls_pkcs12_t’ type.  This is an abstract type that may hold several
‘gnutls_pkcs12_bag_t’ types.  The bag types are the holders of the
actual data, which may be certificates, private keys or encrypted data.
A bag of type encrypted should be decrypted in order for its data to be
accessed.

To reduce the complexity in parsing the structures the simple helper
function *note gnutls_pkcs12_simple_parse:: is provided.  For more
advanced uses, manual parsing of the structure is required using the
functions below.

‘INT *note gnutls_pkcs12_get_bag:: (gnutls_pkcs12_t PKCS12, int INDX, gnutls_pkcs12_bag_t BAG)’
‘INT *note gnutls_pkcs12_verify_mac:: (gnutls_pkcs12_t PKCS12, const char * PASS)’
‘INT *note gnutls_pkcs12_bag_decrypt:: (gnutls_pkcs12_bag_t BAG, const char * PASS)’
‘INT *note gnutls_pkcs12_bag_get_count:: (gnutls_pkcs12_bag_t BAG)’

-- Function: int gnutls_pkcs12_simple_parse (gnutls_pkcs12_t P12, const
          char * PASSWORD, gnutls_x509_privkey_t * KEY,
          gnutls_x509_crt_t ** CHAIN, unsigned int * CHAIN_LEN,
          gnutls_x509_crt_t ** EXTRA_CERTS, unsigned int *
          EXTRA_CERTS_LEN, gnutls_x509_crl_t * CRL, unsigned int FLAGS)
     P12: A pkcs12 type

PASSWORD: optional password used to decrypt the structure, bags and
     keys.

KEY: a structure to store the parsed private key.

CHAIN: the corresponding to key certificate chain (may be ‘NULL’ )

CHAIN_LEN: will be updated with the number of additional (may be
     ‘NULL’ )

EXTRA_CERTS: optional pointer to receive an array of additional
     certificates found in the PKCS12 structure (may be ‘NULL’ ).

EXTRA_CERTS_LEN: will be updated with the number of additional
     certs (may be ‘NULL’ ).

CRL: an optional structure to store the parsed CRL (may be ‘NULL’
     ).

FLAGS: should be zero or one of GNUTLS_PKCS12_SP_*

This function parses a PKCS12 structure in ‘pkcs12’ and extracts
     the private key, the corresponding certificate chain, any
     additional certificates and a CRL. The structures in ‘key’ ,
     ‘chain’ ‘crl’ , and ‘extra_certs’ must not be initialized.

The ‘extra_certs’ and ‘extra_certs_len’ parameters are optional and
     both may be set to ‘NULL’ .  If either is non-‘NULL’ , then both
     must be set.  The value for ‘extra_certs’ is allocated using
     ‘gnutls_malloc()’ .

Encrypted PKCS12 bags and PKCS8 private keys are supported, but
     only with password based security and the same password for all
     operations.

Note that a PKCS12 structure may contain many keys and/or
     certificates, and there is no way to identify which key/certificate
     pair you want.  For this reason this function is useful for PKCS12
     files that contain only one key/certificate pair and/or one CRL.

If the provided structure has encrypted fields but no password is
     provided then this function returns ‘GNUTLS_E_DECRYPTION_FAILED’ .

Note that normally the chain constructed does not include self
     signed certificates, to comply with TLS' requirements.  If,
     however, the flag ‘GNUTLS_PKCS12_SP_INCLUDE_SELF_SIGNED’ is
     specified then self signed certificates will be included in the
     chain.

Prior to using this function the PKCS ‘12’ structure integrity must
     be verified using ‘gnutls_pkcs12_verify_mac()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.1.0
‘INT *note gnutls_pkcs12_bag_get_data:: (gnutls_pkcs12_bag_t BAG, unsigned INDX, gnutls_datum_t * DATA)’
‘INT *note gnutls_pkcs12_bag_get_key_id:: (gnutls_pkcs12_bag_t BAG, unsigned INDX, gnutls_datum_t * ID)’
‘INT *note gnutls_pkcs12_bag_get_friendly_name:: (gnutls_pkcs12_bag_t BAG, unsigned INDX, char ** NAME)’

The functions below are used to generate a PKCS #12 structure.  An
example of their usage is shown at *note PKCS12 structure generation
example::.

‘INT *note gnutls_pkcs12_set_bag:: (gnutls_pkcs12_t PKCS12, gnutls_pkcs12_bag_t BAG)’
‘INT *note gnutls_pkcs12_bag_encrypt:: (gnutls_pkcs12_bag_t BAG, const char * PASS, unsigned int FLAGS)’
‘INT *note gnutls_pkcs12_generate_mac:: (gnutls_pkcs12_t PKCS12, const char * PASS)’
‘INT *note gnutls_pkcs12_bag_set_data:: (gnutls_pkcs12_bag_t BAG, gnutls_pkcs12_bag_type_t TYPE, const gnutls_datum_t * DATA)’
‘INT *note gnutls_pkcs12_bag_set_crl:: (gnutls_pkcs12_bag_t BAG, gnutls_x509_crl_t CRL)’
‘INT *note gnutls_pkcs12_bag_set_crt:: (gnutls_pkcs12_bag_t BAG, gnutls_x509_crt_t CRT)’
‘INT *note gnutls_pkcs12_bag_set_key_id:: (gnutls_pkcs12_bag_t BAG, unsigned INDX, const gnutls_datum_t * ID)’
‘INT *note gnutls_pkcs12_bag_set_friendly_name:: (gnutls_pkcs12_bag_t BAG, unsigned INDX, const char * NAME)’

OpenSSL encrypted keys
......................

Unfortunately the structures discussed in the previous sections are not
the only structures that may hold an encrypted private key.  For example
the OpenSSL library offers a custom key encryption method.  Those
structures are also supported in GnuTLS with *note
gnutls_x509_privkey_import_openssl::.

-- Function: int gnutls_x509_privkey_import_openssl
          (gnutls_x509_privkey_t KEY, const gnutls_datum_t * DATA, const
          char * PASSWORD)
     KEY: The data to store the parsed key

DATA: The DER or PEM encoded key.

PASSWORD: the password to decrypt the key (if it is encrypted).

This function will convert the given PEM encrypted to the native
     gnutls_x509_privkey_t format.  The output will be stored in ‘key’ .

The ‘password’ should be in ASCII. If the password is not provided
     or wrong then ‘GNUTLS_E_DECRYPTION_FAILED’ will be returned.

If the Certificate is PEM encoded it should have a header of
     "PRIVATE KEY" and the "DEK-Info" header.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

File: gnutls.info,  Node: certtool Invocation,  Next: ocsptool Invocation,  Prev: Managing encrypted keys,  Up: More on certificate authentication

4.2.6 Invoking certtool
-----------------------

Tool to parse and generate X.509 certificates, requests and private
keys.  It can be used interactively or non interactively by specifying
the template command line option.

The tool accepts files or supported URIs via the -infile option.  In
case PIN is required for URI access you can provide it using the
environment variables GNUTLS_PIN and GNUTLS_SO_PIN.

certtool help/usage (‘-?’)
..........................

The text printed is the same whether selected with the ‘help’ option
(‘--help’) or the ‘more-help’ option (‘--more-help’).  ‘more-help’ will
print the usage text by passing it through a pager program.  ‘more-help’
is disabled on platforms without a working ‘fork(2)’ function.  The
‘PAGER’ environment variable is used to select the program, defaulting
to ‘more’.  Both will exit with a status code of 0.

certtool - GnuTLS certificate tool
     Usage:  certtool [ -<flag> [<val>] | --<name>[{=| }<val>] ]...

None:

Certificate related options:

-i, --certificate-info     Print information on the given certificate
            --pubkey-info          Print information on a public key
        -s, --generate-self-signed Generate a self-signed certificate
        -c, --generate-certificate Generate a signed certificate
            --generate-proxy       Generates a proxy certificate
        -u, --update-certificate   Update a signed certificate
            --fingerprint          Print the fingerprint of the given certificate
            --key-id               Print the key ID of the given certificate
            --v1                   Generate an X.509 version 1 certificate (with no extensions)
            --sign-params=str      Sign a certificate with a specific signature algorithm

Certificate request related options:

--crq-info             Print information on the given certificate request
        -q, --generate-request     Generate a PKCS #10 certificate request
     				- prohibits the option 'infile'
            --no-crq-extensions    Do not use extensions in certificate requests

PKCS#12 file related options:

--p12-info             Print information on a PKCS #12 structure
            --p12-name=str         The PKCS #12 friendly name to use
            --to-p12               Generate a PKCS #12 structure
            --pbmac1               Use PBMAC1 in a PKCS #12 structure

Private key related options:

-k, --key-info             Print information on a private key
            --p8-info              Print information on a PKCS #8 structure
            --to-rsa               Convert an RSA-PSS key to raw RSA format
        -p, --generate-privkey     Generate a private key
            --key-type=str         Specify the key type to use on key generation
            --bits=num             Specify the number of bits for key generation
            --curve=str            Specify the curve used for EC key generation
            --sec-param=str        Specify the security level [low, legacy, medium, high, ultra]
            --to-p8                Convert a given key to a PKCS #8 structure
        -8, --pkcs8                Use PKCS #8 format for private keys
            --provable             Generate a private key or parameters from a seed using a provable method
            --verify-provable-privkey  Verify a private key generated from a seed using a provable method
            --seed=str             When generating a private key use the given hex-encoded seed

CRL related options:

-l, --crl-info             Print information on the given CRL structure
            --generate-crl         Generate a CRL
            --verify-crl           Verify a Certificate Revocation List using a trusted list
     				- requires the option 'load-ca-certificate'

Certificate verification related options:

-e, --verify-chain         Verify a PEM encoded certificate chain
            --verify               Verify a PEM encoded certificate (chain) against a trusted set
            --verify-hostname=str  Specify a hostname to be used for certificate chain verification
            --verify-email=str     Specify a email to be used for certificate chain verification
     				- prohibits the option 'verify-hostname'
            --verify-purpose=str   Specify a purpose OID to be used for certificate chain verification
            --verify-allow-broken  Allow broken algorithms, such as MD5 for verification
            --verify-profile=str   Specify a security level profile to be used for verification

PKCS#7 structure options:

--p7-generate          Generate a PKCS #7 structure
            --p7-sign              Signs using a PKCS #7 structure
            --p7-detached-sign     Signs using a detached PKCS #7 structure
            --p7-include-cert      The signer's certificate will be included in the cert list
     				- enabled by default
     				- disabled as '--no-p7-include-cert'
            --p7-time              Will include a timestamp in the PKCS #7 structure
            --p7-show-data         Will show the embedded data in the PKCS #7 structure
            --p7-info              Print information on a PKCS #7 structure
            --p7-verify            Verify the provided PKCS #7 structure
            --smime-to-p7          Convert S/MIME to PKCS #7 structure

Other options:

--get-dh-params        List the included PKCS #3 encoded Diffie-Hellman parameters
            --dh-info              Print information PKCS #3 encoded Diffie-Hellman parameters
            --load-privkey=str     Loads a private key file
            --load-pubkey=str      Loads a public key file
            --load-request=str     Loads a certificate request file
            --load-certificate=str Loads a certificate file
            --load-ca-privkey=str  Loads the certificate authority's private key file
            --load-ca-certificate=str Loads the certificate authority's certificate file
            --load-crl=str         Loads the provided CRL
            --load-data=str        Loads auxiliary data
            --password=str         Password to use
            --null-password        Enforce a NULL password
            --empty-password       Enforce an empty password
            --hex-numbers          Print big number in an easier format to parse
            --cprint               In certain operations it prints the information in C-friendly format
            --hash=str             Hash algorithm to use for signing
            --salt-size=num        Specify the RSA-PSS key default salt size
            --label=str            Specify the RSA-OAEP label, encoded in hexadecimal
            --inder                Use DER format for input certificates, private keys, and DH parameters
            --inraw                an alias for the 'inder' option
            --outder               Use DER format for output certificates, private keys, and DH parameters
            --outraw               an alias for the 'outder' option
            --template=str         Template file to use for non-interactive operation
            --stdout-info          Print information to stdout instead of stderr
            --ask-pass             Enable interaction for entering password when in batch mode
            --pkcs-cipher=str      Cipher to use for PKCS #8 and #12 operations
            --provider=str         Specify the PKCS #11 provider library
            --text                 Output textual information before PEM-encoded certificates, private keys, etc
     				- enabled by default
     				- disabled as '--no-text'

Version, usage and configuration options:

-v, --version[=arg]        output version information and exit
        -h, --help                 display extended usage information and exit
        -!, --more-help            extended usage information passed thru pager

Options are specified by doubled hyphens and their name or by a single
     hyphen and the flag character.

Tool to parse and generate X.509 certificates, requests and private keys.
     It can be used interactively or non interactively by
     specifying the template command line option.

The tool accepts files or supported URIs via the --infile option. In case PIN
     is required for URI access you can provide it using the environment variables GNUTLS_PIN
     and GNUTLS_SO_PIN.

Please send bug reports to:  <bugs@gnutls.org>

debug option (-d).
..................

This is the "enable debugging" option.  This option takes a
ArgumentType.NUMBER argument.  Specifies the debug level.

attime option.
..............

This is the "perform validation at the timestamp instead of the system
time" option.  This option takes a ArgumentType.STRING argument
‘timestamp’.  timestamp is an instance in time encoded as Unix time or
in a human readable timestring such as "29 Feb 2004", "2004-02-29".
Full documentation available at
<https://www.gnu.org/software/coreutils/manual/html_node/Date-input-formats.html>
or locally via info '(coreutils) date invocation'.

cert-options options
....................

Certificate related options.

pubkey-info option.
...................

This is the "print information on a public key" option.  The option
combined with -load-request, -load-pubkey, -load-privkey and
-load-certificate will extract the public key of the object in question.

fingerprint option.
...................

This is the "print the fingerprint of the given certificate" option.
This is a simple hash of the DER encoding of the certificate.  It can be
combined with the -hash parameter.  However, it is recommended for
identification to use the key-id which depends only on the certificate's
key.

key-id option.
..............

This is the "print the key id of the given certificate" option.  This is
a hash of the public key of the given certificate.  It identifies the
key uniquely, remains the same on a certificate renewal and depends only
on signed fields of the certificate.

certificate-pubkey option.
..........................

This is the "print certificate's public key" option.  This option is
deprecated as a duplicate of -pubkey-info

*NOTE**: THIS OPTION IS DEPRECATED*

sign-params option.
...................

This is the "sign a certificate with a specific signature algorithm"
option.  This option takes a ArgumentType.STRING argument.  This option
can be combined with -generate-certificate, to sign the certificate with
a specific signature algorithm variant.  The only option supported is
'RSA-PSS', and should be specified when the signer does not have a
certificate which is marked for RSA-PSS use only.

crq-options options
...................

Certificate request related options.

generate-request option (-q).
.............................

This is the "generate a pkcs #10 certificate request" option.

This option has some usage constraints.  It:
   • must not appear in combination with any of the following options:
     infile.

Will generate a PKCS #10 certificate request.  To specify a private key
use -load-privkey.

pkcs12-options options
......................

PKCS#12 file related options.

p12-info option.
................

This is the "print information on a pkcs #12 structure" option.  This
option will dump the contents and print the metadata of the provided
PKCS #12 structure.

p12-name option.
................

This is the "the pkcs #12 friendly name to use" option.  This option
takes a ArgumentType.STRING argument.  The name to be used for the
primary certificate and private key in a PKCS #12 file.

to-p12 option.
..............

This is the "generate a pkcs #12 structure" option.  It requires a
certificate, a private key and possibly a CA certificate to be
specified.

key-options options
...................

Private key related options.

p8-info option.
...............

This is the "print information on a pkcs #8 structure" option.  This
option will print information about encrypted PKCS #8 structures.  That
option does not require the decryption of the structure.

to-rsa option.
..............

This is the "convert an rsa-pss key to raw rsa format" option.  It
requires an RSA-PSS key as input and will output a raw RSA key.  This
command is necessary for compatibility with applications that cannot
read RSA-PSS keys.

generate-privkey option (-p).
.............................

This is the "generate a private key" option.  When generating RSA-PSS or
RSA-OAEP private keys, the -hash option will restrict the allowed hash
for the key; For RSA-PSS keys the -salt-size option is also acceptable.

key-type option.
................

This is the "specify the key type to use on key generation" option.
This option takes a ArgumentType.STRING argument.  This option can be
combined with -generate-privkey, to specify the key type to be
generated.  Valid options are, 'rsa', 'rsa-pss', 'rsa-oaep', 'dsa',
'ecdsa', 'ed25519, 'ed448', 'x25519', and 'x448'.'.  When combined with
certificate generation it can be used to specify an RSA-PSS certificate
when an RSA key is given.

curve option.
.............

This is the "specify the curve used for ec key generation" option.  This
option takes a ArgumentType.STRING argument.  Supported values are
secp192r1, secp224r1, secp256r1, secp384r1 and secp521r1.

sec-param option.
.................

to-p8 option.
.............

This is the "convert a given key to a pkcs #8 structure" option.  This
needs to be combined with -load-privkey.

provable option.
................

This is the "generate a private key or parameters from a seed using a
provable method" option.  This will use the FIPS PUB186-4 algorithms
(i.e., Shawe-Taylor) for provable key generation.  When specified the
private keys or parameters will be generated from a seed, and can be
later validated with -verify-provable-privkey to be correctly generated
from the seed.  You may specify -seed or allow GnuTLS to generate one
(recommended).  This option can be combined with -generate-privkey or
-generate-dh-params.

That option applies to RSA and DSA keys.  On the DSA keys the PQG
parameters are generated using the seed, and on RSA the two primes.

verify-provable-privkey option.
...............................

This is the "verify a private key generated from a seed using a provable
method" option.  This will use the FIPS-186-4 algorithms for provable
key generation.  You may specify -seed or use the seed stored in the
private key structure.

seed option.
............

This is the "when generating a private key use the given hex-encoded
seed" option.  This option takes a ArgumentType.STRING argument.  The
seed acts as a security parameter for the private key, and thus a seed
size which corresponds to the security level of the private key should
be provided (e.g., 256-bits seed).

crl-options options
...................

CRL related options.

generate-crl option.
....................

This is the "generate a crl" option.  This option generates a
Certificate Revocation List.  When combined with -load-crl it would use
the loaded CRL as base for the generated (i.e., all revoked certificates
in the base will be copied to the new CRL). To add new certificates to
the CRL use -load-certificate.

verify-crl option.
..................

This is the "verify a certificate revocation list using a trusted list"
option.

This option has some usage constraints.  It:
   • must appear in combination with the following options:
     load-ca-certificate.

The trusted certificate list must be loaded with -load-ca-certificate.

cert-verify-options options
...........................

Certificate verification related options.

verify-chain option (-e).
.........................

This is the "verify a pem encoded certificate chain" option.  Verifies
the validity of a certificate chain.  That is, an ordered set of
certificates where each one is the issuer of the previous, and the first
is the end-certificate to be validated.  In a proper chain the last
certificate is a self signed one.  It can be combined with
-verify-purpose or -verify-hostname.

verify option.
..............

This is the "verify a pem encoded certificate (chain) against a trusted
set" option.  The trusted certificate list can be loaded with
-load-ca-certificate.  If no certificate list is provided, then the
system's trusted certificate list is used.  Note that during
verification multiple paths may be explored.  On a successful
verification the successful path will be the last one.  It can be
combined with -verify-purpose or -verify-hostname.

verify-hostname option.
.......................

This is the "specify a hostname to be used for certificate chain
verification" option.  This option takes a ArgumentType.STRING argument.
This is to be combined with one of the verify certificate options.

verify-email option.
....................

This is the "specify a email to be used for certificate chain
verification" option.  This option takes a ArgumentType.STRING argument.

This option has some usage constraints.  It:
   • must not appear in combination with any of the following options:
     verify-hostname.

This is to be combined with one of the verify certificate options.

verify-purpose option.
......................

This is the "specify a purpose oid to be used for certificate chain
verification" option.  This option takes a ArgumentType.STRING argument.
This object identifier restricts the purpose of the certificates to be
verified.  Example purposes are 1.3.6.1.5.5.7.3.1 (TLS WWW),
1.3.6.1.5.5.7.3.4 (EMAIL) etc.  Note that a CA certificate without a
purpose set (extended key usage) is valid for any purpose.

verify-allow-broken option.
...........................

This is the "allow broken algorithms, such as md5 for verification"
option.  This can be combined with -p7-verify, -verify or -verify-chain.

verify-profile option.
......................

This is the "specify a security level profile to be used for
verification" option.  This option takes a ArgumentType.STRING argument.
This option can be used to specify a certificate verification profile.
Certificate verification profiles correspond to the security level.
This should be one of 'none', 'very weak', 'low', 'legacy', 'medium',
'high', 'ultra', 'future'.  Note that by default no profile is applied,
unless one is set as minimum in the gnutls configuration file.

pkcs7-options options
.....................

PKCS#7 structure options.

p7-generate option.
...................

This is the "generate a pkcs #7 structure" option.  This option
generates a PKCS #7 certificate container structure.  To add
certificates in the structure use -load-certificate and -load-crl.

p7-sign option.
...............

This is the "signs using a pkcs #7 structure" option.  This option
generates a PKCS #7 structure containing a signature for the provided
data from infile.  The data are stored within the structure.  The signer
certificate has to be specified using -load-certificate and
-load-privkey.  The input to -load-certificate can be a list of
certificates.  In case of a list, the first certificate is used for
signing and the other certificates are included in the structure.

p7-detached-sign option.
........................

This is the "signs using a detached pkcs #7 structure" option.  This
option generates a PKCS #7 structure containing a signature for the
provided data from infile.  The signer certificate has to be specified
using -load-certificate and -load-privkey.  The input to
-load-certificate can be a list of certificates.  In case of a list, the
first certificate is used for signing and the other certificates are
included in the structure.

p7-include-cert option.
.......................

This is the "the signer's certificate will be included in the cert list"
option.

This option has some usage constraints.  It:
   • can be disabled with -no-p7-include-cert.
   • It is enabled by default.

This options works with -p7-sign or -p7-detached-sign and will include
or exclude the signer's certificate into the generated signature.

p7-time option.
...............

This is the "will include a timestamp in the pkcs #7 structure" option.
This option will include a timestamp in the generated signature

p7-show-data option.
....................

This is the "will show the embedded data in the pkcs #7 structure"
option.  This option can be combined with -p7-verify or -p7-info and
will display the embedded signed data in the PKCS #7 structure.

p7-verify option.
.................

This is the "verify the provided pkcs #7 structure" option.  This option
verifies the signed PKCS #7 structure.  The certificate list to use for
verification can be specified with -load-ca-certificate.  When no
certificate list is provided, then the system's certificate list is
used.  Alternatively a direct signer can be provided using
-load-certificate.  A key purpose can be enforced with the
-verify-purpose option, and the -load-data option will utilize detached
data.

other-options options
.....................

Other options.

generate-dh-params option.
..........................

This is the "generate pkcs #3 encoded diffie-hellman parameters" option.
The will generate random parameters to be used with Diffie-Hellman key
exchange.  The output parameters will be in PKCS #3 format.  Note that
it is recommended to use the -get-dh-params option instead.

*NOTE**: THIS OPTION IS DEPRECATED*

get-dh-params option.
.....................

This is the "list the included pkcs #3 encoded diffie-hellman
parameters" option.  Returns stored DH parameters in GnuTLS. Those
parameters returned are defined in RFC7919, and can be considered
standard parameters for a TLS key exchange.  This option is provided for
old applications which require DH parameters to be specified; modern
GnuTLS applications should not require them.

load-privkey option.
....................

This is the "loads a private key file" option.  This option takes a
ArgumentType.STRING argument.  This can be either a file or a PKCS #11
URL

load-pubkey option.
...................

This is the "loads a public key file" option.  This option takes a
ArgumentType.STRING argument.  This can be either a file or a PKCS #11
URL

load-request option.
....................

This is the "loads a certificate request file" option.  This option
takes a ArgumentType.STRING argument.  This option can be used with a
file

load-certificate option.
........................

This is the "loads a certificate file" option.  This option takes a
ArgumentType.STRING argument.  This option can be used with a file

load-ca-privkey option.
.......................

This is the "loads the certificate authority's private key file" option.
This option takes a ArgumentType.STRING argument.  This can be either a
file or a PKCS #11 URL

load-ca-certificate option.
...........................

This is the "loads the certificate authority's certificate file" option.
This option takes a ArgumentType.STRING argument.  This can be either a
file or a PKCS #11 URL

load-crl option.
................

This is the "loads the provided crl" option.  This option takes a
ArgumentType.STRING argument.  This option can be used with a file

load-data option.
.................

This is the "loads auxiliary data" option.  This option takes a
ArgumentType.STRING argument.  This option can be used with a file

password option.
................

This is the "password to use" option.  This option takes a
ArgumentType.STRING argument.  You can use this option to specify the
password in the command line instead of reading it from the tty.  Note,
that the command line arguments are available for view in others in the
system.  Specifying password as " is the same as specifying no password.

null-password option.
.....................

This is the "enforce a null password" option.  This option enforces a
NULL password.  This is different than the empty or no password in
schemas like PKCS #8.

empty-password option.
......................

This is the "enforce an empty password" option.  This option enforces an
empty password.  This is different than the NULL or no password in
schemas like PKCS #8.

cprint option.
..............

This is the "in certain operations it prints the information in
c-friendly format" option.  In certain operations it prints the
information in C-friendly format, suitable for including into C
programs.

rsa option.
...........

This is the "generate rsa key" option.  When combined with
-generate-privkey generates an RSA private key.

*NOTE**: THIS OPTION IS DEPRECATED*

dsa option.
...........

This is the "generate dsa key" option.  When combined with
-generate-privkey generates a DSA private key.

*NOTE**: THIS OPTION IS DEPRECATED*

ecc option.
...........

This is the "generate ecc (ecdsa) key" option.  When combined with
-generate-privkey generates an elliptic curve private key to be used
with ECDSA.

*NOTE**: THIS OPTION IS DEPRECATED*

ecdsa option.
.............

This is an alias for the ‘ecc’ option, *note the ecc option
documentation: certtool ecc.

hash option.
............

This is the "hash algorithm to use for signing" option.  This option
takes a ArgumentType.STRING argument.  Available hash functions are
SHA1, RMD160, SHA256, SHA384, SHA512, SHA3-224, SHA3-256, SHA3-384,
SHA3-512.

salt-size option.
.................

This is the "specify the rsa-pss key default salt size" option.  This
option takes a ArgumentType.NUMBER argument.  Typical keys shouldn't set
or restrict this option.

label option.
.............

This is the "specify the rsa-oaep label, encoded in hexadecimal" option.
This option takes a ArgumentType.STRING argument.  Typical keys
shouldn't set or restrict this option.

inder option.
.............

This is the "use der format for input certificates, private keys, and dh
parameters " option.  The input files will be assumed to be in DER or
RAW format.  Unlike options that in PEM input would allow multiple input
data (e.g.  multiple certificates), when reading in DER format a single
data structure is read.

inraw option.
.............

This is an alias for the ‘inder’ option, *note the inder option
documentation: certtool inder.

outder option.
..............

This is the "use der format for output certificates, private keys, and
dh parameters" option.  The output will be in DER or RAW format.

outraw option.
..............

This is an alias for the ‘outder’ option, *note the outder option
documentation: certtool outder.

ask-pass option.
................

This is the "enable interaction for entering password when in batch
mode" option.  This option will enable interaction to enter password
when in batch mode.  That is useful when the template option has been
specified.

pkcs-cipher option.
...................

This is the "cipher to use for pkcs #8 and #12 operations" option.  This
option takes a ArgumentType.STRING argument ‘Cipher’.  Cipher may be one
of 3des, 3des-pkcs12, aes-128, aes-192, aes-256, rc2-40, arcfour.

provider option.
................

This is the "specify the pkcs #11 provider library" option.  This option
takes a ArgumentType.STRING argument.  This will override the default
options in /usr/local/etc/gnutls/pkcs11.conf

text option.
............

This is the "output textual information before pem-encoded certificates,
private keys, etc" option.

This option has some usage constraints.  It:
   • can be disabled with -no-text.
   • It is enabled by default.

Output textual information before PEM-encoded data

version option (-v).
....................

This is the "output version information and exit" option.  This option
takes a ArgumentType.KEYWORD argument.  Output version of program and
exit.  The default mode is 'v', a simple version.  The 'c' mode will
print copyright information and 'n' will print the full copyright
notice.

help option (-h).
.................

This is the "display extended usage information and exit" option.
Display usage information and exit.

more-help option (-!).
......................

This is the "extended usage information passed thru pager" option.  Pass
the extended usage information through a pager.

certtool exit status
....................

One of the following exit values will be returned:
‘0 (EXIT_SUCCESS)’
     Successful program execution.
‘1 (EXIT_FAILURE)’
     The operation failed or the command syntax was not valid.

certtool See Also
.................

p11tool (1), psktool (1), srptool (1)

certtool Examples
.................

Generating private keys
.......................

To create an RSA private key, run:
     $ certtool --generate-privkey --outfile key.pem --rsa

To create a DSA or elliptic curves (ECDSA) private key use the above
command combined with 'dsa' or 'ecc' options.

Generating certificate requests
...............................

To create a certificate request (needed when the certificate is issued
by another party), run:
     certtool --generate-request --load-privkey key.pem \
        --outfile request.pem

If the private key is stored in a smart card you can generate a request
by specifying the private key object URL.
     $ ./certtool --generate-request --load-privkey "pkcs11:..." \
       --load-pubkey "pkcs11:..." --outfile request.pem

Generating a self-signed certificate
....................................

To create a self signed certificate, use the command:
     $ certtool --generate-privkey --outfile ca-key.pem
     $ certtool --generate-self-signed --load-privkey ca-key.pem \
        --outfile ca-cert.pem

Note that a self-signed certificate usually belongs to a certificate
authority, that signs other certificates.

Generating a certificate
........................

To generate a certificate using the previous request, use the command:
     $ certtool --generate-certificate --load-request request.pem \
        --outfile cert.pem --load-ca-certificate ca-cert.pem \
        --load-ca-privkey ca-key.pem

To generate a certificate using the private key only, use the command:
     $ certtool --generate-certificate --load-privkey key.pem \
        --outfile cert.pem --load-ca-certificate ca-cert.pem \
        --load-ca-privkey ca-key.pem

Certificate information
.......................

To view the certificate information, use:
     $ certtool --certificate-info --infile cert.pem

Changing the certificate format
...............................

To convert the certificate from PEM to DER format, use:
     $ certtool --certificate-info --infile cert.pem --outder --outfile cert.der

PKCS #12 structure generation
.............................

To generate a PKCS #12 structure using the previous key and certificate,
use the command:
     $ certtool --load-certificate cert.pem --load-privkey key.pem \
        --to-p12 --outder --outfile key.p12

Some tools (reportedly web browsers) have problems with that file
because it does not contain the CA certificate for the certificate.  To
work around that problem in the tool, you can use the
-load-ca-certificate parameter as follows:

$ certtool --load-ca-certificate ca.pem \
       --load-certificate cert.pem --load-privkey key.pem \
       --to-p12 --outder --outfile key.p12

Obtaining Diffie-Hellman parameters
...................................

To obtain the RFC7919 parameters for Diffie-Hellman key exchange, use
the command:
     $ certtool --get-dh-params --outfile dh.pem --sec-param medium

Verifying a certificate
.......................

To verify a certificate in a file against the system's CA trust store
use the following command:
     $ certtool --verify --infile cert.pem

It is also possible to simulate hostname verification with the following
options:
     $ certtool --verify --verify-hostname www.example.com --infile cert.pem

Proxy certificate generation
............................

Proxy certificate can be used to delegate your credential to a
temporary, typically short-lived, certificate.  To create one from the
previously created certificate, first create a temporary key and then
generate a proxy certificate for it, using the commands:

$ certtool --generate-privkey > proxy-key.pem
     $ certtool --generate-proxy --load-ca-privkey key.pem \
       --load-privkey proxy-key.pem --load-certificate cert.pem \
       --outfile proxy-cert.pem

Certificate revocation list generation
......................................

To create an empty Certificate Revocation List (CRL) do:

$ certtool --generate-crl --load-ca-privkey x509-ca-key.pem \
                --load-ca-certificate x509-ca.pem

To create a CRL that contains some revoked certificates, place the
certificates in a file and use ‘--load-certificate’ as follows:

$ certtool --generate-crl --load-ca-privkey x509-ca-key.pem \
       --load-ca-certificate x509-ca.pem --load-certificate revoked-certs.pem

To verify a Certificate Revocation List (CRL) do:

$ certtool --verify-crl --load-ca-certificate x509-ca.pem < crl.pem

certtool Files
..............

Certtool's template file format
...............................

A template file can be used to avoid the interactive questions of
certtool.  Initially create a file named 'cert.cfg' that contains the
information about the certificate.  The template can be used as below:

$ certtool --generate-certificate --load-privkey key.pem  \
        --template cert.cfg --outfile cert.pem \
        --load-ca-certificate ca-cert.pem --load-ca-privkey ca-key.pem

An example certtool template file that can be used to generate a
certificate request or a self signed certificate follows.

# X.509 Certificate options
     #
     # DN options

# The organization of the subject.
     organization = "Koko inc."

# The organizational unit of the subject.
     unit = "sleeping dept."

# The locality of the subject.
     # locality =

# The state of the certificate owner.
     state = "Attiki"

# The country of the subject. Two letter code.
     country = GR

# The common name of the certificate owner.
     cn = "Cindy Lauper"

# A user id of the certificate owner.
     #uid = "clauper"

# Set domain components
     #dc = "name"
     #dc = "domain"

# If the supported DN OIDs are not adequate you can set
     # any OID here.
     # For example set the X.520 Title and the X.520 Pseudonym
     # by using OID and string pairs.
     #dn_oid = "2.5.4.12 Dr."
     #dn_oid = "2.5.4.65 jackal"

# This is deprecated and should not be used in new
     # certificates.
     # pkcs9_email = "none@none.org"

# An alternative way to set the certificate's distinguished name directly
     # is with the "dn" option. The attribute names allowed are:
     # C (country), street, O (organization), OU (unit), title, CN (common name),
     # L (locality), ST (state), placeOfBirth, gender, countryOfCitizenship,
     # countryOfResidence, serialNumber, telephoneNumber, surName, initials,
     # generationQualifier, givenName, pseudonym, dnQualifier, postalCode, name,
     # businessCategory, DC, UID, jurisdictionOfIncorporationLocalityName,
     # jurisdictionOfIncorporationStateOrProvinceName,
     # jurisdictionOfIncorporationCountryName, XmppAddr, and numeric OIDs.

#dn = "cn = Nikos,st = New\, Something,C=GR,surName=Mavrogiannopoulos,2.5.4.9=Arkadias"

# The serial number of the certificate
     # The value is in decimal (i.e. 1963) or hex (i.e. 0x07ab).
     # Comment the field for a random serial number.
     serial = 007

# In how many days, counting from today, this certificate will expire.
     # Use -1 if there is no expiration date.
     expiration_days = 700

# Alternatively you may set concrete dates and time. The GNU date string
     # formats are accepted. See:
     # https://www.gnu.org/software/tar/manual/html_node/Date-input-formats.html

#activation_date = "2004-02-29 16:21:42"
     #expiration_date = "2025-02-29 16:24:41"

# X.509 v3 extensions

# A dnsname in case of a WWW server.
     #dns_name = "www.none.org"
     #dns_name = "www.morethanone.org"

# An othername defined by an OID and a hex encoded string
     #other_name = "1.3.6.1.5.2.2 302ca00d1b0b56414e5245494e2e4f5247a11b3019a006020400000002a10f300d1b047269636b1b0561646d696e"
     #other_name_utf8 = "1.2.4.5.6 A UTF8 string"
     #other_name_octet = "1.2.4.5.6 A string that will be encoded as ASN.1 octet string"

# Allows writing an XmppAddr Identifier
     #xmpp_name = juliet@im.example.com

# Names used in PKINIT
     #krb5_principal = user@REALM.COM
     #krb5_principal = HTTP/user@REALM.COM

# A subject alternative name URI
     #uri = "https://www.example.com"

# An IP address in case of a server.
     #ip_address = "192.168.1.1"

# An email in case of a person
     email = "none@none.org"

# TLS feature (rfc7633) extension. That can is used to indicate mandatory TLS
     # extension features to be provided by the server. In practice this is used
     # to require the Status Request (extid: 5) extension from the server. That is,
     # to require the server holding this certificate to provide a stapled OCSP response.
     # You can have multiple lines for multiple TLS features.

# To ask for OCSP status request use:
     #tls_feature = 5

# Challenge password used in certificate requests
     challenge_password = 123456

# Password when encrypting a private key
     #password = secret

# An URL that has CRLs (certificate revocation lists)
     # available. Needed in CA certificates.
     #crl_dist_points = "https://www.getcrl.crl/getcrl/"

# Whether this is a CA certificate or not
     #ca

# Subject Unique ID (in hex)
     #subject_unique_id = 00153224

# Issuer Unique ID (in hex)
     #issuer_unique_id = 00153225

#### Key usage

# The following key usage flags are used by CAs and end certificates

# Whether this certificate will be used to sign data (needed
     # in TLS DHE ciphersuites). This is the digitalSignature flag
     # in RFC5280 terminology.
     signing_key

# Whether this certificate will be used to encrypt data (needed
     # in TLS RSA ciphersuites). Note that it is preferred to use different
     # keys for encryption and signing. This is the keyEncipherment flag
     # in RFC5280 terminology.
     encryption_key

# Whether this key will be used to sign other certificates. The
     # keyCertSign flag in RFC5280 terminology.
     #cert_signing_key

# Whether this key will be used to sign CRLs. The
     # cRLSign flag in RFC5280 terminology.
     #crl_signing_key

# The keyAgreement flag of RFC5280. Its purpose is loosely
     # defined. Not use it unless required by a protocol.
     #key_agreement

# The dataEncipherment flag of RFC5280. Its purpose is loosely
     # defined. Not use it unless required by a protocol.
     #data_encipherment

# The nonRepudiation flag of RFC5280. Its purpose is loosely
     # defined. Not use it unless required by a protocol.
     #non_repudiation

#### Extended key usage (key purposes)

# The following extensions are used in an end certificate
     # to clarify its purpose. Some CAs also use it to indicate
     # the types of certificates they are purposed to sign.

# Whether this certificate will be used for a TLS client;
     # this sets the id-kp-clientAuth (1.3.6.1.5.5.7.3.2) of
     # extended key usage.
     #tls_www_client

# Whether this certificate will be used for a TLS server;
     # this sets the id-kp-serverAuth (1.3.6.1.5.5.7.3.1) of
     # extended key usage.
     #tls_www_server

# Whether this key will be used to sign code. This sets the
     # id-kp-codeSigning (1.3.6.1.5.5.7.3.3) of extended key usage
     # extension.
     #code_signing_key

# Whether this key will be used to sign OCSP data. This sets the
     # id-kp-OCSPSigning (1.3.6.1.5.5.7.3.9) of extended key usage extension.
     #ocsp_signing_key

# Whether this key will be used for time stamping. This sets the
     # id-kp-timeStamping (1.3.6.1.5.5.7.3.8) of extended key usage extension.
     #time_stamping_key

# Whether this key will be used for email protection. This sets the
     # id-kp-emailProtection (1.3.6.1.5.5.7.3.4) of extended key usage extension.
     #email_protection_key

# Whether this key will be used for IPsec IKE operations (1.3.6.1.5.5.7.3.17).
     #ipsec_ike_key

## adding custom key purpose OIDs

# for microsoft smart card logon
     # key_purpose_oid = 1.3.6.1.4.1.311.20.2.2

# for email protection
     # key_purpose_oid = 1.3.6.1.5.5.7.3.4

# for any purpose (must not be used in intermediate CA certificates)
     # key_purpose_oid = 2.5.29.37.0

### end of key purpose OIDs

### Adding arbitrary extensions
     # This requires to provide the extension OIDs, as well as the extension data in
     # hex format. The following two options are available since GnuTLS 3.5.3.
     #add_extension = "1.2.3.4 0x0AAB01ACFE"

# As above but encode the data as an octet string
     #add_extension = "1.2.3.4 octet_string(0x0AAB01ACFE)"

# For portability critical extensions shouldn't be set to certificates.
     #add_critical_extension = "5.6.7.8 0x1AAB01ACFE"

# When generating a certificate from a certificate
     # request, then honor the extensions stored in the request
     # and store them in the real certificate.
     #honor_crq_extensions

# Alternatively only specific extensions can be copied.
     #honor_crq_ext = 2.5.29.17
     #honor_crq_ext = 2.5.29.15

# Path length constraint. Sets the maximum number of
     # certificates that can be used to certify this certificate.
     # (i.e. the certificate chain length)
     #path_len = -1
     #path_len = 2

# OCSP URI
     # ocsp_uri = https://my.ocsp.server/ocsp

# CA issuers URI
     # ca_issuers_uri = https://my.ca.issuer

# Certificate policies
     #policy1 = 1.3.6.1.4.1.5484.1.10.99.1.0
     #policy1_txt = "This is a long policy to summarize"
     #policy1_url = https://www.example.com/a-policy-to-read

#policy2 = 1.3.6.1.4.1.5484.1.10.99.1.1
     #policy2_txt = "This is a short policy"
     #policy2_url = https://www.example.com/another-policy-to-read

# The number of additional certificates that may appear in a
     # path before the anyPolicy is no longer acceptable.
     #inhibit_anypolicy_skip_certs 1

# Name constraints

# DNS
     #nc_permit_dns = example.com
     #nc_exclude_dns = test.example.com

# EMAIL
     #nc_permit_email = "nmav@ex.net"

# Exclude subdomains of example.com
     #nc_exclude_email = .example.com

# Exclude all e-mail addresses of example.com
     #nc_exclude_email = example.com

# IP
     #nc_permit_ip = 192.168.0.0/16
     #nc_exclude_ip = 192.168.5.0/24
     #nc_permit_ip = fc0a:eef2:e7e7:a56e::/64

# Options for proxy certificates
     #proxy_policy_language = 1.3.6.1.5.5.7.21.1

# Options for generating a CRL

# The number of days the next CRL update will be due.
     # next CRL update will be in 43 days
     #crl_next_update = 43

# this is the 5th CRL by this CA
     # The value is in decimal (i.e. 1963) or hex (i.e. 0x07ab).
     # Comment the field for a time-based number.
     # Time-based CRL numbers generated in GnuTLS 3.6.3 and later
     # are significantly larger than those generated in previous
     # versions. Since CRL numbers need to be monotonic, you need
     # to specify the CRL number here manually if you intend to
     # downgrade to an earlier version than 3.6.3 after publishing
     # the CRL as it is not possible to specify CRL numbers greater
     # than 2**63-2 using hex notation in those versions.
     #crl_number = 5

# Specify the update dates more precisely.
     #crl_this_update_date = "2004-02-29 16:21:42"
     #crl_next_update_date = "2025-02-29 16:24:41"

# The date that the certificates will be made seen as
     # being revoked.
     #crl_revocation_date = "2025-02-29 16:24:41"

File: gnutls.info,  Node: ocsptool Invocation,  Next: danetool Invocation,  Prev: certtool Invocation,  Up: More on certificate authentication

4.2.7 Invoking ocsptool
-----------------------

On verification
---------------

Responses are typically signed/issued by designated certificates or
certificate authorities and thus this tool requires on verification the
certificate of the issuer or the full certificate chain in order to
determine the appropriate signing authority.  The specified certificate
of the issuer is assumed trusted.

ocsptool help/usage (‘-?’)
..........................

ocsptool - GnuTLS OCSP tool
     Usage:  ocsptool [ -<flag> [<val>] | --<name>[{=| }<val>] ]...

None:

-d, --debug=num            Enable debugging
     				- it must be in the range:
     				  0 to 9999
        -V, --verbose              More verbose output
            --infile=file          Input file
     				- file must pre-exist
            --outfile=str          Output file
            --ask[=str]            Ask an OCSP/HTTP server on a certificate validity
        -e, --verify-response      Verify response
        -i, --request-info         Print information on a OCSP request
        -j, --response-info        Print information on a OCSP response
        -q, --generate-request     Generates an OCSP request
            --nonce                Use (or not) a nonce to OCSP request
            --load-chain=file      Reads a set of certificates forming a chain from file
     				- file must pre-exist
            --load-issuer=file     Reads issuer's certificate from file
     				- file must pre-exist
            --load-cert=file       Reads the certificate to check from file
     				- file must pre-exist
            --load-trust=file      Read OCSP trust anchors from file
     				- prohibits the option 'load-signer'
     				- file must pre-exist
            --load-signer=file     Reads the OCSP response signer from file
     				- prohibits the option 'load-trust'
     				- file must pre-exist
            --inder                Use DER format for input certificates and private keys
            --outder               Use DER format for output of responses (this is the default)
            --outpem               Use PEM format for output of responses
        -Q, --load-request=file    Reads the DER encoded OCSP request from file
     				- file must pre-exist
        -S, --load-response=file   Reads the DER encoded OCSP response from file
     				- file must pre-exist
            --ignore-errors        Ignore any verification errors
            --verify-allow-broken  Allow broken algorithms, such as MD5 for verification
            --attime=str           Perform validation at the timestamp instead of the system time

Version, usage and configuration options:

Options are specified by doubled hyphens and their name or by a single
     hyphen and the flag character.

ocsptool is a program that can parse and print information about
     OCSP requests/responses, generate requests and verify responses. Unlike
     other GnuTLS applications it outputs DER encoded structures by default
     unless the '--outpem' option is specified.

Please send bug reports to:  <bugs@gnutls.org>

debug option (-d).
..................

This is the "enable debugging" option.  This option takes a
ArgumentType.NUMBER argument.  Specifies the debug level.

ask option.
...........

This is the "ask an ocsp/http server on a certificate validity" option.
This option takes a ArgumentType.STRING argument ‘server name|url’.
Connects to the specified HTTP OCSP server and queries on the validity
of the loaded certificate.  Its argument can be a URL or a plain server
name.  It can be combined with -load-chain, where it checks all
certificates in the provided chain, or with -load-cert and -load-issuer
options.  The latter checks the provided certificate against its
specified issuer certificate.

verify-response option (-e).
............................

This is the "verify response" option.  Verifies the provided OCSP
response against the system trust anchors (unless -load-trust is
provided).  It requires the -load-signer or -load-chain options to
obtain the signer of the OCSP response.

request-info option (-i).
.........................

This is the "print information on a ocsp request" option.  Display
detailed information on the provided OCSP request.

response-info option (-j).
..........................

This is the "print information on a ocsp response" option.  Display
detailed information on the provided OCSP response.

load-trust option.
..................

This is the "read ocsp trust anchors from file" option.  This option
takes a ArgumentType.FILE argument.

This option has some usage constraints.  It:
   • must not appear in combination with any of the following options:
     load-signer.

When verifying an OCSP response read the trust anchors from the provided
file.  When this is not provided, the system's trust anchors will be
used.

outder option.
..............

This is the "use der format for output of responses (this is the
default)" option.  The output will be in DER encoded format.  Unlike
other GnuTLS tools, this is the default for this tool

outpem option.
..............

This is the "use pem format for output of responses" option.  The output
will be in PEM format.

verify-allow-broken option.
...........................

This is the "allow broken algorithms, such as md5 for verification"
option.  This can be combined with -verify-response.

attime option.
..............

version option (-v).
....................

help option (-h).
.................

This is the "display extended usage information and exit" option.
Display usage information and exit.

more-help option (-!).
......................

This is the "extended usage information passed thru pager" option.  Pass
the extended usage information through a pager.

ocsptool exit status
....................

One of the following exit values will be returned:
‘0 (EXIT_SUCCESS)’
     Successful program execution.
‘1 (EXIT_FAILURE)’
     The operation failed or the command syntax was not valid.

ocsptool See Also
.................

certtool (1)

ocsptool Examples
.................

Print information about an OCSP request
.......................................

To parse an OCSP request and print information about the content, the
‘-i’ or ‘--request-info’ parameter may be used as follows.  The ‘-Q’
parameter specify the name of the file containing the OCSP request, and
it should contain the OCSP request in binary DER format.

$ ocsptool -i -Q ocsp-request.der

The input file may also be sent to standard input like this:

$ cat ocsp-request.der | ocsptool --request-info

Print information about an OCSP response
........................................

Similar to parsing OCSP requests, OCSP responses can be parsed using the
‘-j’ or ‘--response-info’ as follows.

$ ocsptool -j -Q ocsp-response.der
     $ cat ocsp-response.der | ocsptool --response-info

Generate an OCSP request
........................

The ‘-q’ or ‘--generate-request’ parameters are used to generate an OCSP
request.  By default the OCSP request is written to standard output in
binary DER format, but can be stored in a file using ‘--outfile’.  To
generate an OCSP request the issuer of the certificate to check needs to
be specified with ‘--load-issuer’ and the certificate to check with
‘--load-cert’.  By default PEM format is used for these files, although
‘--inder’ can be used to specify that the input files are in DER format.

$ ocsptool -q --load-issuer issuer.pem --load-cert client.pem \
                --outfile ocsp-request.der

When generating OCSP requests, the tool will add an OCSP extension
containing a nonce.  This behaviour can be disabled by specifying
‘--no-nonce’.

Verify signature in OCSP response
.................................

To verify the signature in an OCSP response the ‘-e’ or
‘--verify-response’ parameter is used.  The tool will read an OCSP
response in DER format from standard input, or from the file specified
by ‘--load-response’.  The OCSP response is verified against a set of
trust anchors, which are specified using ‘--load-trust’.  The trust
anchors are concatenated certificates in PEM format.  The certificate
that signed the OCSP response needs to be in the set of trust anchors,
or the issuer of the signer certificate needs to be in the set of trust
anchors and the OCSP Extended Key Usage bit has to be asserted in the
signer certificate.

$ ocsptool -e --load-trust issuer.pem \
                --load-response ocsp-response.der

The tool will print status of verification.

Verify signature in OCSP response against given certificate
...........................................................

It is possible to override the normal trust logic if you know that a
certain certificate is supposed to have signed the OCSP response, and
you want to use it to check the signature.  This is achieved using
‘--load-signer’ instead of ‘--load-trust’.  This will load one
certificate and it will be used to verify the signature in the OCSP
response.  It will not check the Extended Key Usage bit.

$ ocsptool -e --load-signer ocsp-signer.pem \
                --load-response ocsp-response.der

This approach is normally only relevant in two situations.  The first is
when the OCSP response does not contain a copy of the signer
certificate, so the ‘--load-trust’ code would fail.  The second is if
you want to avoid the indirect mode where the OCSP response signer
certificate is signed by a trust anchor.

Real-world example
..................

Here is an example of how to generate an OCSP request for a certificate
and to verify the response.  For illustration we'll use the
‘blog.josefsson.org’ host, which (as of writing) uses a certificate from
CACert.  First we'll use ‘gnutls-cli’ to get a copy of the server
certificate chain.  The server is not required to send this information,
but this particular one is configured to do so.

$ echo | gnutls-cli -p 443 blog.josefsson.org --save-cert chain.pem

The saved certificates normally contain a pointer to where the OCSP
responder is located, in the Authority Information Access Information
extension.  For example, from ‘certtool -i < chain.pem’ there is this
information:

Authority Information Access Information (not critical):
     			Access Method: 1.3.6.1.5.5.7.48.1 (id-ad-ocsp)
     			Access Location URI: https://ocsp.CAcert.org/

This means that ocsptool can discover the servers to contact over HTTP.
We can now request information on the chain certificates.

$ ocsptool --ask --load-chain chain.pem

The request is sent via HTTP to the OCSP server address found in the
certificates.  It is possible to override the address of the OCSP server
as well as ask information on a particular certificate using -load-cert
and -load-issuer.

$ ocsptool --ask https://ocsp.CAcert.org/ --load-chain chain.pem

File: gnutls.info,  Node: danetool Invocation,  Prev: ocsptool Invocation,  Up: More on certificate authentication

4.2.8 Invoking danetool
-----------------------

Tool to generate and check DNS resource records for the DANE protocol.

danetool help/usage (‘-?’)
..........................

danetool - GnuTLS DANE tool
     Usage:  danetool [ -<flag> [<val>] | --<name>[{=| }<val>] ]...

None:

-d, --debug=num            Enable debugging
     				- it must be in the range:
     				  0 to 9999
        -V, --verbose              More verbose output
            --outfile=str          Output file
            --load-pubkey=str      Loads a public key file
            --load-certificate=str Loads a certificate file
            --dlv=str              Sets a DLV file
            --hash=str             Hash algorithm to use for signing
            --check=str            Check a host's DANE TLSA entry
            --check-ee             Check only the end-entity's certificate
            --check-ca             Check only the CA's certificate
            --tlsa-rr              Print the DANE RR data on a certificate or public key
     				- requires the option 'host'
            --host=str             Specify the hostname to be used in the DANE RR
            --proto=str            The protocol set for DANE data (tcp, udp etc.)
            --port=str             The port or service to connect to, for DANE data
            --app-proto            an alias for the 'starttls-proto' option
            --starttls-proto=str   The application protocol to be used to obtain the server's certificate (https, ftp, smtp, imap, ldap, xmpp, lmtp, pop3, nntp, sieve, postgres)
            --ca                   Whether the provided certificate or public key is a Certificate Authority
            --x509                 Use the hash of the X.509 certificate, rather than the public key
            --local                an alias for the 'domain' option
            --domain               The provided certificate or public key is issued by the local domain
     				- enabled by default
     				- disabled as '--no-domain'
            --local-dns            Use the local DNS server for DNSSEC resolving
            --insecure             Do not verify any DNSSEC signature
            --inder                Use DER format for input certificates and private keys
            --inraw                an alias for the 'inder' option
            --print-raw            Print the received DANE data in raw format
            --quiet                Suppress several informational messages

Version, usage and configuration options:

Options are specified by doubled hyphens and their name or by a single
     hyphen and the flag character.

Tool to generate and check DNS resource records for the DANE protocol.

Please send bug reports to:  <bugs@gnutls.org>

debug option (-d).
..................

This is the "enable debugging" option.  This option takes a
ArgumentType.NUMBER argument.  Specifies the debug level.

load-pubkey option.
...................

This is the "loads a public key file" option.  This option takes a
ArgumentType.STRING argument.  This can be either a file or a PKCS #11
URL

load-certificate option.
........................

This is the "loads a certificate file" option.  This option takes a
ArgumentType.STRING argument.  This can be either a file or a PKCS #11
URL

dlv option.
...........

This is the "sets a dlv file" option.  This option takes a
ArgumentType.STRING argument.  This sets a DLV file to be used for
DNSSEC verification.

hash option.
............

This is the "hash algorithm to use for signing" option.  This option
takes a ArgumentType.STRING argument.  Available hash functions are
SHA1, RMD160, SHA256, SHA384, SHA512.

check option.
.............

This is the "check a host's dane tlsa entry" option.  This option takes
a ArgumentType.STRING argument.  Obtains the DANE TLSA entry from the
given hostname and prints information.  Note that the actual certificate
of the host can be provided using -load-certificate, otherwise danetool
will connect to the server to obtain it.  The exit code on verification
success will be zero.

check-ee option.
................

This is the "check only the end-entity's certificate" option.  Checks
the end-entity's certificate only.  Trust anchors or CAs are not
considered.

check-ca option.
................

This is the "check only the ca's certificate" option.  Checks the trust
anchor's and CA's certificate only.  End-entities are not considered.

tlsa-rr option.
...............

This is the "print the dane rr data on a certificate or public key"
option.

This option has some usage constraints.  It:
   • must appear in combination with the following options: host.

This command prints the DANE RR data needed to enable DANE on a DNS
server.

host option.
............

This is the "specify the hostname to be used in the dane rr" option.
This option takes a ArgumentType.STRING argument ‘Hostname’.  This
command sets the hostname for the DANE RR.

proto option.
.............

This is the "the protocol set for dane data (tcp, udp etc.)"  option.
This option takes a ArgumentType.STRING argument ‘Protocol’.  This
command specifies the protocol for the service set in the DANE data.

app-proto option.
.................

This is an alias for the ‘starttls-proto’ option, *note the
starttls-proto option documentation: danetool starttls-proto.

starttls-proto option.
......................

This is the "the application protocol to be used to obtain the server's
certificate (https, ftp, smtp, imap, ldap, xmpp, lmtp, pop3, nntp,
sieve, postgres)" option.  This option takes a ArgumentType.STRING
argument.  When the server's certificate isn't provided danetool will
connect to the server to obtain the certificate.  In that case it is
required to know the protocol to talk with the server prior to
initiating the TLS handshake.

ca option.
..........

This is the "whether the provided certificate or public key is a
certificate authority" option.  Marks the DANE RR as a CA certificate if
specified.

x509 option.
............

This is the "use the hash of the x.509 certificate, rather than the
public key" option.  This option forces the generated record to contain
the hash of the full X.509 certificate.  By default only the hash of the
public key is used.

local option.
.............

This is an alias for the ‘domain’ option, *note the domain option
documentation: danetool domain.

domain option.
..............

This is the "the provided certificate or public key is issued by the
local domain" option.

This option has some usage constraints.  It:
   • can be disabled with -no-domain.
   • It is enabled by default.

DANE distinguishes certificates and public keys offered via the DNSSEC
to trusted and local entities.  This flag indicates that this is a
domain-issued certificate, meaning that there could be no CA involved.

local-dns option.
.................

This is the "use the local dns server for dnssec resolving" option.
This option will use the local DNS server for DNSSEC. This is disabled
by default due to many servers not allowing DNSSEC.

insecure option.
................

This is the "do not verify any dnssec signature" option.  Ignores any
DNSSEC signature verification results.

inder option.
.............

This is the "use der format for input certificates and private keys"
option.  The input files will be assumed to be in DER or RAW format.
Unlike options that in PEM input would allow multiple input data (e.g.
multiple certificates), when reading in DER format a single data
structure is read.

inraw option.
.............

This is an alias for the ‘inder’ option, *note the inder option
documentation: danetool inder.

print-raw option.
.................

This is the "print the received dane data in raw format" option.  This
option will print the received DANE data.

quiet option.
.............

This is the "suppress several informational messages" option.  In that
case on the exit code can be used as an indication of verification
success

version option (-v).
....................

help option (-h).
.................

This is the "display extended usage information and exit" option.
Display usage information and exit.

more-help option (-!).
......................

This is the "extended usage information passed thru pager" option.  Pass
the extended usage information through a pager.

danetool exit status
....................

One of the following exit values will be returned:
‘0 (EXIT_SUCCESS)’
     Successful program execution.
‘1 (EXIT_FAILURE)’
     The operation failed or the command syntax was not valid.

danetool See Also
.................

certtool (1)

danetool Examples
.................

DANE TLSA RR generation
.......................

To create a DANE TLSA resource record for a certificate (or public key)
that was issued locally and may or may not be signed by a CA use the
following command.
     $ danetool --tlsa-rr --host www.example.com --load-certificate cert.pem

To create a DANE TLSA resource record for a CA signed certificate, which
will be marked as such use the following command.
     $ danetool --tlsa-rr --host www.example.com --load-certificate cert.pem \
       --no-domain

The former is useful to add in your DNS entry even if your certificate
is signed by a CA. That way even users who do not trust your CA will be
able to verify your certificate using DANE.

In order to create a record for the CA signer of your certificate use
the following.
     $ danetool --tlsa-rr --host www.example.com --load-certificate cert.pem \
       --ca --no-domain

To read a server's DANE TLSA entry, use:
     $ danetool --check www.example.com --proto tcp --port 443

To verify an HTTPS server's DANE TLSA entry, use:
     $ danetool --check www.example.com --proto tcp --port 443 --load-certificate chain.pem

To verify an SMTP server's DANE TLSA entry, use:
     $ danetool --check www.example.com --proto tcp --starttls-proto=smtp --load-certificate chain.pem

File: gnutls.info,  Node: Shared-key and anonymous authentication,  Next: Selecting an appropriate authentication method,  Prev: More on certificate authentication,  Up: Authentication methods

4.3 Shared-key and anonymous authentication
===========================================

In addition to certificate authentication, the TLS protocol may be used
with password, shared-key and anonymous authentication methods.  The
rest of this chapter discusses details of these methods.

* Menu:

* PSK authentication::
* SRP authentication::
* Anonymous authentication::

File: gnutls.info,  Node: PSK authentication,  Next: SRP authentication,  Up: Shared-key and anonymous authentication

4.3.1 PSK authentication
------------------------

* Menu:

* Authentication using PSK::
* psktool Invocation::             Invoking psktool

File: gnutls.info,  Node: Authentication using PSK,  Next: psktool Invocation,  Up: PSK authentication

4.3.1.1 Authentication using PSK
................................

Authentication using Pre-shared keys is a method to authenticate using
usernames and binary keys.  This protocol avoids making use of public
key infrastructure and expensive calculations, thus it is suitable for
constraint clients.  It is available under all TLS protocol versions.

The implementation in GnuTLS is based on [*note TLSPSK::].  The
supported PSK key exchange methods are:

‘PSK:’
     Authentication using the PSK protocol (no forward secrecy).

‘DHE-PSK:’
     Authentication using the PSK protocol and Diffie-Hellman key
     exchange.  This method offers perfect forward secrecy.

‘ECDHE-PSK:’
     Authentication using the PSK protocol and Elliptic curve
     Diffie-Hellman key exchange.  This method offers perfect forward
     secrecy.

‘RSA-PSK:’
     Authentication using the PSK protocol for the client and an RSA
     certificate for the server.  This is not available under TLS 1.3.

Helper functions to generate and maintain PSK keys are also included in
GnuTLS.

‘INT *note gnutls_key_generate:: (gnutls_datum_t * KEY, unsigned int KEY_SIZE)’
‘INT *note gnutls_hex_encode:: (const gnutls_datum_t * DATA, char * RESULT, size_t * RESULT_SIZE)’
‘INT *note gnutls_hex_decode:: (const gnutls_datum_t * HEX_DATA, void * RESULT, size_t * RESULT_SIZE)’

File: gnutls.info,  Node: psktool Invocation,  Prev: Authentication using PSK,  Up: PSK authentication

4.3.1.2 Invoking psktool
........................

Program that generates random keys for use with TLS-PSK. The keys are
stored in hexadecimal format in a key file.

psktool help/usage (‘-?’)
.........................

psktool - GnuTLS PSK tool
     Usage:  psktool [ -<flag> [<val>] | --<name>[{=| }<val>] ]...

None:

-d, --debug=num            Enable debugging
     				- it must be in the range:
     				  0 to 9999
        -s, --keysize=num          Specify the key size in bytes (default is 32-bytes or 256-bits)
     				- it must be in the range:
     				  0 to 512
        -u, --username=str         Specify the username to use
        -p, --pskfile=str          Specify a pre-shared key file

Version, usage and configuration options:

Options are specified by doubled hyphens and their name or by a single
     hyphen and the flag character.

Program  that generates random keys for use with TLS-PSK. The
     keys are stored in hexadecimal format in a key file.

Please send bug reports to:  <bugs@gnutls.org>

debug option (-d).
..................

This is the "enable debugging" option.  This option takes a
ArgumentType.NUMBER argument.  Specifies the debug level.

pskfile option (-p).
....................

This is the "specify a pre-shared key file" option.  This option takes a
ArgumentType.STRING argument.  This option will specify the pre-shared
key file to store the generated keys.

passwd option.
..............

This is an alias for the ‘pskfile’ option, *note the pskfile option
documentation: psktool pskfile.

version option (-v).
....................

help option (-h).
.................

This is the "display extended usage information and exit" option.
Display usage information and exit.

more-help option (-!).
......................

This is the "extended usage information passed thru pager" option.  Pass
the extended usage information through a pager.

psktool exit status
...................

One of the following exit values will be returned:
‘0 (EXIT_SUCCESS)’
     Successful program execution.
‘1 (EXIT_FAILURE)’
     The operation failed or the command syntax was not valid.

psktool See Also
................

gnutls-cli-debug (1), gnutls-serv (1), srptool (1), certtool (1)

psktool Examples
................

To add a user 'psk_identity' in ‘keys.psk’ for use with GnuTLS run:
     $ ./psktool -u psk_identity -p keys.psk
     Generating a random key for user 'psk_identity'
     Key stored to keys.psk
     $ cat keys.psk
     psk_identity:88f3824b3e5659f52d00e959bacab954b6540344
     $

This command will create ‘keys.psk’ if it does not exist and will add
user 'psk_identity'.

File: gnutls.info,  Node: SRP authentication,  Next: Anonymous authentication,  Prev: PSK authentication,  Up: Shared-key and anonymous authentication

4.3.2 SRP authentication
------------------------

* Menu:

* Authentication using SRP::
* srptool Invocation::             Invoking srptool

File: gnutls.info,  Node: Authentication using SRP,  Next: srptool Invocation,  Up: SRP authentication

4.3.2.1 Authentication using SRP
................................

GnuTLS supports authentication via the Secure Remote Password or SRP
protocol (see [*note TOMSRP: RFC2945.] for a description).  The SRP key
exchange is an extension to the TLS protocol, and it provides an
authenticated with a password key exchange.  The peers can be identified
using a single password, or there can be combinations where the client
is authenticated using SRP and the server using a certificate.  It is
only available under TLS 1.2 or earlier versions.

The advantage of SRP authentication, over other proposed secure password
authentication schemes, is that SRP is not susceptible to off-line
dictionary attacks.  Moreover, SRP does not require the server to hold
the user's password.  This kind of protection is similar to the one used
traditionally in the UNIX ‘/etc/passwd’ file, where the contents of this
file did not cause harm to the system security if they were revealed.
The SRP needs instead of the plain password something called a verifier,
which is calculated using the user's password, and if stolen cannot be
used to impersonate the user.

Typical conventions in SRP are a password file, called ‘tpasswd’ that
holds the SRP verifiers (encoded passwords) and another file,
‘tpasswd.conf’, which holds the allowed SRP parameters.  The included in
GnuTLS helper follow those conventions.  The srptool program, discussed
in the next section is a tool to manipulate the SRP parameters.

The implementation in GnuTLS is based on [*note TLSSRP::].  The
supported key exchange methods are shown below.  Enabling any of these
key exchange methods in a session disables support for TLS1.3.

‘SRP:’
     Authentication using the SRP protocol.

‘SRP_DSS:’
     Client authentication using the SRP protocol.  Server is
     authenticated using a certificate with DSA parameters.

‘SRP_RSA:’
     Client authentication using the SRP protocol.  Server is
     authenticated using a certificate with RSA parameters.

-- Function: int gnutls_srp_verifier (const char * USERNAME, const char
          * PASSWORD, const gnutls_datum_t * SALT, const gnutls_datum_t
          * GENERATOR, const gnutls_datum_t * PRIME, gnutls_datum_t *
          RES)
     USERNAME: is the user's name

PASSWORD: is the user's password

SALT: should be some randomly generated bytes

GENERATOR: is the generator of the group

PRIME: is the group's prime

RES: where the verifier will be stored.

This function will create an SRP verifier, as specified in RFC2945.
     The ‘prime’ and ‘generator’ should be one of the static parameters
     defined in gnutls/gnutls.h or may be generated.

The verifier will be allocated with ‘gnutls_malloc’ () and will be
     stored in ‘res’ using binary format.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned, or an
     error code.

‘INT *note gnutls_srp_base64_encode2:: (const gnutls_datum_t * DATA, gnutls_datum_t * RESULT)’
‘INT *note gnutls_srp_base64_decode2:: (const gnutls_datum_t * B64_DATA, gnutls_datum_t * RESULT)’

File: gnutls.info,  Node: srptool Invocation,  Prev: Authentication using SRP,  Up: SRP authentication

4.3.2.2 Invoking srptool
........................

Simple program that emulates the programs in the Stanford SRP (Secure
Remote Password) libraries using GnuTLS. It is intended for use in
places where you don't expect SRP authentication to be the used for
system users.

In brief, to use SRP you need to create two files.  These are the
password file that holds the users and the verifiers associated with
them and the configuration file to hold the group parameters (called
tpasswd.conf).

srptool help/usage (‘-?’)
.........................

srptool - GnuTLS SRP tool
     Usage:  srptool [ -<flag> [<val>] | --<name>[{=| }<val>] ]...

None:

-d, --debug=num            Enable debugging
     				- it must be in the range:
     				  0 to 9999
        -i, --index=num            specify the index of the group parameters in tpasswd.conf to use
        -u, --username=str         specify a username
        -p, --passwd=str           specify a password file
        -s, --salt=num             specify salt size
            --verify               just verify the password
        -v, --passwd-conf=str      specify a password conf file
            --create-conf=str      Generate a password configuration file

Version, usage and configuration options:

Options are specified by doubled hyphens and their name or by a single
     hyphen and the flag character.

Simple program that emulates the programs in the Stanford SRP (Secure
     Remote Password) libraries using GnuTLS.  It is intended for use in  places
     where you don't expect SRP authentication to be the used for system users.

In  brief,  to use SRP you need to create two files. These are the password
     file that holds the users and the verifiers associated with  them  and  the
     configuration file to hold the group parameters (called tpasswd.conf).

Please send bug reports to:  <bugs@gnutls.org>

debug option (-d).
..................

This is the "enable debugging" option.  This option takes a
ArgumentType.NUMBER argument.  Specifies the debug level.

verify option.
..............

This is the "just verify the password" option.  Verifies the password
provided against the password file.

passwd-conf option (-v).
........................

This is the "specify a password conf file" option.  This option takes a
ArgumentType.STRING argument.  Specify a filename or a PKCS #11 URL to
read the CAs from.

create-conf option.
...................

This is the "generate a password configuration file" option.  This
option takes a ArgumentType.STRING argument.  This generates a password
configuration file (tpasswd.conf) containing the required for TLS
parameters.

version option (-v).
....................

help option (-h).
.................

This is the "display extended usage information and exit" option.
Display usage information and exit.

more-help option (-!).
......................

This is the "extended usage information passed thru pager" option.  Pass
the extended usage information through a pager.

srptool exit status
...................

One of the following exit values will be returned:
‘0 (EXIT_SUCCESS)’
     Successful program execution.
‘1 (EXIT_FAILURE)’
     The operation failed or the command syntax was not valid.

srptool See Also
................

gnutls-cli-debug (1), gnutls-serv (1), srptool (1), psktool (1),
certtool (1)

srptool Examples
................

To create ‘tpasswd.conf’ which holds the g and n values for SRP protocol
(generator and a large prime), run:
     $ srptool --create-conf /usr/local/etc/tpasswd.conf

This command will create ‘/usr/local/etc/tpasswd’ and will add user
'test' (you will also be prompted for a password).  Verifiers are stored
by default in the way libsrp expects.
     $ srptool --passwd /usr/local/etc/tpasswd --passwd-conf /usr/local/etc/tpasswd.conf -u test

This command will check against a password.  If the password matches the
one in ‘/usr/local/etc/tpasswd’ you will get an ok.
     $ srptool --passwd /usr/local/etc/tpasswd --passwd\-conf /usr/local/etc/tpasswd.conf --verify -u test

File: gnutls.info,  Node: Anonymous authentication,  Prev: SRP authentication,  Up: Shared-key and anonymous authentication

4.3.3 Anonymous authentication
------------------------------

The anonymous key exchange offers encryption without any indication of
the peer's identity.  This kind of authentication is vulnerable to a man
in the middle attack, but can be used even if there is no prior
communication or shared trusted parties with the peer.  It is useful to
establish a session over which certificate authentication will occur in
order to hide the identities of the participants from passive
eavesdroppers.  It is only available under TLS 1.2 or earlier versions.

Unless in the above case, it is not recommended to use anonymous
authentication.  In the cases where there is no prior communication with
the peers, an alternative with better properties, such as key
continuity, is trust on first use (see *note Verifying a certificate
using trust on first use authentication::).

The available key exchange algorithms for anonymous authentication are
shown below, but note that few public servers support them, and they
have to be explicitly enabled.  These ciphersuites are negotiated only
under TLS 1.2.

‘ANON_DH:’
     This algorithm exchanges Diffie-Hellman parameters.

‘ANON_ECDH:’
     This algorithm exchanges elliptic curve Diffie-Hellman parameters.
     It is more efficient than ANON_DH on equivalent security levels.

File: gnutls.info,  Node: Selecting an appropriate authentication method,  Prev: Shared-key and anonymous authentication,  Up: Authentication methods

4.4 Selecting an appropriate authentication method
==================================================

This section provides some guidance on how to use the available
authentication methods in GnuTLS in various scenarios.

4.4.1 Two peers with an out-of-band channel
-------------------------------------------

Let's consider two peers who need to communicate over an untrusted
channel (the Internet), but have an out-of-band channel available.  The
latter channel is considered safe from eavesdropping and message
modification and thus can be used for an initial bootstrapping of the
protocol.  The options available are:
   • Pre-shared keys (see *note PSK authentication::).  The server and a
     client communicate a shared randomly generated key over the trusted
     channel and use it to negotiate further sessions over the untrusted
     channel.

• Passwords (see *note SRP authentication::).  The client
     communicates to the server its username and password of choice and
     uses it to negotiate further sessions over the untrusted channel.

• Public keys (see *note Certificate authentication::).  The client
     and the server exchange their public keys (or fingerprints of them)
     over the trusted channel.  On future sessions over the untrusted
     channel they verify the key being the same (similar to *note
     Verifying a certificate using trust on first use authentication::).

Provided that the out-of-band channel is trusted all of the above
provide a similar level of protection.  An out-of-band channel may be
the initial bootstrapping of a user's PC in a corporate environment,
in-person communication, communication over an alternative network (e.g.
the phone network), etc.

4.4.2 Two peers without an out-of-band channel
----------------------------------------------

When an out-of-band channel is not available a peer cannot be reliably
authenticated.  What can be done, however, is to allow some form of
registration of users connecting for the first time and ensure that
their keys remain the same after that initial connection.  This is
termed key continuity or trust on first use (TOFU).

The available option is to use public key authentication (see *note
Certificate authentication::).  The client and the server store each
other's public keys (or fingerprints of them) and associate them with
their identity.  On future sessions over the untrusted channel they
verify the keys being the same (see *note Verifying a certificate using
trust on first use authentication::).

To mitigate the uncertainty of the information exchanged in the first
connection other channels over the Internet may be used, e.g., DNSSEC
(see *note Verifying a certificate using DANE::).

4.4.3 Two peers and a trusted third party
-----------------------------------------

When a trusted third party is available (or a certificate authority) the
most suitable option is to use certificate authentication (see *note
Certificate authentication::).  The client and the server obtain
certificates that associate their identity and public keys using a
digital signature by the trusted party and use them to on the subsequent
communications with each other.  Each party verifies the peer's
certificate using the trusted third party's signature.  The parameters
of the third party's signature are present in its certificate which must
be available to all communicating parties.

While the above is the typical authentication method for servers in the
Internet by using the commercial CAs, the users that act as clients in
the protocol rarely possess such certificates.  In that case a hybrid
method can be used where the server is authenticated by the client using
the commercial CAs and the client is authenticated based on some
information the client provided over the initial server-authenticated
channel.  The available options are:
   • Passwords (see *note SRP authentication::).  The client
     communicates to the server its username and password of choice on
     the initial server-authenticated connection and uses it to
     negotiate further sessions.  This is possible because the SRP
     protocol allows for the server to be authenticated using a
     certificate and the client using the password.

• Public keys (see *note Certificate authentication::).  The client
     sends its public key to the server (or a fingerprint of it) over
     the initial server-authenticated connection.  On future sessions
     the client verifies the server using the third party certificate
     and the server verifies that the client's public key remained the
     same (see *note Verifying a certificate using trust on first use
     authentication::).

File: gnutls.info,  Node: Hardware security modules and abstract key types,  Next: How to use GnuTLS in applications,  Prev: Authentication methods,  Up: Top

5 Abstract key types and Hardware security modules
**************************************************

In several cases storing the long term cryptographic keys in a hard disk
or even in memory poses a significant risk.  Once the system they are
stored is compromised the keys must be replaced as the secrecy of future
sessions is no longer guaranteed.  Moreover, past sessions that were not
protected by a perfect forward secrecy offering ciphersuite are also to
be assumed compromised.

If such threats need to be addressed, then it may be wise storing the
keys in a security module such as a smart card, an HSM or the TPM chip.
Those modules ensure the protection of the cryptographic keys by only
allowing operations on them and preventing their extraction.  The
purpose of the abstract key API is to provide an API that will allow the
handle of keys in memory and files, as well as keys stored in such
modules.

In GnuTLS the approach is to handle all keys transparently by the high
level API, e.g., the API that loads a key or certificate from a file.
The high-level API will accept URIs in addition to files that specify
keys on an HSM or in TPM, and a callback function will be used to obtain
any required keys.  The URI format is defined in [*note PKCS11URI::].

More information on the API is provided in the next sections.  Examples
of a URI of a certificate stored in an HSM, as well as a key stored in
the TPM chip are shown below.  To discover the URIs of the objects the
‘p11tool’ (see *note p11tool Invocation::).
     pkcs11:token=Nikos;serial=307521161601031;model=PKCS%2315; \
     manufacturer=EnterSafe;object=test1;type=cert

* Menu:

* Abstract key types::
* Application-specific keys::
* Smart cards and HSMs::
* Trusted Platform Module::

File: gnutls.info,  Node: Abstract key types,  Next: Application-specific keys,  Up: Hardware security modules and abstract key types

5.1 Abstract key types
======================

Since there are many forms of a public or private keys supported by
GnuTLS such as X.509, PKCS #11 or TPM it is desirable to allow common
operations on them.  For these reasons the abstract ‘gnutls_privkey_t’
and ‘gnutls_pubkey_t’ were introduced in ‘gnutls/abstract.h’ header.
Those types are initialized using a specific type of key and then can be
used to perform operations in an abstract way.  For example in order to
sign an X.509 certificate with a key that resides in a token the
following steps can be used.

#include <gnutls/abstract.h>

void sign_cert( gnutls_x509_crt_t to_be_signed)
     {
     gnutls_x509_crt_t ca_cert;
     gnutls_privkey_t abs_key;

/* initialize the abstract key */
       gnutls_privkey_init(&abs_key);

/* keys stored in tokens are identified by URLs */
       gnutls_privkey_import_url(abs_key, key_url);

gnutls_x509_crt_init(&ca_cert);
       gnutls_x509_crt_import_url(&ca_cert, cert_url);

/* sign the certificate to be signed */
       gnutls_x509_crt_privkey_sign(to_be_signed, ca_cert, abs_key,
                                    GNUTLS_DIG_SHA256, 0);
     }

* Menu:

* Abstract public keys::
* Abstract private keys::
* Operations::

File: gnutls.info,  Node: Abstract public keys,  Next: Abstract private keys,  Up: Abstract key types

5.1.1 Public keys
-----------------

An abstract ‘gnutls_pubkey_t’ can be initialized and freed by using the
functions below.

‘INT *note gnutls_pubkey_init:: (gnutls_pubkey_t * KEY)’
‘VOID *note gnutls_pubkey_deinit:: (gnutls_pubkey_t KEY)’

After initialization its values can be imported from an existing
structure like ‘gnutls_x509_crt_t’, or through an ASN.1 encoding of the
X.509 ‘SubjectPublicKeyInfo’ sequence.

‘INT *note gnutls_pubkey_import_x509:: (gnutls_pubkey_t KEY, gnutls_x509_crt_t CRT, unsigned int FLAGS)’
‘INT *note gnutls_pubkey_import_pkcs11:: (gnutls_pubkey_t KEY, gnutls_pkcs11_obj_t OBJ, unsigned int FLAGS)’

‘INT *note gnutls_pubkey_import_url:: (gnutls_pubkey_t KEY, const char * URL, unsigned int FLAGS)’
‘INT *note gnutls_pubkey_import_privkey:: (gnutls_pubkey_t KEY, gnutls_privkey_t PKEY, unsigned int USAGE, unsigned int FLAGS)’
‘INT *note gnutls_pubkey_import:: (gnutls_pubkey_t KEY, const gnutls_datum_t * DATA, gnutls_x509_crt_fmt_t FORMAT)’
‘INT *note gnutls_pubkey_export:: (gnutls_pubkey_t KEY, gnutls_x509_crt_fmt_t FORMAT, void * OUTPUT_DATA, size_t * OUTPUT_DATA_SIZE)’

-- Function: int gnutls_pubkey_export2 (gnutls_pubkey_t KEY,
          gnutls_x509_crt_fmt_t FORMAT, gnutls_datum_t * OUT)
     KEY: Holds the certificate

FORMAT: the format of output params.  One of PEM or DER.

OUT: will contain a certificate PEM or DER encoded

This function will export the public key to DER or PEM format.  The
     contents of the exported data is the SubjectPublicKeyInfo X.509
     structure.

The output buffer will be allocated using ‘gnutls_malloc()’ .

If the structure is PEM encoded, it will have a header of "BEGIN
     CERTIFICATE".

*Returns:* In case of failure a negative error code will be
     returned, and 0 on success.

*Since:* 3.1.3

Other helper functions that allow directly importing from raw X.509
structures are shown below.

‘INT *note gnutls_pubkey_import_x509_raw:: (gnutls_pubkey_t PKEY, const gnutls_datum_t * DATA, gnutls_x509_crt_fmt_t FORMAT, unsigned int FLAGS)’

An important function is *note gnutls_pubkey_import_url:: which will
import public keys from URLs that identify objects stored in tokens (see
*note Smart cards and HSMs:: and *note Trusted Platform Module::).  A
function to check for a supported by GnuTLS URL is *note
gnutls_url_is_supported::.

-- Function: unsigned gnutls_url_is_supported (const char * URL)
     URL: A URI to be tested

Check whether the provided ‘url’ is supported.  Depending on the
     system libraries GnuTLS may support pkcs11, tpmkey or other URLs.

*Returns:* return non-zero if the given URL is supported, and zero
     if it is not known.

*Since:* 3.1.0

Additional functions are available that will return information over a
public key, such as a unique key ID, as well as a function that given a
public key fingerprint would provide a memorable sketch.

Note that *note gnutls_pubkey_get_key_id:: calculates a SHA1 digest of
the public key as a DER-formatted, subjectPublicKeyInfo object.  Other
implementations use different approaches, e.g., some use the "common
method" described in section 4.2.1.2 of [*note RFC5280::] which
calculates a digest on a part of the subjectPublicKeyInfo object.

‘INT *note gnutls_pubkey_get_pk_algorithm:: (gnutls_pubkey_t KEY, unsigned int * BITS)’
‘INT *note gnutls_pubkey_get_preferred_hash_algorithm:: (gnutls_pubkey_t KEY, gnutls_digest_algorithm_t * HASH, unsigned int * MAND)’
‘INT *note gnutls_pubkey_get_key_id:: (gnutls_pubkey_t KEY, unsigned int FLAGS, unsigned char * OUTPUT_DATA, size_t * OUTPUT_DATA_SIZE)’
‘INT *note gnutls_random_art:: (gnutls_random_art_t TYPE, const char * KEY_TYPE, unsigned int KEY_SIZE, void * FPR, size_t FPR_SIZE, gnutls_datum_t * ART)’

To export the key-specific parameters, or obtain a unique key ID the
following functions are provided.

‘INT *note gnutls_pubkey_export_rsa_raw2:: (gnutls_pubkey_t KEY, gnutls_datum_t * M, gnutls_datum_t * E, unsigned FLAGS)’
‘INT *note gnutls_pubkey_export_dsa_raw2:: (gnutls_pubkey_t KEY, gnutls_datum_t * P, gnutls_datum_t * Q, gnutls_datum_t * G, gnutls_datum_t * Y, unsigned FLAGS)’
‘INT *note gnutls_pubkey_export_ecc_raw2:: (gnutls_pubkey_t KEY, gnutls_ecc_curve_t * CURVE, gnutls_datum_t * X, gnutls_datum_t * Y, unsigned int FLAGS)’
‘INT *note gnutls_pubkey_export_ecc_x962:: (gnutls_pubkey_t KEY, gnutls_datum_t * PARAMETERS, gnutls_datum_t * ECPOINT)’

File: gnutls.info,  Node: Abstract private keys,  Next: Operations,  Prev: Abstract public keys,  Up: Abstract key types

5.1.2 Private keys
------------------

An abstract ‘gnutls_privkey_t’ can be initialized and freed by using the
functions below.

‘INT *note gnutls_privkey_init:: (gnutls_privkey_t * KEY)’
‘VOID *note gnutls_privkey_deinit:: (gnutls_privkey_t KEY)’

After initialization its values can be imported from an existing
structure like ‘gnutls_x509_privkey_t’, but unlike public keys it cannot
be exported.  That is to allow abstraction over keys stored in hardware
that makes available only operations.

‘INT *note gnutls_privkey_import_x509:: (gnutls_privkey_t PKEY, gnutls_x509_privkey_t KEY, unsigned int FLAGS)’
‘INT *note gnutls_privkey_import_pkcs11:: (gnutls_privkey_t PKEY, gnutls_pkcs11_privkey_t KEY, unsigned int FLAGS)’

Other helper functions that allow directly importing from raw X.509
structures are shown below.  Again, as with public keys, private keys
can be imported from a hardware module using URLs.

-- Function: int gnutls_privkey_import_url (gnutls_privkey_t KEY, const
          char * URL, unsigned int FLAGS)
     KEY: A key of type ‘gnutls_privkey_t’

URL: A PKCS 11 url

FLAGS: should be zero

This function will import a PKCS11 or TPM URL as a private key.
     The supported URL types can be checked using
     ‘gnutls_url_is_supported()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.1.0

‘INT *note gnutls_privkey_import_x509_raw:: (gnutls_privkey_t PKEY, const gnutls_datum_t * DATA, gnutls_x509_crt_fmt_t FORMAT, const char * PASSWORD, unsigned int FLAGS)’
‘INT *note gnutls_privkey_get_pk_algorithm:: (gnutls_privkey_t KEY, unsigned int * BITS)’
‘GNUTLS_PRIVKEY_TYPE_T *note gnutls_privkey_get_type:: (gnutls_privkey_t KEY)’
‘INT *note gnutls_privkey_status:: (gnutls_privkey_t KEY)’

In order to support cryptographic operations using an external API, the
following function is provided.  This allows for a simple extensibility
API without resorting to PKCS #11.

-- Function: int gnutls_privkey_import_ext4 (gnutls_privkey_t PKEY,
          void * USERDATA, gnutls_privkey_sign_data_func SIGN_DATA_FN,
          gnutls_privkey_sign_hash_func SIGN_HASH_FN,
          gnutls_privkey_decrypt_func DECRYPT_FN,
          gnutls_privkey_deinit_func DEINIT_FN, gnutls_privkey_info_func
          INFO_FN, unsigned int FLAGS)
     PKEY: The private key

USERDATA: private data to be provided to the callbacks

SIGN_DATA_FN: callback for signature operations (may be ‘NULL’ )

SIGN_HASH_FN: callback for signature operations (may be ‘NULL’ )

DECRYPT_FN: callback for decryption operations (may be ‘NULL’ )

DEINIT_FN: a deinitialization function

INFO_FN: returns info about the public key algorithm (should not be
     ‘NULL’ )

FLAGS: Flags for the import

This function will associate the given callbacks with the
     ‘gnutls_privkey_t’ type.  At least one of the callbacks must be
     non-null.  If a deinitialization function is provided then flags is
     assumed to contain ‘GNUTLS_PRIVKEY_IMPORT_AUTO_RELEASE’ .

Note that in contrast with the signing function of
     ‘gnutls_privkey_import_ext3()’ , the signing functions provided to
     this function take explicitly the signature algorithm as parameter
     and different functions are provided to sign the data and hashes.

The ‘sign_hash_fn’ is to be called to sign pre-hashed data.  The
     input to the callback is the output of the hash (such as SHA256)
     corresponding to the signature algorithm.  For RSA PKCS‘1’
     signatures, the signature algorithm can be set to
     ‘GNUTLS_SIGN_RSA_RAW’ , and in that case the data should be handled
     as if they were an RSA PKCS‘1’ DigestInfo structure.

The ‘sign_data_fn’ is to be called to sign data.  The input data
     will be he data to be signed (and hashed), with the provided
     signature algorithm.  This function is to be used for signature
     algorithms like Ed25519 which cannot take pre-hashed data as input.

When both ‘sign_data_fn’ and ‘sign_hash_fn’ functions are provided
     they must be able to operate on all the supported signature
     algorithms, unless prohibited by the type of the algorithm (e.g.,
     as with Ed25519).

The ‘info_fn’ must provide information on the signature algorithms
     supported by this private key, and should support the flags
     ‘GNUTLS_PRIVKEY_INFO_PK_ALGO’ ,
     ‘GNUTLS_PRIVKEY_INFO_HAVE_SIGN_ALGO’ and
     ‘GNUTLS_PRIVKEY_INFO_PK_ALGO_BITS’ .  It must return -1 on unknown
     flags.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.6.0

On the private keys where exporting of parameters is possible (i.e.,
software keys), the following functions are also available.

‘INT *note gnutls_privkey_export_rsa_raw2:: (gnutls_privkey_t KEY, gnutls_datum_t * M, gnutls_datum_t * E, gnutls_datum_t * D, gnutls_datum_t * P, gnutls_datum_t * Q, gnutls_datum_t * U, gnutls_datum_t * E1, gnutls_datum_t * E2, unsigned int FLAGS)’
‘INT *note gnutls_privkey_export_dsa_raw2:: (gnutls_privkey_t KEY, gnutls_datum_t * P, gnutls_datum_t * Q, gnutls_datum_t * G, gnutls_datum_t * Y, gnutls_datum_t * X, unsigned int FLAGS)’
‘INT *note gnutls_privkey_export_ecc_raw2:: (gnutls_privkey_t KEY, gnutls_ecc_curve_t * CURVE, gnutls_datum_t * X, gnutls_datum_t * Y, gnutls_datum_t * K, unsigned int FLAGS)’

File: gnutls.info,  Node: Operations,  Prev: Abstract private keys,  Up: Abstract key types

5.1.3 Operations
----------------

The abstract key types can be used to access signing and signature
verification operations with the underlying keys.

-- Function: int gnutls_pubkey_verify_data2 (gnutls_pubkey_t PUBKEY,
          gnutls_sign_algorithm_t ALGO, unsigned int FLAGS, const
          gnutls_datum_t * DATA, const gnutls_datum_t * SIGNATURE)
     PUBKEY: Holds the public key

ALGO: The signature algorithm used

FLAGS: Zero or an OR list of ‘gnutls_certificate_verify_flags’

DATA: holds the signed data

SIGNATURE: contains the signature

This function will verify the given signed data, using the
     parameters from the certificate.

*Returns:* In case of a verification failure
     ‘GNUTLS_E_PK_SIG_VERIFY_FAILED’ is returned, and zero or positive
     code on success.  For known to be insecure signatures this function
     will return ‘GNUTLS_E_INSUFFICIENT_SECURITY’ unless the flag
     ‘GNUTLS_VERIFY_ALLOW_BROKEN’ is specified.

*Since:* 3.0

-- Function: int gnutls_pubkey_verify_hash2 (gnutls_pubkey_t KEY,
          gnutls_sign_algorithm_t ALGO, unsigned int FLAGS, const
          gnutls_datum_t * HASH, const gnutls_datum_t * SIGNATURE)
     KEY: Holds the public key

ALGO: The signature algorithm used

FLAGS: Zero or an OR list of ‘gnutls_certificate_verify_flags’

HASH: holds the hash digest to be verified

SIGNATURE: contains the signature

This function will verify the given signed digest, using the
     parameters from the public key.  Note that unlike
     ‘gnutls_privkey_sign_hash()’ , this function accepts a signature
     algorithm instead of a digest algorithm.  You can use
     ‘gnutls_pk_to_sign()’ to get the appropriate value.

*Since:* 3.0

-- Function: int gnutls_pubkey_encrypt_data (gnutls_pubkey_t KEY,
          unsigned int FLAGS, const gnutls_datum_t * PLAINTEXT,
          gnutls_datum_t * CIPHERTEXT)
     KEY: Holds the public key

FLAGS: should be 0 for now

PLAINTEXT: The data to be encrypted

CIPHERTEXT: contains the encrypted data

This function will encrypt the given data, using the public key.
     On success the ‘ciphertext’ will be allocated using
     ‘gnutls_malloc()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.0

-- Function: int gnutls_privkey_sign_data (gnutls_privkey_t SIGNER,
          gnutls_digest_algorithm_t HASH, unsigned int FLAGS, const
          gnutls_datum_t * DATA, gnutls_datum_t * SIGNATURE)
     SIGNER: Holds the key

HASH: should be a digest algorithm

FLAGS: Zero or one of ‘gnutls_privkey_flags_t’

DATA: holds the data to be signed

SIGNATURE: will contain the signature allocated with
     ‘gnutls_malloc()’

This function will sign the given data using a signature algorithm
     supported by the private key.  Signature algorithms are always used
     together with a hash functions.  Different hash functions may be
     used for the RSA algorithm, but only the SHA family for the DSA
     keys.

You may use ‘gnutls_pubkey_get_preferred_hash_algorithm()’ to
     determine the hash algorithm.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 2.12.0

-- Function: int gnutls_privkey_sign_hash (gnutls_privkey_t SIGNER,
          gnutls_digest_algorithm_t HASH_ALGO, unsigned int FLAGS, const
          gnutls_datum_t * HASH_DATA, gnutls_datum_t * SIGNATURE)
     SIGNER: Holds the signer's key

HASH_ALGO: The hash algorithm used

FLAGS: Zero or one of ‘gnutls_privkey_flags_t’

HASH_DATA: holds the data to be signed

SIGNATURE: will contain newly allocated signature

This function will sign the given hashed data using a signature
     algorithm supported by the private key.  Signature algorithms are
     always used together with a hash functions.  Different hash
     functions may be used for the RSA algorithm, but only SHA-XXX for
     the DSA keys.

You may use ‘gnutls_pubkey_get_preferred_hash_algorithm()’ to
     determine the hash algorithm.

The flags may be ‘GNUTLS_PRIVKEY_SIGN_FLAG_TLS1_RSA’ or
     ‘GNUTLS_PRIVKEY_SIGN_FLAG_RSA_PSS’ .  In the former case this
     function will ignore ‘hash_algo’ and perform a raw PKCS1 signature,
     and in the latter an RSA-PSS signature will be generated.

Note that, not all algorithm support signing already hashed data.
     When signing with Ed25519, ‘gnutls_privkey_sign_data()’ should be
     used.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 2.12.0

-- Function: int gnutls_privkey_decrypt_data (gnutls_privkey_t KEY,
          unsigned int FLAGS, const gnutls_datum_t * CIPHERTEXT,
          gnutls_datum_t * PLAINTEXT)
     KEY: Holds the key

FLAGS: zero for now

CIPHERTEXT: holds the data to be decrypted

PLAINTEXT: will contain the decrypted data, allocated with
     ‘gnutls_malloc()’

This function will decrypt the given data using the algorithm
     supported by the private key.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 2.12.0

Signing existing structures, such as certificates, CRLs, or certificate
requests, as well as associating public keys with structures is also
possible using the key abstractions.

-- Function: int gnutls_x509_crq_set_pubkey (gnutls_x509_crq_t CRQ,
          gnutls_pubkey_t KEY)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

KEY: holds a public key

This function will set the public parameters from the given public
     key to the request.  The ‘key’ can be deallocated after that.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 2.12.0

-- Function: int gnutls_x509_crt_set_pubkey (gnutls_x509_crt_t CRT,
          gnutls_pubkey_t KEY)
     CRT: should contain a ‘gnutls_x509_crt_t’ type

KEY: holds a public key

This function will set the public parameters from the given public
     key to the certificate.  The ‘key’ can be deallocated after that.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 2.12.0
‘INT *note gnutls_x509_crt_privkey_sign:: (gnutls_x509_crt_t CRT, gnutls_x509_crt_t ISSUER, gnutls_privkey_t ISSUER_KEY, gnutls_digest_algorithm_t DIG, unsigned int FLAGS)’
‘INT *note gnutls_x509_crl_privkey_sign:: (gnutls_x509_crl_t CRL, gnutls_x509_crt_t ISSUER, gnutls_privkey_t ISSUER_KEY, gnutls_digest_algorithm_t DIG, unsigned int FLAGS)’
‘INT *note gnutls_x509_crq_privkey_sign:: (gnutls_x509_crq_t CRQ, gnutls_privkey_t KEY, gnutls_digest_algorithm_t DIG, unsigned int FLAGS)’

File: gnutls.info,  Node: Application-specific keys,  Next: Smart cards and HSMs,  Prev: Abstract key types,  Up: Hardware security modules and abstract key types

5.2 System and application-specific keys
========================================

5.2.1 System-specific keys
--------------------------

In several systems there are keystores which allow to read, store and
use certificates and private keys.  For these systems GnuTLS provides
the system-key API in ‘gnutls/system-keys.h’.  That API provides the
ability to iterate through all stored keys, add and delete keys as well
as use these keys using a URL which starts with "system:".  The format
of the URLs is system-specific.  The ‘systemkey’ tool is also provided
to assist in listing keys and debugging.

The systems supported via this API are the following.
   • Windows Cryptography API (CNG)

-- Function: int gnutls_system_key_iter_get_info
          (gnutls_system_key_iter_t * ITER, unsigned CERT_TYPE, char **
          CERT_URL, char ** KEY_URL, char ** LABEL, gnutls_datum_t *
          DER, unsigned int FLAGS)
     ITER: an iterator of the system keys (must be set to ‘NULL’
     initially)

CERT_TYPE: A value of gnutls_certificate_type_t which indicates the
     type of certificate to look for

CERT_URL: The certificate URL of the pair (may be ‘NULL’ )

KEY_URL: The key URL of the pair (may be ‘NULL’ )

LABEL: The friendly name (if any) of the pair (may be ‘NULL’ )

DER: if non-NULL the DER data of the certificate

FLAGS: should be zero

This function will return on each call a certificate and key pair
     URLs, as well as a label associated with them, and the DER-encoded
     certificate.  When the iteration is complete it will return
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ .

Typically ‘cert_type’ should be ‘GNUTLS_CRT_X509’ .

All values set are allocated and must be cleared using
     ‘gnutls_free()’ ,

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.4.0

‘VOID *note gnutls_system_key_iter_deinit:: (gnutls_system_key_iter_t ITER)’
‘INT *note gnutls_system_key_add_x509:: (gnutls_x509_crt_t CRT, gnutls_x509_privkey_t PRIVKEY, const char * LABEL, char ** CERT_URL, char ** KEY_URL)’
‘INT *note gnutls_system_key_delete:: (const char * CERT_URL, const char * KEY_URL)’

5.2.2 Application-specific keys
-------------------------------

For systems where GnuTLS doesn't provide a system specific store, it may
often be desirable to define a custom class of keys that are identified
via URLs and available to GnuTLS calls such as *note
gnutls_certificate_set_x509_key_file2::.  Such keys can be registered
using the API in ‘gnutls/urls.h’.  The function which registers such
keys is *note gnutls_register_custom_url::.

-- Function: int gnutls_register_custom_url (const gnutls_custom_url_st
          * ST)
     ST: A ‘gnutls_custom_url_st’ structure

Register a custom URL. This will affect the following functions:
     ‘gnutls_url_is_supported()’ , ‘gnutls_privkey_import_url()’ ,
     gnutls_pubkey_import_url, ‘gnutls_x509_crt_import_url()’ and all
     functions that depend on them, e.g.,
     ‘gnutls_certificate_set_x509_key_file2()’ .

The provided structure and callback functions must be valid
     throughout the lifetime of the process.  The registration of an
     existing URL type will fail with ‘GNUTLS_E_INVALID_REQUEST’ .
     Since GnuTLS 3.5.0 this function can be used to override the
     builtin URLs.

This function is not thread safe.

*Returns:* returns zero if the given structure was imported or a
     negative value otherwise.

*Since:* 3.4.0

The input to this function are three callback functions as well as the
prefix of the URL, (e.g., "mypkcs11:") and the length of the prefix.
The types of the callbacks are shown below, and are expected to use the
exported gnutls functions to import the keys and certificates.  E.g., a
typical ‘import_key’ callback should use *note
gnutls_privkey_import_ext4::.

typedef int (*gnutls_privkey_import_url_func)(gnutls_privkey_t pkey,
                                                   const char *url,
                                                   unsigned flags);

typedef int (*gnutls_x509_crt_import_url_func)(gnutls_x509_crt_t pkey,
                                                    const char *url,
                                                    unsigned flags);

/* The following callbacks are optional */

/* This is to enable gnutls_pubkey_import_url() */
     typedef int (*gnutls_pubkey_import_url_func)(gnutls_pubkey_t pkey,
     					     const char *url, unsigned flags);

/* This is to allow constructing a certificate chain. It will be provided
      * the initial certificate URL and the certificate to find its issuer, and must
      * return zero and the DER encoding of the issuer's certificate. If not available,
      * it should return GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE. */
     typedef int (*gnutls_get_raw_issuer_func)(const char *url, gnutls_x509_crt_t crt,
     					  gnutls_datum_t *issuer_der, unsigned flags);

typedef struct custom_url_st {
             const char *name;
             unsigned name_size;
             gnutls_privkey_import_url_func import_key;
             gnutls_x509_crt_import_url_func import_crt;
             gnutls_pubkey_import_url_func import_pubkey;
     	gnutls_get_raw_issuer_func get_issuer;
     } gnutls_custom_url_st;

File: gnutls.info,  Node: Smart cards and HSMs,  Next: Trusted Platform Module,  Prev: Application-specific keys,  Up: Hardware security modules and abstract key types

5.3 Smart cards and HSMs
========================

In this section we present the smart-card and hardware security module
(HSM) support in GnuTLS using PKCS #11 [*note PKCS11::].  Hardware
security modules and smart cards provide a way to store private keys and
perform operations on them without exposing them.  This decouples
cryptographic keys from the applications that use them and provide an
additional security layer against cryptographic key extraction.  Since
this can also be achieved in software components such as in Gnome
keyring, we will use the term security module to describe any
cryptographic key separation subsystem.

PKCS #11 is plugin API allowing applications to access cryptographic
operations on a security module, as well as to objects residing on it.
PKCS #11 modules exist for hardware tokens such as smart cards(1),
cryptographic tokens, as well as for software modules like Gnome
Keyring.  The objects residing on a security module may be certificates,
public keys, private keys or secret keys.  Of those certificates and
public/private key pairs can be used with GnuTLS.  PKCS #11's main
advantage is that it allows operations on private key objects such as
decryption and signing without exposing the key.  In GnuTLS the PKCS #11
functionality is available in ‘gnutls/pkcs11.h’.

�[image src="pkcs11-vision.png"�]

Figure 5.1: PKCS #11 module usage.

* Menu:

* PKCS11 Initialization::
* PKCS11 Manual Initialization::
* Accessing objects that require a PIN::
* Reading objects::
* Writing objects::
* PKCS11 Low Level Access::
* Using a PKCS11 token with TLS::
* Verifying certificates over PKCS11::
* p11tool Invocation::

---------- Footnotes ----------

(1) For example, OpenSC-supported cards.

File: gnutls.info,  Node: PKCS11 Initialization,  Next: PKCS11 Manual Initialization,  Up: Smart cards and HSMs

5.3.1 Initialization
--------------------

To allow all GnuTLS applications to transparently access smart cards and
tokens, PKCS #11 is automatically initialized during the first call of a
PKCS #11 related function, in a thread safe way.  The default
initialization process, utilizes p11-kit configuration, and loads any
appropriate PKCS #11 modules.  The p11-kit configuration files(1) are
typically stored in ‘/usr/local/share/p11-kit/modules/’.  For example a
file that will instruct GnuTLS to load the OpenSC module, could be named
‘/usr/local/share/p11-kit/modules/opensc.module’ and contain the
following:

module: /usr/lib/opensc-pkcs11.so

If you use these configuration files, then there is no need for other
initialization in GnuTLS, except for the PIN and token callbacks (see
next section).  In several cases, however, it is desirable to limit
badly behaving modules (e.g., modules that add an unacceptable delay on
initialization) to single applications.  That can be done using the
"enable-in:" option followed by the base name of applications that this
module should be used.

It is also possible to manually initialize or even disable the PKCS #11
subsystem if the default settings are not desirable or not available
(see *note PKCS11 Manual Initialization:: for more information).

Note that, PKCS #11 modules behave in a peculiar way after a fork; they
require a reinitialization of all the used PKCS #11 resources.  While
GnuTLS automates that process, there are corner cases where it is not
possible to handle it correctly in an automated way(2).  For that, it is
recommended not to mix fork() and PKCS #11 module usage.  It is
recommended to initialize and use any PKCS #11 resources in a single
process.

Older versions of GnuTLS required to call *note gnutls_pkcs11_reinit::
after a fork() call; since 3.3.0 this is no longer required.

---------- Footnotes ----------

(1) <https://p11-glue.github.io/p11-glue/p11-kit.html>

(2) For example when an open session is to be reinitialized, but the
PIN is not available to GnuTLS (e.g., it was entered at a pinpad).

File: gnutls.info,  Node: PKCS11 Manual Initialization,  Next: Accessing objects that require a PIN,  Prev: PKCS11 Initialization,  Up: Smart cards and HSMs

5.3.2 Manual initialization of user-specific modules
----------------------------------------------------

In systems where one cannot rely on a globally available p11-kit
configuration to be available, it is still possible to utilize PKCS #11
objects.  That can be done by loading directly the PKCS #11 shared
module in the application using *note gnutls_pkcs11_add_provider::,
after having called *note gnutls_pkcs11_init:: specifying the
‘GNUTLS_PKCS11_FLAG_MANUAL’ flag.

-- Function: int gnutls_pkcs11_add_provider (const char * NAME, const
          char * PARAMS)
     NAME: The filename of the module

PARAMS: should be NULL or a known string (see description)

This function will load and add a PKCS 11 module to the module list
     used in gnutls.  After this function is called the module will be
     used for PKCS 11 operations.

When loading a module to be used for certificate verification, use
     the string 'trusted' as ‘params’ .

Note that this function is not thread safe.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 2.12.0

In that case, the application will only have access to the modules
explicitly loaded.  If the ‘GNUTLS_PKCS11_FLAG_MANUAL’ flag is specified
and no calls to *note gnutls_pkcs11_add_provider:: are made, then the
PKCS #11 functionality is effectively disabled.

-- Function: int gnutls_pkcs11_init (unsigned int FLAGS, const char *
          DEPRECATED_CONFIG_FILE)
     FLAGS: An ORed sequence of ‘GNUTLS_PKCS11_FLAG_’ *

DEPRECATED_CONFIG_FILE: either NULL or the location of a deprecated
     configuration file

This function will initialize the PKCS 11 subsystem in gnutls.  It
     will read configuration files if ‘GNUTLS_PKCS11_FLAG_AUTO’ is used
     or allow you to independently load PKCS 11 modules using
     ‘gnutls_pkcs11_add_provider()’ if ‘GNUTLS_PKCS11_FLAG_MANUAL’ is
     specified.

You don't need to call this function since GnuTLS 3.3.0 because it
     is being called during the first request PKCS 11 operation.  That
     call will assume the ‘GNUTLS_PKCS11_FLAG_AUTO’ flag.  If another
     flags are required then it must be called independently prior to
     any PKCS 11 operation.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 2.12.0

File: gnutls.info,  Node: Accessing objects that require a PIN,  Next: Reading objects,  Prev: PKCS11 Manual Initialization,  Up: Smart cards and HSMs

5.3.3 Accessing objects that require a PIN
------------------------------------------

Objects stored in token such as a private keys are typically protected
from access by a PIN or password.  This PIN may be required to either
read the object (if allowed) or to perform operations with it.  To allow
obtaining the PIN when accessing a protected object, as well as probe
the user to insert the token the following functions allow to set a
callback.

‘VOID *note gnutls_pkcs11_set_token_function:: (gnutls_pkcs11_token_callback_t FN, void * USERDATA)’
‘VOID *note gnutls_pkcs11_set_pin_function:: (gnutls_pin_callback_t FN, void * USERDATA)’
‘INT *note gnutls_pkcs11_add_provider:: (const char * NAME, const char * PARAMS)’
‘GNUTLS_PIN_CALLBACK_T *note gnutls_pkcs11_get_pin_function:: (void ** USERDATA)’

The callback is of type ‘gnutls_pin_callback_t’ and will have as input
the provided userdata, the PIN attempt number, a URL describing the
token, a label describing the object and flags.  The PIN must be at most
of ‘pin_max’ size and must be copied to pin variable.  The function must
return 0 on success or a negative error code otherwise.

typedef int (*gnutls_pin_callback_t) (void *userdata, int attempt,
                                      const char *token_url,
                                      const char *token_label,
                                      unsigned int flags,
                                      char *pin, size_t pin_max);

The flags are of ‘gnutls_pin_flag_t’ type and are explained below.

‘GNUTLS_PIN_USER’
     The PIN for the user.
‘GNUTLS_PIN_SO’
     The PIN for the security officer (admin).
‘GNUTLS_PIN_FINAL_TRY’
     This is the final try before blocking.
‘GNUTLS_PIN_COUNT_LOW’
     Few tries remain before token blocks.
‘GNUTLS_PIN_CONTEXT_SPECIFIC’
     The PIN is for a specific action and key like signing.
‘GNUTLS_PIN_WRONG’
     Last given PIN was not correct.

Figure 5.2: The ‘gnutls_pin_flag_t’ enumeration.

Note that due to limitations of PKCS #11 there are issues when multiple
libraries are sharing a module.  To avoid this problem GnuTLS uses
p11-kit that provides a middleware to control access to resources over
the multiple users.

To avoid conflicts with multiple registered callbacks for PIN functions,
*note gnutls_pkcs11_get_pin_function:: may be used to check for any
previously set functions.  In addition context specific PIN functions
are allowed, e.g., by using functions below.

‘VOID *note gnutls_certificate_set_pin_function:: (gnutls_certificate_credentials_t CRED, gnutls_pin_callback_t FN, void * USERDATA)’
‘VOID *note gnutls_pubkey_set_pin_function:: (gnutls_pubkey_t KEY, gnutls_pin_callback_t FN, void * USERDATA)’
‘VOID *note gnutls_privkey_set_pin_function:: (gnutls_privkey_t KEY, gnutls_pin_callback_t FN, void * USERDATA)’
‘VOID *note gnutls_pkcs11_obj_set_pin_function:: (gnutls_pkcs11_obj_t OBJ, gnutls_pin_callback_t FN, void * USERDATA)’
‘VOID *note gnutls_x509_crt_set_pin_function:: (gnutls_x509_crt_t CRT, gnutls_pin_callback_t FN, void * USERDATA)’

File: gnutls.info,  Node: Reading objects,  Next: Writing objects,  Prev: Accessing objects that require a PIN,  Up: Smart cards and HSMs

5.3.4 Reading objects
---------------------

All PKCS #11 objects are referenced by GnuTLS functions by URLs as
described in [*note PKCS11URI::].  This allows for a consistent naming
of objects across systems and applications in the same system.  For
example a public key on a smart card may be referenced as:

pkcs11:token=Nikos;serial=307521161601031;model=PKCS%2315; \
     manufacturer=EnterSafe;object=test1;type=public;\
     id=32f153f3e37990b08624141077ca5dec2d15faed

while the smart card itself can be referenced as:
     pkcs11:token=Nikos;serial=307521161601031;model=PKCS%2315;manufacturer=EnterSafe

Objects stored in a PKCS #11 token can typically be extracted if they
are not marked as sensitive.  Usually only private keys are marked as
sensitive and cannot be extracted, while certificates and other data can
be retrieved.  The functions that can be used to enumerate and access
objects are shown below.

‘INT *note gnutls_pkcs11_obj_list_import_url4:: (gnutls_pkcs11_obj_t ** P_LIST, unsigned int * N_LIST, const char * URL, unsigned int FLAGS)’
‘INT *note gnutls_pkcs11_obj_import_url:: (gnutls_pkcs11_obj_t OBJ, const char * URL, unsigned int FLAGS)’
‘INT *note gnutls_pkcs11_obj_export_url:: (gnutls_pkcs11_obj_t OBJ, gnutls_pkcs11_url_type_t DETAILED, char ** URL)’

-- Function: int gnutls_pkcs11_obj_get_info (gnutls_pkcs11_obj_t OBJ,
          gnutls_pkcs11_obj_info_t ITYPE, void * OUTPUT, size_t *
          OUTPUT_SIZE)
     OBJ: should contain a ‘gnutls_pkcs11_obj_t’ type

ITYPE: Denotes the type of information requested

OUTPUT: where output will be stored

OUTPUT_SIZE: contains the maximum size of the output buffer and
     will be overwritten with the actual size.

This function will return information about the PKCS11 certificate
     such as the label, id as well as token information where the key is
     stored.

When output is text, a null terminated string is written to
     ‘output’ and its string length is written to ‘output_size’ (without
     null terminator).  If the buffer is too small, ‘output_size’ will
     contain the expected buffer size (with null terminator for text)
     and return ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ .

In versions previously to 3.6.0 this function included the null
     terminator to ‘output_size’ .  After 3.6.0 the output size doesn't
     include the terminator character.

*Returns:* ‘GNUTLS_E_SUCCESS’ (0) on success or a negative error
     code on error.

*Since:* 2.12.0

‘INT *note gnutls_x509_crt_import_pkcs11:: (gnutls_x509_crt_t CRT, gnutls_pkcs11_obj_t PKCS11_CRT)’
‘INT *note gnutls_x509_crt_import_url:: (gnutls_x509_crt_t CRT, const char * URL, unsigned int FLAGS)’
‘INT *note gnutls_x509_crt_list_import_pkcs11:: (gnutls_x509_crt_t * CERTS, unsigned int CERT_MAX, gnutls_pkcs11_obj_t *const OBJS, unsigned int FLAGS)’

Properties of the physical token can also be accessed and altered with
GnuTLS.  For example data in a token can be erased (initialized), PIN
can be altered, etc.

‘INT *note gnutls_pkcs11_token_init:: (const char * TOKEN_URL, const char * SO_PIN, const char * LABEL)’
‘INT *note gnutls_pkcs11_token_get_url:: (unsigned int SEQ, gnutls_pkcs11_url_type_t DETAILED, char ** URL)’
‘INT *note gnutls_pkcs11_token_get_info:: (const char * URL, gnutls_pkcs11_token_info_t TTYPE, void * OUTPUT, size_t * OUTPUT_SIZE)’
‘INT *note gnutls_pkcs11_token_get_flags:: (const char * URL, unsigned int * FLAGS)’
‘INT *note gnutls_pkcs11_token_set_pin:: (const char * TOKEN_URL, const char * OLDPIN, const char * NEWPIN, unsigned int FLAGS)’

The following examples demonstrate the usage of the API. The first
example will list all available PKCS #11 tokens in a system and the
latter will list all certificates in a token that have a corresponding
private key.

int i;
     char* url;

gnutls_global_init();

for (i=0;;i++)
       {
         ret = gnutls_pkcs11_token_get_url(i, &url);
         if (ret == GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE)
           break;

if (ret < 0)
           exit(1);

fprintf(stdout, "Token[%d]: URL: %s\n", i, url);
         gnutls_free(url);
       }
     gnutls_global_deinit();

/* This example code is placed in the public domain. */

#include <config.h>
#include <gnutls/gnutls.h>
#include <gnutls/pkcs11.h>
#include <stdio.h>
#include <stdlib.h>

#define URL "pkcs11:URL"

int main(int argc, char **argv)
{
	gnutls_pkcs11_obj_t *obj_list;
	gnutls_x509_crt_t xcrt;
	unsigned int obj_list_size = 0;
	gnutls_datum_t cinfo;
	int ret;
	unsigned int i;

ret = gnutls_pkcs11_obj_list_import_url4(
		&obj_list, &obj_list_size, URL,
		GNUTLS_PKCS11_OBJ_FLAG_CRT |
			GNUTLS_PKCS11_OBJ_FLAG_WITH_PRIVKEY);
	if (ret < 0)
		return -1;

/* now all certificates are in obj_list */
	for (i = 0; i < obj_list_size; i++) {
		gnutls_x509_crt_init(&xcrt);

gnutls_x509_crt_import_pkcs11(xcrt, obj_list[i]);

gnutls_x509_crt_print(xcrt, GNUTLS_CRT_PRINT_FULL, &cinfo);

fprintf(stdout, "cert[%d]:\n %s\n\n", i, cinfo.data);

gnutls_free(cinfo.data);
		gnutls_x509_crt_deinit(xcrt);
	}

for (i = 0; i < obj_list_size; i++)
		gnutls_pkcs11_obj_deinit(obj_list[i]);
	gnutls_free(obj_list);

return 0;
}

File: gnutls.info,  Node: Writing objects,  Next: PKCS11 Low Level Access,  Prev: Reading objects,  Up: Smart cards and HSMs

5.3.5 Writing objects
---------------------

With GnuTLS you can copy existing private keys and certificates to a
token.  Note that when copying private keys it is recommended to mark
them as sensitive using the ‘GNUTLS_PKCS11_OBJ_FLAG_MARK_SENSITIVE’ to
prevent its extraction.  An object can be marked as private using the
flag ‘GNUTLS_PKCS11_OBJ_FLAG_MARK_PRIVATE’, to require PIN to be entered
before accessing the object (for operations or otherwise).

-- Function: int gnutls_pkcs11_copy_x509_privkey2 (const char *
          TOKEN_URL, gnutls_x509_privkey_t KEY, const char * LABEL,
          const gnutls_datum_t * CID, unsigned int KEY_USAGE, unsigned
          int FLAGS)
     TOKEN_URL: A PKCS ‘11’ URL specifying a token

KEY: A private key

LABEL: A name to be used for the stored data

CID: The CKA_ID to set for the object -if NULL, the ID will be
     derived from the public key

KEY_USAGE: One of GNUTLS_KEY_*

FLAGS: One of GNUTLS_PKCS11_OBJ_* flags

This function will copy a private key into a PKCS ‘11’ token
     specified by a URL.

Since 3.6.3 the objects are marked as sensitive by default unless
     ‘GNUTLS_PKCS11_OBJ_FLAG_MARK_NOT_SENSITIVE’ is specified.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.4.0

-- Function: int gnutls_pkcs11_copy_x509_crt2 (const char * TOKEN_URL,
          gnutls_x509_crt_t CRT, const char * LABEL, const
          gnutls_datum_t * CID, unsigned int FLAGS)
     TOKEN_URL: A PKCS ‘11’ URL specifying a token

CRT: The certificate to copy

LABEL: The name to be used for the stored data

CID: The CKA_ID to set for the object -if NULL, the ID will be
     derived from the public key

FLAGS: One of GNUTLS_PKCS11_OBJ_FLAG_*

This function will copy a certificate into a PKCS ‘11’ token
     specified by a URL. Valid flags to mark the certificate:
     ‘GNUTLS_PKCS11_OBJ_FLAG_MARK_TRUSTED’ ,
     ‘GNUTLS_PKCS11_OBJ_FLAG_MARK_PRIVATE’ ,
     ‘GNUTLS_PKCS11_OBJ_FLAG_MARK_CA’ ,
     ‘GNUTLS_PKCS11_OBJ_FLAG_MARK_ALWAYS_AUTH’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.4.0

-- Function: int gnutls_pkcs11_delete_url (const char * OBJECT_URL,
          unsigned int FLAGS)
     OBJECT_URL: The URL of the object to delete.

FLAGS: One of GNUTLS_PKCS11_OBJ_* flags

This function will delete objects matching the given URL. Note that
     not all tokens support the delete operation.

*Returns:* On success, the number of objects deleted is returned,
     otherwise a negative error value.

*Since:* 2.12.0

File: gnutls.info,  Node: PKCS11 Low Level Access,  Next: Using a PKCS11 token with TLS,  Prev: Writing objects,  Up: Smart cards and HSMs

5.3.6 Low Level Access
----------------------

When it is needed to use PKCS#11 functionality which is not wrapped by
GnuTLS, it is possible to extract the PKCS#11 session, object or token
pointers.  That allows an application to still access the low-level
functionality, while at the same time take advantage of the URI
addressing scheme supported by GnuTLS.

-- Function: int gnutls_pkcs11_token_get_ptr (const char * URL, void **
          PTR, unsigned long * SLOT_ID, unsigned int FLAGS)
     URL: should contain a PKCS‘11’ URL identifying a token

PTR: will contain the CK_FUNCTION_LIST_PTR pointer

SLOT_ID: will contain the slot_id (may be ‘NULL’ )

FLAGS: should be zero

This function will return the function pointer of the specified
     token by the URL. The returned pointers are valid until gnutls is
     deinitialized, c.f.  ‘_global_deinit()’ .

*Returns:* ‘GNUTLS_E_SUCCESS’ (0) on success or a negative error
     code on error.

*Since:* 3.6.3

-- Function: int gnutls_pkcs11_obj_get_ptr (gnutls_pkcs11_obj_t OBJ,
          void ** PTR, void ** SESSION, void ** OHANDLE, unsigned long *
          SLOT_ID, unsigned int FLAGS)
     OBJ: should contain a ‘gnutls_pkcs11_obj_t’ type

PTR: will contain the CK_FUNCTION_LIST_PTR pointer (may be ‘NULL’ )

SESSION: will contain the CK_SESSION_HANDLE of the object

OHANDLE: will contain the CK_OBJECT_HANDLE of the object

SLOT_ID: the identifier of the slot (may be ‘NULL’ )

FLAGS: Or sequence of GNUTLS_PKCS11_OBJ_* flags

Obtains the PKCS‘11’ session handles of an object.  ‘session’ and
     ‘ohandle’ must be deinitialized by the caller.  The returned
     pointers are independent of the ‘obj’ lifetime.

*Returns:* ‘GNUTLS_E_SUCCESS’ (0) on success or a negative error
     code on error.

*Since:* 3.6.3

File: gnutls.info,  Node: Using a PKCS11 token with TLS,  Next: Verifying certificates over PKCS11,  Prev: PKCS11 Low Level Access,  Up: Smart cards and HSMs

5.3.7 Using a PKCS #11 token with TLS
-------------------------------------

It is possible to use a PKCS #11 token to a TLS session, as shown in
*note ex-pkcs11-client::.  In addition the following functions can be
used to load PKCS #11 key and certificates by specifying a PKCS #11 URL
instead of a filename.

‘INT *note gnutls_certificate_set_x509_trust_file:: (gnutls_certificate_credentials_t CRED, const char * CAFILE, gnutls_x509_crt_fmt_t TYPE)’
‘INT *note gnutls_certificate_set_x509_key_file2:: (gnutls_certificate_credentials_t RES, const char * CERTFILE, const char * KEYFILE, gnutls_x509_crt_fmt_t TYPE, const char * PASS, unsigned int FLAGS)’

File: gnutls.info,  Node: Verifying certificates over PKCS11,  Next: p11tool Invocation,  Prev: Using a PKCS11 token with TLS,  Up: Smart cards and HSMs

5.3.8 Verifying certificates over PKCS #11
------------------------------------------

The PKCS #11 API can be used to allow all applications in the same
operating system to access shared cryptographic keys and certificates in
a uniform way, as in *note Figure 5.1: fig-pkcs11-vision.  That way
applications could load their trusted certificate list, as well as user
certificates from a common PKCS #11 module.  Such a provider is the
p11-kit trust storage module(1) and it provides access to the trusted
Root CA certificates in a system.  That provides a more dynamic list of
Root CA certificates, as opposed to a static list in a file or
directory.

That store, allows for distrusting of CAs or certificates, as well as
categorization of the Root CAs (Web verification, Code signing, etc.),
in addition to restricting their purpose via stapled extensions(2).
GnuTLS will utilize the p11-kit trust module as the default trust store
if configured to; i.e., if '-with-default-trust-store-pkcs11=pkcs11:' is
given to the configure script.

---------- Footnotes ----------

(1) <https://p11-glue.github.io/p11-glue/trust-module.html>

(2) See the 'Restricting the scope of CA certificates' post at
<https://nmav.gnutls.org/2016/06/restricting-scope-of-ca-certificates.html>

File: gnutls.info,  Node: p11tool Invocation,  Prev: Verifying certificates over PKCS11,  Up: Smart cards and HSMs

5.3.9 Invoking p11tool
----------------------

Program that allows operations on PKCS #11 smart cards and security
modules.

To use PKCS #11 tokens with GnuTLS the p11-kit configuration files need
to be setup.  That is create a .module file in
/usr/local/share/p11-kit/modules with the contents 'module:
/path/to/pkcs11.so'.  Alternatively the configuration file
/usr/local/etc/gnutls/pkcs11.conf has to exist and contain a number of
lines of the form 'load=/usr/lib/opensc-pkcs11.so'.

You can provide the PIN to be used for the PKCS #11 operations with the
environment variables GNUTLS_PIN and GNUTLS_SO_PIN.

p11tool help/usage (‘-?’)
.........................

p11tool - GnuTLS PKCS #11 tool
     Usage:  p11tool [ -<flag> [<val>] | --<name>[{=| }<val>] ]... [url]

None:

Tokens:

--list-tokens          List all available tokens
            --list-token-urls      List the URLs available tokens
            --list-mechanisms      List all available mechanisms in a token
            --initialize           Initializes a PKCS #11 token
            --initialize-pin       Initializes/Resets a PKCS #11 token user PIN
            --initialize-so-pin    Initializes/Resets a PKCS #11 token security officer PIN
            --set-pin=str          Specify the PIN to use on token operations
            --set-so-pin=str       Specify the Security Officer's PIN to use on token initialization

Object listing:

--list-all             List all available objects in a token
            --list-all-certs       List all available certificates in a token
            --list-certs           List all certificates that have an associated private key
            --list-all-privkeys    List all available private keys in a token
            --list-privkeys        an alias for the 'list-all-privkeys' option
            --list-keys            an alias for the 'list-all-privkeys' option
            --list-all-trusted     List all available certificates marked as trusted
            --export               Export the object specified by the URL
     				- prohibits these options:
     				export-stapled
     				export-chain
     				export-pubkey
            --export-stapled       Export the certificate object specified by the URL
     				- prohibits these options:
     				export
     				export-chain
     				export-pubkey
            --export-chain         Export the certificate specified by the URL and its chain of trust
     				- prohibits these options:
     				export-stapled
     				export
     				export-pubkey
            --export-pubkey        Export the public key for a private key
     				- prohibits these options:
     				export-stapled
     				export
     				export-chain
            --info                 List information on an available object in a token
            --trusted              an alias for the 'mark-trusted' option
            --distrusted           an alias for the 'mark-distrusted' option

Key generation:

--generate-privkey=str Generate private-public key pair of given type
            --bits=num             Specify the number of bits for the key generate
            --curve=str            Specify the curve used for EC key generation
            --sec-param=str        Specify the security level

Writing objects:

--set-id=str           Set the CKA_ID (in hex) for the specified by the URL object
     				- prohibits the option 'write'
            --set-label=str        Set the CKA_LABEL for the specified by the URL object
     				- prohibits these options:
     				write
     				set-id
            --write                Writes the loaded objects to a PKCS #11 token
            --delete               Deletes the objects matching the given PKCS #11 URL
            --label=str            Sets a label for the write operation
            --id=str               Sets an ID for the write operation
            --mark-wrap            Marks the generated key to be a wrapping key
            --mark-trusted         Marks the object to be written as trusted
     				- prohibits the option 'mark-distrusted'
            --mark-distrusted      When retrieving objects, it requires the objects to be distrusted
     				- prohibits the option 'mark-trusted'
            --mark-decrypt         Marks the object to be written for decryption
            --mark-sign            Marks the object to be written for signature generation
            --mark-ca              Marks the object to be written as a CA
            --mark-private         Marks the object to be written as private
            --ca                   an alias for the 'mark-ca' option
            --private              an alias for the 'mark-private' option
            --mark-always-authenticate  Marks the object to be written as always authenticate
            --secret-key=str       Provide a hex encoded secret key
            --load-privkey=file    Private key file to use
     				- file must pre-exist
            --load-pubkey=file     Public key file to use
     				- file must pre-exist
            --load-certificate=file Certificate file to use
     				- file must pre-exist

Other options:

-d, --debug=num            Enable debugging
     				- it must be in the range:
     				  0 to 9999
            --outfile=str          Output file
            --login                Force (user) login to token
            --so-login             Force security officer login to token
            --admin-login          an alias for the 'so-login' option
            --test-sign            Tests the signature operation of the provided object
            --sign-params=str      Sign with a specific signature algorithm
            --hash=str             Hash algorithm to use for signing
            --generate-random=num  Generate random data
        -8, --pkcs8                Use PKCS #8 format for private keys
            --inder                Use DER/RAW format for input
            --inraw                an alias for the 'inder' option
            --outder               Use DER format for output certificates, private keys, and DH parameters
            --outraw               an alias for the 'outder' option
            --provider=file        Specify the PKCS #11 provider library
            --detailed-url         Print detailed URLs
            --only-urls            Print a compact listing using only the URLs
            --batch                Disable all interaction with the tool

Version, usage and configuration options:

Options are specified by doubled hyphens and their name or by a single
     hyphen and the flag character.
     Operands and options may be intermixed.  They will be reordered.

Program that allows operations on PKCS #11 smart cards
     and security modules.

To use PKCS #11 tokens with GnuTLS the p11-kit configuration files need to be setup.
     That is create a .module file in /usr/local/share/p11-kit/modules with the contents 'module: /path/to/pkcs11.so'.
     Alternatively the configuration file /usr/local/etc/gnutls/pkcs11.conf has to exist and contain a number
     of lines of the form 'load=/usr/lib/opensc-pkcs11.so'.

You can provide the PIN to be used for the PKCS #11 operations with the environment variables
     GNUTLS_PIN and GNUTLS_SO_PIN.

Please send bug reports to:  <bugs@gnutls.org>

token-related-options options
.............................

Tokens.

list-token-urls option.
.......................

This is the "list the urls available tokens" option.  This is a more
compact version of -list-tokens.

initialize-so-pin option.
.........................

This is the "initializes/resets a pkcs #11 token security officer pin"
option.  This initializes the security officer's PIN. When used
non-interactively use the GNUTLS_NEW_SO_PIN environment variables to
initialize SO's PIN.

set-pin option.
...............

This is the "specify the pin to use on token operations" option.  This
option takes a ArgumentType.STRING argument.  Alternatively the
GNUTLS_PIN environment variable may be used.

set-so-pin option.
..................

This is the "specify the security officer's pin to use on token
initialization" option.  This option takes a ArgumentType.STRING
argument.  Alternatively the GNUTLS_SO_PIN environment variable may be
used.

object-list-related-options options
...................................

Object listing.

list-all option.
................

This is the "list all available objects in a token" option.  All objects
available in the token will be listed.  That includes objects which are
potentially unaccessible using this tool.

list-all-certs option.
......................

This is the "list all available certificates in a token" option.  That
option will also provide more information on the certificates, for
example, expand the attached extensions in a trust token (like
p11-kit-trust).

list-certs option.
..................

This is the "list all certificates that have an associated private key"
option.  That option will only display certificates which have a private
key associated with them (share the same ID).

list-all-privkeys option.
.........................

This is the "list all available private keys in a token" option.  Lists
all the private keys in a token that match the specified URL.

list-privkeys option.
.....................

This is an alias for the ‘list-all-privkeys’ option, *note the
list-all-privkeys option documentation: p11tool list-all-privkeys.

list-keys option.
.................

This is an alias for the ‘list-all-privkeys’ option, *note the
list-all-privkeys option documentation: p11tool list-all-privkeys.

export-stapled option.
......................

This is the "export the certificate object specified by the url" option.

This option has some usage constraints.  It:
   • must not appear in combination with any of the following options:
     export, export-chain, export-pubkey.

Exports the certificate specified by the URL while including any
attached extensions to it.  Since attached extensions are a p11-kit
extension, this option is only available on p11-kit registered trust
modules.

export-chain option.
....................

This is the "export the certificate specified by the url and its chain
of trust" option.

This option has some usage constraints.  It:
   • must not appear in combination with any of the following options:
     export-stapled, export, export-pubkey.

Exports the certificate specified by the URL and generates its chain of
trust based on the stored certificates in the module.

export-pubkey option.
.....................

This is the "export the public key for a private key" option.

This option has some usage constraints.  It:
   • must not appear in combination with any of the following options:
     export-stapled, export, export-chain.

Exports the public key for the specified private key

trusted option.
...............

This is an alias for the ‘mark-trusted’ option, *note the mark-trusted
option documentation: p11tool mark-trusted.

distrusted option.
..................

This is an alias for the ‘mark-distrusted’ option, *note the
mark-distrusted option documentation: p11tool mark-distrusted.

keygen-related-options options
..............................

Key generation.

generate-privkey option.
........................

This is the "generate private-public key pair of given type" option.
This option takes a ArgumentType.STRING argument.  Generates a
private-public key pair in the specified token.  Acceptable types are
RSA, ECDSA, Ed25519, and DSA. Should be combined with -sec-param or
-bits.

generate-rsa option.
....................

This is the "generate an rsa private-public key pair" option.  Generates
an RSA private-public key pair on the specified token.  Should be
combined with -sec-param or -bits.

*NOTE**: THIS OPTION IS DEPRECATED*

generate-dsa option.
....................

This is the "generate a dsa private-public key pair" option.  Generates
a DSA private-public key pair on the specified token.  Should be
combined with -sec-param or -bits.

*NOTE**: THIS OPTION IS DEPRECATED*

generate-ecc option.
....................

This is the "generate an ecdsa private-public key pair" option.
Generates an ECDSA private-public key pair on the specified token.
Should be combined with -curve, -sec-param or -bits.

*NOTE**: THIS OPTION IS DEPRECATED*

bits option.
............

This is the "specify the number of bits for the key generate" option.
This option takes a ArgumentType.NUMBER argument.  For applications
which have no key-size restrictions the -sec-param option is
recommended, as the sec-param levels will adapt to the acceptable
security levels with the new versions of gnutls.

curve option.
.............

This is the "specify the curve used for ec key generation" option.  This
option takes a ArgumentType.STRING argument.  Supported values are
secp192r1, secp224r1, secp256r1, secp384r1 and secp521r1.

sec-param option.
.................

This is the "specify the security level" option.  This option takes a
ArgumentType.STRING argument ‘Security parameter’.  This is alternative
to the bits option.  Available options are [low, legacy, medium, high,
ultra].

write-object-related-options options
....................................

Writing objects.

set-id option.
..............

This is the "set the cka_id (in hex) for the specified by the url
object" option.  This option takes a ArgumentType.STRING argument.

This option has some usage constraints.  It:
   • must not appear in combination with any of the following options:
     write.

Modifies or sets the CKA_ID in the specified by the URL object.  The ID
should be specified in hexadecimal format without a '0x' prefix.

set-label option.
.................

This is the "set the cka_label for the specified by the url object"
option.  This option takes a ArgumentType.STRING argument.

This option has some usage constraints.  It:
   • must not appear in combination with any of the following options:
     write, set-id.

Modifies or sets the CKA_LABEL in the specified by the URL object

write option.
.............

This is the "writes the loaded objects to a pkcs #11 token" option.  It
can be used to write private, public keys, certificates or secret keys
to a token.  Must be combined with one of -load-privkey, -load-pubkey,
-load-certificate option.

When writing a certificate object, its CKA_ID is set to the same CKA_ID
of the corresponding public key, if it exists on the token; otherwise it
will be derived from the X.509 Subject Key Identifier of the
certificate.  If this behavior is undesired, write the public key to the
token beforehand.

id option.
..........

This is the "sets an id for the write operation" option.  This option
takes a ArgumentType.STRING argument.  Sets the CKA_ID to be set by the
write operation.  The ID should be specified in hexadecimal format
without a '0x' prefix.

mark-wrap option.
.................

This is the "marks the generated key to be a wrapping key" option.
Marks the generated key with the CKA_WRAP flag.

mark-trusted option.
....................

This is the "marks the object to be written as trusted" option.

This option has some usage constraints.  It:
   • must not appear in combination with any of the following options:
     mark-distrusted.
   • can be disabled with -no-mark-trusted.

Marks the object to be generated/written with the CKA_TRUST flag.

mark-distrusted option.
.......................

This is the "when retrieving objects, it requires the objects to be
distrusted" option.

This option has some usage constraints.  It:
   • must not appear in combination with any of the following options:
     mark-trusted.

Ensures that the objects retrieved have the CKA_X_TRUST flag.  This is
p11-kit trust module extension, thus this flag is only valid with
p11-kit registered trust modules.

mark-decrypt option.
....................

This is the "marks the object to be written for decryption" option.
Marks the object to be generated/written with the CKA_DECRYPT flag set
to true.

mark-sign option.
.................

This is the "marks the object to be written for signature generation"
option.  Marks the object to be generated/written with the CKA_SIGN flag
set to true.

mark-ca option.
...............

This is the "marks the object to be written as a ca" option.  Marks the
object to be generated/written with the CKA_CERTIFICATE_CATEGORY as CA.

mark-private option.
....................

This is the "marks the object to be written as private" option.  Marks
the object to be generated/written with the CKA_PRIVATE flag.  The
written object will require a PIN to be used.

ca option.
..........

This is an alias for the ‘mark-ca’ option, *note the mark-ca option
documentation: p11tool mark-ca.

private option.
...............

This is an alias for the ‘mark-private’ option, *note the mark-private
option documentation: p11tool mark-private.

mark-always-authenticate option.
................................

This is the "marks the object to be written as always authenticate"
option.  Marks the object to be generated/written with the
CKA_ALWAYS_AUTHENTICATE flag.  The written object will Mark the object
as requiring authentication (pin entry) before every operation.

secret-key option.
..................

This is the "provide a hex encoded secret key" option.  This option
takes a ArgumentType.STRING argument.  This secret key will be written
to the module if -write is specified.

other-options options
.....................

Other options.

debug option (-d).
..................

This is the "enable debugging" option.  This option takes a
ArgumentType.NUMBER argument.  Specifies the debug level.

so-login option.
................

This is the "force security officer login to token" option.  Forces
login to the token as security officer (admin).

admin-login option.
...................

This is an alias for the ‘so-login’ option, *note the so-login option
documentation: p11tool so-login.

test-sign option.
.................

This is the "tests the signature operation of the provided object"
option.  It can be used to test the correct operation of the signature
operation.  If both a private and a public key are available this
operation will sign and verify the signed data.

sign-params option.
...................

This is the "sign with a specific signature algorithm" option.  This
option takes a ArgumentType.STRING argument.  This option can be
combined with -test-sign, to sign with a specific signature algorithm
variant.  The only option supported is 'RSA-PSS', and should be
specified in order to use RSA-PSS signature on RSA keys.

hash option.
............

This is the "hash algorithm to use for signing" option.  This option
takes a ArgumentType.STRING argument.  This option can be combined with
test-sign.  Available hash functions are SHA1, RMD160, SHA256, SHA384,
SHA512, SHA3-224, SHA3-256, SHA3-384, SHA3-512.

generate-random option.
.......................

This is the "generate random data" option.  This option takes a
ArgumentType.NUMBER argument.  Asks the token to generate a number of
bytes of random bytes.

inder option.
.............

This is the "use der/raw format for input" option.  Use DER/RAW format
for input certificates and private keys.

inraw option.
.............

This is an alias for the ‘inder’ option, *note the inder option
documentation: p11tool inder.

outder option.
..............

This is the "use der format for output certificates, private keys, and
dh parameters" option.  The output will be in DER or RAW format.

outraw option.
..............

This is an alias for the ‘outder’ option, *note the outder option
documentation: p11tool outder.

provider option.
................

This is the "specify the pkcs #11 provider library" option.  This option
takes a ArgumentType.FILE argument.  This will override the default
options in /usr/local/etc/gnutls/pkcs11.conf

provider-opts option.
.....................

This is the "specify parameters for the pkcs #11 provider library"
option.  This option takes a ArgumentType.STRING argument.  This is a
PKCS#11 internal option used by few modules.  Mainly for testing PKCS#11
modules.

*NOTE**: THIS OPTION IS DEPRECATED*

batch option.
.............

This is the "disable all interaction with the tool" option.  In batch
mode there will be no prompts, all parameters need to be specified on
command line.

version option (-v).
....................

help option (-h).
.................

This is the "display extended usage information and exit" option.
Display usage information and exit.

more-help option (-!).
......................

This is the "extended usage information passed thru pager" option.  Pass
the extended usage information through a pager.

p11tool exit status
...................

One of the following exit values will be returned:
‘0 (EXIT_SUCCESS)’
     Successful program execution.
‘1 (EXIT_FAILURE)’
     The operation failed or the command syntax was not valid.

p11tool See Also
................

certtool (1)

p11tool Examples
................

To view all tokens in your system use:
     $ p11tool --list-tokens

To view all objects in a token use:
     $ p11tool --login --list-all "pkcs11:TOKEN-URL"

To store a private key and a certificate in a token run:
     $ p11tool --login --write "pkcs11:URL" --load-privkey key.pem \
               --label "Mykey"
     $ p11tool --login --write "pkcs11:URL" --load-certificate cert.pem \
               --label "Mykey"
Note that some tokens require the same label to be used for the
certificate and its corresponding private key.

To generate an RSA private key inside the token use:
     $ p11tool --login --generate-privkey rsa --bits 1024 --label "MyNewKey" \
               --outfile MyNewKey.pub "pkcs11:TOKEN-URL"
The bits parameter in the above example is explicitly set because some
tokens only support limited choices in the bit length.  The output file
is the corresponding public key.  This key can be used to general a
certificate request with certtool.
     certtool --generate-request --load-privkey "pkcs11:KEY-URL" \
        --load-pubkey MyNewKey.pub --outfile request.pem

File: gnutls.info,  Node: Trusted Platform Module,  Prev: Smart cards and HSMs,  Up: Hardware security modules and abstract key types

5.4 Trusted Platform Module (TPM)
=================================

In this section we present the Trusted Platform Module (TPM) support in
GnuTLS.  Note that we recommend against using TPM with this API because
it is restricted to TPM 1.2.  We recommend instead to use PKCS#11
wrappers for TPM such as CHAPS(1) or opencryptoki(2).  These will allow
using the standard smart card and HSM functionality (see *note Smart
cards and HSMs::) for TPM keys.

There was a big hype when the TPM chip was introduced into computers.
Briefly it is a co-processor in your PC that allows it to perform
calculations independently of the main processor.  This has good and bad
side-effects.  In this section we focus on the good ones; these are the
fact that you can use the TPM chip to perform cryptographic operations
on keys stored in it, without accessing them.  That is very similar to
the operation of a PKCS #11 smart card.  The chip allows for storage and
usage of RSA keys, but has quite some operational differences from PKCS
#11 module, and thus require different handling.  The basic TPM
operations supported and used by GnuTLS, are key generation and signing.
That support is currently limited to TPM 1.2.

The next sections assume that the TPM chip in the system is already
initialized and in a operational state.  If not, ensure that the TPM
chip is enabled by your BIOS, that the ‘tcsd’ daemon is running, and
that TPM ownership is set (by running ‘tpm_takeownership’).

In GnuTLS the TPM functionality is available in ‘gnutls/tpm.h’.

* Menu:

* Keys in TPM::
* Key generation::
* Using keys::
* tpmtool Invocation::

---------- Footnotes ----------

(1) <https://github.com/google/chaps-linux>

(2) <https://sourceforge.net/projects/opencryptoki/>

File: gnutls.info,  Node: Keys in TPM,  Next: Key generation,  Up: Trusted Platform Module

5.4.1 Keys in TPM
-----------------

The RSA keys in the TPM module may either be stored in a flash memory
within TPM or stored in a file in disk.  In the former case the key can
provide operations as with PKCS #11 and is identified by a URL. The URL
is described in [*note TPMURI::] and is of the following form.
tpmkey:uuid=42309df8-d101-11e1-a89a-97bb33c23ad1;storage=user

It consists from a unique identifier of the key as well as the part of
the flash memory the key is stored at.  The two options for the storage
field are 'user' and 'system'.  The user keys are typically only
available to the generating user and the system keys to all users.  The
stored in TPM keys are called registered keys.

The keys that are stored in the disk are exported from the TPM but in an
encrypted form.  To access them two passwords are required.  The first
is the TPM Storage Root Key (SRK), and the other is a key-specific
password.  Also those keys are identified by a URL of the form:
tpmkey:file=/path/to/file

When objects require a PIN to be accessed the same callbacks as with
PKCS #11 objects are expected (see *note Accessing objects that require
a PIN::).  Note that the PIN function may be called multiple times to
unlock the SRK and the specific key in use.  The label in the key
function will then be set to 'SRK' when unlocking the SRK key, or to
'TPM' when unlocking any other key.

File: gnutls.info,  Node: Key generation,  Next: Using keys,  Prev: Keys in TPM,  Up: Trusted Platform Module

5.4.2 Key generation
--------------------

All keys used by the TPM must be generated by the TPM. This can be done
using *note gnutls_tpm_privkey_generate::.

-- Function: int gnutls_tpm_privkey_generate (gnutls_pk_algorithm_t PK,
          unsigned int BITS, const char * SRK_PASSWORD, const char *
          KEY_PASSWORD, gnutls_tpmkey_fmt_t FORMAT,
          gnutls_x509_crt_fmt_t PUB_FORMAT, gnutls_datum_t * PRIVKEY,
          gnutls_datum_t * PUBKEY, unsigned int FLAGS)
     PK: the public key algorithm

BITS: the security bits

SRK_PASSWORD: a password to protect the exported key (optional)

KEY_PASSWORD: the password for the TPM (optional)

FORMAT: the format of the private key

PUB_FORMAT: the format of the public key

PRIVKEY: the generated key

PUBKEY: the corresponding public key (may be null)

FLAGS: should be a list of GNUTLS_TPM_* flags

This function will generate a private key in the TPM chip.  The
     private key will be generated within the chip and will be exported
     in a wrapped with TPM's master key form.  Furthermore the wrapped
     key can be protected with the provided ‘password’ .

Note that bits in TPM is quantized value.  If the input value is
     not one of the allowed values, then it will be quantized to one of
     512, 1024, 2048, 4096, 8192 and 16384.

Allowed flags are:

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.1.0

‘INT *note gnutls_tpm_get_registered:: (gnutls_tpm_key_list_t * LIST)’
‘VOID *note gnutls_tpm_key_list_deinit:: (gnutls_tpm_key_list_t LIST)’
‘INT *note gnutls_tpm_key_list_get_url:: (gnutls_tpm_key_list_t LIST, unsigned int IDX, char ** URL, unsigned int FLAGS)’

-- Function: int gnutls_tpm_privkey_delete (const char * URL, const
          char * SRK_PASSWORD)
     URL: the URL describing the key

SRK_PASSWORD: a password for the SRK key

This function will unregister the private key from the TPM chip.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.1.0

File: gnutls.info,  Node: Using keys,  Next: tpmtool Invocation,  Prev: Key generation,  Up: Trusted Platform Module

5.4.3 Using keys
----------------

Importing keys
..............

The TPM keys can be used directly by the abstract key types and do not
require any special structures.  Moreover functions like *note
gnutls_certificate_set_x509_key_file2:: can access TPM URLs.

‘INT *note gnutls_privkey_import_tpm_raw:: (gnutls_privkey_t PKEY, const gnutls_datum_t * FDATA, gnutls_tpmkey_fmt_t FORMAT, const char * SRK_PASSWORD, const char * KEY_PASSWORD, unsigned int FLAGS)’
‘INT *note gnutls_pubkey_import_tpm_raw:: (gnutls_pubkey_t PKEY, const gnutls_datum_t * FDATA, gnutls_tpmkey_fmt_t FORMAT, const char * SRK_PASSWORD, unsigned int FLAGS)’

-- Function: int gnutls_privkey_import_tpm_url (gnutls_privkey_t PKEY,
          const char * URL, const char * SRK_PASSWORD, const char *
          KEY_PASSWORD, unsigned int FLAGS)
     PKEY: The private key

URL: The URL of the TPM key to be imported

SRK_PASSWORD: The password for the SRK key (optional)

KEY_PASSWORD: A password for the key (optional)

FLAGS: One of the GNUTLS_PRIVKEY_* flags

This function will import the given private key to the abstract
     ‘gnutls_privkey_t’ type.

Note that unless ‘GNUTLS_PRIVKEY_DISABLE_CALLBACKS’ is specified,
     if incorrect (or NULL) passwords are given the PKCS11 callback
     functions will be used to obtain the correct passwords.  Otherwise
     if the SRK password is wrong ‘GNUTLS_E_TPM_SRK_PASSWORD_ERROR’ is
     returned and if the key password is wrong or not provided then
     ‘GNUTLS_E_TPM_KEY_PASSWORD_ERROR’ is returned.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.1.0

-- Function: int gnutls_pubkey_import_tpm_url (gnutls_pubkey_t PKEY,
          const char * URL, const char * SRK_PASSWORD, unsigned int
          FLAGS)
     PKEY: The public key

URL: The URL of the TPM key to be imported

SRK_PASSWORD: The password for the SRK key (optional)

FLAGS: should be zero

This function will import the given private key to the abstract
     ‘gnutls_privkey_t’ type.

Note that unless ‘GNUTLS_PUBKEY_DISABLE_CALLBACKS’ is specified, if
     incorrect (or NULL) passwords are given the PKCS11 callback
     functions will be used to obtain the correct passwords.  Otherwise
     if the SRK password is wrong ‘GNUTLS_E_TPM_SRK_PASSWORD_ERROR’ is
     returned.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.1.0

Listing and deleting keys
.........................

The registered keys (that are stored in the TPM) can be listed using one
of the following functions.  Those keys are unfortunately only
identified by their UUID and have no label or other human friendly
identifier.  Keys can be deleted from permanent storage using *note
gnutls_tpm_privkey_delete::.

-- Function: int gnutls_tpm_privkey_delete (const char * URL, const
          char * SRK_PASSWORD)
     URL: the URL describing the key

SRK_PASSWORD: a password for the SRK key

This function will unregister the private key from the TPM chip.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.1.0

File: gnutls.info,  Node: tpmtool Invocation,  Prev: Using keys,  Up: Trusted Platform Module

5.4.4 Invoking tpmtool
----------------------

Program that allows handling cryptographic data from the TPM chip.

tpmtool help/usage (‘-?’)
.........................

tpmtool - GnuTLS TPM tool
     Usage:  tpmtool [ -<flag> [<val>] | --<name>[{=| }<val>] ]...

None:

-d, --debug=num            Enable debugging
     				- it must be in the range:
     				  0 to 9999
            --infile=file          Input file
     				- file must pre-exist
            --outfile=str          Output file
            --generate-rsa         Generate an RSA private-public key pair
            --register             Any generated key will be registered in the TPM
     				- requires the option 'generate-rsa'
            --signing              Any generated key will be a signing key
     				- prohibits the option 'legacy'
     				- requires the option 'generate-rsa'
            --legacy               Any generated key will be a legacy key
     				- prohibits the option 'signing'
     				- requires the option 'generate-rsa'
            --user                 Any registered key will be a user key
     				- prohibits the option 'system'
     				- requires the option 'register'
            --system               Any registered key will be a system key
     				- prohibits the option 'user'
     				- requires the option 'register'
            --pubkey=str           Prints the public key of the provided key
            --list                 Lists all stored keys in the TPM
            --delete=str           Delete the key identified by the given URL (UUID)
            --test-sign=str        Tests the signature operation of the provided object
            --sec-param=str        Specify the security level [low, legacy, medium, high, ultra]
            --bits=num             Specify the number of bits for key generate
            --inder                Use the DER format for keys
            --outder               Use DER format for output keys
            --srk-well-known       SRK has well known password (20 bytes of zeros)

Version, usage and configuration options:

Options are specified by doubled hyphens and their name or by a single
     hyphen and the flag character.

Program that allows handling cryptographic data from the TPM chip.

Please send bug reports to:  <bugs@gnutls.org>

debug option (-d).
..................

This is the "enable debugging" option.  This option takes a
ArgumentType.NUMBER argument.  Specifies the debug level.

generate-rsa option.
....................

This is the "generate an rsa private-public key pair" option.  Generates
an RSA private-public key pair in the TPM chip.  The key may be stored
in file system and protected by a PIN, or stored (registered) in the TPM
chip flash.

user option.
............

This is the "any registered key will be a user key" option.

This option has some usage constraints.  It:
   • must not appear in combination with any of the following options:
     system.
   • must appear in combination with the following options: register.

The generated key will be stored in a user specific persistent storage.

system option.
..............

This is the "any registered key will be a system key" option.

This option has some usage constraints.  It:
   • must not appear in combination with any of the following options:
     user.
   • must appear in combination with the following options: register.

The generated key will be stored in system persistent storage.

test-sign option.
.................

This is the "tests the signature operation of the provided object"
option.  This option takes a ArgumentType.STRING argument ‘url’.  It can
be used to test the correct operation of the signature operation.  This
operation will sign and verify the signed data.

sec-param option.
.................

This is the "specify the security level [low, legacy, medium, high,
ultra]" option.  This option takes a ArgumentType.STRING argument
‘Security parameter’.  This is alternative to the bits option.  Note
however that the values allowed by the TPM chip are quantized and given
values may be rounded up.

inder option.
.............

This is the "use the der format for keys" option.  The input files will
be assumed to be in the portable DER format of TPM. The default format
is a custom format used by various TPM tools

outder option.
..............

This is the "use der format for output keys" option.  The output will be
in the TPM portable DER format.

version option (-v).
....................

help option (-h).
.................

This is the "display extended usage information and exit" option.
Display usage information and exit.

more-help option (-!).
......................

This is the "extended usage information passed thru pager" option.  Pass
the extended usage information through a pager.

tpmtool exit status
...................

One of the following exit values will be returned:
‘0 (EXIT_SUCCESS)’
     Successful program execution.
‘1 (EXIT_FAILURE)’
     The operation failed or the command syntax was not valid.

tpmtool See Also
................

p11tool (1), certtool (1)

tpmtool Examples
................

To generate a key that is to be stored in file system use:
     $ tpmtool --generate-rsa --bits 2048 --outfile tpmkey.pem

To generate a key that is to be stored in TPM's flash use:
     $ tpmtool --generate-rsa --bits 2048 --register --user

To get the public key of a TPM key use:
     $ tpmtool --pubkey tpmkey:uuid=58ad734b-bde6-45c7-89d8-756a55ad1891;storage=user \
               --outfile pubkey.pem

or if the key is stored in the file system:
     $ tpmtool --pubkey tpmkey:file=tmpkey.pem --outfile pubkey.pem

To list all keys stored in TPM use:
     $ tpmtool --list

File: gnutls.info,  Node: How to use GnuTLS in applications,  Next: GnuTLS application examples,  Prev: Hardware security modules and abstract key types,  Up: Top

6 How to use GnuTLS in applications
***********************************

* Menu:

* Introduction to the library::
* Preparation::
* Session initialization::
* Associating the credentials::
* Setting up the transport layer::
* TLS handshake::
* Data transfer and termination::
* Buffered data transfer::
* Handling alerts::
* Priority Strings::
* Selecting cryptographic key sizes::
* Advanced topics::

File: gnutls.info,  Node: Introduction to the library,  Next: Preparation,  Up: How to use GnuTLS in applications

6.1 Introduction
================

This chapter tries to explain the basic functionality of the current
GnuTLS library.  Note that there may be additional functionality not
discussed here but included in the library.  Checking the header files
in ‘/usr/include/gnutls/’ and the manpages is recommended.

* Menu:

* General idea::
* Error handling::
* Common types::
* Debugging and auditing::
* Thread safety::
* Running in a sandbox::
* Sessions and fork::
* Callback functions::

File: gnutls.info,  Node: General idea,  Next: Error handling,  Up: Introduction to the library

6.1.1 General idea
------------------

A brief description of how GnuTLS sessions operate is shown at *note
Figure 6.1: fig-gnutls-design.  This section will become more clear when
it is completely read.  As shown in the figure, there is a read-only
global state that is initialized once by the global initialization
function.  This global structure, among others, contains the memory
allocation functions used, structures needed for the ASN.1 parser and
depending on the system's CPU, pointers to hardware accelerated
encryption functions.  This structure is never modified by any GnuTLS
function, except for the deinitialization function which frees all
allocated memory and must be called after the program has permanently
finished using GnuTLS.

�[image src="gnutls-internals.png"�]

Figure 6.1: High level design of GnuTLS.

The credentials structures are used by the authentication methods, such
as certificate authentication.  They store certificates, privates keys,
and other information that is needed to prove the identity to the peer,
and/or verify the identity of the peer.  The information stored in the
credentials structures is initialized once and then can be shared by
many TLS sessions.

A GnuTLS session contains all the required state and information to
handle one secure connection.  The session communicates with the peers
using the provided functions of the transport layer.  Every session has
a unique session ID shared with the peer.

Since TLS sessions can be resumed, servers need a database back-end to
hold the session's parameters.  Every GnuTLS session after a successful
handshake calls the appropriate back-end function (see *note resume::)
to store the newly negotiated session.  The session database is examined
by the server just after having received the client hello(1), and if the
session ID sent by the client, matches a stored session, the stored
session will be retrieved, and the new session will be a resumed one,
and will share the same session ID with the previous one.

---------- Footnotes ----------

(1) The first message in a TLS handshake

File: gnutls.info,  Node: Error handling,  Next: Common types,  Prev: General idea,  Up: Introduction to the library

6.1.2 Error handling
--------------------

There two types of GnuTLS functions.  The first type returns a boolean
value, true (non-zero) or false (zero) value; these functions are
defined to return an unsigned integer type.  The other type returns a
signed integer type with zero (or a positive number) indicating success
and a negative value indicating failure.  For the latter type it is
recommended to check for errors as following.
         ret = gnutls_function();
         if (ret < 0) {
             return -1;
         }
The above example checks for a failure condition rather than for
explicit success (e.g., equality to zero).  That has the advantage that
future extensions of the API can be extended to provide additional
information via positive returned values (see for example *note
gnutls_certificate_set_x509_key_file::).

In GnuTLS, many objects are represented as opaque types that are
initialized by passing an address to storage of that type to a pointer
parameter of a function name ‘gnutls_OBJ_init’, and which have a
counterpart function ‘gnutls_OBJ_deinit’.  It is safe, but not
mandatory, to pre-initialize the opaque storage to contain all zeroes
(such as by using ‘calloc()’ or ‘memset()’).  If the initializer
succeeds, the storage must be passed to the counterpart deinitializer
when the object is no longer in use to avoid memory leaks.  As of
version 3.8.0, if the initializer function fails, it is safe, but not
mandatory, to call the counterpart deinitializer, regardless of whether
the storage was pre-initialized.  However, this was not guaranteed in
earlier versions; for maximum portability to older library versions,
callers should either pre-initialize the storage to zero before
initialization or refrain from calling the deinitializer if the
initializer fails.

For certain operations such as TLS handshake and TLS packet receive
there is the notion of fatal and non-fatal error codes.  Fatal errors
terminate the TLS session immediately and further sends and receives
will be disallowed.  Such an example is ‘GNUTLS_E_DECRYPTION_FAILED’.
Non-fatal errors may warn about something, i.e., a warning alert was
received, or indicate the some action has to be taken.  This is the case
with the error code ‘GNUTLS_E_REHANDSHAKE’ returned by *note
gnutls_record_recv::.  This error code indicates that the server
requests a re-handshake.  The client may ignore this request, or may
reply with an alert.  You can test if an error code is a fatal one by
using the *note gnutls_error_is_fatal::.  All errors can be converted to
a descriptive string using *note gnutls_strerror::.

If any non fatal errors, that require an action, are to be returned by a
function, these error codes will be documented in the function's
reference.  For example the error codes
‘GNUTLS_E_WARNING_ALERT_RECEIVED’ and ‘GNUTLS_E_FATAL_ALERT_RECEIVED’
that may returned when receiving data, should be handled by notifying
the user of the alert (as explained in *note Handling alerts::).  See
*note Error codes::, for a description of the available error codes.

File: gnutls.info,  Node: Common types,  Next: Debugging and auditing,  Prev: Error handling,  Up: Introduction to the library

6.1.3 Common types
------------------

All strings that are to provided as input to GnuTLS functions should be
in UTF-8 unless otherwise specified.  Output strings are also in UTF-8
format unless otherwise specified.  When functions take as input
passwords, they will normalize them using [*note RFC7613::] rules (since
GnuTLS 3.5.7).

When data of a fixed size are provided to GnuTLS functions then the
helper structure ‘gnutls_datum_t’ is often used.  Its definition is
shown below.
  typedef struct
  {
    unsigned char *data;
    unsigned int size;
  } gnutls_datum_t;

In functions where this structure is a returned type, if the function
succeeds, it is expected from the caller to use ‘gnutls_free()’ to
deinitialize the data element after use, unless otherwise specified.  If
the function fails, the contents of the ‘gnutls_datum_t’ should be
considered undefined and must not be deinitialized.

Other functions that require data for scattered read use a structure
similar to ‘struct iovec’ typically used by ‘readv’.  It is shown below.
  typedef struct
  {
    void *iov_base;             /* Starting address */
    size_t iov_len;             /* Number of bytes to transfer */
  } giovec_t;

File: gnutls.info,  Node: Debugging and auditing,  Next: Thread safety,  Prev: Common types,  Up: Introduction to the library

6.1.4 Debugging and auditing
----------------------------

In many cases things may not go as expected and further information, to
assist debugging, from GnuTLS is desired.  Those are the cases where the
*note gnutls_global_set_log_level:: and *note
gnutls_global_set_log_function:: are to be used.  Those will print
verbose information on the GnuTLS functions internal flow.

‘VOID *note gnutls_global_set_log_level:: (int LEVEL)’
‘VOID *note gnutls_global_set_log_function:: (gnutls_log_func LOG_FUNC)’

Alternatively the environment variable ‘GNUTLS_DEBUG_LEVEL’ can be set
to a logging level and GnuTLS will output debugging output to standard
error.  Other available environment variables are shown in *note Table
6.1: tab:environment.

Variable               Purpose
                       
--------------------------------------------------------------------------
‘GNUTLS_DEBUG_LEVEL’   When set to a numeric value, it sets the default
                       debugging level for GnuTLS applications.
                       
‘SSLKEYLOGFILE’        When set to a filename, GnuTLS will append to it
                       the session keys in the NSS Key Log format.
                       That format can be read by wireshark and will
                       allow decryption of the session for debugging.
                       
‘GNUTLS_CPUID_OVERRIDE’That environment variable can be used to
                       explicitly enable/disable the use of certain CPU
                       capabilities.  Note that CPU detection cannot be
                       overridden, i.e., VIA options cannot be enabled
                       on an Intel CPU. The currently available options
                       are:
                          • 0x1: Disable all run-time detected
                            optimizations
                          • 0x2: Enable AES-NI
                          • 0x4: Enable SSSE3
                          • 0x8: Enable PCLMUL
                          • 0x10: Enable AVX
                          • 0x20: Enable SHA_NI
                          • 0x100000: Enable VIA padlock
                          • 0x200000: Enable VIA PHE
                          • 0x400000: Enable VIA PHE SHA512
                       
‘GNUTLS_FORCE_FIPS_MODE’In setups where GnuTLS is compiled with support
                       for FIPS140-2 (see *note FIPS140-2 mode::) if
                       set to one it will force the FIPS mode
                       enablement.

Table 6.1: Environment variables used by the library.

When debugging is not required, important issues, such as detected
attacks on the protocol still need to be logged.  This is provided by
the logging function set by *note
gnutls_global_set_audit_log_function::.  The provided function will
receive an message and the corresponding TLS session.  The session
information might be used to derive IP addresses or other information
about the peer involved.

-- Function: void gnutls_global_set_audit_log_function
          (gnutls_audit_log_func LOG_FUNC)
     LOG_FUNC: it is the audit log function

This is the function to set the audit logging function.  This is a
     function to report important issues, such as possible attacks in
     the protocol.  This is different from
     ‘gnutls_global_set_log_function()’ because it will report also
     session-specific events.  The session parameter will be null if
     there is no corresponding TLS session.

‘gnutls_audit_log_func’ is of the form, void
     (*gnutls_audit_log_func)( gnutls_session_t, const char*);

*Since:* 3.0

File: gnutls.info,  Node: Thread safety,  Next: Running in a sandbox,  Prev: Debugging and auditing,  Up: Introduction to the library

6.1.5 Thread safety
-------------------

The GnuTLS library is thread safe by design, meaning that objects of the
library such as TLS sessions, can be safely divided across threads as
long as a single thread accesses a single object.  This is sufficient to
support a server which handles several sessions per thread.  Read-only
access to objects, for example the credentials holding structures, is
also thread-safe.

A ‘gnutls_session_t’ object could also be shared by two threads, one
sending, the other receiving.  However, care must be taken on the
following use cases:
   • The re-handshake process in TLS 1.2 or earlier must be handled only
     in a single thread and no other thread may be performing any
     operation.
   • The flag ‘GNUTLS_AUTO_REAUTH’ cannot be used safely in this mode of
     operation.
   • Any other operation which may send or receive data, like key update
     (c.f., *note gnutls_session_key_update::), must not be performed
     while threads are receiving or writing.
   • The termination of a session should be handled, either by a single
     thread being active, or by the sender thread using *note
     gnutls_bye:: with ‘GNUTLS_SHUT_WR’ and the receiving thread waiting
     for a return value of zero (or timeout on certain servers which do
     not respond).
   • The functions *note gnutls_transport_set_errno:: and *note
     gnutls_record_get_direction:: should not be relied during parallel
     operation.

For several aspects of the library (e.g., the random generator, PKCS#11
operations), the library may utilize mutex locks (e.g., pthreads on
GNU/Linux and CriticalSection on Windows) which are transparently setup
on library initialization.  Prior to version 3.3.0 these were setup by
explicitly calling *note gnutls_global_init::.(1)

Note that, on Glibc systems, unless the application is explicitly linked
with the libpthread library, no mutex locks are used and setup by
GnuTLS. It will use the Glibc mutex stubs.

---------- Footnotes ----------

(1) On special systems you could manually specify the locking system
using the function *note gnutls_global_set_mutex:: before calling any
other GnuTLS function.  Setting mutexes manually is not recommended.

File: gnutls.info,  Node: Running in a sandbox,  Next: Sessions and fork,  Prev: Thread safety,  Up: Introduction to the library

6.1.6 Running in a sandbox
--------------------------

Given that TLS protocol handling as well as X.509 certificate parsing
are complicated processes involving several thousands lines of code, it
is often desirable (and recommended) to run the TLS session handling in
a sandbox like seccomp.  That has to be allowed by the overall software
design, but if available, it adds an additional layer of protection by
preventing parsing errors from becoming vessels for further security
issues such as code execution.

GnuTLS requires the following system calls to be available for its
proper operation.

• nanosleep
   • time
   • gettimeofday
   • clock_gettime
   • getrusage
   • getpid
   • send
   • recv
   • sendmsg
   • read (to read from /dev/urandom)
   • getrandom (this is Linux-kernel specific)
   • poll

As well as any calls needed for memory allocation to work.  Note
however, that GnuTLS depends on libc for the system calls, and there is
no guarantee that libc will call the expected system call.  For that it
is recommended to test your program in all the targeted platforms when
filters like seccomp are in place.

An example with a seccomp filter from GnuTLS' test suite is at:
<https://gitlab.com/gnutls/gnutls/blob/master/tests/seccomp.c>.

File: gnutls.info,  Node: Sessions and fork,  Next: Callback functions,  Prev: Running in a sandbox,  Up: Introduction to the library

6.1.7 Sessions and fork
-----------------------

A ‘gnutls_session_t’ object can be shared by two processes after a fork,
one sending, the other receiving.  In that case rehandshakes, cannot and
must not be performed.  As with threads, the termination of a session
should be handled by the sender process using *note gnutls_bye:: with
‘GNUTLS_SHUT_WR’ and the receiving process waiting for a return value of
zero.

File: gnutls.info,  Node: Callback functions,  Prev: Sessions and fork,  Up: Introduction to the library

6.1.8 Callback functions
------------------------

There are several cases where GnuTLS may need out of band input from
your program.  This is now implemented using some callback functions,
which your program is expected to register.

An example of this type of functions are the push and pull callbacks
which are used to specify the functions that will retrieve and send data
to the transport layer.

‘VOID *note gnutls_transport_set_push_function:: (gnutls_session_t SESSION, gnutls_push_func PUSH_FUNC)’
‘VOID *note gnutls_transport_set_pull_function:: (gnutls_session_t SESSION, gnutls_pull_func PULL_FUNC)’

Other callback functions may require more complicated input and data to
be allocated.  Such an example is *note
gnutls_srp_set_server_credentials_function::.  All callbacks should
allocate and free memory using ‘gnutls_malloc’ and ‘gnutls_free’.

File: gnutls.info,  Node: Preparation,  Next: Session initialization,  Prev: Introduction to the library,  Up: How to use GnuTLS in applications

6.2 Preparation
===============

To use GnuTLS, you have to perform some changes to your sources and your
build system.  The necessary changes are explained in the following
subsections.

* Menu:

* Headers::
* Initialization::
* Version check::
* Building the source::

File: gnutls.info,  Node: Headers,  Next: Initialization,  Up: Preparation

6.2.1 Headers
-------------

All the data types and functions of the GnuTLS library are defined in
the header file ‘gnutls/gnutls.h’.  This must be included in all
programs that make use of the GnuTLS library.

File: gnutls.info,  Node: Initialization,  Next: Version check,  Prev: Headers,  Up: Preparation

6.2.2 Initialization
--------------------

The GnuTLS library is initialized on load; prior to 3.3.0 was
initialized by calling *note gnutls_global_init::(1).  *note
gnutls_global_init:: in versions after 3.3.0 is thread-safe (see *note
Thread safety::).

The initialization typically enables CPU-specific acceleration, performs
any required precalculations needed, opens any required system devices
(e.g., /dev/urandom on Linux) and initializes subsystems that could be
used later.

The resources allocated by the initialization process will be released
on library deinitialization.

Note that on certain systems file descriptors may be kept open by GnuTLS
(e.g.  /dev/urandom) on library load.  Applications closing all unknown
file descriptors must immediately call *note gnutls_global_init::, after
that, to ensure they don't disrupt GnuTLS' operation.

---------- Footnotes ----------

(1) The original behavior of requiring explicit initialization can
obtained by setting the GNUTLS_NO_IMPLICIT_INIT environment variable to
1, or by using the macro GNUTLS_SKIP_GLOBAL_INIT in a global section of
your program -the latter works in systems with support for weak symbols
only.

File: gnutls.info,  Node: Version check,  Next: Building the source,  Prev: Initialization,  Up: Preparation

6.2.3 Version check
-------------------

It is often desirable to check that the version of 'gnutls' used is
indeed one which fits all requirements.  Even with binary compatibility
new features may have been introduced but due to problem with the
dynamic linker an old version is actually used.  So you may want to
check that the version is okay right after program start-up.  See the
function *note gnutls_check_version::.

On the other hand, it is often desirable to support more than one
versions of the library.  In that case you could utilize compile-time
feature checks using the ‘GNUTLS_VERSION_NUMBER’ macro.  For example, to
conditionally add code for GnuTLS 3.2.1 or later, you may use:
     #if GNUTLS_VERSION_NUMBER >= 0x030201
      ...
     #endif

File: gnutls.info,  Node: Building the source,  Prev: Version check,  Up: Preparation

6.2.4 Building the source
-------------------------

If you want to compile a source file including the ‘gnutls/gnutls.h’
header file, you must make sure that the compiler can find it in the
directory hierarchy.  This is accomplished by adding the path to the
directory in which the header file is located to the compilers include
file search path (via the ‘-I’ option).

However, the path to the include file is determined at the time the
source is configured.  To solve this problem, the library uses the
external package ‘pkg-config’ that knows the path to the include file
and other configuration options.  The options that need to be added to
the compiler invocation at compile time are output by the ‘--cflags’
option to ‘pkg-config gnutls’.  The following example shows how it can
be used at the command line:

gcc -c foo.c `pkg-config gnutls --cflags`

Adding the output of ‘pkg-config gnutls --cflags’ to the compilers
command line will ensure that the compiler can find the
‘gnutls/gnutls.h’ header file.

A similar problem occurs when linking the program with the library.
Again, the compiler has to find the library files.  For this to work,
the path to the library files has to be added to the library search path
(via the ‘-L’ option).  For this, the option ‘--libs’ to ‘pkg-config
gnutls’ can be used.  For convenience, this option also outputs all
other options that are required to link the program with the library
(for instance, the ‘-ltasn1’ option).  The example shows how to link
‘foo.o’ with the library to a program ‘foo’.

gcc -o foo foo.o `pkg-config gnutls --libs`

Of course you can also combine both examples to a single command by
specifying both options to ‘pkg-config’:

gcc -o foo foo.c `pkg-config gnutls --cflags --libs`

When a program uses the GNU autoconf system, then the following line or
similar can be used to detect the presence of GnuTLS.

PKG_CHECK_MODULES([LIBGNUTLS], [gnutls >= 3.3.0])

AC_SUBST([LIBGNUTLS_CFLAGS])
     AC_SUBST([LIBGNUTLS_LIBS])

File: gnutls.info,  Node: Session initialization,  Next: Associating the credentials,  Prev: Preparation,  Up: How to use GnuTLS in applications

6.3 Session initialization
==========================

In the previous sections we have discussed the global initialization
required for GnuTLS as well as the initialization required for each
authentication method's credentials (see *note Authentication::).  In
this section we elaborate on the TLS or DTLS session initiation.  Each
session is initialized using *note gnutls_init:: which among others is
used to specify the type of the connection (server or client), and the
underlying protocol type, i.e., datagram (UDP) or reliable (TCP).

-- Function: int gnutls_init (gnutls_session_t * SESSION, unsigned int
          FLAGS)
     SESSION: is a pointer to a ‘gnutls_session_t’ type.

FLAGS: indicate if this session is to be used for server or client.

This function initializes the provided session.  Every session must
     be initialized before use, and after successful initialization and
     use must be deinitialized by calling ‘gnutls_deinit()’ .

‘flags’ can be any combination of flags from ‘gnutls_init_flags_t’
     .

Note that since version 3.1.2 this function enables some common TLS
     extensions such as session tickets and OCSP certificate status
     request in client side by default.  To prevent that use the
     ‘GNUTLS_NO_DEFAULT_EXTENSIONS’ flag.

Note that it is never mandatory to use ‘gnutls_deinit()’ after this
     function fails.  Since gnutls 3.8.0, it is safe to unconditionally
     use ‘gnutls_deinit()’ even after failure regardless of whether the
     memory was initialized prior to ‘gnutls_init()’ ; however, clients
     wanting to be portable to older versions of the library should
     either skip deinitialization on failure, or pre-initialize the
     memory passed in to ‘gnutls_init()’ to all zeroes via ‘memset()’ or
     similar.

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, or an error code.

‘GNUTLS_SERVER’
     Connection end is a server.
‘GNUTLS_CLIENT’
     Connection end is a client.
‘GNUTLS_DATAGRAM’
     Connection is datagram oriented (DTLS). Since 3.0.0.
‘GNUTLS_NONBLOCK’
     Connection should not block.  Since 3.0.0.
‘GNUTLS_NO_DEFAULT_EXTENSIONS’
     Do not enable any TLS extensions by default such as session tickets
     and OCSP certificate status request (since 3.1.2).  As TLS 1.2 and
     later require extensions this option is considered obsolete and
     should not be used.
‘GNUTLS_NO_REPLAY_PROTECTION’
     Disable any replay protection in DTLS. This must only be used if
     replay protection is achieved using other means.  Since 3.2.2.
‘GNUTLS_NO_SIGNAL’
     In systems where SIGPIPE is delivered on send, it will be disabled.
     That flag has effect in systems which support the MSG_NOSIGNAL
     sockets flag (since 3.4.2).
‘GNUTLS_ALLOW_ID_CHANGE’
     Allow the peer to replace its certificate, or change its ID during
     a rehandshake.  This change is often used in attacks and thus
     prohibited by default.  Since 3.5.0.
‘GNUTLS_ENABLE_FALSE_START’
     Enable the TLS false start on client side if the negotiated
     ciphersuites allow it.  This will enable sending data prior to the
     handshake being complete, and may introduce a risk of crypto
     failure when combined with certain key exchanged; for that GnuTLS
     may not enable that option in ciphersuites that are known to be not
     safe for false start.  Since 3.5.0.
‘GNUTLS_FORCE_CLIENT_CERT’
     When in client side and only a single cert is specified, send that
     certificate irrespective of the issuers expected by the server.
     Since 3.5.0.
‘GNUTLS_NO_TICKETS’
     Flag to indicate that the session should not use resumption with
     session tickets.
‘GNUTLS_KEY_SHARE_TOP’
     Generate key share for the first group which is enabled.  For
     example x25519.  This option is the most performant for client
     (less CPU spent generating keys), but if the server doesn't support
     the advertised option it may result to more roundtrips needed to
     discover the server's choice.
‘GNUTLS_KEY_SHARE_TOP2’
     Generate key shares for the top-2 different groups which are
     enabled.  For example (ECDH + x25519).  This is the default.
‘GNUTLS_KEY_SHARE_TOP3’
     Generate key shares for the top-3 different groups which are
     enabled.  That is, as each group is associated with a key type (EC,
     finite field, x25519), generate three keys using ‘GNUTLS_PK_DH’ ,
     ‘GNUTLS_PK_EC’ , ‘GNUTLS_PK_ECDH_X25519’ if all of them are
     enabled.
‘GNUTLS_POST_HANDSHAKE_AUTH’
     Enable post handshake authentication for server and client.  When
     set and a server requests authentication after handshake
     ‘GNUTLS_E_REAUTH_REQUEST’ will be returned by
     ‘gnutls_record_recv()’ .  A client should then call
     ‘gnutls_reauth()’ to re-authenticate.
‘GNUTLS_NO_AUTO_REKEY’
     Disable auto-rekeying under TLS1.3.  If this option is not
     specified gnutls will force a rekey after 2^24 records have been
     sent.
‘GNUTLS_SAFE_PADDING_CHECK’
     Flag to indicate that the TLS 1.3 padding check will be done in a
     safe way which doesn't leak the pad size based on GnuTLS processing
     time.  This is of use to applications which hide the length of
     transferred data via the TLS1.3 padding mechanism and are already
     taking steps to hide the data processing time.  This comes at a
     performance penalty.
‘GNUTLS_ENABLE_EARLY_START’
     Under TLS1.3 allow the server to return earlier than the full
     handshake finish; similarly to false start the handshake will be
     completed once data are received by the client, while the server is
     able to transmit sooner.  This is not enabled by default as it
     could break certain existing server assumptions and use-cases.
     Since 3.6.4.
‘GNUTLS_ENABLE_RAWPK’
     Allows raw public-keys to be negotiated during the handshake.
     Since 3.6.6.
‘GNUTLS_AUTO_REAUTH’
     Enable transparent re-authentication in client side when the server
     requests to.  That is, reauthentication is handled within
     ‘gnutls_record_recv()’ , and the ‘GNUTLS_E_REHANDSHAKE’ or
     ‘GNUTLS_E_REAUTH_REQUEST’ are not returned.  This must be enabled
     with ‘GNUTLS_POST_HANDSHAKE_AUTH’ for TLS1.3.  Enabling this flag
     requires to restore interrupted calls to ‘gnutls_record_recv()’
     based on the output of ‘gnutls_record_get_direction()’ , since
     ‘gnutls_record_recv()’ could be interrupted when sending when this
     flag is enabled.  Note this flag may not be used if you are using
     the same session for sending and receiving in different threads.
‘GNUTLS_ENABLE_EARLY_DATA’
     Under TLS1.3 allow the server to receive early data sent as part of
     the initial ClientHello (0-RTT). This can also be used to
     explicitly indicate that the client will send early data.  This is
     not enabled by default as early data has weaker security properties
     than other data.  Since 3.6.5.
‘GNUTLS_NO_AUTO_SEND_TICKET’
     Under TLS1.3 disable auto-sending of session tickets during the
     handshake.
‘GNUTLS_NO_END_OF_EARLY_DATA’
     Under TLS1.3 suppress sending EndOfEarlyData message.  Since 3.7.2.
‘GNUTLS_NO_TICKETS_TLS12’
     Flag to indicate that the session should not use resumption with
     session tickets.  This flag only has effect if TLS 1.2 is used.
‘GNUTLS_NO_STATUS_REQUEST’
     Prevents client from including the "status_request" TLS extension
     in the client hello, thus disabling the receival of certificate
     status information.  Since 3.8.0.

Figure 6.2: The ‘gnutls_init_flags_t’ enumeration.

After the session initialization details on the allowed ciphersuites and
protocol versions should be set using the priority functions such as
*note gnutls_priority_set:: and *note gnutls_priority_set_direct::.  We
elaborate on them in *note Priority Strings::.  The credentials used for
the key exchange method, such as certificates or usernames and passwords
should also be associated with the session current session using *note
gnutls_credentials_set::.

-- Function: int gnutls_credentials_set (gnutls_session_t SESSION,
          gnutls_credentials_type_t TYPE, void * CRED)
     SESSION: is a ‘gnutls_session_t’ type.

TYPE: is the type of the credentials

CRED: the credentials to set

Sets the needed credentials for the specified type.  E.g.
     username, password - or public and private keys etc.  The ‘cred’
     parameter is a structure that depends on the specified type and on
     the current session (client or server).

In order to minimize memory usage, and share credentials between
     several threads gnutls keeps a pointer to cred, and not the whole
     cred structure.  Thus you will have to keep the structure allocated
     until you call ‘gnutls_deinit()’ .

For ‘GNUTLS_CRD_ANON’ , ‘cred’ should be
     ‘gnutls_anon_client_credentials_t’ in case of a client.  In case of
     a server it should be ‘gnutls_anon_server_credentials_t’ .

For ‘GNUTLS_CRD_SRP’ , ‘cred’ should be
     ‘gnutls_srp_client_credentials_t’ in case of a client, and
     ‘gnutls_srp_server_credentials_t’ , in case of a server.

For ‘GNUTLS_CRD_CERTIFICATE’ , ‘cred’ should be
     ‘gnutls_certificate_credentials_t’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

File: gnutls.info,  Node: Associating the credentials,  Next: Setting up the transport layer,  Prev: Session initialization,  Up: How to use GnuTLS in applications

6.4 Associating the credentials
===============================

* Menu:

* Certificate credentials::
* Raw public-key credentials::
* SRP credentials::
* PSK credentials::
* Anonymous credentials::

Each authentication method is associated with a key exchange method, and
a credentials type.  The contents of the credentials is
method-dependent, e.g.  certificates for certificate authentication and
should be initialized and associated with a session (see *note
gnutls_credentials_set::).  A mapping of the key exchange methods with
the credential types is shown in *note Table 6.2: tab:key-exchange-cred.

Authentication     Key exchange       Client         Server
method                                credentials    credentials
                                                     
--------------------------------------------------------------------
Certificate and    ‘KX_RSA’,          ‘CRD_CERTIFICATE’‘CRD_CERTIFICATE’
Raw public-key     ‘KX_DHE_RSA’,                     
                   ‘KX_DHE_DSS’,
                   ‘KX_ECDHE_RSA’,
                   ‘KX_ECDHE_ECDSA’
Password and       ‘KX_SRP_RSA’,      ‘CRD_SRP’      ‘CRD_CERTIFICATE’,
certificate        ‘KX_SRP_DSS’                      ‘CRD_SRP’
                                                     
Password           ‘KX_SRP’           ‘CRD_SRP’      ‘CRD_SRP’
                                                     
Anonymous          ‘KX_ANON_DH’,      ‘CRD_ANON’     ‘CRD_ANON’
                   ‘KX_ANON_ECDH’                    
Pre-shared key     ‘KX_PSK’,          ‘CRD_PSK’      ‘CRD_PSK’
                   ‘KX_DHE_PSK’,                     
                   ‘KX_ECDHE_PSK’

Table 6.2: Key exchange algorithms and the corresponding credential
types.

File: gnutls.info,  Node: Certificate credentials,  Next: Raw public-key credentials,  Up: Associating the credentials

6.4.1 Certificates
------------------

Server certificate authentication
.................................

When using certificates the server is required to have at least one
certificate and private key pair.  Clients may not hold such a pair, but
a server could require it.  In this section we discuss general issues
applying to both client and server certificates.  The next section will
elaborate on issues arising from client authentication only.

In order to use certificate credentials one must first initialize a
credentials structure of type ‘gnutls_certificate_credentials_t’.  After
use this structure must be freed.  This can be done with the following
functions.

‘INT *note gnutls_certificate_allocate_credentials:: (gnutls_certificate_credentials_t * RES)’
‘VOID *note gnutls_certificate_free_credentials:: (gnutls_certificate_credentials_t SC)’

After the credentials structures are initialized, the certificate and
key pair must be loaded.  This occurs before any TLS session is
initialized, and the same structures are reused for multiple sessions.
Depending on the certificate type different loading functions are
available, as shown below.  For X.509 certificates, the functions will
accept and use a certificate chain that leads to a trusted authority.
The certificate chain must be ordered in such way that every certificate
certifies the one before it.  The trusted authority's certificate need
not to be included since the peer should possess it already.

‘INT *note gnutls_certificate_set_x509_key_file2:: (gnutls_certificate_credentials_t RES, const char * CERTFILE, const char * KEYFILE, gnutls_x509_crt_fmt_t TYPE, const char * PASS, unsigned int FLAGS)’
‘INT *note gnutls_certificate_set_x509_key_mem2:: (gnutls_certificate_credentials_t RES, const gnutls_datum_t * CERT, const gnutls_datum_t * KEY, gnutls_x509_crt_fmt_t TYPE, const char * PASS, unsigned int FLAGS)’
‘INT *note gnutls_certificate_set_x509_key:: (gnutls_certificate_credentials_t RES, gnutls_x509_crt_t * CERT_LIST, int CERT_LIST_SIZE, gnutls_x509_privkey_t KEY)’

It is recommended to use the higher level functions such as *note
gnutls_certificate_set_x509_key_file2:: which accept not only file names
but URLs that specify objects stored in token, or system certificates
and keys (see *note Application-specific keys::).  For these cases,
another important function is *note
gnutls_certificate_set_pin_function::, that allows setting a callback
function to retrieve a PIN if the input keys are protected by PIN.

-- Function: void gnutls_certificate_set_pin_function
          (gnutls_certificate_credentials_t CRED, gnutls_pin_callback_t
          FN, void * USERDATA)
     CRED: is a ‘gnutls_certificate_credentials_t’ type.

FN: A PIN callback

USERDATA: Data to be passed in the callback

This function will set a callback function to be used when required
     to access a protected object.  This function overrides any other
     global PIN functions.

Note that this function must be called right after initialization
     to have effect.

*Since:* 3.1.0

If the imported keys and certificates need to be accessed before any TLS
session is established, it is convenient to use *note
gnutls_certificate_set_key:: in combination with *note
gnutls_pcert_import_x509_raw:: and *note
gnutls_privkey_import_x509_raw::.

-- Function: int gnutls_certificate_set_key
          (gnutls_certificate_credentials_t RES, const char ** NAMES,
          int NAMES_SIZE, gnutls_pcert_st * PCERT_LIST, int
          PCERT_LIST_SIZE, gnutls_privkey_t KEY)
     RES: is a ‘gnutls_certificate_credentials_t’ type.

NAMES: is an array of DNS names belonging to the public-key (NULL
     if none)

NAMES_SIZE: holds the size of the names list

PCERT_LIST: contains a certificate list (chain) or raw public-key

PCERT_LIST_SIZE: holds the size of the certificate list

KEY: is a ‘gnutls_privkey_t’ key corresponding to the first
     public-key in pcert_list

This function sets a public/private key pair in the
     gnutls_certificate_credentials_t type.  The given public key may be
     encapsulated in a certificate or can be given as a raw key.  This
     function may be called more than once, in case multiple key pairs
     exist for the server.  For clients that want to send more than
     their own end- entity certificate (e.g., also an intermediate CA
     cert), the full certificate chain must be provided in ‘pcert_list’
     .

Note that the ‘key’ will become part of the credentials structure
     and must not be deallocated.  It will be automatically deallocated
     when the ‘res’ structure is deinitialized.

If this function fails, the ‘res’ structure is at an undefined
     state and it must not be reused to load other keys or certificates.

Note that, this function by default returns zero on success and a
     negative value on error.  Since 3.5.6, when the flag
     ‘GNUTLS_CERTIFICATE_API_V2’ is set using
     ‘gnutls_certificate_set_flags()’ it returns an index (greater or
     equal to zero).  That index can be used for other functions to
     refer to the added key-pair.

Since GnuTLS 3.6.6 this function also handles raw public keys.

*Returns:* On success this functions returns zero, and otherwise a
     negative value on error (see above for modifying that behavior).

*Since:* 3.0

If multiple certificates are used with the functions above each client's
request will be served with the certificate that matches the requested
name (see *note Server name indication::).

As an alternative to loading from files or buffers, a callback may be
used for the server or the client to specify the certificate and the key
at the handshake time.  In that case a certificate should be selected
according the peer's signature algorithm preferences.  To get those
preferences use *note gnutls_sign_algorithm_get_requested::.  Both
functions are shown below.

‘VOID *note gnutls_certificate_set_retrieve_function:: (gnutls_certificate_credentials_t CRED, gnutls_certificate_retrieve_function * FUNC)’
‘VOID *note gnutls_certificate_set_retrieve_function2:: (gnutls_certificate_credentials_t CRED, gnutls_certificate_retrieve_function2 * FUNC)’
‘VOID *note gnutls_certificate_set_retrieve_function3:: (gnutls_certificate_credentials_t CRED, gnutls_certificate_retrieve_function3 * FUNC)’
‘INT *note gnutls_sign_algorithm_get_requested:: (gnutls_session_t SESSION, size_t INDX, gnutls_sign_algorithm_t * ALGO)’

The functions above do not handle the requested server name
automatically.  A server would need to check the name requested by the
client using *note gnutls_server_name_get::, and serve the appropriate
certificate.  Note that some of these functions require the
‘gnutls_pcert_st’ structure to be filled in.  Helper functions to fill
in the structure are listed below.

typedef struct gnutls_pcert_st
{
  gnutls_pubkey_t pubkey;
  gnutls_datum_t cert;
  gnutls_certificate_type_t type;
} gnutls_pcert_st;

‘INT *note gnutls_pcert_import_x509:: (gnutls_pcert_st * PCERT, gnutls_x509_crt_t CRT, unsigned int FLAGS)’
‘INT *note gnutls_pcert_import_x509_raw:: (gnutls_pcert_st * PCERT, const gnutls_datum_t * CERT, gnutls_x509_crt_fmt_t FORMAT, unsigned int FLAGS)’
‘VOID *note gnutls_pcert_deinit:: (gnutls_pcert_st * PCERT)’

In a handshake, the negotiated cipher suite depends on the certificate's
parameters, so some key exchange methods might not be available with all
certificates.  GnuTLS will disable ciphersuites that are not compatible
with the key, or the enabled authentication methods.  For example keys
marked as sign-only, will not be able to access the plain RSA
ciphersuites, that require decryption.  It is not recommended to use RSA
keys for both signing and encryption.  If possible use a different key
for the ‘DHE-RSA’ which uses signing and ‘RSA’ that requires decryption.
All the key exchange methods shown in *note Table 4.1: tab:key-exchange.
are available in certificate authentication.

Client certificate authentication
.................................

If a certificate is to be requested from the client during the
handshake, the server will send a certificate request message.  This
behavior is controlled by *note gnutls_certificate_server_set_request::.
The request contains a list of the by the server accepted certificate
signers.  This list is constructed using the trusted certificate
authorities of the server.  In cases where the server supports a large
number of certificate authorities it makes sense not to advertise all of
the names to save bandwidth.  That can be controlled using the function
*note gnutls_certificate_send_x509_rdn_sequence::.  This however will
have the side-effect of not restricting the client to certificates
signed by server's acceptable signers.

-- Function: void gnutls_certificate_server_set_request
          (gnutls_session_t SESSION, gnutls_certificate_request_t REQ)
     SESSION: is a ‘gnutls_session_t’ type.

REQ: is one of GNUTLS_CERT_REQUEST, GNUTLS_CERT_REQUIRE,
     GNUTLS_CERT_IGNORE

This function specifies if we (in case of a server) are going to
     send a certificate request message to the client.  If ‘req’ is
     GNUTLS_CERT_REQUIRE then the server will return the
     ‘GNUTLS_E_NO_CERTIFICATE_FOUND’ error if the peer does not provide
     a certificate.  If you do not call this function then the client
     will not be asked to send a certificate.  Invoking the function
     with ‘req’ GNUTLS_CERT_IGNORE has the same effect.

-- Function: void gnutls_certificate_send_x509_rdn_sequence
          (gnutls_session_t SESSION, int STATUS)
     SESSION: a ‘gnutls_session_t’ type.

STATUS: is 0 or 1

If status is non zero, this function will order gnutls not to send
     the rdnSequence in the certificate request message.  That is the
     server will not advertise its trusted CAs to the peer.  If status
     is zero then the default behaviour will take effect, which is to
     advertise the server's trusted CAs.

This function has no effect in clients, and in authentication
     methods other than certificate with X.509 certificates.

On the client side, it needs to set its certificates on the credentials
structure, similarly to server side from a file, or via a callback.
Once the certificates are available in the credentials structure, the
client will send them if during the handshake the server requests a
certificate signed by the issuer of its CA.

In the case a single certificate is available and the server does not
specify a signer's list, then that certificate is always sent.  It is,
however possible, to send a certificate even when the advertised CA list
by the server contains CAs other than its signer.  That can be achieved
using the ‘GNUTLS_FORCE_CLIENT_CERT’ flag in *note gnutls_init::.

‘INT *note gnutls_certificate_set_x509_key_file:: (gnutls_certificate_credentials_t RES, const char * CERTFILE, const char * KEYFILE, gnutls_x509_crt_fmt_t TYPE)’
‘INT *note gnutls_certificate_set_x509_simple_pkcs12_file:: (gnutls_certificate_credentials_t RES, const char * PKCS12FILE, gnutls_x509_crt_fmt_t TYPE, const char * PASSWORD)’
‘VOID *note gnutls_certificate_set_retrieve_function2:: (gnutls_certificate_credentials_t CRED, gnutls_certificate_retrieve_function2 * FUNC)’

Client or server certificate verification
.........................................

Certificate verification is possible by loading the trusted authorities
into the credentials structure by using the following functions,
applicable to X.509 certificates.  In modern systems it is recommended
to utilize *note gnutls_certificate_set_x509_system_trust:: which will
load the trusted authorities from the system store.

-- Function: int gnutls_certificate_set_x509_system_trust
          (gnutls_certificate_credentials_t CRED)
     CRED: is a ‘gnutls_certificate_credentials_t’ type.

This function adds the system's default trusted CAs in order to
     verify client or server certificates.

In the case the system is currently unsupported
     ‘GNUTLS_E_UNIMPLEMENTED_FEATURE’ is returned.

*Returns:* the number of certificates processed or a negative error
     code on error.

*Since:* 3.0.20
‘INT *note gnutls_certificate_set_x509_trust_file:: (gnutls_certificate_credentials_t CRED, const char * CAFILE, gnutls_x509_crt_fmt_t TYPE)’
‘INT *note gnutls_certificate_set_x509_trust_dir:: (gnutls_certificate_credentials_t CRED, const char * CA_DIR, gnutls_x509_crt_fmt_t TYPE)’

The peer's certificate will be automatically verified if *note
gnutls_session_set_verify_cert:: is called prior to handshake.

Alternatively, one must set a callback function during the handshake
using *note gnutls_certificate_set_verify_function::, which will verify
the peer's certificate once received.  The verification should happen
using *note gnutls_certificate_verify_peers3:: within the callback.  It
will verify the certificate's signature and the owner of the
certificate.  That will provide a brief verification output.  If a
detailed output is required one should call *note
gnutls_certificate_get_peers:: to obtain the raw certificate of the peer
and verify it using the functions discussed in *note X.509
certificates::.

In both the automatic and the manual cases, the verification status
returned can be printed using *note
gnutls_certificate_verification_status_print::.

-- Function: void gnutls_session_set_verify_cert (gnutls_session_t
          SESSION, const char * HOSTNAME, unsigned FLAGS)
     SESSION: is a gnutls session

HOSTNAME: is the expected name of the peer; may be ‘NULL’

FLAGS: flags for certificate verification -
     ‘gnutls_certificate_verify_flags’

This function instructs GnuTLS to verify the peer's certificate
     using the provided hostname.  If the verification fails the
     handshake will also fail with
     ‘GNUTLS_E_CERTIFICATE_VERIFICATION_ERROR’ .  In that case the
     verification result can be obtained using
     ‘gnutls_session_get_verify_cert_status()’ .

The ‘hostname’ pointer provided must remain valid for the lifetime
     of the session.  More precisely it should be available during any
     subsequent handshakes.  If no hostname is provided, no hostname
     verification will be performed.  For a more advanced verification
     function check ‘gnutls_session_set_verify_cert2()’ .

If ‘flags’ is provided which contain a profile, this function
     should be called after any session priority setting functions.

The ‘gnutls_session_set_verify_cert()’ function is intended to be
     used by TLS clients to verify the server's certificate.

*Since:* 3.4.6

‘INT *note gnutls_certificate_verify_peers3:: (gnutls_session_t SESSION, const char * HOSTNAME, unsigned int * STATUS)’
‘VOID *note gnutls_certificate_set_verify_function:: (gnutls_certificate_credentials_t CRED, gnutls_certificate_verify_function * FUNC)’

Note that when using raw public-keys verification will not work because
there is no corresponding certificate body belonging to the raw key that
can be verified.  In that case the *note
gnutls_certificate_verify_peers:: family of functions will return a
GNUTLS_E_INVALID_REQUEST error code.  For authenticating raw public-keys
one must use an out-of-band mechanism, e.g.  by comparing hashes or
using trust on first use (see *note Verifying a certificate using trust
on first use authentication::).

File: gnutls.info,  Node: Raw public-key credentials,  Next: SRP credentials,  Prev: Certificate credentials,  Up: Associating the credentials

6.4.2 Raw public-keys
---------------------

As of version 3.6.6 GnuTLS supports *note Raw public-keys::.  With raw
public-keys only the public-key part (that is normally embedded in a
certificate) is transmitted to the peer.  In order to load a raw
public-key and its corresponding private key in a credentials structure
one can use the following functions.

‘INT *note gnutls_certificate_set_key:: (gnutls_certificate_credentials_t RES, const char ** NAMES, int NAMES_SIZE, gnutls_pcert_st * PCERT_LIST, int PCERT_LIST_SIZE, gnutls_privkey_t KEY)’
‘INT *note gnutls_certificate_set_rawpk_key_mem:: (gnutls_certificate_credentials_t CRED, const gnutls_datum_t * SPKI, const gnutls_datum_t * PKEY, gnutls_x509_crt_fmt_t FORMAT, const char * PASS, unsigned int KEY_USAGE, const char ** NAMES, unsigned int NAMES_LENGTH, unsigned int FLAGS)’
‘INT *note gnutls_certificate_set_rawpk_key_file:: (gnutls_certificate_credentials_t CRED, const char * RAWPKFILE, const char * PRIVKEYFILE, gnutls_x509_crt_fmt_t FORMAT, const char * PASS, unsigned int KEY_USAGE, const char ** NAMES, unsigned int NAMES_LENGTH, unsigned int PRIVKEY_FLAGS, unsigned int PKCS11_FLAGS)’

File: gnutls.info,  Node: SRP credentials,  Next: PSK credentials,  Prev: Raw public-key credentials,  Up: Associating the credentials

6.4.3 SRP
---------

The initialization functions in SRP credentials differ between client
and server.  Clients supporting SRP should set the username and password
prior to connection, to the credentials structure.  Alternatively *note
gnutls_srp_set_client_credentials_function:: may be used instead, to
specify a callback function that should return the SRP username and
password.  The callback is called once during the TLS handshake.

‘INT *note gnutls_srp_allocate_server_credentials:: (gnutls_srp_server_credentials_t * SC)’
‘INT *note gnutls_srp_allocate_client_credentials:: (gnutls_srp_client_credentials_t * SC)’
‘VOID *note gnutls_srp_free_server_credentials:: (gnutls_srp_server_credentials_t SC)’
‘VOID *note gnutls_srp_free_client_credentials:: (gnutls_srp_client_credentials_t SC)’
‘INT *note gnutls_srp_set_client_credentials:: (gnutls_srp_client_credentials_t RES, const char * USERNAME, const char * PASSWORD)’

-- Function: void gnutls_srp_set_client_credentials_function
          (gnutls_srp_client_credentials_t CRED,
          gnutls_srp_client_credentials_function * FUNC)
     CRED: is a ‘gnutls_srp_server_credentials_t’ type.

FUNC: is the callback function

This function can be used to set a callback to retrieve the
     username and password for client SRP authentication.  The
     callback's function form is:

int (*callback)(gnutls_session_t, char** username, char**password);

The ‘username’ and ‘password’ must be allocated using
     ‘gnutls_malloc()’ .

The ‘username’ should be an ASCII string or UTF-8 string.  In case
     of a UTF-8 string it is recommended to be following the PRECIS
     framework for usernames (rfc8265).  The password can be in ASCII
     format, or normalized using ‘gnutls_utf8_password_normalize()’ .

The callback function will be called once per handshake before the
     initial hello message is sent.

The callback should not return a negative error code the second
     time called, since the handshake procedure will be aborted.

The callback function should return 0 on success.  -1 indicates an
     error.

In server side the default behavior of GnuTLS is to read the usernames
and SRP verifiers from password files.  These password file format is
compatible the with the _Stanford srp libraries_ format.  If a different
password file format is to be used, then *note
gnutls_srp_set_server_credentials_function:: should be called, to set an
appropriate callback.

-- Function: int gnutls_srp_set_server_credentials_file
          (gnutls_srp_server_credentials_t RES, const char *
          PASSWORD_FILE, const char * PASSWORD_CONF_FILE)
     RES: is a ‘gnutls_srp_server_credentials_t’ type.

PASSWORD_FILE: is the SRP password file (tpasswd)

PASSWORD_CONF_FILE: is the SRP password conf file (tpasswd.conf)

This function sets the password files, in a
     ‘gnutls_srp_server_credentials_t’ type.  Those password files hold
     usernames and verifiers and will be used for SRP authentication.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned, or an
     error code.

-- Function: void gnutls_srp_set_server_credentials_function
          (gnutls_srp_server_credentials_t CRED,
          gnutls_srp_server_credentials_function * FUNC)
     CRED: is a ‘gnutls_srp_server_credentials_t’ type.

FUNC: is the callback function

This function can be used to set a callback to retrieve the user's
     SRP credentials.  The callback's function form is:

int (*callback)(gnutls_session_t, const char* username,
     gnutls_datum_t *salt, gnutls_datum_t *verifier, gnutls_datum_t
     *generator, gnutls_datum_t *prime);

‘username’ contains the actual username.  The ‘salt’ , ‘verifier’ ,
     ‘generator’ and ‘prime’ must be filled in using the
     ‘gnutls_malloc()’ .  For convenience ‘prime’ and ‘generator’ may
     also be one of the static parameters defined in gnutls.h.

Initially, the data field is NULL in every ‘gnutls_datum_t’
     structure that the callback has to fill in.  When the callback is
     done GnuTLS deallocates all of those buffers which are non-NULL,
     regardless of the return value.

In order to prevent attackers from guessing valid usernames, if a
     user does not exist, g and n values should be filled in using a
     random user's parameters.  In that case the callback must return
     the special value (1).  See ‘gnutls_srp_set_server_fake_salt_seed’
     too.  If this is not required for your application, return a
     negative number from the callback to abort the handshake.

The callback function will only be called once per handshake.  The
     callback function should return 0 on success, while -1 indicates an
     error.

File: gnutls.info,  Node: PSK credentials,  Next: Anonymous credentials,  Prev: SRP credentials,  Up: Associating the credentials

6.4.4 PSK
---------

The initialization functions in PSK credentials differ between client
and server.

‘INT *note gnutls_psk_allocate_server_credentials:: (gnutls_psk_server_credentials_t * SC)’
‘INT *note gnutls_psk_allocate_client_credentials:: (gnutls_psk_client_credentials_t * SC)’
‘VOID *note gnutls_psk_free_server_credentials:: (gnutls_psk_server_credentials_t SC)’
‘VOID *note gnutls_psk_free_client_credentials:: (gnutls_psk_client_credentials_t SC)’

Clients supporting PSK should supply the username and key before a TLS
session is established.  Alternatively *note
gnutls_psk_set_client_credentials_function:: can be used to specify a
callback function.  This has the advantage that the callback will be
called only if PSK has been negotiated.

‘INT *note gnutls_psk_set_client_credentials:: (gnutls_psk_client_credentials_t RES, const char * USERNAME, const gnutls_datum_t * KEY, gnutls_psk_key_flags FLAGS)’

-- Function: void gnutls_psk_set_client_credentials_function
          (gnutls_psk_client_credentials_t CRED,
          gnutls_psk_client_credentials_function * FUNC)
     CRED: is a ‘gnutls_psk_server_credentials_t’ type.

FUNC: is the callback function

This function can be used to set a callback to retrieve the
     username and password for client PSK authentication.  The
     callback's function form is: int (*callback)(gnutls_session_t,
     char** username, gnutls_datum_t* key);

The ‘username’ and ‘key’ ->data must be allocated using
     ‘gnutls_malloc()’ .  The ‘username’ should be an ASCII string or
     UTF-8 string.  In case of a UTF-8 string it is recommended to be
     following the PRECIS framework for usernames (rfc8265).

The callback function will be called once per handshake.

The callback function should return 0 on success.  -1 indicates an
     error.

In server side the default behavior of GnuTLS is to read the usernames
and PSK keys from a password file.  The password file should contain
usernames and keys in hexadecimal format.  The name of the password file
can be stored to the credentials structure by calling *note
gnutls_psk_set_server_credentials_file::.  If a different password file
format is to be used, then a callback should be set instead by *note
gnutls_psk_set_server_credentials_function::.

The server can help the client chose a suitable username and password,
by sending a hint.  Note that there is no common profile for the PSK
hint and applications are discouraged to use it.  A server, may specify
the hint by calling *note gnutls_psk_set_server_credentials_hint::.  The
client can retrieve the hint, for example in the callback function,
using *note gnutls_psk_client_get_hint::.

-- Function: int gnutls_psk_set_server_credentials_file
          (gnutls_psk_server_credentials_t RES, const char *
          PASSWORD_FILE)
     RES: is a ‘gnutls_psk_server_credentials_t’ type.

PASSWORD_FILE: is the PSK password file (passwd.psk)

This function sets the password file, in a
     ‘gnutls_psk_server_credentials_t’ type.  This password file holds
     usernames and keys and will be used for PSK authentication.

Each entry in the file consists of a username, followed by a colon
     (':') and a hex-encoded key.  If the username contains a colon or
     any other special character, it can be hex-encoded preceded by a
     '#'.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise an error code is returned.

‘VOID *note gnutls_psk_set_server_credentials_function:: (gnutls_psk_server_credentials_t CRED, gnutls_psk_server_credentials_function * FUNC)’
‘INT *note gnutls_psk_set_server_credentials_hint:: (gnutls_psk_server_credentials_t RES, const char * HINT)’
‘CONST CHAR * *note gnutls_psk_client_get_hint:: (gnutls_session_t SESSION)’

File: gnutls.info,  Node: Anonymous credentials,  Prev: PSK credentials,  Up: Associating the credentials

6.4.5 Anonymous
---------------

The key exchange methods for anonymous authentication since GnuTLS 3.6.0
will utilize the RFC7919 parameters, unless explicit parameters have
been provided and associated with an anonymous credentials structure.
Check *note Parameter generation:: for more information.  The
initialization functions for the credentials are shown below.

‘INT *note gnutls_anon_allocate_server_credentials:: (gnutls_anon_server_credentials_t * SC)’
‘INT *note gnutls_anon_allocate_client_credentials:: (gnutls_anon_client_credentials_t * SC)’
‘VOID *note gnutls_anon_free_server_credentials:: (gnutls_anon_server_credentials_t SC)’
‘VOID *note gnutls_anon_free_client_credentials:: (gnutls_anon_client_credentials_t SC)’

File: gnutls.info,  Node: Setting up the transport layer,  Next: TLS handshake,  Prev: Associating the credentials,  Up: How to use GnuTLS in applications

6.5 Setting up the transport layer
==================================

The next step is to setup the underlying transport layer details.  The
Berkeley sockets are implicitly used by GnuTLS, thus a call to *note
gnutls_transport_set_int:: would be sufficient to specify the socket
descriptor.

‘VOID *note gnutls_transport_set_int:: (gnutls_session_t SESSION, int FD)’
‘VOID *note gnutls_transport_set_int2:: (gnutls_session_t SESSION, int RECV_FD, int SEND_FD)’

If however another transport layer than TCP is selected, then a pointer
should be used instead to express the parameter to be passed to custom
functions.  In that case the following functions should be used instead.

‘VOID *note gnutls_transport_set_ptr:: (gnutls_session_t SESSION, gnutls_transport_ptr_t PTR)’
‘VOID *note gnutls_transport_set_ptr2:: (gnutls_session_t SESSION, gnutls_transport_ptr_t RECV_PTR, gnutls_transport_ptr_t SEND_PTR)’

Moreover all of the following push and pull callbacks should be set.

-- Function: void gnutls_transport_set_push_function (gnutls_session_t
          SESSION, gnutls_push_func PUSH_FUNC)
     SESSION: is a ‘gnutls_session_t’ type.

PUSH_FUNC: a callback function similar to ‘write()’

This is the function where you set a push function for gnutls to
     use in order to send data.  If you are going to use berkeley style
     sockets, you do not need to use this function since the default
     send(2) will probably be ok.  Otherwise you should specify this
     function for gnutls to be able to send data.  The callback should
     return a positive number indicating the bytes sent, and -1 on
     error.

‘push_func’ is of the form, ssize_t
     (*gnutls_push_func)(gnutls_transport_ptr_t, const void*, size_t);

-- Function: void gnutls_transport_set_vec_push_function
          (gnutls_session_t SESSION, gnutls_vec_push_func VEC_FUNC)
     SESSION: is a ‘gnutls_session_t’ type.

VEC_FUNC: a callback function similar to ‘writev()’

Using this function you can override the default writev(2) function
     for gnutls to send data.  Setting this callback instead of
     ‘gnutls_transport_set_push_function()’ is recommended since it
     introduces less overhead in the TLS handshake process.

‘vec_func’ is of the form, ssize_t (*gnutls_vec_push_func)
     (gnutls_transport_ptr_t, const giovec_t * iov, int iovcnt);

*Since:* 2.12.0

-- Function: void gnutls_transport_set_pull_function (gnutls_session_t
          SESSION, gnutls_pull_func PULL_FUNC)
     SESSION: is a ‘gnutls_session_t’ type.

PULL_FUNC: a callback function similar to ‘read()’

This is the function where you set a function for gnutls to receive
     data.  Normally, if you use berkeley style sockets, do not need to
     use this function since the default recv(2) will probably be ok.
     The callback should return 0 on connection termination, a positive
     number indicating the number of bytes received, and -1 on error.

‘gnutls_pull_func’ is of the form, ssize_t
     (*gnutls_pull_func)(gnutls_transport_ptr_t, void*, size_t);

-- Function: void gnutls_transport_set_pull_timeout_function
          (gnutls_session_t SESSION, gnutls_pull_timeout_func FUNC)
     SESSION: is a ‘gnutls_session_t’ type.

FUNC: a callback function

This is the function where you set a function for gnutls to know
     whether data are ready to be received.  It should wait for data a
     given time frame in milliseconds.  The callback should return 0 on
     timeout, a positive number if data can be received, and -1 on
     error.  You'll need to override this function if ‘select()’ is not
     suitable for the provided transport calls.

As with ‘select()’ , if the timeout value is zero the callback
     should return zero if no data are immediately available.  The
     special value ‘GNUTLS_INDEFINITE_TIMEOUT’ indicates that the
     callback should wait indefinitely for data.

‘gnutls_pull_timeout_func’ is of the form, int
     (*gnutls_pull_timeout_func)(gnutls_transport_ptr_t, unsigned int
     ms);

This callback is necessary when ‘gnutls_handshake_set_timeout()’ or
     ‘gnutls_record_set_timeout()’ are set, under TLS1.3 and for
     enforcing the DTLS mode timeouts when in blocking mode.

For compatibility with future GnuTLS versions this callback must be
     set when a custom pull function is registered.  The callback will
     not be used when the session is in TLS mode with non-blocking
     sockets.  That is, when ‘GNUTLS_NONBLOCK’ is specified for a TLS
     session in ‘gnutls_init()’ .

The helper function ‘gnutls_system_recv_timeout()’ is provided to
     simplify writing callbacks.

*Since:* 3.0

The functions above accept a callback function which should return the
number of bytes written, or -1 on error and should set ‘errno’
appropriately.  In some environments, setting ‘errno’ is unreliable.
For example Windows have several errno variables in different CRTs, or
in other systems it may be a non thread-local variable.  If this is a
concern to you, call *note gnutls_transport_set_errno:: with the
intended errno value instead of setting ‘errno’ directly.

-- Function: void gnutls_transport_set_errno (gnutls_session_t SESSION,
          int ERR)
     SESSION: is a ‘gnutls_session_t’ type.

ERR: error value to store in session-specific errno variable.

Store ‘err’ in the session-specific errno variable.  Useful values
     for ‘err’ are EINTR, EAGAIN and EMSGSIZE, other values are treated
     will be treated as real errors in the push/pull function.

This function is useful in replacement push and pull functions set
     by ‘gnutls_transport_set_push_function()’ and
     ‘gnutls_transport_set_pull_function()’ under Windows, where the
     replacements may not have access to the same ‘errno’ variable that
     is used by GnuTLS (e.g., the application is linked to msvcr71.dll
     and gnutls is linked to msvcrt.dll).

This function is unreliable if you are using the same ‘session’ in
     different threads for sending and receiving.

GnuTLS currently only interprets the EINTR, EAGAIN and EMSGSIZE errno
values and returns the corresponding GnuTLS error codes:
   • ‘GNUTLS_E_INTERRUPTED’
   • ‘GNUTLS_E_AGAIN’
   • ‘GNUTLS_E_LARGE_PACKET’
The EINTR and EAGAIN values are returned by interrupted system calls, or
when non blocking IO is used.  All GnuTLS functions can be resumed
(called again), if any of the above error codes is returned.  The
EMSGSIZE value is returned when attempting to send a large datagram.

In the case of DTLS it is also desirable to override the generic
transport functions with functions that emulate the operation of
‘recvfrom’ and ‘sendto’.  In addition DTLS requires timers during the
receive of a handshake message, set using the *note
gnutls_transport_set_pull_timeout_function:: function.  To check the
retransmission timers the function *note gnutls_dtls_get_timeout:: is
provided, which returns the time remaining until the next
retransmission, or better the time until *note gnutls_handshake:: should
be called again.

-- Function: void gnutls_transport_set_pull_timeout_function
          (gnutls_session_t SESSION, gnutls_pull_timeout_func FUNC)
     SESSION: is a ‘gnutls_session_t’ type.

FUNC: a callback function

‘gnutls_pull_timeout_func’ is of the form, int
     (*gnutls_pull_timeout_func)(gnutls_transport_ptr_t, unsigned int
     ms);

The helper function ‘gnutls_system_recv_timeout()’ is provided to
     simplify writing callbacks.

*Since:* 3.0

-- Function: unsigned int gnutls_dtls_get_timeout (gnutls_session_t
          SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

This function will return the milliseconds remaining for a
     retransmission of the previously sent handshake message.  This
     function is useful when DTLS is used in non-blocking mode, to
     estimate when to call ‘gnutls_handshake()’ if no packets have been
     received.

*Returns:* the remaining time in milliseconds.

*Since:* 3.0

* Menu:

* Asynchronous operation::
* Reducing round-trips::
* Zero-roundtrip mode::
* Anti-replay protection::
* DTLS sessions::
* DTLS and SCTP::

File: gnutls.info,  Node: Asynchronous operation,  Next: Reducing round-trips,  Up: Setting up the transport layer

6.5.1 Asynchronous operation
----------------------------

GnuTLS can be used with asynchronous socket or event-driven programming.
The approach is similar to using Berkeley sockets under such an
environment.  The blocking, due to network interaction, calls such as
*note gnutls_handshake::, *note gnutls_record_recv::, can be set to
non-blocking by setting the underlying sockets to non-blocking.  If
other push and pull functions are setup, then they should behave the
same way as ‘recv’ and ‘send’ when used in a non-blocking way, i.e.,
return -1 and set errno to ‘EAGAIN’.  Since, during a TLS protocol
session GnuTLS does not block except for network interaction, the non
blocking ‘EAGAIN’ errno will be propagated and GnuTLS functions will
return the ‘GNUTLS_E_AGAIN’ error code.  Such calls can be resumed the
same way as a system call would.  The only exception is *note
gnutls_record_send::, which if interrupted subsequent calls need not to
include the data to be sent (can be called with NULL argument).

When using the ‘poll’ or ‘select’ system calls though, one should
remember that they only apply to the kernel sockets API. To check for
any available buffered data in a GnuTLS session, utilize *note
gnutls_record_check_pending::, either before the ‘poll’ system call, or
after a call to *note gnutls_record_recv::.  Data queued by *note
gnutls_record_send:: (when interrupted) can be discarded using *note
gnutls_record_discard_queued::.

An example of GnuTLS' usage with asynchronous operation can be found in
‘doc/examples/tlsproxy’.

The following paragraphs describe the detailed requirements for
non-blocking operation when using the TLS or DTLS protocols.

6.5.1.1 TLS protocol
....................

There are no special requirements for the TLS protocol operation in
non-blocking mode if a non-blocking socket is used.

It is recommended, however, for future compatibility, when in
non-blocking mode, to call the *note gnutls_init:: function with the
‘GNUTLS_NONBLOCK’ flag set (see *note Session initialization::).

6.5.1.2 Datagram TLS protocol
.............................

When in non-blocking mode the function, the *note gnutls_init:: function
must be called with the ‘GNUTLS_NONBLOCK’ flag set (see *note Session
initialization::).

In contrast with the TLS protocol, the pull timeout function is
required, but will only be called with a timeout of zero.  In that case
it should indicate whether there are data to be received or not.  When
not using the default pull function, then *note
gnutls_transport_set_pull_timeout_function:: should be called.

Although in the TLS protocol implementation each call to receive or send
function implies to restoring the same function that was interrupted, in
the DTLS protocol this requirement isn't true.  There are cases where a
retransmission is required, which are indicated by a received message
and thus *note gnutls_record_get_direction:: must be called to decide
which direction to check prior to restoring a function call.

-- Function: int gnutls_record_get_direction (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

This function is useful to determine whether a GnuTLS function was
     interrupted while sending or receiving, so that ‘select()’ or
     ‘poll()’ may be called appropriately.

It provides information about the internals of the record protocol
     and is only useful if a prior gnutls function call, e.g.
     ‘gnutls_handshake()’ , was interrupted and returned
     ‘GNUTLS_E_INTERRUPTED’ or ‘GNUTLS_E_AGAIN’ .  After such an
     interrupt applications may call ‘select()’ or ‘poll()’ before
     restoring the interrupted GnuTLS function.

This function's output is unreliable if you are using the same
     ‘session’ in different threads for sending and receiving.

*Returns:* 0 if interrupted while trying to read data, or 1 while
     trying to write data.

When calling *note gnutls_handshake:: through a multi-plexer, to be able
to handle properly the DTLS handshake retransmission timers, the
function *note gnutls_dtls_get_timeout:: should be used to estimate when
to call *note gnutls_handshake:: if no data have been received.

File: gnutls.info,  Node: Reducing round-trips,  Next: Zero-roundtrip mode,  Prev: Asynchronous operation,  Up: Setting up the transport layer

6.5.2 Reducing round-trips
--------------------------

The full TLS 1.2 handshake requires 2 round-trips to complete, and when
combined with TCP's SYN and SYN-ACK negotiation it extends to 3 full
round-trips.  While, TLS 1.3 reduces that to two round-trips when under
TCP, it still adds considerable latency, making the protocol unsuitable
for certain applications.

To optimize the handshake latency, in client side, it is possible to
take advantage of the TCP fast open [*note RFC7413::] mechanism on
operating systems that support it.  That can be done either by manually
crafting the push and pull callbacks, or by utilizing *note
gnutls_transport_set_fastopen::.  In that case the initial TCP handshake
is eliminated, reducing the TLS 1.2 handshake round-trip to 2, and the
TLS 1.3 handshake to a single round-trip.  Note, that when this function
is used, any connection failures will be reported during the *note
gnutls_handshake:: function call with error code ‘GNUTLS_E_PUSH_ERROR’.

-- Function: void gnutls_transport_set_fastopen (gnutls_session_t
          SESSION, int FD, struct sockaddr * CONNECT_ADDR, socklen_t
          CONNECT_ADDRLEN, unsigned int FLAGS)
     SESSION: is a ‘gnutls_session_t’ type.

FD: is the session's socket descriptor

CONNECT_ADDR: is the address we want to connect to

CONNECT_ADDRLEN: is the length of ‘connect_addr’

FLAGS: must be zero

Enables TCP Fast Open (TFO) for the specified TLS client session.
     That means that TCP connection establishment and the transmission
     of the first TLS client hello packet are combined.  The peer's
     address must be specified in ‘connect_addr’ and ‘connect_addrlen’ ,
     and the socket specified by ‘fd’ should not be connected.

TFO only works for TCP sockets of type AF_INET and AF_INET6.  If
     the OS doesn't support TCP fast open this function will result to
     gnutls using ‘connect()’ transparently during the first write.

*Note:* This function overrides all the transport callback
     functions.  If this is undesirable, TCP Fast Open must be
     implemented on the user callback functions without calling this
     function.  When using this function, transport callbacks must not
     be set, and ‘gnutls_transport_set_ptr()’ or
     ‘gnutls_transport_set_int()’ must not be called.

On GNU/Linux TFO has to be enabled at the system layer, that is in
     /proc/sys/net/ipv4/tcp_fastopen, bit 0 has to be set.

This function has no effect on server sessions.

*Since:* 3.5.3

When restricted to TLS 1.2, and non-resumed sessions, it is possible to
further reduce the round-trips to a single one by taking advantage of
the *note False Start:: TLS extension.  This can be enabled by setting
the GNUTLS_ENABLE_FALSE_START flag on *note gnutls_init::.

Under TLS 1.3, the server side can start transmitting before the
handshake is complete (i.e., while the client Finished message is still
in flight), when no client certificate authentication is requested.
This, unlike false start, is part of protocol design with no known
security implications.  It can be enabled by setting the
GNUTLS_ENABLE_EARLY_START on *note gnutls_init::, and the *note
gnutls_handshake:: function will return early, allowing the server to
send data earlier.

File: gnutls.info,  Node: Zero-roundtrip mode,  Next: Anti-replay protection,  Prev: Reducing round-trips,  Up: Setting up the transport layer

6.5.3 Zero-roundtrip mode
-------------------------

Under TLS 1.3, when the client has already connected to the server and
is resuming a session, it can start transmitting application data during
handshake.  This is called zero round-trip time (0-RTT) mode, and the
application data sent in this mode is called early data.  The client can
send early data with *note gnutls_record_send_early_data::.  The client
should call this function before calling *note gnutls_handshake:: and
after calling *note gnutls_session_set_data::.

Note, however, that early data has weaker security properties than
normal application data sent after handshake, such as lack of forward
secrecy, no guarantees of non-replay between connections.  Thus it is
disabled on the server side by default.  To enable it, the server needs
to:
  1. Set GNUTLS_ENABLE_EARLY_DATA on *note gnutls_init::.  Note that
     this option only has effect on server.

2. Enable anti-replay measure.  See *note Anti-replay protection:: for
     the details.

The server caches the received early data until it is read.  To set the
maximum amount of data to be stored in the cache, use *note
gnutls_record_set_max_early_data_size::.  After receiving the
EndOfEarlyData handshake message, the server can start retrieving the
received data with *note gnutls_record_recv_early_data::.  You can call
the function either after the handshake is complete, or through a
handshake hook (*note gnutls_handshake_set_hook_function::).

When sending early data, the client should respect the maximum amount of
early data, which may have been previously advertised by the server.  It
can be checked using *note gnutls_record_get_max_early_data_size::,
right after calling *note gnutls_session_set_data::.

After sending early data, to check whether the sent early data was
accepted by the server, use *note gnutls_session_get_flags:: and compare
the result with GNUTLS_SFLAGS_EARLY_DATA.  Similarly, on the server
side, the same function and flag can be used to check whether it has
actually accepted early data.

File: gnutls.info,  Node: Anti-replay protection,  Next: DTLS sessions,  Prev: Zero-roundtrip mode,  Up: Setting up the transport layer

6.5.4 Anti-replay protection
----------------------------

When 0-RTT mode is used, the server must protect itself from replay
attacks, where adversary client reuses duplicate session ticket to send
early data, before the server authenticates the client.

GnuTLS provides a simple mechanism against replay attacks, following the
method called ClientHello recording.  When a session ticket is accepted,
the server checks if the ClientHello message has been already seen.  If
there is a duplicate, the server rejects early data.

The problem of this approach is that the number of recorded messages
grows indefinitely.  To prevent that, the server can limit the recording
to a certain time window, which can be configured with *note
gnutls_anti_replay_set_window::.

The anti-replay mechanism shall be globally initialized with *note
gnutls_anti_replay_init::, and then attached to a session using *note
gnutls_anti_replay_enable::.  It can be deinitialized with *note
gnutls_anti_replay_deinit::.

The server must also set up a database back-end to store ClientHello
messages.  That can be achieved using *note
gnutls_anti_replay_set_add_function:: and *note
gnutls_anti_replay_set_ptr::.

Note that, if the back-end stores arbitrary number of ClientHello, it
needs to periodically clean up the stored entries based on the time
window set with *note gnutls_anti_replay_set_window::.  The cleanup can
be implemented by iterating through the database entries and calling
*note gnutls_db_check_entry_expire_time::.  This is similar to session
database cleanup used by TLS1.2 sessions.

The full set up of the server using early data would be like the
following example:
     #define MAX_EARLY_DATA_SIZE 16384

static int
     db_add_func(void *dbf, gnutls_datum_t key, gnutls_datum_t data)
     {
         /* Return GNUTLS_E_DB_ENTRY_EXISTS, if KEY is found in the database.
          * Otherwise, store it and return 0.
          */
     }

static int
     handshake_hook_func(gnutls_session_t session, unsigned int htype,
                         unsigned when, unsigned int incoming, const gnutls_datum_t *msg)
     {
         int ret;
         char buf[MAX_EARLY_DATA_SIZE];

assert(htype == GNUTLS_HANDSHAKE_END_OF_EARLY_DATA);
         assert(when == GNUTLS_HOOK_POST);

if (gnutls_session_get_flags(session) & GNUTLS_SFLAGS_EARLY_DATA) {
             ret = gnutls_record_recv_early_data(session, buf, sizeof(buf));
             assert(ret >= 0);
         }

return ret;
     }

int main(void)
     {
       ...
       /* Initialize anti-replay measure, which can be shared
        * among multiple sessions.
        */
       gnutls_anti_replay_init(&anti_replay);

/* Set the database back-end function for the anti-replay data. */
       gnutls_anti_replay_set_add_function(anti_replay, db_add_func);
       gnutls_anti_replay_set_ptr(anti_replay, NULL);

...

gnutls_init(&server, GNUTLS_SERVER | GNUTLS_ENABLE_EARLY_DATA);
       gnutls_record_set_max_early_data_size(server, MAX_EARLY_DATA_SIZE);

...

/* Set the anti-replay measure to the session.
        */
       gnutls_anti_replay_enable(server, anti_replay);
       ...

/* Retrieve early data in a handshake hook;
        * you can also do that after handshake.
        */
       gnutls_handshake_set_hook_function(server, GNUTLS_HANDSHAKE_END_OF_EARLY_DATA,
                                          GNUTLS_HOOK_POST, handshake_hook_func);
       ...
     }

File: gnutls.info,  Node: DTLS sessions,  Next: DTLS and SCTP,  Prev: Anti-replay protection,  Up: Setting up the transport layer

6.5.5 DTLS sessions
-------------------

Because datagram TLS can operate over connections where the client
cannot be reliably verified, functionality in the form of cookies, is
available to prevent denial of service attacks to servers.  GnuTLS
requires a server to generate a secret key that is used to sign a
cookie(1).  That cookie is sent to the client using *note
gnutls_dtls_cookie_send::, and the client must reply using the correct
cookie.  The server side should verify the initial message sent by
client using *note gnutls_dtls_cookie_verify::.  If successful the
session should be initialized and associated with the cookie using *note
gnutls_dtls_prestate_set::, before proceeding to the handshake.

‘INT *note gnutls_key_generate:: (gnutls_datum_t * KEY, unsigned int KEY_SIZE)’
‘INT *note gnutls_dtls_cookie_send:: (gnutls_datum_t * KEY, void * CLIENT_DATA, size_t CLIENT_DATA_SIZE, gnutls_dtls_prestate_st * PRESTATE, gnutls_transport_ptr_t PTR, gnutls_push_func PUSH_FUNC)’
‘INT *note gnutls_dtls_cookie_verify:: (gnutls_datum_t * KEY, void * CLIENT_DATA, size_t CLIENT_DATA_SIZE, void * _MSG, size_t MSG_SIZE, gnutls_dtls_prestate_st * PRESTATE)’
‘VOID *note gnutls_dtls_prestate_set:: (gnutls_session_t SESSION, gnutls_dtls_prestate_st * PRESTATE)’

Note that the above apply to server side only and they are not mandatory
to be used.  Not using them, however, allows denial of service attacks.
The client side cookie handling is part of *note gnutls_handshake::.

Datagrams are typically restricted by a maximum transfer unit (MTU). For
that both client and server side should set the correct maximum transfer
unit for the layer underneath GnuTLS.  This will allow proper
fragmentation of DTLS messages and prevent messages from being silently
discarded by the transport layer.  The "correct" maximum transfer unit
can be obtained through a path MTU discovery mechanism [*note
RFC4821::].

‘VOID *note gnutls_dtls_set_mtu:: (gnutls_session_t SESSION, unsigned int MTU)’
‘UNSIGNED INT *note gnutls_dtls_get_mtu:: (gnutls_session_t SESSION)’
‘UNSIGNED INT *note gnutls_dtls_get_data_mtu:: (gnutls_session_t SESSION)’

---------- Footnotes ----------

(1) A key of 128 bits or 16 bytes should be sufficient for this
purpose.

File: gnutls.info,  Node: DTLS and SCTP,  Prev: DTLS sessions,  Up: Setting up the transport layer

6.5.6 DTLS and SCTP
-------------------

Although DTLS can run under any reliable or unreliable layer, there are
special requirements for SCTP according to [*note RFC6083::].  We
summarize the most important below, however for a full treatment we
refer to [*note RFC6083::].

• The MTU set via *note gnutls_dtls_set_mtu:: must be 2^14.
   • Replay detection must be disabled; use the flag
     ‘GNUTLS_NO_REPLAY_PROTECTION’ with *note gnutls_init::.
   • Retransmission of messages must be disabled; use *note
     gnutls_dtls_set_timeouts:: with a retransmission timeout larger
     than the total.
   • Handshake, Alert and ChangeCipherSpec messages must be sent over
     stream 0 with unlimited reliability and with the ordered delivery
     feature.
   • During a rehandshake, the caching of messages with unknown epoch is
     not handled by GnuTLS; this must be implemented in a special pull
     function.

File: gnutls.info,  Node: TLS handshake,  Next: Data transfer and termination,  Prev: Setting up the transport layer,  Up: How to use GnuTLS in applications

6.6 TLS handshake
=================

Once a session has been initialized and a network connection has been
set up, TLS and DTLS protocols perform a handshake.  The handshake is
the actual key exchange.

-- Function: int gnutls_handshake (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

This function performs the handshake of the TLS/SSL protocol, and
     initializes the TLS session parameters.

The non-fatal errors expected by this function are:
     ‘GNUTLS_E_INTERRUPTED’ , ‘GNUTLS_E_AGAIN’ ,
     ‘GNUTLS_E_WARNING_ALERT_RECEIVED’ .  When this function is called
     for re-handshake under TLS 1.2 or earlier, the non-fatal error code
     ‘GNUTLS_E_GOT_APPLICATION_DATA’ may also be returned.

The former two interrupt the handshake procedure due to the
     transport layer being interrupted, and the latter because of a
     "warning" alert that was sent by the peer (it is always a good idea
     to check any received alerts).  On these non-fatal errors call this
     function again, until it returns 0; cf.
     ‘gnutls_record_get_direction()’ and ‘gnutls_error_is_fatal()’ .  In
     DTLS sessions the non-fatal error ‘GNUTLS_E_LARGE_PACKET’ is also
     possible, and indicates that the MTU should be adjusted.

When this function is called by a server after a rehandshake
     request under TLS 1.2 or earlier the
     ‘GNUTLS_E_GOT_APPLICATION_DATA’ error code indicates that some data
     were pending prior to peer initiating the handshake.  Under TLS 1.3
     this function when called after a successful handshake, is a no-op
     and always succeeds in server side; in client side this function is
     equivalent to ‘gnutls_session_key_update()’ with ‘GNUTLS_KU_PEER’
     flag.

This function handles both full and abbreviated TLS handshakes
     (resumption).  For abbreviated handshakes, in client side, the
     ‘gnutls_session_set_data()’ should be called prior to this function
     to set parameters from a previous session.  In server side,
     resumption is handled by either setting a DB back-end, or setting
     up keys for session tickets.

*Returns:* ‘GNUTLS_E_SUCCESS’ on a successful handshake, otherwise
     a negative error code.

-- Function: void gnutls_handshake_set_timeout (gnutls_session_t
          SESSION, unsigned int MS)
     SESSION: is a ‘gnutls_session_t’ type.

MS: is a timeout value in milliseconds

This function sets the timeout for the TLS handshake process to the
     provided value.  Use an ‘ms’ value of zero to disable timeout, or
     ‘GNUTLS_DEFAULT_HANDSHAKE_TIMEOUT’ for a reasonable default value.
     For the DTLS protocol, the more detailed
     ‘gnutls_dtls_set_timeouts()’ is provided.

This function requires to set a pull timeout callback.  See
     ‘gnutls_transport_set_pull_timeout_function()’ .

*Since:* 3.1.0

In GnuTLS 3.5.0 and later it is recommended to use *note
gnutls_session_set_verify_cert:: for the handshake process to ensure the
verification of the peer's identity.  That will verify the peer's
certificate, against the trusted CA store while accounting for stapled
OCSP responses during the handshake; any error will be returned as a
handshake error.

In older GnuTLS versions it is required to verify the peer's certificate
during the handshake by setting a callback with *note
gnutls_certificate_set_verify_function::, and then using *note
gnutls_certificate_verify_peers3:: from it.  See *note Certificate
authentication:: for more information.

‘VOID *note gnutls_session_set_verify_cert:: (gnutls_session_t SESSION, const char * HOSTNAME, unsigned FLAGS)’
‘INT *note gnutls_certificate_verify_peers3:: (gnutls_session_t SESSION, const char * HOSTNAME, unsigned int * STATUS)’

File: gnutls.info,  Node: Data transfer and termination,  Next: Buffered data transfer,  Prev: TLS handshake,  Up: How to use GnuTLS in applications

6.7 Data transfer and termination
=================================

Once the handshake is complete and peer's identity has been verified
data can be exchanged.  The available functions resemble the POSIX
‘recv’ and ‘send’ functions.  It is suggested to use *note
gnutls_error_is_fatal:: to check whether the error codes returned by
these functions are fatal for the protocol or can be ignored.

-- Function: ssize_t gnutls_record_send (gnutls_session_t SESSION,
          const void * DATA, size_t DATA_SIZE)
     SESSION: is a ‘gnutls_session_t’ type.

DATA: contains the data to send

DATA_SIZE: is the length of the data

This function has the similar semantics with ‘send()’ .  The only
     difference is that it accepts a GnuTLS session, and uses different
     error codes.  Note that if the send buffer is full, ‘send()’ will
     block this function.  See the ‘send()’ documentation for more
     information.

You can replace the default push function which is ‘send()’ , by
     using ‘gnutls_transport_set_push_function()’ .

If the EINTR is returned by the internal push function then
     ‘GNUTLS_E_INTERRUPTED’ will be returned.  If ‘GNUTLS_E_INTERRUPTED’
     or ‘GNUTLS_E_AGAIN’ is returned, you must call this function again
     with the exact same parameters, or provide a ‘NULL’ pointer for
     ‘data’ and 0 for ‘data_size’ , in order to write the same data as
     before.  If you wish to discard the previous data instead of
     retrying, you must call ‘gnutls_record_discard_queued()’ before
     calling this function with different parameters.  Note that the
     latter works only on special transports (e.g., UDP). cf.
     ‘gnutls_record_get_direction()’ .

Note that in DTLS this function will return the
     ‘GNUTLS_E_LARGE_PACKET’ error code if the send data exceed the data
     MTU value - as returned by ‘gnutls_dtls_get_data_mtu()’ .  The
     errno value EMSGSIZE also maps to ‘GNUTLS_E_LARGE_PACKET’ .  Note
     that since 3.2.13 this function can be called under cork in DTLS
     mode, and will refuse to send data over the MTU size by returning
     ‘GNUTLS_E_LARGE_PACKET’ .

-- Function: ssize_t gnutls_record_recv (gnutls_session_t SESSION, void
          * DATA, size_t DATA_SIZE)
     SESSION: is a ‘gnutls_session_t’ type.

DATA: the buffer that the data will be read into

DATA_SIZE: the number of requested bytes

This function has the similar semantics with ‘recv()’ .  The only
     difference is that it accepts a GnuTLS session, and uses different
     error codes.  In the special case that the peer requests a
     renegotiation, the caller will receive an error code of
     ‘GNUTLS_E_REHANDSHAKE’ .  In case of a client, this message may be
     simply ignored, replied with an alert ‘GNUTLS_A_NO_RENEGOTIATION’ ,
     or replied with a new handshake, depending on the client's will.  A
     server receiving this error code can only initiate a new handshake
     or terminate the session.

If ‘EINTR’ is returned by the internal pull function (the default
     is ‘recv()’ ) then ‘GNUTLS_E_INTERRUPTED’ will be returned.  If
     ‘GNUTLS_E_INTERRUPTED’ or ‘GNUTLS_E_AGAIN’ is returned, you must
     call this function again to get the data.  See also
     ‘gnutls_record_get_direction()’ .

*Returns:* The number of bytes received and zero on EOF (for stream
     connections).  A negative error code is returned in case of an
     error.  The number of bytes received might be less than the
     requested ‘data_size’ .

-- Function: int gnutls_error_is_fatal (int ERROR)
     ERROR: is a GnuTLS error code, a negative error code

If a GnuTLS function returns a negative error code you may feed
     that value to this function to see if the error condition is fatal
     to a TLS session (i.e., must be terminated).

Note that you may also want to check the error code manually, since
     some non-fatal errors to the protocol (such as a warning alert or a
     rehandshake request) may be fatal for your program.

This function is only useful if you are dealing with errors from
     functions that relate to a TLS session (e.g., record layer or
     handshake layer handling functions).

*Returns:* Non-zero value on fatal errors or zero on non-fatal.

Although, in the TLS protocol the receive function can be called at any
time, when DTLS is used the GnuTLS receive functions must be called once
a message is available for reading, even if no data are expected.  This
is because in DTLS various (internal) actions may be required due to
retransmission timers.  Moreover, an extended receive function is shown
below, which allows the extraction of the message's sequence number.
Due to the unreliable nature of the protocol, this field allows
distinguishing out-of-order messages.

-- Function: ssize_t gnutls_record_recv_seq (gnutls_session_t SESSION,
          void * DATA, size_t DATA_SIZE, unsigned char * SEQ)
     SESSION: is a ‘gnutls_session_t’ type.

DATA: the buffer that the data will be read into

DATA_SIZE: the number of requested bytes

SEQ: is the packet's 64-bit sequence number.  Should have space for
     8 bytes.

This function is the same as ‘gnutls_record_recv()’ , except that
     it returns in addition to data, the sequence number of the data.
     This is useful in DTLS where record packets might be received
     out-of-order.  The returned 8-byte sequence number is an integer in
     big-endian format and should be treated as a unique message
     identification.

*Returns:* The number of bytes received and zero on EOF. A negative
     error code is returned in case of an error.  The number of bytes
     received might be less than ‘data_size’ .

*Since:* 3.0

The *note gnutls_record_check_pending:: helper function is available to
allow checking whether data are available to be read in a GnuTLS session
buffers.  Note that this function complements but does not replace
‘poll’, i.e., *note gnutls_record_check_pending:: reports no data to be
read, ‘poll’ should be called to check for data in the network buffers.

-- Function: size_t gnutls_record_check_pending (gnutls_session_t
          SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

This function checks if there are unread data in the gnutls
     buffers.  If the return value is non-zero the next call to
     ‘gnutls_record_recv()’ is guaranteed not to block.

*Returns:* Returns the size of the data or zero.
‘INT *note gnutls_record_get_direction:: (gnutls_session_t SESSION)’

Once a TLS or DTLS session is no longer needed, it is recommended to use
*note gnutls_bye:: to terminate the session.  That way the peer is
notified securely about the intention of termination, which allows
distinguishing it from a malicious connection termination.  A session
can be deinitialized with the *note gnutls_deinit:: function.

-- Function: int gnutls_bye (gnutls_session_t SESSION,
          gnutls_close_request_t HOW)
     SESSION: is a ‘gnutls_session_t’ type.

HOW: is an integer

Terminates the current TLS/SSL connection.  The connection should
     have been initiated using ‘gnutls_handshake()’ .  ‘how’ should be
     one of ‘GNUTLS_SHUT_RDWR’ , ‘GNUTLS_SHUT_WR’ .

In case of ‘GNUTLS_SHUT_RDWR’ the TLS session gets terminated and
     further receives and sends will be disallowed.  If the return value
     is zero you may continue using the underlying transport layer.
     ‘GNUTLS_SHUT_RDWR’ sends an alert containing a close request and
     waits for the peer to reply with the same message.

In case of ‘GNUTLS_SHUT_WR’ the TLS session gets terminated and
     further sends will be disallowed.  In order to reuse the connection
     you should wait for an EOF from the peer.  ‘GNUTLS_SHUT_WR’ sends
     an alert containing a close request.

Note that not all implementations will properly terminate a TLS
     connection.  Some of them, usually for performance reasons, will
     terminate only the underlying transport layer, and thus not
     distinguishing between a malicious party prematurely terminating
     the connection and normal termination.

This function may also return ‘GNUTLS_E_AGAIN’ or
     ‘GNUTLS_E_INTERRUPTED’ ; cf.  ‘gnutls_record_get_direction()’ .

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, or an error code, see
     function documentation for entire semantics.

-- Function: void gnutls_deinit (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

This function clears all buffers associated with the ‘session’ .
     This function will also remove session data from the session
     database if the session was terminated abnormally.

File: gnutls.info,  Node: Buffered data transfer,  Next: Handling alerts,  Prev: Data transfer and termination,  Up: How to use GnuTLS in applications

6.8 Buffered data transfer
==========================

Although *note gnutls_record_send:: is sufficient to transmit data to
the peer, when many small chunks of data are to be transmitted it is
inefficient and wastes bandwidth due to the TLS record overhead.  In
that case it is preferable to combine the small chunks before
transmission.  The following functions provide that functionality.

-- Function: void gnutls_record_cork (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

If called, ‘gnutls_record_send()’ will no longer send any records.
     Any sent records will be cached until ‘gnutls_record_uncork()’ is
     called.

This function is safe to use with DTLS after GnuTLS 3.3.0.

*Since:* 3.1.9

-- Function: int gnutls_record_uncork (gnutls_session_t SESSION,
          unsigned int FLAGS)
     SESSION: is a ‘gnutls_session_t’ type.

FLAGS: Could be zero or ‘GNUTLS_RECORD_WAIT’

This resets the effect of ‘gnutls_record_cork()’ , and flushes any
     pending data.  If the ‘GNUTLS_RECORD_WAIT’ flag is specified then
     this function will block until the data is sent or a fatal error
     occurs (i.e., the function will retry on ‘GNUTLS_E_AGAIN’ and
     ‘GNUTLS_E_INTERRUPTED’ ).

If the flag ‘GNUTLS_RECORD_WAIT’ is not specified and the function
     is interrupted then the ‘GNUTLS_E_AGAIN’ or ‘GNUTLS_E_INTERRUPTED’
     errors will be returned.  To obtain the data left in the corked
     buffer use ‘gnutls_record_check_corked()’ .

*Returns:* On success the number of transmitted data is returned,
     or otherwise a negative error code.

*Since:* 3.1.9

File: gnutls.info,  Node: Handling alerts,  Next: Priority Strings,  Prev: Buffered data transfer,  Up: How to use GnuTLS in applications

6.9 Handling alerts
===================

During a TLS connection alert messages may be exchanged by the two
peers.  Those messages may be fatal, meaning the connection must be
terminated afterwards, or warning when something needs to be reported to
the peer, but without interrupting the session.  The error codes
‘GNUTLS_E_WARNING_ALERT_RECEIVED’ or ‘GNUTLS_E_FATAL_ALERT_RECEIVED’
signal those alerts when received, and may be returned by all GnuTLS
functions that receive data from the peer, being *note
gnutls_handshake:: and *note gnutls_record_recv::.

If those error codes are received the alert and its level should be
logged or reported to the peer using the functions below.

-- Function: gnutls_alert_description_t gnutls_alert_get
          (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

This function will return the last alert number received.  This
     function should be called when ‘GNUTLS_E_WARNING_ALERT_RECEIVED’ or
     ‘GNUTLS_E_FATAL_ALERT_RECEIVED’ errors are returned by a gnutls
     function.  The peer may send alerts if he encounters an error.  If
     no alert has been received the returned value is undefined.

*Returns:* the last alert received, a ‘gnutls_alert_description_t’
     value.

-- Function: const char * gnutls_alert_get_name
          (gnutls_alert_description_t ALERT)
     ALERT: is an alert number.

This function will return a string that describes the given alert
     number, or ‘NULL’ .  See ‘gnutls_alert_get()’ .

*Returns:* string corresponding to ‘gnutls_alert_description_t’
     value.

The peer may also be warned or notified of a fatal issue by using one of
the functions below.  All the available alerts are listed in *note The
Alert Protocol::.

-- Function: int gnutls_alert_send (gnutls_session_t SESSION,
          gnutls_alert_level_t LEVEL, gnutls_alert_description_t DESC)
     SESSION: is a ‘gnutls_session_t’ type.

LEVEL: is the level of the alert

DESC: is the alert description

This function will send an alert to the peer in order to inform him
     of something important (eg.  his Certificate could not be
     verified).  If the alert level is Fatal then the peer is expected
     to close the connection, otherwise he may ignore the alert and
     continue.

The error code of the underlying record send function will be
     returned, so you may also receive ‘GNUTLS_E_INTERRUPTED’ or
     ‘GNUTLS_E_AGAIN’ as well.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise an error code is returned.

-- Function: int gnutls_error_to_alert (int ERR, int * LEVEL)
     ERR: is a negative integer

LEVEL: the alert level will be stored there

Get an alert depending on the error code returned by a gnutls
     function.  All alerts sent by this function should be considered
     fatal.  The only exception is when ‘err’ is ‘GNUTLS_E_REHANDSHAKE’
     , where a warning alert should be sent to the peer indicating that
     no renegotiation will be performed.

If there is no mapping to a valid alert the alert to indicate
     internal error (‘GNUTLS_A_INTERNAL_ERROR’ ) is returned.

*Returns:* the alert code to use for a particular error code.

File: gnutls.info,  Node: Priority Strings,  Next: Selecting cryptographic key sizes,  Prev: Handling alerts,  Up: How to use GnuTLS in applications

6.10 Priority strings
=====================

How to use Priority Strings
---------------------------

The GnuTLS priority strings specify the TLS session's handshake
algorithms and options in a compact, easy-to-use format.  These strings
are intended as a user-specified override of the library defaults.

That is, we recommend applications using the default settings (c.f.
*note gnutls_set_default_priority:: or *note
gnutls_set_default_priority_append::), and provide the user with access
to priority strings for overriding the default behavior, on
configuration files, or other UI. Following such a principle, makes the
GnuTLS library as the default settings provider.  That is necessary and
a good practice, because TLS protocol hardening and phasing out of
legacy algorithms, is easier to coordinate when happens in a single
library.

‘INT *note gnutls_set_default_priority:: (gnutls_session_t SESSION)’
‘INT *note gnutls_set_default_priority_append:: (gnutls_session_t SESSION, const char * ADD_PRIO, const char ** ERR_POS, unsigned FLAGS)’
‘INT *note gnutls_priority_set_direct:: (gnutls_session_t SESSION, const char * PRIORITIES, const char ** ERR_POS)’

The priority string translation to the internal GnuTLS form requires
processing and the generated internal form also occupies some memory.
For that, it is recommended to do that processing once in server side,
and share the generated data across sessions.  The following functions
allow the generation of a "priority cache" and the sharing of it across
sessions.

‘INT *note gnutls_priority_init2:: (gnutls_priority_t * PRIORITY_CACHE, const char * PRIORITIES, const char ** ERR_POS, unsigned FLAGS)’
‘INT *note gnutls_priority_init:: (gnutls_priority_t * PRIORITY_CACHE, const char * PRIORITIES, const char ** ERR_POS)’
‘INT *note gnutls_priority_set:: (gnutls_session_t SESSION, gnutls_priority_t PRIORITY)’
‘VOID *note gnutls_priority_deinit:: (gnutls_priority_t PRIORITY_CACHE)’

Using Priority Strings
----------------------

A priority string string may contain a single initial keyword such as in
*note Table 6.3: tab:prio-keywords. and may be followed by additional
algorithm or special keywords.  Note that their description is
intentionally avoiding specific algorithm details, as the priority
strings are not constant between gnutls versions (they are periodically
updated to account for cryptographic advances while providing
compatibility with old clients and servers).

Keyword        Description
------------------------------------------------------------------
@KEYWORD       Means that a compile-time specified system
               configuration file (see
               *note System-wide configuration of the library::)
               will be used to expand the provided keyword.
               That is used to impose system-specific policies.
               It may be followed by additional options that
               will be appended to the system string (e.g.,
               "@SYSTEM:+SRP"). The system file should have the
               format 'KEYWORD=VALUE', e.g.,
               'SYSTEM=NORMAL:+ARCFOUR-128'.
               
               Since version 3.5.1 it is allowed to specify
               fallback keywords such as @KEYWORD1,@KEYWORD2,
               and the first valid keyword will be used.
               
PERFORMANCE    All the known to be secure ciphersuites are
               enabled, limited to 128 bit ciphers and sorted
               by terms of speed performance.  The message
               authenticity security level is of 64 bits or
               more, and the certificate verification profile
               is set to GNUTLS_PROFILE_LOW (80-bits).
               
NORMAL         Means all the known to be secure ciphersuites.
               The ciphers are sorted by security margin,
               although the 256-bit ciphers are included as a
               fallback only.  The message authenticity
               security level is of 64 bits or more, and the
               certificate verification profile is set to
               GNUTLS_PROFILE_LOW (80-bits).
               
               This priority string implicitly enables ECDHE
               and DHE. The ECDHE ciphersuites are placed first
               in the priority order, but due to compatibility
               issues with the DHE ciphersuites they are placed
               last in the priority order, after the plain RSA
               ciphersuites.
               
LEGACY         This sets the NORMAL settings that were used for
               GnuTLS 3.2.x or earlier.  There is no
               verification profile set, and the allowed DH
               primes are considered weak today (but are often
               used by misconfigured servers).
               
PFS            Means all the known to be secure ciphersuites
               that support perfect forward secrecy (ECDHE and
               DHE). The ciphers are sorted by security margin,
               although the 256-bit ciphers are included as a
               fallback only.  The message authenticity
               security level is of 80 bits or more, and the
               certificate verification profile is set to
               GNUTLS_PROFILE_LOW (80-bits).  This option is
               available since 3.2.4 or later.
               
SECURE128      Means all known to be secure ciphersuites that
               offer a security level 128-bit or more.  The
               message authenticity security level is of 80
               bits or more, and the certificate verification
               profile is set to GNUTLS_PROFILE_LOW (80-bits).
               
SECURE192      Means all the known to be secure ciphersuites
               that offer a security level 192-bit or more.
               The message authenticity security level is of
               128 bits or more, and the certificate
               verification profile is set to
               GNUTLS_PROFILE_HIGH (128-bits).
               
SECURE256      Currently alias for SECURE192.  This option,
               will enable ciphers which use a 256-bit key but,
               due to limitations of the TLS protocol, the
               overall security level will be 192-bits (the
               security level depends on more factors than
               cipher key size).
               
SUITEB128      Means all the NSA Suite B cryptography (RFC5430)
               ciphersuites with an 128 bit security level, as
               well as the enabling of the corresponding
               verification profile.
               
SUITEB192      Means all the NSA Suite B cryptography (RFC5430)
               ciphersuites with an 192 bit security level, as
               well as the enabling of the corresponding
               verification profile.
               
NONE           Means nothing is enabled.  This disables even
               protocol versions.  It should be followed by the
               algorithms to be enabled.  Note that using this
               option to build a priority string gives detailed
               control into the resulting settings, however
               with new revisions of the TLS protocol new
               priority items are routinely added, and such
               strings are not forward compatible with new
               protocols.  As such, we advice against using
               that option for applications targeting multiple
               versions of the GnuTLS library, and recommend
               using the defaults (see above) or adjusting the
               defaults via
               *note gnutls_set_default_priority_append::.

Table 6.3: Supported initial keywords.

Unless the initial keyword is "NONE" the defaults (in preference order)
are for TLS protocols TLS 1.2, TLS1.1, TLS1.0; for certificate types
X.509.  In key exchange algorithms when in NORMAL or SECURE levels the
perfect forward secrecy algorithms take precedence of the other
protocols.  In all cases all the supported key exchange algorithms are
enabled.

Note that the SECURE levels distinguish between overall security level
and message authenticity security level.  That is because the message
authenticity security level requires the adversary to break the
algorithms at real-time during the protocol run, whilst the overall
security level refers to off-line adversaries (e.g.  adversaries
breaking the ciphertext years after it was captured).

The NONE keyword, if used, must followed by keywords specifying the
algorithms and protocols to be enabled.  The other initial keywords do
not require, but may be followed by such keywords.  All level keywords
can be combined, and for example a level of "SECURE256:+SECURE128" is
allowed.

The order with which every algorithm or protocol is specified is
significant.  Algorithms specified before others will take precedence.
The supported in the GnuTLS version corresponding to this document
algorithms and protocols are shown in *note Table 6.4:
tab:prio-algorithms.; to list the supported algorithms in your currently
using version use ‘gnutls-cli -l’.

To avoid collisions in order to specify a protocol version with "VERS-",
signature algorithms with "SIGN-" and certificate types with "CTYPE-".
All other algorithms don't need a prefix.  Each specified keyword
(except for _special keywords_) can be prefixed with any of the
following characters.

'!' or '-'
     appended with an algorithm will remove this algorithm.
"+"
     appended with an algorithm will add this algorithm.

Type           Keywords
------------------------------------------------------------------
Ciphers        Examples are AES-128-GCM, AES-256-GCM,
               AES-256-CBC, GOST28147-TC26Z-CNT; see also
               *note Table 3.1: tab:ciphers. for more options.
               Catch all name is CIPHER-ALL which will add all
               the algorithms from NORMAL priority.  The
               shortcut for secure GOST algorithms is
               CIPHER-GOST-ALL.
               
Key exchange   RSA, RSA-PSK, RSA-EXPORT, DHE-RSA, DHE-DSS, SRP,
               SRP-RSA, SRP-DSS, PSK, DHE-PSK, ECDHE-PSK,
               ECDHE-RSA, ECDHE-ECDSA, VKO-GOST-12, ANON-ECDH,
               ANON-DH. Catch all name is KX-ALL which will add
               all the algorithms from NORMAL priority.  Under
               TLS1.3, the DHE-PSK and ECDHE-PSK strings are
               equivalent and instruct for a Diffie-Hellman key
               exchange using the enabled groups.  The shortcut
               for secure GOST algorithms is KX-GOST-ALL.
               
MAC            MD5, SHA1, SHA256, SHA384, GOST28147-TC26Z-IMIT,
               AEAD (used with GCM ciphers only).  All
               algorithms from NORMAL priority can be accessed
               with MAC-ALL. The shortcut for secure GOST
               algorithms is MAC-GOST-ALL.
               
Compression    COMP-NULL, COMP-DEFLATE. Catch all is COMP-ALL.
algorithms     
TLS versions   VERS-TLS1.0, VERS-TLS1.1, VERS-TLS1.2,
               VERS-TLS1.3, VERS-DTLS0.9, VERS-DTLS1.0,
               VERS-DTLS1.2.  Catch all are VERS-ALL, and will
               enable all protocols from NORMAL priority.  To
               distinguish between TLS and DTLS versions you
               can use VERS-TLS-ALL and VERS-DTLS-ALL.
               
Signature      SIGN-RSA-SHA1, SIGN-RSA-SHA224, SIGN-RSA-SHA256,
algorithms     SIGN-RSA-SHA384, SIGN-RSA-SHA512, SIGN-DSA-SHA1,
               SIGN-DSA-SHA224, SIGN-DSA-SHA256, SIGN-RSA-MD5,
               SIGN-ECDSA-SHA1, SIGN-ECDSA-SHA224,
               SIGN-ECDSA-SHA256, SIGN-ECDSA-SHA384,
               SIGN-ECDSA-SHA512, SIGN-EdDSA-Ed25519,
               SIGN-EdDSA-Ed448, SIGN-RSA-PSS-SHA256,
               SIGN-RSA-PSS-SHA384, SIGN-RSA-PSS-SHA512,
               SIGN-GOSTR341001, SIGN-GOSTR341012-256,
               SIGN-GOSTR341012-512.  Catch all which enables
               all algorithms from NORMAL priority is SIGN-ALL.
               Shortcut which enables secure GOST algorithms is
               SIGN-GOST-ALL. This option is only considered
               for TLS 1.2 and later.
               
Groups         GROUP-SECP192R1, GROUP-SECP224R1,
               GROUP-SECP256R1, GROUP-SECP384R1,
               GROUP-SECP521R1, GROUP-X25519, GROUP-X448,
               GROUP-GC256B, GROUP-GC512A, GROUP-FFDHE2048,
               GROUP-FFDHE3072, GROUP-FFDHE4096,
               GROUP-FFDHE6144, and GROUP-FFDHE8192.  Groups
               include both elliptic curve groups, e.g.,
               SECP256R1, as well as finite field groups such
               as FFDHE2048.  Catch all which enables all
               groups from NORMAL priority is GROUP-ALL. The
               helper keywords GROUP-DH-ALL, GROUP-GOST-ALL and
               GROUP-EC-ALL are also available, restricting the
               groups to finite fields (DH), GOST curves and
               generic elliptic curves.
               
Elliptic       CURVE-SECP192R1, CURVE-SECP224R1,
curves         CURVE-SECP256R1, CURVE-SECP384R1,
(legacy)       CURVE-SECP521R1, CURVE-X25519, and CURVE-X448.
               Catch all which enables all curves from NORMAL
               priority is CURVE-ALL. Note that the CURVE
               keyword is kept for backwards compatibility
               only, for new applications see the GROUP keyword
               above.
               
Certificate    Certificate types can be given in a symmetric
types          fashion (i.e.  the same for both client and
               server) or, as of GnuTLS 3.6.4, in an asymmetric
               fashion (i.e.  different for the client than for
               the server).  Alternative certificate types must
               be explicitly enabled via flags in
               *note gnutls_init::.
               
               The currently supported types are CTYPE-X509,
               CTYPE-RAWPK which apply both to client and
               server; catch all is CTYPE-ALL. The types
               CTYPE-CLI-X509, CTYPE-SRV-X509, CTYPE-CLI-RAWPK,
               CTYPE-SRV-RAWPK can be used to specialize on
               client or server; catch all is CTYPE-CLI-ALL and
               CTYPE-SRV-ALL. The type 'X509' is aliased to
               'X.509' for legacy reasons.
               
Generic        The keyword GOST is a shortcut for secure GOST
               algorithms (MACs, ciphers, KXes, groups and
               signatures).  For example the following string
               will enable all TLS 1.2 GOST ciphersuites:
               'NONE:+VERS-TLS1.2:+GOST'.

Table 6.4: The supported algorithm keywords in priority strings.

Note that the finite field groups (indicated by the FFDHE prefix) and
DHE key exchange methods are generally slower(1) than their elliptic
curves counterpart (ECDHE).

The available special keywords are shown in *note Table 6.5:
tab:prio-special1. and *note Table 6.6: tab:prio-special2.

Keyword                          Description
                                 
------------------------------------------------------------------
%COMPAT                          will enable compatibility
                                 mode.  It might mean that
                                 violations of the protocols
                                 are allowed as long as maximum
                                 compatibility with problematic
                                 clients and servers is
                                 achieved.  More specifically
                                 this string will tolerate
                                 packets over the maximum
                                 allowed TLS record, and add a
                                 padding to TLS Client Hello
                                 packet to prevent it being in
                                 the 256-512 range which is
                                 known to be causing issues
                                 with a commonly used firewall
                                 (see the %DUMBFW option).
                                 
%DUMBFW                          will add a private extension
                                 with bogus data that make the
                                 client hello exceed 512 bytes.
                                 This avoids a black hole
                                 behavior in some firewalls.
                                 This is the [*note RFC7685::]
                                 client hello padding
                                 extension, also enabled with
                                 %COMPAT.
                                 
%NO_EXTENSIONS                   will prevent the sending of
                                 any TLS extensions in client
                                 side.  Note that TLS 1.2
                                 requires extensions to be
                                 used, as well as safe
                                 renegotiation thus this option
                                 must be used with care.  When
                                 this option is set no versions
                                 later than TLS1.2 can be
                                 negotiated.
                                 
%NO_SHUFFLE_EXTENSIONS           will prevent randomizing the
                                 order of ClientHello
                                 extensions.  By default, those
                                 extensions are randomized to
                                 make fingerprinting harder.
                                 
%NO_STATUS_REQUEST               will prevent sending of the
                                 TLS status_request extension
                                 in client side.
                                 
%NO_TICKETS                      will prevent the advertizing
                                 of the TLS session ticket
                                 extension.
                                 
%NO_TICKETS_TLS12                will prevent the advertizing
                                 of the TLS session ticket
                                 extension in TLS 1.2.  This is
                                 implied by the PFS keyword.
                                 
%NO_SESSION_HASH                 will prevent the advertizing
                                 the TLS extended master secret
                                 (session hash) extension.
                                 
%FORCE_SESSION_HASH              negotiate the TLS extended
                                 master secret (session hash)
                                 extension.  Specifying both
                                 %NO_SESSION_HASH and
                                 %FORCE_SESSION_HASH is not
                                 supported, and the behavior is
                                 undefined.
                                 
%SERVER_PRECEDENCE               The ciphersuite will be
                                 selected according to server
                                 priorities and not the
                                 client's.
                                 
%SSL3_RECORD_VERSION             will use SSL3.0 record version
                                 in client hello.  By default
                                 GnuTLS will set the minimum
                                 supported version as the
                                 client hello record version
                                 (do not confuse that version
                                 with the proposed handshake
                                 version at the client hello).
                                 
%LATEST_RECORD_VERSION           will use the latest TLS
                                 version record version in
                                 client hello.

Table 6.5: Special priority string keywords.

Keyword                          Description
                                 
------------------------------------------------------------------
%STATELESS_COMPRESSION           ignored; no longer used.
                                 
%DISABLE_WILDCARDS               will disable matching
                                 wildcards when comparing
                                 hostnames in certificates.
                                 
%NO_ETM                          will disable the
                                 encrypt-then-mac TLS extension
                                 (RFC7366).  This is implied by
                                 the %COMPAT keyword.
                                 
%FORCE_ETM                       negotiate CBC ciphersuites
                                 only when both sides of the
                                 connection support
                                 encrypt-then-mac TLS extension
                                 (RFC7366).
                                 
%DISABLE_SAFE_RENEGOTIATION      will completely disable safe
                                 renegotiation.  Do not use
                                 unless you know what you are
                                 doing.
                                 
%UNSAFE_RENEGOTIATION            will allow handshakes and
                                 re-handshakes without the safe
                                 renegotiation extension.  Note
                                 that for clients this mode is
                                 insecure (you may be under
                                 attack), and for servers it
                                 will allow insecure clients to
                                 connect (which could be fooled
                                 by an attacker).  Do not use
                                 unless you know what you are
                                 doing and want maximum
                                 compatibility.
                                 
%PARTIAL_RENEGOTIATION           will allow initial handshakes
                                 to proceed, but not
                                 re-handshakes.  This leaves
                                 the client vulnerable to
                                 attack, and servers will be
                                 compatible with non-upgraded
                                 clients for initial
                                 handshakes.  This is currently
                                 the default for clients and
                                 servers, for compatibility
                                 reasons.
                                 
%SAFE_RENEGOTIATION              will enforce safe
                                 renegotiation.  Clients and
                                 servers will refuse to talk to
                                 an insecure peer.  Currently
                                 this causes interoperability
                                 problems, but is required for
                                 full protection.
                                 
%FALLBACK_SCSV                   will enable the use of the
                                 fallback signaling cipher
                                 suite value in the client
                                 hello.  Note that this should
                                 be set only by applications
                                 that try to reconnect with a
                                 downgraded protocol version.
                                 See RFC7507 for details.
                                 
%DISABLE_TLS13_COMPAT_MODE       will disable TLS 1.3 middlebox
                                 compatibility mode (RFC8446,
                                 Appendix D.4) for
                                 non-compliant middleboxes.
                                 
%VERIFY_ALLOW_BROKEN             will allow signatures with
                                 known to be broken algorithms
                                 (such as MD5 or SHA1) in
                                 certificate chains.
                                 
%VERIFY_ALLOW_SIGN_RSA_MD5       will allow RSA-MD5 signatures
                                 in certificate chains.
                                 
%VERIFY_ALLOW_SIGN_WITH_SHA1     will allow signatures with
                                 SHA1 hash algorithm in
                                 certificate chains.
                                 
%VERIFY_DISABLE_CRL_CHECKS       will disable CRL or OCSP
                                 checks in the verification of
                                 the certificate chain.
                                 
%VERIFY_ALLOW_X509_V1_CA_CRT     will allow V1 CAs in chains.
                                 
%PROFILE_(LOW|LEGACY|MEDIUM|HIGH|ULTRA|FUTURE)require a certificate
                                 verification profile the
                                 corresponds to the specified
                                 security level, see
                                 *note Table 6.7: tab:key-sizes.
                                 for the mappings to values.
                                 
%PROFILE_(SUITEB128|SUITEB192)   require a certificate
                                 verification profile the
                                 corresponds to SUITEB. Note
                                 that an initial keyword that
                                 enables SUITEB automatically
                                 sets the profile.

Table 6.6: More priority string keywords.

Finally the ciphersuites enabled by any priority string can be listed
using the ‘gnutls-cli’ application (see *note gnutls-cli Invocation::),
or by using the priority functions as in *note Listing the ciphersuites
in a priority string::.

Example priority strings are:
     The system imposed security level:
         "SYSTEM"

The default priority without the HMAC-MD5:
         "NORMAL:-MD5"

Specifying RSA with AES-128-CBC:
         "NONE:+VERS-TLS-ALL:+MAC-ALL:+RSA:+AES-128-CBC:+SIGN-ALL:+COMP-NULL"

Specifying the defaults plus ARCFOUR-128:
         "NORMAL:+ARCFOUR-128"

Enabling the 128-bit secure ciphers, while disabling TLS 1.0:
         "SECURE128:-VERS-TLS1.0"

Enabling the 128-bit and 192-bit secure ciphers, while disabling all TLS versions
     except TLS 1.2:
         "SECURE128:+SECURE192:-VERS-ALL:+VERS-TLS1.2"

---------- Footnotes ----------

(1) It depends on the group in use.  Groups with less bits are always
faster, but the number of bits ties with the security parameter.  See
*note Selecting cryptographic key sizes:: for the acceptable security
levels.

File: gnutls.info,  Node: Selecting cryptographic key sizes,  Next: Advanced topics,  Prev: Priority Strings,  Up: How to use GnuTLS in applications

6.11 Selecting cryptographic key sizes
======================================

Because many algorithms are involved in TLS, it is not easy to set a
consistent security level.  For this reason in *note Table 6.7:
tab:key-sizes. we present some correspondence between key sizes of
symmetric algorithms and public key algorithms based on [*note
ECRYPT::].  Those can be used to generate certificates with appropriate
key sizes as well as select parameters for Diffie-Hellman and SRP
authentication.

SecurityRSA, DH   ECC     Security       Description
bits    and SRP   key     parameter      
        parameter size    (profile)
        size
-----------------------------------------------------------------
<64     <768      <128    ‘INSECURE’     Considered to be
                                         insecure
                                         
64      768       128     ‘VERY WEAK’    Short term protection
                                         against individuals
                                         
72      1008      160     ‘WEAK’         Short term protection
                                         against small
                                         organizations
                                         
80      1024      160     ‘LOW’          Very short term
                                         protection against
                                         agencies (corresponds
                                         to ENISA legacy
                                         level)
                                         
96      1776      192     ‘LEGACY’       Legacy standard level
                                         
112     2048      224     ‘MEDIUM’       Medium-term
                                         protection
                                         
128     3072      256     ‘HIGH’         Long term protection
                                         (corresponds to ENISA
                                         future level)
                                         
192     8192      384     ‘ULTRA’        Even longer term
                                         protection
                                         
256     15424     512     ‘FUTURE’       Foreseeable future

Table 6.7: Key sizes and security parameters.

The first column provides a security parameter in a number of bits.
This gives an indication of the number of combinations to be tried by an
adversary to brute force a key.  For example to test all possible keys
in a 112 bit security parameter 2^{112} combinations have to be tried.
For today's technology this is infeasible.  The next two columns
correlate the security parameter with actual bit sizes of parameters for
DH, RSA, SRP and ECC algorithms.  A mapping to ‘gnutls_sec_param_t’
value is given for each security parameter, on the next column, and
finally a brief description of the level.

Note, however, that the values suggested here are nothing more than an
educated guess that is valid today.  There are no guarantees that an
algorithm will remain unbreakable or that these values will remain
constant in time.  There could be scientific breakthroughs that cannot
be predicted or total failure of the current public key systems by
quantum computers.  On the other hand though the cryptosystems used in
TLS are selected in a conservative way and such catastrophic
breakthroughs or failures are believed to be unlikely.  The NIST
publication SP 800-57 [*note NISTSP80057::] contains a similar table.

When using GnuTLS and a decision on bit sizes for a public key algorithm
is required, use of the following functions is recommended:

-- Function: unsigned int gnutls_sec_param_to_pk_bits
          (gnutls_pk_algorithm_t ALGO, gnutls_sec_param_t PARAM)
     ALGO: is a public key algorithm

PARAM: is a security parameter

When generating private and public key pairs a difficult question
     is which size of "bits" the modulus will be in RSA and the group
     size in DSA. The easy answer is 1024, which is also wrong.  This
     function will convert a human understandable security parameter to
     an appropriate size for the specific algorithm.

*Returns:* The number of bits, or (0).

*Since:* 2.12.0

-- Function: gnutls_sec_param_t gnutls_pk_bits_to_sec_param
          (gnutls_pk_algorithm_t ALGO, unsigned int BITS)
     ALGO: is a public key algorithm

BITS: is the number of bits

This is the inverse of ‘gnutls_sec_param_to_pk_bits()’ .  Given an
     algorithm and the number of bits, it will return the security
     parameter.  This is a rough indication.

*Returns:* The security parameter.

*Since:* 2.12.0

Those functions will convert a human understandable security parameter
of ‘gnutls_sec_param_t’ type, to a number of bits suitable for a public
key algorithm.

‘CONST CHAR * *note gnutls_sec_param_get_name:: (gnutls_sec_param_t PARAM)’

The following functions will set the minimum acceptable group size for
Diffie-Hellman and SRP authentication.
‘VOID *note gnutls_dh_set_prime_bits:: (gnutls_session_t SESSION, unsigned int BITS)’
‘VOID *note gnutls_srp_set_prime_bits:: (gnutls_session_t SESSION, unsigned int BITS)’

File: gnutls.info,  Node: Advanced topics,  Prev: Selecting cryptographic key sizes,  Up: How to use GnuTLS in applications

6.12 Advanced topics
====================

* Menu:

* Virtual hosts and credentials::
* Session resumption::
* Certificate verification::
* TLS 1.2 re-authentication::
* TLS 1.3 re-authentication and re-key::
* Parameter generation::
* Deriving keys for other applications/protocols::
* Channel Bindings::
* Interoperability::
* Compatibility with the OpenSSL library::

File: gnutls.info,  Node: Virtual hosts and credentials,  Next: Session resumption,  Up: Advanced topics

6.12.1 Virtual hosts and credentials
------------------------------------

Often when operating with virtual hosts, one may not want to associate a
particular certificate set to the credentials function early, before the
virtual host is known.  That can be achieved by calling *note
gnutls_credentials_set:: within a handshake pre-hook for client hello.
That message contains the peer's intended hostname, and if read, and the
appropriate credentials are set, gnutls will be able to continue in the
handshake process.  A brief usage example is shown below.

static int ext_hook_func(void *ctx, unsigned tls_id,
                              const unsigned char *data, unsigned size)
     {
     	if (tls_id == 0) { /* server name */
     		/* figure the advertised name - the following hack
                      * relies on the fact that this extension only supports
                      * DNS names, and due to a protocol bug cannot be extended
                      * to support anything else. */
     		if (name < 5) return 0;
     		name = data+5;
     		name_size = size-5;
     	}
     	return 0;
     }

static int
     handshake_hook_func(gnutls_session_t session, unsigned int htype,
                         unsigned when, unsigned int incoming, const gnutls_datum_t *msg)
     {
         int ret;

assert(htype == GNUTLS_HANDSHAKE_CLIENT_HELLO);
         assert(when == GNUTLS_HOOK_PRE);

ret = gnutls_ext_raw_parse(NULL, ext_hook_func, msg,
                                    GNUTLS_EXT_RAW_FLAG_TLS_CLIENT_HELLO);
         assert(ret >= 0);

gnutls_credentials_set(session, GNUTLS_CRD_CERTIFICATE, cred);

return ret;
     }

int main(void)
     {
       ...

gnutls_handshake_set_hook_function(server, GNUTLS_HANDSHAKE_CLIENT_HELLO,
                                          GNUTLS_HOOK_PRE, handshake_hook_func);
       ...
     }

-- Function: void gnutls_handshake_set_hook_function (gnutls_session_t
          SESSION, unsigned int HTYPE, int WHEN,
          gnutls_handshake_hook_func FUNC)
     SESSION: is a ‘gnutls_session_t’ type

HTYPE: the ‘gnutls_handshake_description_t’ of the message to hook
     at

WHEN: ‘GNUTLS_HOOK_’ * depending on when the hook function should
     be called

FUNC: is the function to be called

This function will set a callback to be called after or before the
     specified handshake message has been received or generated.  This
     is a generalization of
     ‘gnutls_handshake_set_post_client_hello_function()’ .

To call the hook function prior to the message being generated or
     processed use ‘GNUTLS_HOOK_PRE’ as ‘when’ parameter,
     ‘GNUTLS_HOOK_POST’ to call after, and ‘GNUTLS_HOOK_BOTH’ for both
     cases.

This callback must return 0 on success or a gnutls error code to
     terminate the handshake.

To hook at all handshake messages use an ‘htype’ of
     ‘GNUTLS_HANDSHAKE_ANY’ .

*Warning:* You should not use this function to terminate the
     handshake based on client input unless you know what you are doing.
     Before the handshake is finished there is no way to know if there
     is a man-in-the-middle attack being performed.

File: gnutls.info,  Node: Session resumption,  Next: Certificate verification,  Prev: Virtual hosts and credentials,  Up: Advanced topics

6.12.2 Session resumption
-------------------------

To reduce time and network traffic spent in a handshake the client can
request session resumption from a server that previously shared a
session with the client.

Under TLS 1.2, in order to support resumption a server can either store
the session security parameters in a local database or use session
tickets (see *note Session tickets::) to delegate storage to the client.

Under TLS 1.3, session resumption is only available through session
tickets, and multiple tickets could be sent from server to client.  That
provides the following advantages:
   • When tickets are not re-used the subsequent client sessions cannot
     be associated with each other by an eavesdropper
   • On post-handshake authentication the server may send different
     tickets asynchronously for each identity used by client.

Client side
...........

The client has to retrieve and store the session parameters.  Before
establishing a new session to the same server the parameters must be
re-associated with the GnuTLS session using *note
gnutls_session_set_data::.

‘INT *note gnutls_session_get_data2:: (gnutls_session_t SESSION, gnutls_datum_t * DATA)’
‘INT *note gnutls_session_set_data:: (gnutls_session_t SESSION, const void * SESSION_DATA, size_t SESSION_DATA_SIZE)’

Keep in mind that sessions will be expired after some time, depending on
the server, and a server may choose not to resume a session even when
requested to.  The expiration is to prevent temporal session keys from
becoming long-term keys.  Also note that as a client you must enable,
using the priority functions, at least the algorithms used in the last
session.

-- Function: int gnutls_session_is_resumed (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Checks whether session is resumed or not.  This is functional for
     both server and client side.

*Returns:* non zero if this session is resumed, or a zero if this
     is a new session.

-- Function: int gnutls_session_get_id2 (gnutls_session_t SESSION,
          gnutls_datum_t * SESSION_ID)
     SESSION: is a ‘gnutls_session_t’ type.

SESSION_ID: will point to the session ID.

Returns the TLS session identifier.  The session ID is selected by
     the server, and in older versions of TLS was a unique identifier
     shared between client and server which was persistent across
     resumption.  In the latest version of TLS (1.3) or TLS 1.2 with
     session tickets, the notion of session identifiers is undefined and
     cannot be relied for uniquely identifying sessions across client
     and server.

In client side this function returns the identifier returned by the
     server, and cannot be assumed to have any relation to session
     resumption.  In server side this function is guaranteed to return a
     persistent identifier of the session since GnuTLS 3.6.4, which may
     not necessarily map into the TLS session ID value.  Prior to that
     version the value could only be considered a persistent identifier,
     under TLS1.2 or earlier and when no session tickets were in use.

The session identifier value returned is always less than
     ‘GNUTLS_MAX_SESSION_ID_SIZE’ and should be treated as constant.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise an error code is returned.

*Since:* 3.1.4

Server side
...........

A server enabling both session tickets and a storage for session data
would use session tickets when clients support it and the storage
otherwise.

A storing server needs to specify callback functions to store, retrieve
and delete session data.  These can be registered with the functions
below.  The stored sessions in the database can be checked using *note
gnutls_db_check_entry:: for expiration.

‘VOID *note gnutls_db_set_retrieve_function:: (gnutls_session_t SESSION, gnutls_db_retr_func RETR_FUNC)’
‘VOID *note gnutls_db_set_store_function:: (gnutls_session_t SESSION, gnutls_db_store_func STORE_FUNC)’
‘VOID *note gnutls_db_set_ptr:: (gnutls_session_t SESSION, void * PTR)’
‘VOID *note gnutls_db_set_remove_function:: (gnutls_session_t SESSION, gnutls_db_remove_func REM_FUNC)’
‘INT *note gnutls_db_check_entry:: (gnutls_session_t SESSION, gnutls_datum_t SESSION_ENTRY)’

A server supporting session tickets must generate ticket encryption and
authentication keys using *note gnutls_session_ticket_key_generate::.
Those keys should be associated with the GnuTLS session using *note
gnutls_session_ticket_enable_server::.

Those will be the initial keys, but GnuTLS will rotate them regularly.
The key rotation interval can be changed with *note
gnutls_db_set_cache_expiration:: and will be set to three times the
ticket expiration time (ie.  three times the value given in that
function).  Every such interval, new keys will be generated from those
initial keys.  This is a necessary mechanism to prevent the keys from
becoming long-term keys and as such preserve forward-secrecy in the
issued session tickets.  If no explicit key rotation interval is
provided, GnuTLS will rotate them every 18 hours by default.

The master key can be shared between processes or between systems.
Processes which share the same master key will generate the same rotated
subkeys, assuming they share the same time (irrespective of timezone
differences).

-- Function: int gnutls_session_ticket_enable_server (gnutls_session_t
          SESSION, const gnutls_datum_t * KEY)
     SESSION: is a ‘gnutls_session_t’ type.

KEY: key to encrypt session parameters.

Request that the server should attempt session resumption using
     session tickets, i.e., by delegating storage to the client.  ‘key’
     must be initialized using ‘gnutls_session_ticket_key_generate()’ .
     To avoid leaking that key, use ‘gnutls_memset()’ prior to releasing
     it.

The default ticket expiration time can be overridden using
     ‘gnutls_db_set_cache_expiration()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned, or an
     error code.

*Since:* 2.10.0

-- Function: int gnutls_session_ticket_key_generate (gnutls_datum_t *
          KEY)
     KEY: is a pointer to a ‘gnutls_datum_t’ which will contain a newly
     created key.

Generate a random key to encrypt security parameters within
     SessionTicket.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned, or an
     error code.

*Since:* 2.10.0

-- Function: int gnutls_session_resumption_requested (gnutls_session_t
          SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Check whether the client has asked for session resumption.  This
     function is valid only on server side.

*Returns:* non zero if session resumption was asked, or a zero if
     not.

The expiration time for session resumption, either in tickets or stored
data is set using *note gnutls_db_set_cache_expiration::.  This function
also controls the ticket key rotation period.  Currently, the session
key rotation interval is set to 3 times the expiration time set by this
function.

Under TLS 1.3, the server sends by default 2 tickets, and can send
additional session tickets at any time using *note
gnutls_session_ticket_send::.

-- Function: int gnutls_session_ticket_send (gnutls_session_t SESSION,
          unsigned NR, unsigned FLAGS)
     SESSION: is a ‘gnutls_session_t’ type.

NR: the number of tickets to send

FLAGS: must be zero

Sends a fresh session ticket to the peer.  This is relevant only in
     server side under TLS1.3.  This function may also return
     ‘GNUTLS_E_AGAIN’ or ‘GNUTLS_E_INTERRUPTED’ and in that case it must
     be called again.

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, or a negative error code.

File: gnutls.info,  Node: Certificate verification,  Next: TLS 1.2 re-authentication,  Prev: Session resumption,  Up: Advanced topics

6.12.3 Certificate verification
-------------------------------

In this section the functionality for additional certificate
verification methods is listed.  These methods are intended to be used
in addition to normal PKI verification, in order to reduce the risk of a
compromised CA being undetected.

6.12.3.1 Trust on first use
...........................

The GnuTLS library includes functionality to use an SSH-like trust on
first use authentication.  The available functions to store and verify
public keys are listed below.

-- Function: int gnutls_verify_stored_pubkey (const char * DB_NAME,
          gnutls_tdb_t TDB, const char * HOST, const char * SERVICE,
          gnutls_certificate_type_t CERT_TYPE, const gnutls_datum_t *
          CERT, unsigned int FLAGS)
     DB_NAME: A file specifying the stored keys (use NULL for the
     default)

TDB: A storage structure or NULL to use the default

HOST: The peer's name

SERVICE: non-NULL if this key is specific to a service (e.g.  http)

CERT_TYPE: The type of the certificate

CERT: The raw (der) data of the certificate

FLAGS: should be 0.

This function will try to verify a raw public-key or a public-key
     provided via a raw (DER-encoded) certificate using a list of stored
     public keys.  The ‘service’ field if non-NULL should be a port
     number.

The ‘db_name’ variable if non-null specifies a custom backend for
     the retrieval of entries.  If it is NULL then the default file
     backend will be used.  In POSIX-like systems the file backend uses
     the $HOME/.gnutls/known_hosts file.

Note that if the custom storage backend is provided the retrieval
     function should return ‘GNUTLS_E_CERTIFICATE_KEY_MISMATCH’ if the
     host/service pair is found but key doesn't match,
     ‘GNUTLS_E_NO_CERTIFICATE_FOUND’ if no such host/service with the
     given key is found, and 0 if it was found.  The storage function
     should return 0 on success.

As of GnuTLS 3.6.6 this function also verifies raw public keys.

*Returns:* If no associated public key is found then
     ‘GNUTLS_E_NO_CERTIFICATE_FOUND’ will be returned.  If a key is
     found but does not match ‘GNUTLS_E_CERTIFICATE_KEY_MISMATCH’ is
     returned.  On success, ‘GNUTLS_E_SUCCESS’ (0) is returned, or a
     negative error value on other errors.

*Since:* 3.0.13

-- Function: int gnutls_store_pubkey (const char * DB_NAME,
          gnutls_tdb_t TDB, const char * HOST, const char * SERVICE,
          gnutls_certificate_type_t CERT_TYPE, const gnutls_datum_t *
          CERT, time_t EXPIRATION, unsigned int FLAGS)
     DB_NAME: A file specifying the stored keys (use NULL for the
     default)

TDB: A storage structure or NULL to use the default

HOST: The peer's name

SERVICE: non-NULL if this key is specific to a service (e.g.  http)

CERT_TYPE: The type of the certificate

CERT: The data of the certificate

EXPIRATION: The expiration time (use 0 to disable expiration)

FLAGS: should be 0.

This function will store a raw public-key or a public-key provided
     via a raw (DER-encoded) certificate to the list of stored public
     keys.  The key will be considered valid until the provided
     expiration time.

The ‘tdb’ variable if non-null specifies a custom backend for the
     storage of entries.  If it is NULL then the default file backend
     will be used.

Unless an alternative ‘tdb’ is provided, the storage format is a
     textual format consisting of a line for each host with fields
     separated by '|'.  The contents of the fields are a
     format-identifier which is set to 'g0', the hostname that the rest
     of the data applies to, the numeric port or host name, the
     expiration time in seconds since the epoch (0 for no expiration),
     and a base64 encoding of the raw (DER) public key information
     (SPKI) of the peer.

As of GnuTLS 3.6.6 this function also accepts raw public keys.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.0.13

In addition to the above the *note gnutls_store_commitment:: can be used
to implement a key-pinning architecture as in [*note KEYPIN::].  This
provides a way for web server to commit on a public key that is not yet
active.

-- Function: int gnutls_store_commitment (const char * DB_NAME,
          gnutls_tdb_t TDB, const char * HOST, const char * SERVICE,
          gnutls_digest_algorithm_t HASH_ALGO, const gnutls_datum_t *
          HASH, time_t EXPIRATION, unsigned int FLAGS)
     DB_NAME: A file specifying the stored keys (use NULL for the
     default)

TDB: A storage structure or NULL to use the default

HOST: The peer's name

SERVICE: non-NULL if this key is specific to a service (e.g.  http)

HASH_ALGO: The hash algorithm type

HASH: The raw hash

EXPIRATION: The expiration time (use 0 to disable expiration)

FLAGS: should be 0 or ‘GNUTLS_SCOMMIT_FLAG_ALLOW_BROKEN’ .

This function will store the provided hash commitment to the list
     of stored public keys.  The key with the given hash will be
     considered valid until the provided expiration time.

The ‘tdb’ variable if non-null specifies a custom backend for the
     storage of entries.  If it is NULL then the default file backend
     will be used.

Note that this function is not thread safe with the default
     backend.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.0

The storage and verification functions may be used with the default text
file based back-end, or another back-end may be specified.  That should
contain storage and retrieval functions and specified as below.

‘INT *note gnutls_tdb_init:: (gnutls_tdb_t * TDB)’
‘VOID *note gnutls_tdb_deinit:: (gnutls_tdb_t TDB)’
‘VOID *note gnutls_tdb_set_verify_func:: (gnutls_tdb_t TDB, gnutls_tdb_verify_func VERIFY)’
‘VOID *note gnutls_tdb_set_store_func:: (gnutls_tdb_t TDB, gnutls_tdb_store_func STORE)’
‘VOID *note gnutls_tdb_set_store_commitment_func:: (gnutls_tdb_t TDB, gnutls_tdb_store_commitment_func CSTORE)’

6.12.3.2 DANE verification
..........................

Since the DANE library is not included in GnuTLS it requires programs to
be linked against it.  This can be achieved with the following commands.

gcc -o foo foo.c `pkg-config gnutls-dane --cflags --libs`

When a program uses the GNU autoconf system, then the following line or
similar can be used to detect the presence of the library.

PKG_CHECK_MODULES([LIBDANE], [gnutls-dane >= 3.0.0])

AC_SUBST([LIBDANE_CFLAGS])
     AC_SUBST([LIBDANE_LIBS])

The high level functionality provided by the DANE library is shown
below.

-- Function: int dane_verify_crt (dane_state_t S, const gnutls_datum_t
          * CHAIN, unsigned CHAIN_SIZE, gnutls_certificate_type_t
          CHAIN_TYPE, const char * HOSTNAME, const char * PROTO,
          unsigned int PORT, unsigned int SFLAGS, unsigned int VFLAGS,
          unsigned int * VERIFY)
     S: A DANE state structure (may be NULL)

CHAIN: A certificate chain

CHAIN_SIZE: The size of the chain

CHAIN_TYPE: The type of the certificate chain

HOSTNAME: The hostname associated with the chain

PROTO: The protocol of the service connecting (e.g.  tcp)

PORT: The port of the service connecting (e.g.  443)

SFLAGS: Flags for the initialization of ‘s’ (if NULL)

VFLAGS: Verification flags; an OR'ed list of ‘dane_verify_flags_t’
     .

VERIFY: An OR'ed list of ‘dane_verify_status_t’ .

This function will verify the given certificate chain against the
     CA constrains and/or the certificate available via DANE. If no
     information via DANE can be obtained the flag
     ‘DANE_VERIFY_NO_DANE_INFO’ is set.  If a DNSSEC signature is not
     available for the DANE record then the verify flag
     ‘DANE_VERIFY_NO_DNSSEC_DATA’ is set.

Due to the many possible options of DANE, there is no single threat
     model countered.  When notifying the user about DANE verification
     results it may be better to mention: DANE verification did not
     reject the certificate, rather than mentioning a successful DANE
     verification.

Note that this function is designed to be run in addition to PKIX -
     certificate chain - verification.  To be run independently the
     ‘DANE_VFLAG_ONLY_CHECK_EE_USAGE’ flag should be specified; then the
     function will check whether the key of the peer matches the key
     advertised in the DANE entry.

*Returns:* a negative error code on error and ‘DANE_E_SUCCESS’ (0)
     when the DANE entries were successfully parsed, irrespective of
     whether they were verified (see ‘verify’ for that information).  If
     no usable entries were encountered
     ‘DANE_E_REQUESTED_DATA_NOT_AVAILABLE’ will be returned.

‘INT *note dane_verify_session_crt:: (dane_state_t S, gnutls_session_t SESSION, const char * HOSTNAME, const char * PROTO, unsigned int PORT, unsigned int SFLAGS, unsigned int VFLAGS, unsigned int * VERIFY)’
‘CONST CHAR * *note dane_strerror:: (int ERROR)’

Note that the ‘dane_state_t’ structure that is accepted by both
verification functions is optional.  It is required when many queries
are performed to optimize against multiple re-initializations of the
resolving back-end and loading of DNSSEC keys.

The following flags are returned by the verify functions to indicate the
status of the verification.

‘DANE_VERIFY_CA_CONSTRAINTS_VIOLATED’
     The CA constraints were violated.
‘DANE_VERIFY_CERT_DIFFERS’
     The certificate obtained via DNS differs.
‘DANE_VERIFY_UNKNOWN_DANE_INFO’
     No known DANE data was found in the DNS record.

Figure 6.3: The DANE verification status flags.

In order to generate a DANE TLSA entry to use in a DNS server you may
use danetool (see *note danetool Invocation::).

File: gnutls.info,  Node: TLS 1.2 re-authentication,  Next: TLS 1.3 re-authentication and re-key,  Prev: Certificate verification,  Up: Advanced topics

6.12.4 TLS 1.2 re-authentication
--------------------------------

In TLS 1.2 or earlier there is no distinction between re-key,
re-authentication, and re-negotiation.  All of these use cases are
handled by the TLS' rehandshake process.  For that reason in GnuTLS
rehandshake is not transparent to the application, and the application
must explicitly take control of that process.  In addition GnuTLS since
version 3.5.0 will not allow the peer to switch identities during a
rehandshake.  The threat addressed by that behavior depends on the
application protocol, but primarily it protects applications from being
misled by a rehandshake which switches the peer's identity.
Applications can disable this protection by using the
‘GNUTLS_ALLOW_ID_CHANGE’ flag in *note gnutls_init::.

The following paragraphs explain how to safely use the rehandshake
process.

6.12.4.1 Client side
....................

According to the TLS specification a client may initiate a rehandshake
at any time.  That can be achieved by calling *note gnutls_handshake::
and rely on its return value for the outcome of the handshake (the
server may deny a rehandshake).  If a server requests a re-handshake,
then a call to *note gnutls_record_recv:: will return
GNUTLS_E_REHANDSHAKE in the client, instructing it to call *note
gnutls_handshake::.  To deny a rehandshake request by the server it is
recommended to send a warning alert of type GNUTLS_A_NO_RENEGOTIATION.

Due to limitations of early protocol versions, it is required to check
whether safe renegotiation is in place, i.e., using *note
gnutls_safe_renegotiation_status::, which ensures that the server
remains the same as the initial.

To make re-authentication transparent to the application when requested
by the server, use the ‘GNUTLS_AUTO_REAUTH’ flag on the *note
gnutls_init:: call.  In that case the re-authentication will happen in
the call of *note gnutls_record_recv:: that received the
reauthentication request.

-- Function: unsigned gnutls_safe_renegotiation_status
          (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Can be used to check whether safe renegotiation is being used in
     the current session.

*Returns:* 0 when safe renegotiation is not used and non (0) when
     safe renegotiation is used.

*Since:* 2.10.0

6.12.4.2 Server side
....................

A server which wants to instruct the client to re-authenticate, should
call *note gnutls_rehandshake:: and wait for the client to
re-authenticate.  It is recommended to only request re-handshake when
safe renegotiation is enabled for that session (see *note
gnutls_safe_renegotiation_status:: and the discussion in *note Safe
renegotiation::).  A server could also encounter the
GNUTLS_E_REHANDSHAKE error code while receiving data.  That indicates a
client-initiated re-handshake request.  In that case the server could
ignore that request, perform handshake (unsafe when done generally), or
even drop the connection.

-- Function: int gnutls_rehandshake (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

This function can only be called in server side, and instructs a
     TLS 1.2 or earlier client to renegotiate parameters (perform a
     handshake), by sending a hello request message.

If this function succeeds, the calling application should call
     ‘gnutls_record_recv()’ until ‘GNUTLS_E_REHANDSHAKE’ is returned to
     clear any pending data.  If the ‘GNUTLS_E_REHANDSHAKE’ error code
     is not seen, then the handshake request was not followed by the
     peer (the TLS protocol does not require the client to do, and such
     compliance should be handled by the application protocol).

Once the ‘GNUTLS_E_REHANDSHAKE’ error code is seen, the calling
     application should proceed to calling ‘gnutls_handshake()’ to
     negotiate the new parameters.

If the client does not wish to renegotiate parameters he may reply
     with an alert message, and in that case the return code seen by
     subsequent ‘gnutls_record_recv()’ will be
     ‘GNUTLS_E_WARNING_ALERT_RECEIVED’ with the specific alert being
     ‘GNUTLS_A_NO_RENEGOTIATION’ .  A client may also choose to ignore
     this request.

Under TLS 1.3 this function is equivalent to
     ‘gnutls_session_key_update()’ with the ‘GNUTLS_KU_PEER’ flag.  In
     that case subsequent calls to ‘gnutls_record_recv()’ will not
     return ‘GNUTLS_E_REHANDSHAKE’ , and calls to ‘gnutls_handshake()’
     in server side are a no-op.

This function always fails with ‘GNUTLS_E_INVALID_REQUEST’ when
     called in client side.

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, otherwise a negative
     error code.

File: gnutls.info,  Node: TLS 1.3 re-authentication and re-key,  Next: Parameter generation,  Prev: TLS 1.2 re-authentication,  Up: Advanced topics

6.12.5 TLS 1.3 re-authentication and re-key
-------------------------------------------

The TLS 1.3 protocol distinguishes between re-key and re-authentication.
The re-key process ensures that fresh keys are supplied to the already
negotiated parameters, and on GnuTLS can be initiated using *note
gnutls_session_key_update::.  The re-key process can be one-way (i.e.,
the calling party only changes its keys), or two-way where the peer is
requested to change keys as well.

The re-authentication process, allows the connected client to switch
identity by presenting a new certificate.  Unlike TLS 1.2, the server is
not allowed to change identities.  That client re-authentication, or
post-handshake authentication can be initiated only by the server using
*note gnutls_reauth::, and only if a client has advertised support for
it.  Both server and client have to explicitly enable support for post
handshake authentication using the ‘GNUTLS_POST_HANDSHAKE_AUTH’ flag at
*note gnutls_init::.

A client receiving a re-authentication request will "see" the error code
‘GNUTLS_E_REAUTH_REQUEST’ at *note gnutls_record_recv::.  At this point,
it should also call *note gnutls_reauth::.

To make re-authentication transparent to the application when requested
by the server, use the ‘GNUTLS_AUTO_REAUTH’ and
‘GNUTLS_POST_HANDSHAKE_AUTH’ flags on the *note gnutls_init:: call.  In
that case the re-authentication will happen in the call of *note
gnutls_record_recv:: that received the reauthentication request.

File: gnutls.info,  Node: Parameter generation,  Next: Deriving keys for other applications/protocols,  Prev: TLS 1.3 re-authentication and re-key,  Up: Advanced topics

6.12.6 Parameter generation
---------------------------

Prior to GnuTLS 3.6.0 for the ephemeral or anonymous Diffie-Hellman (DH)
TLS ciphersuites the application was required to generate or provide DH
parameters.  That is no longer necessary as GnuTLS utilizes DH
parameters and negotiation from [*note RFC7919::].

Applications can tune the used parameters by explicitly specifying them
in the priority string.  In server side applications can set the minimum
acceptable level of DH parameters by calling *note
gnutls_certificate_set_known_dh_params::, *note
gnutls_anon_set_server_known_dh_params::, or *note
gnutls_psk_set_server_known_dh_params::, depending on the type of the
credentials, to set the lower acceptable parameter limits.  Typical
applications should rely on the default settings.

‘INT *note gnutls_certificate_set_known_dh_params:: (gnutls_certificate_credentials_t RES, gnutls_sec_param_t SEC_PARAM)’
‘INT *note gnutls_anon_set_server_known_dh_params:: (gnutls_anon_server_credentials_t RES, gnutls_sec_param_t SEC_PARAM)’
‘INT *note gnutls_psk_set_server_known_dh_params:: (gnutls_psk_server_credentials_t RES, gnutls_sec_param_t SEC_PARAM)’

6.12.6.1 Legacy parameter generation
....................................

Note that older than 3.5.6 versions of GnuTLS provided functions to
generate or import arbitrary DH parameters from a file.  This practice
is still supported but discouraged in current versions.  There is no
known advantage from using random parameters, while there have been
several occasions where applications were utilizing incorrect, weak or
insecure parameters.  This is the main reason GnuTLS includes the
well-known parameters of [*note RFC7919::] and recommends applications
utilizing them.

In older applications which require to specify explicit DH parameters,
we recommend using ‘certtool’ (of GnuTLS 3.5.6 or later) with the
‘--get-dh-params’ option to obtain the FFDHE parameters discussed above.
The output parameters of the tool are in PKCS#3 format and can be
imported by most existing applications.

The following functions are still supported but considered obsolete.

‘INT *note gnutls_dh_params_generate2:: (gnutls_dh_params_t DPARAMS, unsigned int BITS)’
‘INT *note gnutls_dh_params_import_pkcs3:: (gnutls_dh_params_t PARAMS, const gnutls_datum_t * PKCS3_PARAMS, gnutls_x509_crt_fmt_t FORMAT)’
‘VOID *note gnutls_certificate_set_dh_params:: (gnutls_certificate_credentials_t RES, gnutls_dh_params_t DH_PARAMS)’

File: gnutls.info,  Node: Deriving keys for other applications/protocols,  Next: Channel Bindings,  Prev: Parameter generation,  Up: Advanced topics

6.12.7 Deriving keys for other applications/protocols
-----------------------------------------------------

In several cases, after a TLS connection is established, it is desirable
to derive keys to be used in another application or protocol (e.g., in
an other TLS session using pre-shared keys).  The following describe
GnuTLS' implementation of RFC5705 to extract keys based on a session's
master secret.

The API to use is *note gnutls_prf_rfc5705::.  The function needs to be
provided with a label, and additional context data to mix in the
‘context’ parameter.

-- Function: int gnutls_prf_rfc5705 (gnutls_session_t SESSION, size_t
          LABEL_SIZE, const char * LABEL, size_t CONTEXT_SIZE, const
          char * CONTEXT, size_t OUTSIZE, char * OUT)
     SESSION: is a ‘gnutls_session_t’ type.

LABEL_SIZE: length of the ‘label’ variable.

LABEL: label used in PRF computation, typically a short string.

CONTEXT_SIZE: length of the ‘extra’ variable.

CONTEXT: optional extra data to seed the PRF with.

OUTSIZE: size of pre-allocated output buffer to hold the output.

OUT: pre-allocated buffer to hold the generated data.

Exports keying material from TLS/DTLS session to an application, as
     specified in RFC5705.

In the TLS versions prior to 1.3, it applies the TLS
     Pseudo-Random-Function (PRF) on the master secret and the provided
     data, seeded with the client and server random fields.

In TLS 1.3, it applies HKDF on the exporter master secret derived
     from the master secret.

The ‘label’ variable usually contains a string denoting the purpose
     for the generated data.

The ‘context’ variable can be used to add more data to the seed,
     after the random variables.  It can be used to make sure the
     generated output is strongly connected to some additional data
     (e.g., a string used in user authentication).

The output is placed in ‘out’ , which must be pre-allocated.

Note that, to provide the RFC5705 context, the ‘context’ variable
     must be non-null.

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, or an error code.

*Since:* 3.4.4

For example, after establishing a TLS session using *note
gnutls_handshake::, you can obtain 32-bytes to be used as key, using
this call:

#define MYLABEL "EXPORTER-My-protocol-name"
     #define MYCONTEXT "my-protocol's-1st-session"

char out[32];
     rc = gnutls_prf_rfc5705 (session, sizeof(MYLABEL)-1, MYLABEL,
                              sizeof(MYCONTEXT)-1, MYCONTEXT, 32, out);

The output key depends on TLS' master secret, and is the same on both
client and server.

For legacy applications which need to use a more flexible API, there is
*note gnutls_prf::, which in addition, allows to switch the mix of the
client and server random nonces, using the ‘server_random_first’
parameter.  For additional flexibility and low-level access to the
TLS1.2 PRF, there is a low-level TLS PRF interface called *note
gnutls_prf_raw::.  That however is not functional under newer protocol
versions.

File: gnutls.info,  Node: Channel Bindings,  Next: Interoperability,  Prev: Deriving keys for other applications/protocols,  Up: Advanced topics

6.12.8 Channel bindings
-----------------------

In user authentication protocols (e.g., EAP or SASL mechanisms) it is
useful to have a unique string that identifies the secure channel that
is used, to bind together the user authentication with the secure
channel.  This can protect against man-in-the-middle attacks in some
situations.  That unique string is called a "channel binding".  For
background and discussion see [*note RFC5056::].

In GnuTLS you can extract a channel binding using the *note
gnutls_session_channel_binding:: function.  Currently only the following
types are supported:

• ‘GNUTLS_CB_TLS_UNIQUE’: corresponds to the ‘tls-unique’ channel
     binding for TLS defined in [*note RFC5929::]
   • ‘GNUTLS_CB_TLS_EXPORTER’: corresponds to the ‘tls-exporter’ channel
     binding for TLS defined in [*note RFC9266::]

The following example describes how to print the channel binding data.
Note that it must be run after a successful TLS handshake.

{
       gnutls_datum_t cb;
       int rc;

rc = gnutls_session_channel_binding (session,
                                            GNUTLS_CB_TLS_UNIQUE,
                                            &cb);
       if (rc)
         fprintf (stderr, "Channel binding error: %s\n",
                  gnutls_strerror (rc));
       else
         {
           size_t i;
           printf ("- Channel binding 'tls-unique': ");
           for (i = 0; i < cb.size; i++)
             printf ("%02x", cb.data[i]);
           printf ("\n");
         }
     }

File: gnutls.info,  Node: Interoperability,  Next: Compatibility with the OpenSSL library,  Prev: Channel Bindings,  Up: Advanced topics

6.12.9 Interoperability
-----------------------

The TLS protocols support many ciphersuites, extensions and version
numbers.  As a result, few implementations are not able to properly
interoperate once faced with extensions or version protocols they do not
support and understand.  The TLS protocol allows for a graceful
downgrade to the commonly supported options, but practice shows it is
not always implemented correctly.

Because there is no way to achieve maximum interoperability with broken
peers without sacrificing security, GnuTLS ignores such peers by
default.  This might not be acceptable in cases where maximum
compatibility is required.  Thus we allow enabling compatibility with
broken peers using priority strings (see *note Priority Strings::).  A
conservative priority string that would disable certain TLS protocol
options that are known to cause compatibility problems, is shown below.
NORMAL:%COMPAT

For very old broken peers that do not tolerate TLS version numbers over
TLS 1.0 another priority string is:
NORMAL:-VERS-ALL:+VERS-TLS1.0:+VERS-SSL3.0:%COMPAT
This priority string will in addition to above, only enable SSL 3.0 and
TLS 1.0 as protocols.

File: gnutls.info,  Node: Compatibility with the OpenSSL library,  Prev: Interoperability,  Up: Advanced topics

6.12.10 Compatibility with the OpenSSL library
----------------------------------------------

To ease GnuTLS' integration with existing applications, a compatibility
layer with the OpenSSL library is included in the ‘gnutls-openssl’
library.  This compatibility layer is not complete and it is not
intended to completely re-implement the OpenSSL API with GnuTLS.  It
only provides limited source-level compatibility.

The prototypes for the compatibility functions are in the
‘gnutls/openssl.h’ header file.  The limitations imposed by the
compatibility layer include:

• Error handling is not thread safe.

File: gnutls.info,  Node: GnuTLS application examples,  Next: System-wide configuration of the library,  Prev: How to use GnuTLS in applications,  Up: Top

7 GnuTLS application examples
*****************************

In this chapter several examples of real-world use cases are listed.
The examples are simplified to promote readability and contain little or
no error checking.

* Menu:

* Client examples::
* Server examples::
* More advanced client and servers::
* OCSP example::
* Miscellaneous examples::

File: gnutls.info,  Node: Client examples,  Next: Server examples,  Up: GnuTLS application examples

7.1 Client examples
===================

This section contains examples of TLS and SSL clients, using GnuTLS.
Note that some of the examples require functions implemented by another
example.

* Menu:

* Client example with X.509 certificate support::
* Datagram TLS client example::
* Client using a smart card with TLS::
* Client with Resume capability example::
* Client example with SSH-style certificate verification::

File: gnutls.info,  Node: Client example with X.509 certificate support,  Next: Datagram TLS client example,  Up: Client examples

7.1.1 Client example with X.509 certificate support
---------------------------------------------------

Let's assume now that we want to create a TCP client which communicates
with servers that use X.509 certificate authentication.  The following
client is a very simple TLS client, which uses the high level
verification functions for certificates, but does not support session
resumption.

Note that this client utilizes functionality present in the latest
GnuTLS version.  For a reasonably portable version see *note Legacy
client example with X.509 certificate support::.

/* This example code is placed in the public domain. */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <gnutls/gnutls.h>
#include <gnutls/x509.h>
#include "examples.h"

/* A very basic TLS client, with X.509 authentication and server certificate
 * verification. Note that error recovery is minimal for simplicity.
 */

#define CHECK(x) assert((x) >= 0)
#define LOOP_CHECK(rval, cmd)                                             \
	do {                                                              \
		rval = cmd;                                               \
	} while (rval == GNUTLS_E_AGAIN || rval == GNUTLS_E_INTERRUPTED); \
	assert(rval >= 0)

#define MAX_BUF 1024
#define MSG "GET / HTTP/1.0\r\n\r\n"

extern int tcp_connect(void);
extern void tcp_close(int sd);

int main(void)
{
	int ret, sd, ii;
	gnutls_session_t session;
	char buffer[MAX_BUF + 1], *desc;
	gnutls_datum_t out;
	int type;
	unsigned status;
	gnutls_certificate_credentials_t xcred;

if (gnutls_check_version("3.4.6") == NULL) {
		fprintf(stderr,
			"GnuTLS 3.4.6 or later is required for this example\n");
		exit(1);
	}

/* for backwards compatibility with gnutls < 3.3.0 */
	CHECK(gnutls_global_init());

/* X509 stuff */
	CHECK(gnutls_certificate_allocate_credentials(&xcred));

/* sets the system trusted CAs for Internet PKI */
	CHECK(gnutls_certificate_set_x509_system_trust(xcred));

/* If client holds a certificate it can be set using the following:
	 *
	 gnutls_certificate_set_x509_key_file (xcred, "cert.pem", "key.pem", 
	 GNUTLS_X509_FMT_PEM); 
	 */

/* Initialize TLS session */
	CHECK(gnutls_init(&session, GNUTLS_CLIENT));

CHECK(gnutls_server_name_set(session, GNUTLS_NAME_DNS,
				     "www.example.com",
				     strlen("www.example.com")));

/* It is recommended to use the default priorities */
	CHECK(gnutls_set_default_priority(session));

/* put the x509 credentials to the current session
	 */
	CHECK(gnutls_credentials_set(session, GNUTLS_CRD_CERTIFICATE, xcred));
	gnutls_session_set_verify_cert(session, "www.example.com", 0);

/* connect to the peer
	 */
	sd = tcp_connect();

gnutls_transport_set_int(session, sd);
	gnutls_handshake_set_timeout(session, GNUTLS_DEFAULT_HANDSHAKE_TIMEOUT);

/* Perform the TLS handshake
	 */
	do {
		ret = gnutls_handshake(session);
	} while (ret < 0 && gnutls_error_is_fatal(ret) == 0);
	if (ret < 0) {
		if (ret == GNUTLS_E_CERTIFICATE_VERIFICATION_ERROR) {
			/* check certificate verification status */
			type = gnutls_certificate_type_get(session);
			status = gnutls_session_get_verify_cert_status(session);
			CHECK(gnutls_certificate_verification_status_print(
				status, type, &out, 0));
			printf("cert verify output: %s\n", out.data);
			gnutls_free(out.data);
		}
		fprintf(stderr, "*** Handshake failed: %s\n",
			gnutls_strerror(ret));
		goto end;
	} else {
		desc = gnutls_session_get_desc(session);
		printf("- Session info: %s\n", desc);
		gnutls_free(desc);
	}

/* send data */
	LOOP_CHECK(ret, gnutls_record_send(session, MSG, strlen(MSG)));

LOOP_CHECK(ret, gnutls_record_recv(session, buffer, MAX_BUF));
	if (ret == 0) {
		printf("- Peer has closed the TLS connection\n");
		goto end;
	} else if (ret < 0 && gnutls_error_is_fatal(ret) == 0) {
		fprintf(stderr, "*** Warning: %s\n", gnutls_strerror(ret));
	} else if (ret < 0) {
		fprintf(stderr, "*** Error: %s\n", gnutls_strerror(ret));
		goto end;
	}

if (ret > 0) {
		printf("- Received %d bytes: ", ret);
		for (ii = 0; ii < ret; ii++) {
			fputc(buffer[ii], stdout);
		}
		fputs("\n", stdout);
	}

CHECK(gnutls_bye(session, GNUTLS_SHUT_RDWR));

end:

tcp_close(sd);

gnutls_deinit(session);

gnutls_certificate_free_credentials(xcred);

gnutls_global_deinit();

return 0;
}

File: gnutls.info,  Node: Datagram TLS client example,  Next: Client using a smart card with TLS,  Prev: Client example with X.509 certificate support,  Up: Client examples

7.1.2 Datagram TLS client example
---------------------------------

This is a client that uses UDP to connect to a server.  This is the DTLS
equivalent to the TLS example with X.509 certificates.

/* This example code is placed in the public domain. */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <assert.h>
#include <unistd.h>
#include <gnutls/gnutls.h>
#include <gnutls/dtls.h>

/* A very basic Datagram TLS client, over UDP with X.509 authentication.
 */

#define MAX_BUF 1024
#define MSG "GET / HTTP/1.0\r\n\r\n"

extern int udp_connect(void);
extern void udp_close(int sd);
extern int verify_certificate_callback(gnutls_session_t session);

int main(void)
{
	int ret, sd, ii;
	gnutls_session_t session;
	char buffer[MAX_BUF + 1];
	gnutls_certificate_credentials_t xcred;

if (gnutls_check_version("3.1.4") == NULL) {
		fprintf(stderr,
			"GnuTLS 3.1.4 or later is required for this example\n");
		exit(1);
	}

/* for backwards compatibility with gnutls < 3.3.0 */
	CHECK(gnutls_global_init());

/* X509 stuff */
	CHECK(gnutls_certificate_allocate_credentials(&xcred));

/* sets the system trusted CAs for Internet PKI */
	CHECK(gnutls_certificate_set_x509_system_trust(xcred));

/* Initialize TLS session */
	CHECK(gnutls_init(&session, GNUTLS_CLIENT | GNUTLS_DATAGRAM));

/* Use default priorities */
	CHECK(gnutls_set_default_priority(session));

/* put the x509 credentials to the current session */
	CHECK(gnutls_credentials_set(session, GNUTLS_CRD_CERTIFICATE, xcred));
	CHECK(gnutls_server_name_set(session, GNUTLS_NAME_DNS,
				     "www.example.com",
				     strlen("www.example.com")));

gnutls_session_set_verify_cert(session, "www.example.com", 0);

/* connect to the peer */
	sd = udp_connect();

gnutls_transport_set_int(session, sd);

/* set the connection MTU */
	gnutls_dtls_set_mtu(session, 1000);
	/* gnutls_dtls_set_timeouts(session, 1000, 60000); */

/* Perform the TLS handshake */
	do {
		ret = gnutls_handshake(session);
	} while (ret == GNUTLS_E_INTERRUPTED || ret == GNUTLS_E_AGAIN);
	/* Note that DTLS may also receive GNUTLS_E_LARGE_PACKET */

if (ret < 0) {
		fprintf(stderr, "*** Handshake failed\n");
		gnutls_perror(ret);
		goto end;
	} else {
		char *desc;

desc = gnutls_session_get_desc(session);
		printf("- Session info: %s\n", desc);
		gnutls_free(desc);
	}

LOOP_CHECK(ret, gnutls_record_send(session, MSG, strlen(MSG)));

if (ret > 0) {
		printf("- Received %d bytes: ", ret);
		for (ii = 0; ii < ret; ii++) {
			fputc(buffer[ii], stdout);
		}
		fputs("\n", stdout);
	}

/* It is suggested not to use GNUTLS_SHUT_RDWR in DTLS
	 * connections because the peer's closure message might
	 * be lost */
	CHECK(gnutls_bye(session, GNUTLS_SHUT_WR));

end:

udp_close(sd);

gnutls_deinit(session);

gnutls_certificate_free_credentials(xcred);

gnutls_global_deinit();

return 0;
}

File: gnutls.info,  Node: Client using a smart card with TLS,  Next: Client with Resume capability example,  Prev: Datagram TLS client example,  Up: Client examples

7.1.3 Using a smart card with TLS
---------------------------------

This example will demonstrate how to load keys and certificates from a
smart-card or any other PKCS #11 token, and use it in a TLS connection.
The difference between this and the *note Client example with X.509
certificate support:: is that the client keys are provided as PKCS #11
URIs instead of files.

/* This example code is placed in the public domain. */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <gnutls/gnutls.h>
#include <gnutls/x509.h>
#include <gnutls/pkcs11.h>
#include <assert.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <getpass.h> /* for getpass() */

/* A TLS client that loads the certificate and key.
 */

#define CHECK(x) assert((x) >= 0)

#define MAX_BUF 1024
#define MSG "GET / HTTP/1.0\r\n\r\n"
#define MIN(x, y) (((x) < (y)) ? (x) : (y))

#define CAFILE "/etc/ssl/certs/ca-certificates.crt"

/* The URLs of the objects can be obtained
 * using p11tool --list-all --login
 */
#define KEY_URL                                                     \
	"pkcs11:manufacturer=SomeManufacturer;object=Private%20Key" \
	";objecttype=private;id=%db%5b%3e%b5%72%33"
#define CERT_URL                                                   \
	"pkcs11:manufacturer=SomeManufacturer;object=Certificate;" \
	"objecttype=cert;id=db%5b%3e%b5%72%33"

extern int tcp_connect(void);
extern void tcp_close(int sd);

static int pin_callback(void *user, int attempt, const char *token_url,
			const char *token_label, unsigned int flags, char *pin,
			size_t pin_max)
{
	const char *password;
	int len;

printf("PIN required for token '%s' with URL '%s'\n", token_label,
	       token_url);
	if (flags & GNUTLS_PIN_FINAL_TRY)
		printf("*** This is the final try before locking!\n");
	if (flags & GNUTLS_PIN_COUNT_LOW)
		printf("*** Only few tries left before locking!\n");
	if (flags & GNUTLS_PIN_WRONG)
		printf("*** Wrong PIN\n");

password = getpass("Enter pin: ");
	/* FIXME: ensure that we are in UTF-8 locale */
	if (password == NULL || password[0] == 0) {
		fprintf(stderr, "No password given\n");
		exit(1);
	}

len = MIN(pin_max - 1, strlen(password));
	memcpy(pin, password, len);
	pin[len] = 0;

return 0;
}

int main(void)
{
	int ret, sd, ii;
	gnutls_session_t session;
	char buffer[MAX_BUF + 1];
	gnutls_certificate_credentials_t xcred;
	/* Allow connections to servers that have OpenPGP keys as well.
	 */

if (gnutls_check_version("3.1.4") == NULL) {
		fprintf(stderr,
			"GnuTLS 3.1.4 or later is required for this example\n");
		exit(1);
	}

/* for backwards compatibility with gnutls < 3.3.0 */
	CHECK(gnutls_global_init());

/* The PKCS11 private key operations may require PIN.
	 * Register a callback. */
	gnutls_pkcs11_set_pin_function(pin_callback, NULL);

/* X509 stuff */
	CHECK(gnutls_certificate_allocate_credentials(&xcred));

/* sets the trusted cas file
	 */
	CHECK(gnutls_certificate_set_x509_trust_file(xcred, CAFILE,
						     GNUTLS_X509_FMT_PEM));

CHECK(gnutls_certificate_set_x509_key_file(xcred, CERT_URL, KEY_URL,
						   GNUTLS_X509_FMT_DER));

/* Note that there is no server certificate verification in this example
	 */

/* Initialize TLS session
	 */
	CHECK(gnutls_init(&session, GNUTLS_CLIENT));

/* Use default priorities */
	CHECK(gnutls_set_default_priority(session));

/* put the x509 credentials to the current session
	 */
	CHECK(gnutls_credentials_set(session, GNUTLS_CRD_CERTIFICATE, xcred));

/* connect to the peer
	 */
	sd = tcp_connect();

gnutls_transport_set_int(session, sd);

/* Perform the TLS handshake
	 */
	ret = gnutls_handshake(session);

if (ret < 0) {
		fprintf(stderr, "*** Handshake failed\n");
		gnutls_perror(ret);
		goto end;
	} else {
		char *desc;

desc = gnutls_session_get_desc(session);
		printf("- Session info: %s\n", desc);
		gnutls_free(desc);
	}

CHECK(gnutls_record_send(session, MSG, strlen(MSG)));

ret = gnutls_record_recv(session, buffer, MAX_BUF);
	if (ret == 0) {
		printf("- Peer has closed the TLS connection\n");
		goto end;
	} else if (ret < 0) {
		fprintf(stderr, "*** Error: %s\n", gnutls_strerror(ret));
		goto end;
	}

printf("- Received %d bytes: ", ret);
	for (ii = 0; ii < ret; ii++) {
		fputc(buffer[ii], stdout);
	}
	fputs("\n", stdout);

CHECK(gnutls_bye(session, GNUTLS_SHUT_RDWR));

end:

tcp_close(sd);

gnutls_deinit(session);

gnutls_certificate_free_credentials(xcred);

gnutls_global_deinit();

return 0;
}

File: gnutls.info,  Node: Client with Resume capability example,  Next: Client example with SSH-style certificate verification,  Prev: Client using a smart card with TLS,  Up: Client examples

7.1.4 Client with resume capability example
-------------------------------------------

This is a modification of the simple client example.  Here we
demonstrate the use of session resumption.  The client tries to connect
once using TLS, close the connection and then try to establish a new
connection using the previously negotiated data.

/* This example code is placed in the public domain. */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <gnutls/gnutls.h>

extern void check_alert(gnutls_session_t session, int ret);
extern int tcp_connect(void);
extern void tcp_close(int sd);

/* A very basic TLS client, with X.509 authentication and server certificate
 * verification as well as session resumption.
 *
 * Note that error recovery is minimal for simplicity.
 */

#define MAX_BUF 1024
#define MSG "GET / HTTP/1.0\r\n\r\n"

int main(void)
{
	int ret;
	int sd, ii;
	gnutls_session_t session;
	char buffer[MAX_BUF + 1];
	gnutls_certificate_credentials_t xcred;

/* variables used in session resuming 
	 */
	int t;
	gnutls_datum_t sdata;

/* for backwards compatibility with gnutls < 3.3.0 */
	CHECK(gnutls_global_init());

CHECK(gnutls_certificate_allocate_credentials(&xcred));
	CHECK(gnutls_certificate_set_x509_system_trust(xcred));

for (t = 0; t < 2; t++) { /* connect 2 times to the server */

sd = tcp_connect();

CHECK(gnutls_init(&session, GNUTLS_CLIENT));

CHECK(gnutls_server_name_set(session, GNUTLS_NAME_DNS,
					     "www.example.com",
					     strlen("www.example.com")));
		gnutls_session_set_verify_cert(session, "www.example.com", 0);

CHECK(gnutls_set_default_priority(session));

gnutls_transport_set_int(session, sd);
		gnutls_handshake_set_timeout(session,
					     GNUTLS_DEFAULT_HANDSHAKE_TIMEOUT);

gnutls_credentials_set(session, GNUTLS_CRD_CERTIFICATE, xcred);

if (t > 0) {
			/* if this is not the first time we connect */
			CHECK(gnutls_session_set_data(session, sdata.data,
						      sdata.size));
			gnutls_free(sdata.data);
		}

/* Perform the TLS handshake
		 */
		do {
			ret = gnutls_handshake(session);
		} while (ret < 0 && gnutls_error_is_fatal(ret) == 0);

if (ret < 0) {
			fprintf(stderr, "*** Handshake failed\n");
			gnutls_perror(ret);
			goto end;
		} else {
			printf("- Handshake was completed\n");
		}

if (t == 0) { /* the first time we connect */
			/* get the session data */
			CHECK(gnutls_session_get_data2(session, &sdata));
		} else { /* the second time we connect */

/* check if we actually resumed the previous session */
			if (gnutls_session_is_resumed(session) != 0) {
				printf("- Previous session was resumed\n");
			} else {
				fprintf(stderr,
					"*** Previous session was NOT resumed\n");
			}
		}

LOOP_CHECK(ret, gnutls_record_send(session, MSG, strlen(MSG)));

LOOP_CHECK(ret, gnutls_record_recv(session, buffer, MAX_BUF));
		if (ret == 0) {
			printf("- Peer has closed the TLS connection\n");
			goto end;
		} else if (ret < 0 && gnutls_error_is_fatal(ret) == 0) {
			fprintf(stderr, "*** Warning: %s\n",
				gnutls_strerror(ret));
		} else if (ret < 0) {
			fprintf(stderr, "*** Error: %s\n",
				gnutls_strerror(ret));
			goto end;
		}

if (ret > 0) {
			printf("- Received %d bytes: ", ret);
			for (ii = 0; ii < ret; ii++) {
				fputc(buffer[ii], stdout);
			}
			fputs("\n", stdout);
		}

gnutls_bye(session, GNUTLS_SHUT_RDWR);

end:

tcp_close(sd);

gnutls_deinit(session);

} /* for() */

gnutls_certificate_free_credentials(xcred);

gnutls_global_deinit();

return 0;
}

File: gnutls.info,  Node: Client example with SSH-style certificate verification,  Prev: Client with Resume capability example,  Up: Client examples

7.1.5 Client example with SSH-style certificate verification
------------------------------------------------------------

This is an alternative verification function that will use the X.509
certificate authorities for verification, but also assume an trust on
first use (SSH-like) authentication system.  That is the user is
prompted on unknown public keys and known public keys are considered
trusted.

/* This example code is placed in the public domain. */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <gnutls/gnutls.h>
#include <gnutls/x509.h>
#include <assert.h>
#include "examples.h"

#define CHECK(x) assert((x) >= 0)

/* This function will verify the peer's certificate, check
 * if the hostname matches. In addition it will perform an
 * SSH-style authentication, where ultimately trusted keys
 * are only the keys that have been seen before.
 */
int _ssh_verify_certificate_callback(gnutls_session_t session)
{
	unsigned int status;
	const gnutls_datum_t *cert_list;
	unsigned int cert_list_size;
	int ret, type;
	gnutls_datum_t out;
	const char *hostname;

/* read hostname */
	hostname = gnutls_session_get_ptr(session);

/* This verification function uses the trusted CAs in the credentials
	 * structure. So you must have installed one or more CA certificates.
	 */
	CHECK(gnutls_certificate_verify_peers3(session, hostname, &status));

type = gnutls_certificate_type_get(session);

CHECK(gnutls_certificate_verification_status_print(status, type, &out,
							   0));
	printf("%s", out.data);

gnutls_free(out.data);

if (status != 0) /* Certificate is not trusted */
		return GNUTLS_E_CERTIFICATE_ERROR;

/* Do SSH verification */
	cert_list = gnutls_certificate_get_peers(session, &cert_list_size);
	if (cert_list == NULL) {
		printf("No certificate was found!\n");
		return GNUTLS_E_CERTIFICATE_ERROR;
	}

/* service may be obtained alternatively using getservbyport() */
	ret = gnutls_verify_stored_pubkey(NULL, NULL, hostname, "https", type,
					  &cert_list[0], 0);
	if (ret == GNUTLS_E_NO_CERTIFICATE_FOUND) {
		printf("Host %s is not known.", hostname);
		if (status == 0)
			printf("Its certificate is valid for %s.\n", hostname);

/* the certificate must be printed and user must be asked on
		 * whether it is trustworthy. --see gnutls_x509_crt_print() */

/* if not trusted */
		return GNUTLS_E_CERTIFICATE_ERROR;
	} else if (ret == GNUTLS_E_CERTIFICATE_KEY_MISMATCH) {
		printf("Warning: host %s is known but has another key associated.",
		       hostname);
		printf("It might be that the server has multiple keys, or you are under attack\n");
		if (status == 0)
			printf("Its certificate is valid for %s.\n", hostname);

/* the certificate must be printed and user must be asked on
		 * whether it is trustworthy. --see gnutls_x509_crt_print() */

/* if not trusted */
		return GNUTLS_E_CERTIFICATE_ERROR;
	} else if (ret < 0) {
		printf("gnutls_verify_stored_pubkey: %s\n",
		       gnutls_strerror(ret));
		return ret;
	}

/* user trusts the key -> store it */
	if (ret != 0) {
		CHECK(gnutls_store_pubkey(NULL, NULL, hostname, "https", type,
					  &cert_list[0], 0, 0));
	}

/* notify gnutls to continue handshake normally */
	return 0;
}

File: gnutls.info,  Node: Server examples,  Next: More advanced client and servers,  Prev: Client examples,  Up: GnuTLS application examples

7.2 Server examples
===================

This section contains examples of TLS and SSL servers, using GnuTLS.

* Menu:

* Echo server with X.509 authentication::
* DTLS echo server with X.509 authentication::

File: gnutls.info,  Node: Echo server with X.509 authentication,  Next: DTLS echo server with X.509 authentication,  Up: Server examples

7.2.1 Echo server with X.509 authentication
-------------------------------------------

This example is a very simple echo server which supports X.509
authentication.

/* This example code is placed in the public domain. */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <string.h>
#include <unistd.h>
#include <gnutls/gnutls.h>
#include <assert.h>

#define KEYFILE "key.pem"
#define CERTFILE "cert.pem"
#define CAFILE "/etc/ssl/certs/ca-certificates.crt"
#define CRLFILE "crl.pem"

#define CHECK(x) assert((x) >= 0)
#define LOOP_CHECK(rval, cmd) \
	do {                  \
		rval = cmd;   \
	} while (rval == GNUTLS_E_AGAIN || rval == GNUTLS_E_INTERRUPTED)

/* The OCSP status file contains up to date information about revocation
 * of the server's certificate. That can be periodically be updated
 * using:
 * $ ocsptool --ask --load-cert your_cert.pem --load-issuer your_issuer.pem
 *            --load-signer your_issuer.pem --outfile ocsp-status.der
 */
#define OCSP_STATUS_FILE "ocsp-status.der"

/* This is a sample TLS 1.0 echo server, using X.509 authentication and
 * OCSP stapling support.
 */

#define MAX_BUF 1024
#define PORT 5556 /* listen to 5556 port */

int main(void)
{
	int listen_sd;
	int sd, ret;
	gnutls_certificate_credentials_t x509_cred;
	gnutls_priority_t priority_cache;
	struct sockaddr_in sa_serv;
	struct sockaddr_in sa_cli;
	socklen_t client_len;
	char topbuf[512];
	gnutls_session_t session;
	char buffer[MAX_BUF + 1];
	int optval = 1;

/* for backwards compatibility with gnutls < 3.3.0 */
	CHECK(gnutls_global_init());

CHECK(gnutls_certificate_allocate_credentials(&x509_cred));

CHECK(gnutls_certificate_set_x509_trust_file(x509_cred, CAFILE,
						     GNUTLS_X509_FMT_PEM));

CHECK(gnutls_certificate_set_x509_crl_file(x509_cred, CRLFILE,
						   GNUTLS_X509_FMT_PEM));

/* The following code sets the certificate key pair as well as, 
	 * an OCSP response which corresponds to it. It is possible
	 * to set multiple key-pairs and multiple OCSP status responses
	 * (the latter since 3.5.6). See the manual pages of the individual
	 * functions for more information.
	 */
	CHECK(gnutls_certificate_set_x509_key_file(x509_cred, CERTFILE, KEYFILE,
						   GNUTLS_X509_FMT_PEM));

CHECK(gnutls_certificate_set_ocsp_status_request_file(
		x509_cred, OCSP_STATUS_FILE, 0));

CHECK(gnutls_priority_init(&priority_cache, NULL, NULL));

/* Instead of the default options as shown above one could specify
	 * additional options such as server precedence in ciphersuite selection
	 * as follows:
	 * gnutls_priority_init2(&priority_cache,
	 *                       "%SERVER_PRECEDENCE",
	 *                       NULL, GNUTLS_PRIORITY_INIT_DEF_APPEND);
	 */

#if GNUTLS_VERSION_NUMBER >= 0x030506
	/* only available since GnuTLS 3.5.6, on previous versions see
	 * gnutls_certificate_set_dh_params(). */
	gnutls_certificate_set_known_dh_params(x509_cred,
					       GNUTLS_SEC_PARAM_MEDIUM);
#endif

/* Socket operations
	 */
	listen_sd = socket(AF_INET, SOCK_STREAM, 0);

memset(&sa_serv, '\0', sizeof(sa_serv));
	sa_serv.sin_family = AF_INET;
	sa_serv.sin_addr.s_addr = INADDR_ANY;
	sa_serv.sin_port = htons(PORT); /* Server Port number */

setsockopt(listen_sd, SOL_SOCKET, SO_REUSEADDR, (void *)&optval,
		   sizeof(int));

bind(listen_sd, (struct sockaddr *)&sa_serv, sizeof(sa_serv));

listen(listen_sd, 1024);

printf("Server ready. Listening to port '%d'.\n\n", PORT);

client_len = sizeof(sa_cli);
	for (;;) {
		CHECK(gnutls_init(&session, GNUTLS_SERVER));
		CHECK(gnutls_priority_set(session, priority_cache));
		CHECK(gnutls_credentials_set(session, GNUTLS_CRD_CERTIFICATE,
					     x509_cred));

/* We don't request any certificate from the client.
		 * If we did we would need to verify it. One way of
		 * doing that is shown in the "Verifying a certificate"
		 * example.
		 */
		gnutls_certificate_server_set_request(session,
						      GNUTLS_CERT_IGNORE);
		gnutls_handshake_set_timeout(session,
					     GNUTLS_DEFAULT_HANDSHAKE_TIMEOUT);

sd = accept(listen_sd, (struct sockaddr *)&sa_cli, &client_len);

printf("- connection from %s, port %d\n",
		       inet_ntop(AF_INET, &sa_cli.sin_addr, topbuf,
				 sizeof(topbuf)),
		       ntohs(sa_cli.sin_port));

gnutls_transport_set_int(session, sd);

LOOP_CHECK(ret, gnutls_handshake(session));
		if (ret < 0) {
			close(sd);
			gnutls_deinit(session);
			fprintf(stderr, "*** Handshake has failed (%s)\n\n",
				gnutls_strerror(ret));
			continue;
		}
		printf("- Handshake was completed\n");

/* see the Getting peer's information example */
		/* print_info(session); */

for (;;) {
			LOOP_CHECK(ret, gnutls_record_recv(session, buffer,
							   MAX_BUF));

if (ret == 0) {
				printf("\n- Peer has closed the GnuTLS connection\n");
				break;
			} else if (ret < 0 && gnutls_error_is_fatal(ret) == 0) {
				fprintf(stderr, "*** Warning: %s\n",
					gnutls_strerror(ret));
			} else if (ret < 0) {
				fprintf(stderr,
					"\n*** Received corrupted "
					"data(%d). Closing the connection.\n\n",
					ret);
				break;
			} else if (ret > 0) {
				/* echo data back to the client
				 */
				CHECK(gnutls_record_send(session, buffer, ret));
			}
		}
		printf("\n");
		/* do not wait for the peer to close the connection.
		 */
		LOOP_CHECK(ret, gnutls_bye(session, GNUTLS_SHUT_WR));

close(sd);
		gnutls_deinit(session);
	}
	close(listen_sd);

gnutls_certificate_free_credentials(x509_cred);
	gnutls_priority_deinit(priority_cache);

gnutls_global_deinit();

return 0;
}

File: gnutls.info,  Node: DTLS echo server with X.509 authentication,  Prev: Echo server with X.509 authentication,  Up: Server examples

7.2.2 DTLS echo server with X.509 authentication
------------------------------------------------

This example is a very simple echo server using Datagram TLS and X.509
authentication.

/* This example code is placed in the public domain. */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <sys/select.h>
#include <netdb.h>
#include <string.h>
#include <unistd.h>
#include <gnutls/gnutls.h>
#include <gnutls/dtls.h>

#define KEYFILE "key.pem"
#define CERTFILE "cert.pem"
#define CAFILE "/etc/ssl/certs/ca-certificates.crt"
#define CRLFILE "crl.pem"

/* This is a sample DTLS echo server, using X.509 authentication.
 * Note that error checking is minimal to simplify the example.
 */

#define LOOP_CHECK(rval, cmd) \
	do {                  \
		rval = cmd;   \
	} while (rval == GNUTLS_E_AGAIN || rval == GNUTLS_E_INTERRUPTED)

#define MAX_BUFFER 1024
#define PORT 5557

typedef struct {
	gnutls_session_t session;
	int fd;
	struct sockaddr *cli_addr;
	socklen_t cli_addr_size;
} priv_data_st;

static int pull_timeout_func(gnutls_transport_ptr_t ptr, unsigned int ms);
static ssize_t push_func(gnutls_transport_ptr_t p, const void *data,
			 size_t size);
static ssize_t pull_func(gnutls_transport_ptr_t p, void *data, size_t size);
static const char *human_addr(const struct sockaddr *sa, socklen_t salen,
			      char *buf, size_t buflen);
static int wait_for_connection(int fd);

/* Use global credentials and parameters to simplify
 * the example. */
static gnutls_certificate_credentials_t x509_cred;
static gnutls_priority_t priority_cache;

int main(void)
{
	int listen_sd;
	int sock, ret;
	struct sockaddr_in sa_serv;
	struct sockaddr_in cli_addr;
	socklen_t cli_addr_size;
	gnutls_session_t session;
	char buffer[MAX_BUFFER];
	priv_data_st priv;
	gnutls_datum_t cookie_key;
	gnutls_dtls_prestate_st prestate;
	int mtu = 1400;
	unsigned char sequence[8];

/* this must be called once in the program
	 */
	gnutls_global_init();

gnutls_certificate_allocate_credentials(&x509_cred);
	gnutls_certificate_set_x509_trust_file(x509_cred, CAFILE,
					       GNUTLS_X509_FMT_PEM);

gnutls_certificate_set_x509_crl_file(x509_cred, CRLFILE,
					     GNUTLS_X509_FMT_PEM);

ret = gnutls_certificate_set_x509_key_file(x509_cred, CERTFILE, KEYFILE,
						   GNUTLS_X509_FMT_PEM);
	if (ret < 0) {
		printf("No certificate or key were found\n");
		exit(1);
	}

gnutls_certificate_set_known_dh_params(x509_cred,
					       GNUTLS_SEC_PARAM_MEDIUM);

/* pre-3.6.3 equivalent:
	 * gnutls_priority_init(&priority_cache,
	 *                      "NORMAL:-VERS-TLS-ALL:+VERS-DTLS1.0:%SERVER_PRECEDENCE",
	 *                      NULL);
	 */
	gnutls_priority_init2(&priority_cache, "%SERVER_PRECEDENCE", NULL,
			      GNUTLS_PRIORITY_INIT_DEF_APPEND);

gnutls_key_generate(&cookie_key, GNUTLS_COOKIE_KEY_SIZE);

/* Socket operations
	 */
	listen_sd = socket(AF_INET, SOCK_DGRAM, 0);

memset(&sa_serv, '\0', sizeof(sa_serv));
	sa_serv.sin_family = AF_INET;
	sa_serv.sin_addr.s_addr = INADDR_ANY;
	sa_serv.sin_port = htons(PORT);

{ /* DTLS requires the IP don't fragment (DF) bit to be set */
#if defined(IP_DONTFRAG)
		int optval = 1;
		setsockopt(listen_sd, IPPROTO_IP, IP_DONTFRAG,
			   (const void *)&optval, sizeof(optval));
#elif defined(IP_MTU_DISCOVER)
		int optval = IP_PMTUDISC_DO;
		setsockopt(listen_sd, IPPROTO_IP, IP_MTU_DISCOVER,
			   (const void *)&optval, sizeof(optval));
#endif
	}

bind(listen_sd, (struct sockaddr *)&sa_serv, sizeof(sa_serv));

printf("UDP server ready. Listening to port '%d'.\n\n", PORT);

for (;;) {
		printf("Waiting for connection...\n");
		sock = wait_for_connection(listen_sd);
		if (sock < 0)
			continue;

cli_addr_size = sizeof(cli_addr);
		ret = recvfrom(sock, buffer, sizeof(buffer), MSG_PEEK,
			       (struct sockaddr *)&cli_addr, &cli_addr_size);
		if (ret > 0) {
			memset(&prestate, 0, sizeof(prestate));
			ret = gnutls_dtls_cookie_verify(&cookie_key, &cli_addr,
							sizeof(cli_addr),
							buffer, ret, &prestate);
			if (ret < 0) { /* cookie not valid */
				priv_data_st s;

memset(&s, 0, sizeof(s));
				s.fd = sock;
				s.cli_addr = (void *)&cli_addr;
				s.cli_addr_size = sizeof(cli_addr);

printf("Sending hello verify request to %s\n",
				       human_addr((struct sockaddr *)&cli_addr,
						  sizeof(cli_addr), buffer,
						  sizeof(buffer)));

gnutls_dtls_cookie_send(
					&cookie_key, &cli_addr,
					sizeof(cli_addr), &prestate,
					(gnutls_transport_ptr_t)&s, push_func);

/* discard peeked data */
				recvfrom(sock, buffer, sizeof(buffer), 0,
					 (struct sockaddr *)&cli_addr,
					 &cli_addr_size);
				usleep(100);
				continue;
			}
			printf("Accepted connection from %s\n",
			       human_addr((struct sockaddr *)&cli_addr,
					  sizeof(cli_addr), buffer,
					  sizeof(buffer)));
		} else
			continue;

gnutls_init(&session, GNUTLS_SERVER | GNUTLS_DATAGRAM);
		gnutls_priority_set(session, priority_cache);
		gnutls_credentials_set(session, GNUTLS_CRD_CERTIFICATE,
				       x509_cred);

gnutls_dtls_prestate_set(session, &prestate);
		gnutls_dtls_set_mtu(session, mtu);

priv.session = session;
		priv.fd = sock;
		priv.cli_addr = (struct sockaddr *)&cli_addr;
		priv.cli_addr_size = sizeof(cli_addr);

gnutls_transport_set_ptr(session, &priv);
		gnutls_transport_set_push_function(session, push_func);
		gnutls_transport_set_pull_function(session, pull_func);
		gnutls_transport_set_pull_timeout_function(session,
							   pull_timeout_func);

LOOP_CHECK(ret, gnutls_handshake(session));
		/* Note that DTLS may also receive GNUTLS_E_LARGE_PACKET.
		 * In that case the MTU should be adjusted.
		 */

if (ret < 0) {
			fprintf(stderr, "Error in handshake(): %s\n",
				gnutls_strerror(ret));
			gnutls_deinit(session);
			continue;
		}

printf("- Handshake was completed\n");

for (;;) {
			LOOP_CHECK(ret, gnutls_record_recv_seq(session, buffer,
							       MAX_BUFFER,
							       sequence));

if (ret < 0 && gnutls_error_is_fatal(ret) == 0) {
				fprintf(stderr, "*** Warning: %s\n",
					gnutls_strerror(ret));
				continue;
			} else if (ret < 0) {
				fprintf(stderr, "Error in recv(): %s\n",
					gnutls_strerror(ret));
				break;
			}

if (ret == 0) {
				printf("EOF\n\n");
				break;
			}

buffer[ret] = 0;
			printf("received[%.2x%.2x%.2x%.2x%.2x%.2x%.2x%.2x]: %s\n",
			       sequence[0], sequence[1], sequence[2],
			       sequence[3], sequence[4], sequence[5],
			       sequence[6], sequence[7], buffer);

/* reply back */
			LOOP_CHECK(ret,
				   gnutls_record_send(session, buffer, ret));
			if (ret < 0) {
				fprintf(stderr, "Error in send(): %s\n",
					gnutls_strerror(ret));
				break;
			}
		}

LOOP_CHECK(ret, gnutls_bye(session, GNUTLS_SHUT_WR));
		gnutls_deinit(session);
	}
	close(listen_sd);

gnutls_certificate_free_credentials(x509_cred);
	gnutls_priority_deinit(priority_cache);

gnutls_global_deinit();

return 0;
}

static int wait_for_connection(int fd)
{
	fd_set rd, wr;
	int n;

FD_ZERO(&rd);
	FD_ZERO(&wr);

FD_SET(fd, &rd);

/* waiting part */
	n = select(fd + 1, &rd, &wr, NULL, NULL);
	if (n == -1 && errno == EINTR)
		return -1;
	if (n < 0) {
		perror("select()");
		exit(1);
	}

return fd;
}

/* Wait for data to be received within a timeout period in milliseconds
 */
static int pull_timeout_func(gnutls_transport_ptr_t ptr, unsigned int ms)
{
	fd_set rfds;
	struct timeval tv;
	priv_data_st *priv = ptr;
	struct sockaddr_in cli_addr;
	socklen_t cli_addr_size;
	int ret;
	char c;

FD_ZERO(&rfds);
	FD_SET(priv->fd, &rfds);

tv.tv_sec = ms / 1000;
	tv.tv_usec = (ms % 1000) * 1000;

ret = select(priv->fd + 1, &rfds, NULL, NULL, &tv);

if (ret <= 0)
		return ret;

/* only report ok if the next message is from the peer we expect
	 * from 
	 */
	cli_addr_size = sizeof(cli_addr);
	ret = recvfrom(priv->fd, &c, 1, MSG_PEEK, (struct sockaddr *)&cli_addr,
		       &cli_addr_size);
	if (ret > 0) {
		if (cli_addr_size == priv->cli_addr_size &&
		    memcmp(&cli_addr, priv->cli_addr, sizeof(cli_addr)) == 0)
			return 1;
	}

return 0;
}

static ssize_t push_func(gnutls_transport_ptr_t p, const void *data,
			 size_t size)
{
	priv_data_st *priv = p;

return sendto(priv->fd, data, size, 0, priv->cli_addr,
		      priv->cli_addr_size);
}

static ssize_t pull_func(gnutls_transport_ptr_t p, void *data, size_t size)
{
	priv_data_st *priv = p;
	struct sockaddr_in cli_addr;
	socklen_t cli_addr_size;
	char buffer[64];
	int ret;

cli_addr_size = sizeof(cli_addr);
	ret = recvfrom(priv->fd, data, size, 0, (struct sockaddr *)&cli_addr,
		       &cli_addr_size);
	if (ret == -1)
		return ret;

if (cli_addr_size == priv->cli_addr_size &&
	    memcmp(&cli_addr, priv->cli_addr, sizeof(cli_addr)) == 0)
		return ret;

printf("Denied connection from %s\n",
	       human_addr((struct sockaddr *)&cli_addr, sizeof(cli_addr),
			  buffer, sizeof(buffer)));

gnutls_transport_set_errno(priv->session, EAGAIN);
	return -1;
}

static const char *human_addr(const struct sockaddr *sa, socklen_t salen,
			      char *buf, size_t buflen)
{
	const char *save_buf = buf;
	size_t l;

if (!buf || !buflen)
		return NULL;

*buf = '\0';

switch (sa->sa_family) {
#if HAVE_IPV6
	case AF_INET6:
		snprintf(buf, buflen, "IPv6 ");
		break;
#endif

case AF_INET:
		snprintf(buf, buflen, "IPv4 ");
		break;
	}

l = strlen(buf);
	buf += l;
	buflen -= l;

if (getnameinfo(sa, salen, buf, buflen, NULL, 0, NI_NUMERICHOST) != 0)
		return NULL;

l = strlen(buf);
	buf += l;
	buflen -= l;

strncat(buf, " port ", buflen);

l = strlen(buf);
	buf += l;
	buflen -= l;

if (getnameinfo(sa, salen, NULL, 0, buf, buflen, NI_NUMERICSERV) != 0)
		return NULL;

return save_buf;
}

File: gnutls.info,  Node: More advanced client and servers,  Next: OCSP example,  Prev: Server examples,  Up: GnuTLS application examples

7.3 More advanced client and servers
====================================

This section has various, more advanced topics in client and servers.

* Menu:

* Client example with anonymous authentication::
* Using a callback to select the certificate to use::
* Obtaining session information::
* Advanced certificate verification example::
* Client example with PSK authentication::
* Client example with SRP authentication::
* Legacy client example with X.509 certificate support::
* Client example in C++::
* Echo server with PSK authentication::
* Echo server with SRP authentication::
* Echo server with anonymous authentication::
* Helper functions for TCP connections::
* Helper functions for UDP connections::

File: gnutls.info,  Node: Client example with anonymous authentication,  Next: Using a callback to select the certificate to use,  Up: More advanced client and servers

7.3.1 Client example with anonymous authentication
--------------------------------------------------

The simplest client using TLS is the one that doesn't do any
authentication.  This means no external certificates or passwords are
needed to set up the connection.  As could be expected, the connection
is vulnerable to man-in-the-middle (active or redirection) attacks.
However, the data are integrity protected and encrypted from passive
eavesdroppers.

Note that due to the vulnerable nature of this method very few public
servers support it.

/* This example code is placed in the public domain. */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <assert.h>
#include <gnutls/gnutls.h>

/* A very basic TLS client, with anonymous authentication.
 */

#define LOOP_CHECK(rval, cmd)                                             \
	do {                                                              \
		rval = cmd;                                               \
	} while (rval == GNUTLS_E_AGAIN || rval == GNUTLS_E_INTERRUPTED); \
	assert(rval >= 0)

#define MAX_BUF 1024
#define MSG "GET / HTTP/1.0\r\n\r\n"

extern int tcp_connect(void);
extern void tcp_close(int sd);

int main(void)
{
	int ret, sd, ii;
	gnutls_session_t session;
	char buffer[MAX_BUF + 1];
	gnutls_anon_client_credentials_t anoncred;
	/* Need to enable anonymous KX specifically. */

gnutls_global_init();

gnutls_anon_allocate_client_credentials(&anoncred);

/* Initialize TLS session 
	 */
	gnutls_init(&session, GNUTLS_CLIENT);

/* Use default priorities */
	gnutls_priority_set_direct(session, "PERFORMANCE:+ANON-ECDH:+ANON-DH",
				   NULL);

/* put the anonymous credentials to the current session
	 */
	gnutls_credentials_set(session, GNUTLS_CRD_ANON, anoncred);

/* connect to the peer
	 */
	sd = tcp_connect();

gnutls_transport_set_int(session, sd);
	gnutls_handshake_set_timeout(session, GNUTLS_DEFAULT_HANDSHAKE_TIMEOUT);

/* Perform the TLS handshake
	 */
	do {
		ret = gnutls_handshake(session);
	} while (ret < 0 && gnutls_error_is_fatal(ret) == 0);

if (ret < 0) {
		fprintf(stderr, "*** Handshake failed\n");
		gnutls_perror(ret);
		goto end;
	} else {
		char *desc;

desc = gnutls_session_get_desc(session);
		printf("- Session info: %s\n", desc);
		gnutls_free(desc);
	}

LOOP_CHECK(ret, gnutls_record_send(session, MSG, strlen(MSG)));

if (ret > 0) {
		printf("- Received %d bytes: ", ret);
		for (ii = 0; ii < ret; ii++) {
			fputc(buffer[ii], stdout);
		}
		fputs("\n", stdout);
	}

LOOP_CHECK(ret, gnutls_bye(session, GNUTLS_SHUT_RDWR));

end:

tcp_close(sd);

gnutls_deinit(session);

gnutls_anon_free_client_credentials(anoncred);

gnutls_global_deinit();

return 0;
}

File: gnutls.info,  Node: Using a callback to select the certificate to use,  Next: Obtaining session information,  Prev: Client example with anonymous authentication,  Up: More advanced client and servers

7.3.2 Using a callback to select the certificate to use
-------------------------------------------------------

There are cases where a client holds several certificate and key pairs,
and may not want to load all of them in the credentials structure.  The
following example demonstrates the use of the certificate selection
callback.

/* This example code is placed in the public domain. */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <assert.h>
#include <gnutls/gnutls.h>
#include <gnutls/x509.h>
#include <gnutls/abstract.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>

/* A TLS client that loads the certificate and key.
 */

#define CHECK(x) assert((x) >= 0)

#define MAX_BUF 1024
#define MSG "GET / HTTP/1.0\r\n\r\n"

#define CERT_FILE "cert.pem"
#define KEY_FILE "key.pem"
#define CAFILE "/etc/ssl/certs/ca-certificates.crt"

extern int tcp_connect(void);
extern void tcp_close(int sd);

static int cert_callback(gnutls_session_t session,
			 const gnutls_datum_t *req_ca_rdn, int nreqs,
			 const gnutls_pk_algorithm_t *sign_algos,
			 int sign_algos_length, gnutls_pcert_st **pcert,
			 unsigned int *pcert_length, gnutls_privkey_t *pkey);

gnutls_pcert_st pcrt;
gnutls_privkey_t key;

/* Load the certificate and the private key.
 */
static void load_keys(void)
{
	gnutls_datum_t data;

CHECK(gnutls_load_file(CERT_FILE, &data));

CHECK(gnutls_pcert_import_x509_raw(&pcrt, &data, GNUTLS_X509_FMT_PEM,
					   0));

gnutls_free(data.data);

CHECK(gnutls_load_file(KEY_FILE, &data));

CHECK(gnutls_privkey_init(&key));

CHECK(gnutls_privkey_import_x509_raw(key, &data, GNUTLS_X509_FMT_PEM,
					     NULL, 0));
	gnutls_free(data.data);
}

int main(void)
{
	int ret, sd, ii;
	gnutls_session_t session;
	char buffer[MAX_BUF + 1];
	gnutls_certificate_credentials_t xcred;

if (gnutls_check_version("3.1.4") == NULL) {
		fprintf(stderr,
			"GnuTLS 3.1.4 or later is required for this example\n");
		exit(1);
	}

/* for backwards compatibility with gnutls < 3.3.0 */
	CHECK(gnutls_global_init());

load_keys();

/* X509 stuff */
	CHECK(gnutls_certificate_allocate_credentials(&xcred));

/* sets the trusted cas file
	 */
	CHECK(gnutls_certificate_set_x509_trust_file(xcred, CAFILE,
						     GNUTLS_X509_FMT_PEM));

gnutls_certificate_set_retrieve_function2(xcred, cert_callback);

/* Initialize TLS session 
	 */
	CHECK(gnutls_init(&session, GNUTLS_CLIENT));

/* Use default priorities */
	CHECK(gnutls_set_default_priority(session));

/* put the x509 credentials to the current session
	 */
	CHECK(gnutls_credentials_set(session, GNUTLS_CRD_CERTIFICATE, xcred));

/* connect to the peer
	 */
	sd = tcp_connect();

gnutls_transport_set_int(session, sd);

/* Perform the TLS handshake
	 */
	ret = gnutls_handshake(session);

if (ret < 0) {
		fprintf(stderr, "*** Handshake failed\n");
		gnutls_perror(ret);
		goto end;
	} else {
		char *desc;

desc = gnutls_session_get_desc(session);
		printf("- Session info: %s\n", desc);
		gnutls_free(desc);
	}

CHECK(gnutls_record_send(session, MSG, strlen(MSG)));

printf("- Received %d bytes: ", ret);
	for (ii = 0; ii < ret; ii++) {
		fputc(buffer[ii], stdout);
	}
	fputs("\n", stdout);

CHECK(gnutls_bye(session, GNUTLS_SHUT_RDWR));

end:

tcp_close(sd);

gnutls_deinit(session);

gnutls_certificate_free_credentials(xcred);

gnutls_global_deinit();

return 0;
}

/* This callback should be associated with a session by calling
 * gnutls_certificate_client_set_retrieve_function( session, cert_callback),
 * before a handshake.
 */

/* Print the server's trusted CAs
	 */
	if (nreqs > 0)
		printf("- Server's trusted authorities:\n");
	else
		printf("- Server did not send us any trusted authorities names.\n");

/* print the names (if any) */
	for (i = 0; i < nreqs; i++) {
		len = sizeof(issuer_dn);
		ret = gnutls_x509_rdn_get(&req_ca_rdn[i], issuer_dn, &len);
		if (ret >= 0) {
			printf("   [%d]: ", i);
			printf("%s\n", issuer_dn);
		}
	}

/* Select a certificate and return it.
	 * The certificate must be of any of the "sign algorithms"
	 * supported by the server.
	 */
	type = gnutls_certificate_type_get(session);
	if (type == GNUTLS_CRT_X509) {
		*pcert_length = 1;
		*pcert = &pcrt;
		*pkey = key;
	} else {
		return -1;
	}

return 0;
}

File: gnutls.info,  Node: Obtaining session information,  Next: Advanced certificate verification example,  Prev: Using a callback to select the certificate to use,  Up: More advanced client and servers

7.3.3 Obtaining session information
-----------------------------------

Most of the times it is desirable to know the security properties of the
current established session.  This includes the underlying ciphers and
the protocols involved.  That is the purpose of the following function.
Note that this function will print meaningful values only if called
after a successful *note gnutls_handshake::.

/* This example code is placed in the public domain. */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <stdio.h>
#include <stdlib.h>
#include <gnutls/gnutls.h>
#include <gnutls/x509.h>

#include "examples.h"

/* This function will print some details of the
 * given session.
 */
int print_info(gnutls_session_t session)
{
	gnutls_credentials_type_t cred;
	gnutls_kx_algorithm_t kx;
	int dhe, ecdh, group;
	char *desc;

/* get a description of the session connection, protocol,
	 * cipher/key exchange */
	desc = gnutls_session_get_desc(session);
	if (desc != NULL) {
		printf("- Session: %s\n", desc);
	}

dhe = ecdh = 0;

kx = gnutls_kx_get(session);

/* Check the authentication type used and switch
	 * to the appropriate.
	 */
	cred = gnutls_auth_get_type(session);
	switch (cred) {
#ifdef ENABLE_SRP
	case GNUTLS_CRD_SRP:
		printf("- SRP session with username %s\n",
		       gnutls_srp_server_get_username(session));
		break;
#endif

case GNUTLS_CRD_PSK:
		/* This returns NULL in server side.
		 */
		if (gnutls_psk_client_get_hint(session) != NULL)
			printf("- PSK authentication. PSK hint '%s'\n",
			       gnutls_psk_client_get_hint(session));
		/* This returns NULL in client side.
		 */
		if (gnutls_psk_server_get_username(session) != NULL)
			printf("- PSK authentication. Connected as '%s'\n",
			       gnutls_psk_server_get_username(session));

if (kx == GNUTLS_KX_ECDHE_PSK)
			ecdh = 1;
		else if (kx == GNUTLS_KX_DHE_PSK)
			dhe = 1;
		break;

case GNUTLS_CRD_ANON: /* anonymous authentication */

printf("- Anonymous authentication.\n");
		if (kx == GNUTLS_KX_ANON_ECDH)
			ecdh = 1;
		else if (kx == GNUTLS_KX_ANON_DH)
			dhe = 1;
		break;

case GNUTLS_CRD_CERTIFICATE: /* certificate authentication */

/* Check if we have been using ephemeral Diffie-Hellman.
		 */
		if (kx == GNUTLS_KX_DHE_RSA || kx == GNUTLS_KX_DHE_DSS)
			dhe = 1;
		else if (kx == GNUTLS_KX_ECDHE_RSA ||
			 kx == GNUTLS_KX_ECDHE_ECDSA)
			ecdh = 1;

/* if the certificate list is available, then
		 * print some information about it.
		 */
		print_x509_certificate_info(session);
		break;
	default:
		break;
	} /* switch */

/* read the negotiated group - if any */
	group = gnutls_group_get(session);
	if (group != 0) {
		printf("- Negotiated group %s\n", gnutls_group_get_name(group));
	} else {
		if (ecdh != 0)
			printf("- Ephemeral ECDH using curve %s\n",
			       gnutls_ecc_curve_get_name(
				       gnutls_ecc_curve_get(session)));
		else if (dhe != 0)
			printf("- Ephemeral DH using prime of %d bits\n",
			       gnutls_dh_get_prime_bits(session));
	}

return 0;
}

File: gnutls.info,  Node: Advanced certificate verification example,  Next: Client example with PSK authentication,  Prev: Obtaining session information,  Up: More advanced client and servers

7.3.4 Advanced certificate verification
---------------------------------------

An example is listed below which uses the high level verification
functions to verify a given certificate chain against a set of CAs and
CRLs.

/* This example code is placed in the public domain. */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <gnutls/gnutls.h>
#include <gnutls/x509.h>

#include "examples.h"

#define CHECK(x) assert((x) >= 0)

/* All the available CRLs
 */
gnutls_x509_crl_t *crl_list;
int crl_list_size;

/* All the available trusted CAs
 */
gnutls_x509_crt_t *ca_list;
int ca_list_size;

static int print_details_func(gnutls_x509_crt_t cert, gnutls_x509_crt_t issuer,
			      gnutls_x509_crl_t crl,
			      unsigned int verification_output);

/* This function will try to verify the peer's certificate chain, and
 * also check if the hostname matches.
 */
void verify_certificate_chain(const char *hostname,
			      const gnutls_datum_t *cert_chain,
			      int cert_chain_length)
{
	int i;
	gnutls_x509_trust_list_t tlist;
	gnutls_x509_crt_t *cert;
	gnutls_datum_t txt;
	unsigned int output;

/* Initialize the trusted certificate list. This should be done
	 * once on initialization. gnutls_x509_crt_list_import2() and
	 * gnutls_x509_crl_list_import2() can be used to load them.
	 */
	CHECK(gnutls_x509_trust_list_init(&tlist, 0));

CHECK(gnutls_x509_trust_list_add_cas(tlist, ca_list, ca_list_size, 0));
	CHECK(gnutls_x509_trust_list_add_crls(tlist, crl_list, crl_list_size,
					      GNUTLS_TL_VERIFY_CRL, 0));

cert = gnutls_calloc(cert_chain_length, sizeof(*cert));
	assert(cert != NULL);

/* Import all the certificates in the chain to
	 * native certificate format.
	 */
	for (i = 0; i < cert_chain_length; i++) {
		CHECK(gnutls_x509_crt_init(&cert[i]));
		CHECK(gnutls_x509_crt_import(cert[i], &cert_chain[i],
					     GNUTLS_X509_FMT_DER));
	}

CHECK(gnutls_x509_trust_list_verify_named_crt(
		tlist, cert[0], hostname, strlen(hostname),
		GNUTLS_VERIFY_DISABLE_CRL_CHECKS, &output, print_details_func));

/* if this certificate is not explicitly trusted verify against CAs 
	 */
	if (output != 0) {
		CHECK(gnutls_x509_trust_list_verify_crt(
			tlist, cert, cert_chain_length, 0, &output,
			print_details_func));
	}

if (output & GNUTLS_CERT_INVALID) {
		fprintf(stderr, "Not trusted\n");
		CHECK(gnutls_certificate_verification_status_print(
			output, GNUTLS_CRT_X509, &txt, 0));

fprintf(stderr, "Error: %s\n", txt.data);
		gnutls_free(txt.data);
	} else
		fprintf(stderr, "Trusted\n");

/* Check if the name in the first certificate matches our destination!
	 */
	if (!gnutls_x509_crt_check_hostname(cert[0], hostname)) {
		printf("The certificate's owner does not match hostname '%s'\n",
		       hostname);
	}

for (i = 0; i < cert_chain_length; i++) {
		gnutls_x509_crt_deinit(cert[i]);
	}
	gnutls_free(cert);

gnutls_x509_trust_list_deinit(tlist, 1);

return;
}

static int print_details_func(gnutls_x509_crt_t cert, gnutls_x509_crt_t issuer,
			      gnutls_x509_crl_t crl,
			      unsigned int verification_output)
{
	char name[512];
	char issuer_name[512];
	size_t name_size;
	size_t issuer_name_size;

issuer_name_size = sizeof(issuer_name);
	gnutls_x509_crt_get_issuer_dn(cert, issuer_name, &issuer_name_size);

name_size = sizeof(name);
	gnutls_x509_crt_get_dn(cert, name, &name_size);

fprintf(stdout, "\tSubject: %s\n", name);
	fprintf(stdout, "\tIssuer: %s\n", issuer_name);

if (issuer != NULL) {
		issuer_name_size = sizeof(issuer_name);
		gnutls_x509_crt_get_dn(issuer, issuer_name, &issuer_name_size);

fprintf(stdout, "\tVerified against: %s\n", issuer_name);
	}

if (crl != NULL) {
		issuer_name_size = sizeof(issuer_name);
		gnutls_x509_crl_get_issuer_dn(crl, issuer_name,
					      &issuer_name_size);

fprintf(stdout, "\tVerified against CRL of: %s\n", issuer_name);
	}

fprintf(stdout, "\tVerification output: %x\n\n", verification_output);

return 0;
}

File: gnutls.info,  Node: Client example with PSK authentication,  Next: Client example with SRP authentication,  Prev: Advanced certificate verification example,  Up: More advanced client and servers

7.3.5 Client example with PSK authentication
--------------------------------------------

The following client is a very simple PSK TLS client which connects to a
server and authenticates using a _username_ and a _key_.

/* This example code is placed in the public domain. */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <assert.h>
#include <gnutls/gnutls.h>

/* A very basic TLS client, with PSK authentication.
 */

#define MAX_BUF 1024
#define MSG "GET / HTTP/1.0\r\n\r\n"

extern int tcp_connect(void);
extern void tcp_close(int sd);

int main(void)
{
	int ret, sd, ii;
	gnutls_session_t session;
	char buffer[MAX_BUF + 1];
	const char *err;
	gnutls_psk_client_credentials_t pskcred;
	const gnutls_datum_t key = { (void *)"DEADBEEF", 8 };

if (gnutls_check_version("3.6.3") == NULL) {
		fprintf(stderr,
			"GnuTLS 3.6.3 or later is required for this example\n");
		exit(1);
	}

CHECK(gnutls_global_init());

CHECK(gnutls_psk_allocate_client_credentials(&pskcred));
	CHECK(gnutls_psk_set_client_credentials(pskcred, "test", &key,
						GNUTLS_PSK_KEY_HEX));

/* Initialize TLS session
	 */
	CHECK(gnutls_init(&session, GNUTLS_CLIENT));

ret = gnutls_set_default_priority_append(
		session, "-KX-ALL:+ECDHE-PSK:+DHE-PSK:+PSK", &err, 0);

/* Alternative for pre-3.6.3 versions:
	 * gnutls_priority_set_direct(session, "NORMAL:+ECDHE-PSK:+DHE-PSK:+PSK", &err)
	 */
	if (ret < 0) {
		if (ret == GNUTLS_E_INVALID_REQUEST) {
			fprintf(stderr, "Syntax error at: %s\n", err);
		}
		exit(1);
	}

/* put the x509 credentials to the current session
	 */
	CHECK(gnutls_credentials_set(session, GNUTLS_CRD_PSK, pskcred));

/* connect to the peer
	 */
	sd = tcp_connect();

gnutls_transport_set_int(session, sd);
	gnutls_handshake_set_timeout(session, GNUTLS_DEFAULT_HANDSHAKE_TIMEOUT);

/* Perform the TLS handshake
	 */
	do {
		ret = gnutls_handshake(session);
	} while (ret < 0 && gnutls_error_is_fatal(ret) == 0);

if (ret < 0) {
		fprintf(stderr, "*** Handshake failed\n");
		gnutls_perror(ret);
		goto end;
	} else {
		char *desc;

desc = gnutls_session_get_desc(session);
		printf("- Session info: %s\n", desc);
		gnutls_free(desc);
	}

LOOP_CHECK(ret, gnutls_record_send(session, MSG, strlen(MSG)));

if (ret > 0) {
		printf("- Received %d bytes: ", ret);
		for (ii = 0; ii < ret; ii++) {
			fputc(buffer[ii], stdout);
		}
		fputs("\n", stdout);
	}

CHECK(gnutls_bye(session, GNUTLS_SHUT_RDWR));

end:

tcp_close(sd);

gnutls_deinit(session);

gnutls_psk_free_client_credentials(pskcred);

gnutls_global_deinit();

return 0;
}

File: gnutls.info,  Node: Client example with SRP authentication,  Next: Legacy client example with X.509 certificate support,  Prev: Client example with PSK authentication,  Up: More advanced client and servers

7.3.6 Client example with SRP authentication
--------------------------------------------

The following client is a very simple SRP TLS client which connects to a
server and authenticates using a _username_ and a _password_.  The
server may authenticate itself using a certificate, and in that case it
has to be verified.

/* This example code is placed in the public domain. */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <gnutls/gnutls.h>

/* Those functions are defined in other examples.
 */
extern void check_alert(gnutls_session_t session, int ret);
extern int tcp_connect(void);
extern void tcp_close(int sd);

#define MAX_BUF 1024
#define USERNAME "user"
#define PASSWORD "pass"
#define CAFILE "/etc/ssl/certs/ca-certificates.crt"
#define MSG "GET / HTTP/1.0\r\n\r\n"

int main(void)
{
	int ret;
	int sd, ii;
	gnutls_session_t session;
	char buffer[MAX_BUF + 1];
	gnutls_srp_client_credentials_t srp_cred;
	gnutls_certificate_credentials_t cert_cred;

if (gnutls_check_version("3.1.4") == NULL) {
		fprintf(stderr,
			"GnuTLS 3.1.4 or later is required for this example\n");
		exit(1);
	}

/* for backwards compatibility with gnutls < 3.3.0 */
	gnutls_global_init();

gnutls_srp_allocate_client_credentials(&srp_cred);
	gnutls_certificate_allocate_credentials(&cert_cred);

gnutls_certificate_set_x509_trust_file(cert_cred, CAFILE,
					       GNUTLS_X509_FMT_PEM);
	gnutls_srp_set_client_credentials(srp_cred, USERNAME, PASSWORD);

/* connects to server
	 */
	sd = tcp_connect();

/* Initialize TLS session
	 */
	gnutls_init(&session, GNUTLS_CLIENT);

/* Set the priorities.
	 */
	gnutls_priority_set_direct(session, "NORMAL:+SRP:+SRP-RSA:+SRP-DSS",
				   NULL);

/* put the SRP credentials to the current session
	 */
	gnutls_credentials_set(session, GNUTLS_CRD_SRP, srp_cred);
	gnutls_credentials_set(session, GNUTLS_CRD_CERTIFICATE, cert_cred);

gnutls_transport_set_int(session, sd);
	gnutls_handshake_set_timeout(session, GNUTLS_DEFAULT_HANDSHAKE_TIMEOUT);

/* Perform the TLS handshake
	 */
	do {
		ret = gnutls_handshake(session);
	} while (ret < 0 && gnutls_error_is_fatal(ret) == 0);

if (ret < 0) {
		fprintf(stderr, "*** Handshake failed\n");
		gnutls_perror(ret);
		goto end;
	} else {
		char *desc;

desc = gnutls_session_get_desc(session);
		printf("- Session info: %s\n", desc);
		gnutls_free(desc);
	}

gnutls_record_send(session, MSG, strlen(MSG));

ret = gnutls_record_recv(session, buffer, MAX_BUF);
	if (gnutls_error_is_fatal(ret) != 0 || ret == 0) {
		if (ret == 0) {
			printf("- Peer has closed the GnuTLS connection\n");
			goto end;
		} else {
			fprintf(stderr, "*** Error: %s\n",
				gnutls_strerror(ret));
			goto end;
		}
	} else
		check_alert(session, ret);

if (ret > 0) {
		printf("- Received %d bytes: ", ret);
		for (ii = 0; ii < ret; ii++) {
			fputc(buffer[ii], stdout);
		}
		fputs("\n", stdout);
	}
	gnutls_bye(session, GNUTLS_SHUT_RDWR);

end:

tcp_close(sd);

gnutls_deinit(session);

gnutls_srp_free_client_credentials(srp_cred);
	gnutls_certificate_free_credentials(cert_cred);

gnutls_global_deinit();

return 0;
}

File: gnutls.info,  Node: Legacy client example with X.509 certificate support,  Next: Client example in C++,  Prev: Client example with SRP authentication,  Up: More advanced client and servers

7.3.7 Legacy client example with X.509 certificate support
----------------------------------------------------------

For applications that need to maintain compatibility with the GnuTLS
3.1.x library, this client example is identical to *note Client example
with X.509 certificate support:: but utilizes APIs that were available
in GnuTLS 3.1.4.

/* This example code is placed in the public domain. */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <gnutls/gnutls.h>
#include <gnutls/x509.h>
#include "examples.h"

/* A very basic TLS client, with X.509 authentication and server certificate
 * verification utilizing the GnuTLS 3.1.x API. 
 * Note that error recovery is minimal for simplicity.
 */

#define MAX_BUF 1024
#define CAFILE "/etc/ssl/certs/ca-certificates.crt"
#define MSG "GET / HTTP/1.0\r\n\r\n"

extern int tcp_connect(void);
extern void tcp_close(int sd);
static int _verify_certificate_callback(gnutls_session_t session);

int main(void)
{
	int ret, sd, ii;
	gnutls_session_t session;
	char buffer[MAX_BUF + 1];
	gnutls_certificate_credentials_t xcred;

if (gnutls_check_version("3.1.4") == NULL) {
		fprintf(stderr,
			"GnuTLS 3.1.4 or later is required for this example\n");
		exit(1);
	}

CHECK(gnutls_global_init());

/* X509 stuff */
	CHECK(gnutls_certificate_allocate_credentials(&xcred));

/* sets the trusted cas file
	 */
	CHECK(gnutls_certificate_set_x509_trust_file(xcred, CAFILE,
						     GNUTLS_X509_FMT_PEM));
	gnutls_certificate_set_verify_function(xcred,
					       _verify_certificate_callback);

/* If client holds a certificate it can be set using the following:
	 *
	 gnutls_certificate_set_x509_key_file (xcred, 
	 "cert.pem", "key.pem", 
	 GNUTLS_X509_FMT_PEM); 
	 */

/* Initialize TLS session 
	 */
	CHECK(gnutls_init(&session, GNUTLS_CLIENT));

gnutls_session_set_ptr(session, (void *)"www.example.com");

gnutls_server_name_set(session, GNUTLS_NAME_DNS, "www.example.com",
			       strlen("www.example.com"));

/* use default priorities */
	CHECK(gnutls_set_default_priority(session));
#if 0
	/* if more fine-graned control is required */
	ret = gnutls_priority_set_direct(session, "NORMAL", &err);
	if (ret < 0) {
		if (ret == GNUTLS_E_INVALID_REQUEST) {
			fprintf(stderr, "Syntax error at: %s\n", err);
		}
		exit(1);
	}
#endif

/* put the x509 credentials to the current session
	 */
	CHECK(gnutls_credentials_set(session, GNUTLS_CRD_CERTIFICATE, xcred));

/* connect to the peer
	 */
	sd = tcp_connect();

gnutls_transport_set_int(session, sd);
	gnutls_handshake_set_timeout(session, GNUTLS_DEFAULT_HANDSHAKE_TIMEOUT);

/* Perform the TLS handshake
	 */
	do {
		ret = gnutls_handshake(session);
	} while (ret < 0 && gnutls_error_is_fatal(ret) == 0);

if (ret < 0) {
		fprintf(stderr, "*** Handshake failed\n");
		gnutls_perror(ret);
		goto end;
	} else {
		char *desc;

desc = gnutls_session_get_desc(session);
		printf("- Session info: %s\n", desc);
		gnutls_free(desc);
	}

LOOP_CHECK(ret, gnutls_record_send(session, MSG, strlen(MSG)));

if (ret > 0) {
		printf("- Received %d bytes: ", ret);
		for (ii = 0; ii < ret; ii++) {
			fputc(buffer[ii], stdout);
		}
		fputs("\n", stdout);
	}

CHECK(gnutls_bye(session, GNUTLS_SHUT_RDWR));

end:

tcp_close(sd);

gnutls_deinit(session);

gnutls_certificate_free_credentials(xcred);

gnutls_global_deinit();

return 0;
}

/* This function will verify the peer's certificate, and check
 * if the hostname matches, as well as the activation, expiration dates.
 */
static int _verify_certificate_callback(gnutls_session_t session)
{
	unsigned int status;
	int type;
	const char *hostname;
	gnutls_datum_t out;

/* read hostname */
	hostname = gnutls_session_get_ptr(session);

/* This verification function uses the trusted CAs in the credentials
	 * structure. So you must have installed one or more CA certificates.
	 */

CHECK(gnutls_certificate_verify_peers3(session, hostname, &status));

type = gnutls_certificate_type_get(session);

CHECK(gnutls_certificate_verification_status_print(status, type, &out,
							   0));

printf("%s", out.data);

gnutls_free(out.data);

if (status != 0) /* Certificate is not trusted */
		return GNUTLS_E_CERTIFICATE_ERROR;

/* notify gnutls to continue handshake normally */
	return 0;
}

File: gnutls.info,  Node: Client example in C++,  Next: Echo server with PSK authentication,  Prev: Legacy client example with X.509 certificate support,  Up: More advanced client and servers

7.3.8 Client example using the C++ API
--------------------------------------

The following client is a simple example of a client client utilizing
the GnuTLS C++ API.

#include <config.h>
#include <iostream>
#include <stdexcept>
#include <gnutls/gnutls.h>
#include <gnutls/gnutlsxx.h>
#include <cstring> /* for strlen */

/* A very basic TLS client, with anonymous authentication.
 * written by Eduardo Villanueva Che.
 */

#define MAX_BUF 1024
#define SA struct sockaddr

#define CAFILE "ca.pem"
#define MSG "GET / HTTP/1.0\r\n\r\n"

extern "C"
{
    int tcp_connect(void);
    void tcp_close(int sd);
}

int main(void)
{
    int sd = -1;
    gnutls_global_init();

try
    {

/* Allow connections to servers that have OpenPGP keys as well.
         */
        gnutls::client_session session;

/* X509 stuff */
        gnutls::certificate_credentials credentials;

/* sets the trusted cas file
         */
        credentials.set_x509_trust_file(CAFILE, GNUTLS_X509_FMT_PEM);
        /* put the x509 credentials to the current session
         */
        session.set_credentials(credentials);

/* Use default priorities */
        session.set_priority ("NORMAL", NULL);

/* connect to the peer
         */
        sd = tcp_connect();
        session.set_transport_ptr((gnutls_transport_ptr_t) (ptrdiff_t)sd);

/* Perform the TLS handshake
         */
        int ret = session.handshake();
        if (ret < 0)
        {
            throw std::runtime_error("Handshake failed");
        }
        else
        {
            std::cout << "- Handshake was completed" << std::endl;
        }

session.send(MSG, strlen(MSG));
        char buffer[MAX_BUF + 1];
        ret = session.recv(buffer, MAX_BUF);
        if (ret == 0)
        {
            throw std::runtime_error("Peer has closed the TLS connection");
        }
        else if (ret < 0)
        {
            throw std::runtime_error(gnutls_strerror(ret));
        }

std::cout << "- Received " << ret << " bytes:" << std::endl;
        std::cout.write(buffer, ret);
        std::cout << std::endl;

session.bye(GNUTLS_SHUT_RDWR);
    }
    catch (std::exception &ex)
    {
        std::cerr << "Exception caught: " << ex.what() << std::endl;
    }

if (sd != -1)
        tcp_close(sd);

gnutls_global_deinit();

return 0;
}

File: gnutls.info,  Node: Echo server with PSK authentication,  Next: Echo server with SRP authentication,  Prev: Client example in C++,  Up: More advanced client and servers

7.3.9 Echo server with PSK authentication
-----------------------------------------

This is a server which supports PSK authentication.

/* This example code is placed in the public domain. */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#define KEYFILE "key.pem"
#define CERTFILE "cert.pem"
#define CAFILE "/etc/ssl/certs/ca-certificates.crt"
#define CRLFILE "crl.pem"

#define LOOP_CHECK(rval, cmd) \
	do {                  \
		rval = cmd;   \
	} while (rval == GNUTLS_E_AGAIN || rval == GNUTLS_E_INTERRUPTED)

/* This is a sample TLS echo server, supporting X.509 and PSK
   authentication.
 */

#define SOCKET_ERR(err, s)  \
	if (err == -1) {    \
		perror(s);  \
		return (1); \
	}
#define MAX_BUF 1024
#define PORT 5556 /* listen to 5556 port */

static int pskfunc(gnutls_session_t session, const char *username,
		   gnutls_datum_t *key)
{
	printf("psk: username %s\n", username);
	key->data = gnutls_malloc(4);
	key->data[0] = 0xDE;
	key->data[1] = 0xAD;
	key->data[2] = 0xBE;
	key->data[3] = 0xEF;
	key->size = 4;
	return 0;
}

int main(void)
{
	int err, listen_sd;
	int sd, ret;
	struct sockaddr_in sa_serv;
	struct sockaddr_in sa_cli;
	socklen_t client_len;
	char topbuf[512];
	gnutls_session_t session;
	gnutls_certificate_credentials_t x509_cred;
	gnutls_psk_server_credentials_t psk_cred;
	gnutls_priority_t priority_cache;
	char buffer[MAX_BUF + 1];
	int optval = 1;
	int kx;

if (gnutls_check_version("3.1.4") == NULL) {
		fprintf(stderr,
			"GnuTLS 3.1.4 or later is required for this example\n");
		exit(1);
	}

/* for backwards compatibility with gnutls < 3.3.0 */
	gnutls_global_init();

gnutls_certificate_allocate_credentials(&x509_cred);
	gnutls_certificate_set_x509_trust_file(x509_cred, CAFILE,
					       GNUTLS_X509_FMT_PEM);

gnutls_certificate_set_x509_crl_file(x509_cred, CRLFILE,
					     GNUTLS_X509_FMT_PEM);

gnutls_certificate_set_x509_key_file(x509_cred, CERTFILE, KEYFILE,
					     GNUTLS_X509_FMT_PEM);

gnutls_psk_allocate_server_credentials(&psk_cred);
	gnutls_psk_set_server_credentials_function(psk_cred, pskfunc);

/* pre-3.6.3 equivalent:
	 * gnutls_priority_init(&priority_cache,
	 *                      "NORMAL:+PSK:+ECDHE-PSK:+DHE-PSK",
	 *                      NULL);
	 */
	gnutls_priority_init2(&priority_cache, "+ECDHE-PSK:+DHE-PSK:+PSK", NULL,
			      GNUTLS_PRIORITY_INIT_DEF_APPEND);

gnutls_certificate_set_known_dh_params(x509_cred,
					       GNUTLS_SEC_PARAM_MEDIUM);

/* Socket operations
	 */
	listen_sd = socket(AF_INET, SOCK_STREAM, 0);
	SOCKET_ERR(listen_sd, "socket");

memset(&sa_serv, '\0', sizeof(sa_serv));
	sa_serv.sin_family = AF_INET;
	sa_serv.sin_addr.s_addr = INADDR_ANY;
	sa_serv.sin_port = htons(PORT); /* Server Port number */

setsockopt(listen_sd, SOL_SOCKET, SO_REUSEADDR, (void *)&optval,
		   sizeof(int));

err = bind(listen_sd, (struct sockaddr *)&sa_serv, sizeof(sa_serv));
	SOCKET_ERR(err, "bind");
	err = listen(listen_sd, 1024);
	SOCKET_ERR(err, "listen");

printf("Server ready. Listening to port '%d'.\n\n", PORT);

client_len = sizeof(sa_cli);
	for (;;) {
		gnutls_init(&session, GNUTLS_SERVER);
		gnutls_priority_set(session, priority_cache);
		gnutls_credentials_set(session, GNUTLS_CRD_CERTIFICATE,
				       x509_cred);
		gnutls_credentials_set(session, GNUTLS_CRD_PSK, psk_cred);

/* request client certificate if any.
		 */
		gnutls_certificate_server_set_request(session,
						      GNUTLS_CERT_REQUEST);

sd = accept(listen_sd, (struct sockaddr *)&sa_cli, &client_len);

printf("- connection from %s, port %d\n",
		       inet_ntop(AF_INET, &sa_cli.sin_addr, topbuf,
				 sizeof(topbuf)),
		       ntohs(sa_cli.sin_port));

gnutls_transport_set_int(session, sd);
		LOOP_CHECK(ret, gnutls_handshake(session));
		if (ret < 0) {
			close(sd);
			gnutls_deinit(session);
			fprintf(stderr, "*** Handshake has failed (%s)\n\n",
				gnutls_strerror(ret));
			continue;
		}
		printf("- Handshake was completed\n");

kx = gnutls_kx_get(session);
		if (kx == GNUTLS_KX_PSK || kx == GNUTLS_KX_DHE_PSK ||
		    kx == GNUTLS_KX_ECDHE_PSK) {
			printf("- User %s was connected\n",
			       gnutls_psk_server_get_username(session));
		}

/* see the Getting peer's information example */
		/* print_info(session); */

for (;;) {
			LOOP_CHECK(ret, gnutls_record_recv(session, buffer,
							   MAX_BUF));

if (ret == 0) {
				printf("\n- Peer has closed the GnuTLS connection\n");
				break;
			} else if (ret < 0 && gnutls_error_is_fatal(ret) == 0) {
				fprintf(stderr, "*** Warning: %s\n",
					gnutls_strerror(ret));
			} else if (ret < 0) {
				fprintf(stderr,
					"\n*** Received corrupted "
					"data(%d). Closing the connection.\n\n",
					ret);
				break;
			} else if (ret > 0) {
				/* echo data back to the client
				 */
				gnutls_record_send(session, buffer, ret);
			}
		}
		printf("\n");
		/* do not wait for the peer to close the connection.
		 */
		LOOP_CHECK(ret, gnutls_bye(session, GNUTLS_SHUT_WR));

close(sd);
		gnutls_deinit(session);
	}
	close(listen_sd);

gnutls_certificate_free_credentials(x509_cred);
	gnutls_psk_free_server_credentials(psk_cred);

gnutls_priority_deinit(priority_cache);

gnutls_global_deinit();

return 0;
}

File: gnutls.info,  Node: Echo server with SRP authentication,  Next: Echo server with anonymous authentication,  Prev: Echo server with PSK authentication,  Up: More advanced client and servers

7.3.10 Echo server with SRP authentication
------------------------------------------

This is a server which supports SRP authentication.  It is also possible
to combine this functionality with a certificate server.  Here it is
separate for simplicity.

/* This example code is placed in the public domain. */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#define SRP_PASSWD "tpasswd"
#define SRP_PASSWD_CONF "tpasswd.conf"

#define KEYFILE "key.pem"
#define CERTFILE "cert.pem"
#define CAFILE "/etc/ssl/certs/ca-certificates.crt"

#define LOOP_CHECK(rval, cmd) \
	do {                  \
		rval = cmd;   \
	} while (rval == GNUTLS_E_AGAIN || rval == GNUTLS_E_INTERRUPTED)

/* This is a sample TLS-SRP echo server.
 */

#define SOCKET_ERR(err, s)  \
	if (err == -1) {    \
		perror(s);  \
		return (1); \
	}
#define MAX_BUF 1024
#define PORT 5556 /* listen to 5556 port */

int main(void)
{
	int err, listen_sd;
	int sd, ret;
	struct sockaddr_in sa_serv;
	struct sockaddr_in sa_cli;
	socklen_t client_len;
	char topbuf[512];
	gnutls_session_t session;
	gnutls_srp_server_credentials_t srp_cred;
	gnutls_certificate_credentials_t cert_cred;
	char buffer[MAX_BUF + 1];
	int optval = 1;
	char name[256];

strcpy(name, "Echo Server");

if (gnutls_check_version("3.1.4") == NULL) {
		fprintf(stderr,
			"GnuTLS 3.1.4 or later is required for this example\n");
		exit(1);
	}

/* for backwards compatibility with gnutls < 3.3.0 */
	gnutls_global_init();

/* SRP_PASSWD a password file (created with the included srptool utility) 
	 */
	gnutls_srp_allocate_server_credentials(&srp_cred);
	gnutls_srp_set_server_credentials_file(srp_cred, SRP_PASSWD,
					       SRP_PASSWD_CONF);

gnutls_certificate_allocate_credentials(&cert_cred);
	gnutls_certificate_set_x509_trust_file(cert_cred, CAFILE,
					       GNUTLS_X509_FMT_PEM);
	gnutls_certificate_set_x509_key_file(cert_cred, CERTFILE, KEYFILE,
					     GNUTLS_X509_FMT_PEM);

/* TCP socket operations
	 */
	listen_sd = socket(AF_INET, SOCK_STREAM, 0);
	SOCKET_ERR(listen_sd, "socket");

memset(&sa_serv, '\0', sizeof(sa_serv));
	sa_serv.sin_family = AF_INET;
	sa_serv.sin_addr.s_addr = INADDR_ANY;
	sa_serv.sin_port = htons(PORT); /* Server Port number */

setsockopt(listen_sd, SOL_SOCKET, SO_REUSEADDR, (void *)&optval,
		   sizeof(int));

err = bind(listen_sd, (struct sockaddr *)&sa_serv, sizeof(sa_serv));
	SOCKET_ERR(err, "bind");
	err = listen(listen_sd, 1024);
	SOCKET_ERR(err, "listen");

printf("%s ready. Listening to port '%d'.\n\n", name, PORT);

client_len = sizeof(sa_cli);
	for (;;) {
		gnutls_init(&session, GNUTLS_SERVER);
		gnutls_priority_set_direct(session,
					   "NORMAL"
					   ":-KX-ALL:+SRP:+SRP-DSS:+SRP-RSA",
					   NULL);
		gnutls_credentials_set(session, GNUTLS_CRD_SRP, srp_cred);
		/* for the certificate authenticated ciphersuites.
		 */
		gnutls_credentials_set(session, GNUTLS_CRD_CERTIFICATE,
				       cert_cred);

sd = accept(listen_sd, (struct sockaddr *)&sa_cli, &client_len);

printf("- connection from %s, port %d\n",
		       inet_ntop(AF_INET, &sa_cli.sin_addr, topbuf,
				 sizeof(topbuf)),
		       ntohs(sa_cli.sin_port));

gnutls_transport_set_int(session, sd);

/* print_info(session); */

for (;;) {
			LOOP_CHECK(ret, gnutls_record_recv(session, buffer,
							   MAX_BUF));

if (ret == 0) {
				printf("\n- Peer has closed the GnuTLS connection\n");
				break;
			} else if (ret < 0 && gnutls_error_is_fatal(ret) == 0) {
				fprintf(stderr, "*** Warning: %s\n",
					gnutls_strerror(ret));
			} else if (ret < 0) {
				fprintf(stderr,
					"\n*** Received corrupted "
					"data(%d). Closing the connection.\n\n",
					ret);
				break;
			} else if (ret > 0) {
				/* echo data back to the client
				 */
				gnutls_record_send(session, buffer, ret);
			}
		}
		printf("\n");
		/* do not wait for the peer to close the connection. */
		LOOP_CHECK(ret, gnutls_bye(session, GNUTLS_SHUT_WR));

close(sd);
		gnutls_deinit(session);
	}
	close(listen_sd);

gnutls_srp_free_server_credentials(srp_cred);
	gnutls_certificate_free_credentials(cert_cred);

gnutls_global_deinit();

return 0;
}

File: gnutls.info,  Node: Echo server with anonymous authentication,  Next: Helper functions for TCP connections,  Prev: Echo server with SRP authentication,  Up: More advanced client and servers

7.3.11 Echo server with anonymous authentication
------------------------------------------------

This example server supports anonymous authentication, and could be used
to serve the example client for anonymous authentication.

/* This example code is placed in the public domain. */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

/* This is a sample TLS 1.0 echo server, for anonymous authentication only.
 */

#define SOCKET_ERR(err, s)  \
	if (err == -1) {    \
		perror(s);  \
		return (1); \
	}
#define MAX_BUF 1024
#define PORT 5556 /* listen to 5556 port */

int main(void)
{
	int err, listen_sd;
	int sd, ret;
	struct sockaddr_in sa_serv;
	struct sockaddr_in sa_cli;
	socklen_t client_len;
	char topbuf[512];
	gnutls_session_t session;
	gnutls_anon_server_credentials_t anoncred;
	char buffer[MAX_BUF + 1];
	int optval = 1;

if (gnutls_check_version("3.1.4") == NULL) {
		fprintf(stderr,
			"GnuTLS 3.1.4 or later is required for this example\n");
		exit(1);
	}

/* for backwards compatibility with gnutls < 3.3.0 */
	gnutls_global_init();

gnutls_anon_allocate_server_credentials(&anoncred);

gnutls_anon_set_server_known_dh_params(anoncred,
					       GNUTLS_SEC_PARAM_MEDIUM);

/* Socket operations
	 */
	listen_sd = socket(AF_INET, SOCK_STREAM, 0);
	SOCKET_ERR(listen_sd, "socket");

memset(&sa_serv, '\0', sizeof(sa_serv));
	sa_serv.sin_family = AF_INET;
	sa_serv.sin_addr.s_addr = INADDR_ANY;
	sa_serv.sin_port = htons(PORT); /* Server Port number */

setsockopt(listen_sd, SOL_SOCKET, SO_REUSEADDR, (void *)&optval,
		   sizeof(int));

err = bind(listen_sd, (struct sockaddr *)&sa_serv, sizeof(sa_serv));
	SOCKET_ERR(err, "bind");
	err = listen(listen_sd, 1024);
	SOCKET_ERR(err, "listen");

printf("Server ready. Listening to port '%d'.\n\n", PORT);

client_len = sizeof(sa_cli);
	for (;;) {
		gnutls_init(&session, GNUTLS_SERVER);
		gnutls_priority_set_direct(session,
					   "NORMAL:+ANON-ECDH:+ANON-DH", NULL);
		gnutls_credentials_set(session, GNUTLS_CRD_ANON, anoncred);

sd = accept(listen_sd, (struct sockaddr *)&sa_cli, &client_len);

printf("- connection from %s, port %d\n",
		       inet_ntop(AF_INET, &sa_cli.sin_addr, topbuf,
				 sizeof(topbuf)),
		       ntohs(sa_cli.sin_port));

gnutls_transport_set_int(session, sd);

do {
			ret = gnutls_handshake(session);
		} while (ret < 0 && gnutls_error_is_fatal(ret) == 0);

if (ret < 0) {
			close(sd);
			gnutls_deinit(session);
			fprintf(stderr, "*** Handshake has failed (%s)\n\n",
				gnutls_strerror(ret));
			continue;
		}
		printf("- Handshake was completed\n");

/* see the Getting peer's information example */
		/* print_info(session); */

for (;;) {
			ret = gnutls_record_recv(session, buffer, MAX_BUF);

if (ret == 0) {
				printf("\n- Peer has closed the GnuTLS connection\n");
				break;
			} else if (ret < 0 && gnutls_error_is_fatal(ret) == 0) {
				fprintf(stderr, "*** Warning: %s\n",
					gnutls_strerror(ret));
			} else if (ret < 0) {
				fprintf(stderr,
					"\n*** Received corrupted "
					"data(%d). Closing the connection.\n\n",
					ret);
				break;
			} else if (ret > 0) {
				/* echo data back to the client
				 */
				gnutls_record_send(session, buffer, ret);
			}
		}
		printf("\n");
		/* do not wait for the peer to close the connection.
		 */
		gnutls_bye(session, GNUTLS_SHUT_WR);

close(sd);
		gnutls_deinit(session);
	}
	close(listen_sd);

gnutls_anon_free_server_credentials(anoncred);

gnutls_global_deinit();

return 0;
}

File: gnutls.info,  Node: Helper functions for TCP connections,  Next: Helper functions for UDP connections,  Prev: Echo server with anonymous authentication,  Up: More advanced client and servers

7.3.12 Helper functions for TCP connections
-------------------------------------------

Those helper function abstract away TCP connection handling from the
other examples.  It is required to build some examples.

/* This example code is placed in the public domain. */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <unistd.h>

/* tcp.c */
int tcp_connect(void);
void tcp_close(int sd);

/* Connects to the peer and returns a socket
 * descriptor.
 */
extern int tcp_connect(void)
{
	const char *PORT = "5556";
	const char *SERVER = "127.0.0.1";
	int err, sd;
	struct sockaddr_in sa;

/* connects to server
	 */
	sd = socket(AF_INET, SOCK_STREAM, 0);

memset(&sa, '\0', sizeof(sa));
	sa.sin_family = AF_INET;
	sa.sin_port = htons(atoi(PORT));
	inet_pton(AF_INET, SERVER, &sa.sin_addr);

err = connect(sd, (struct sockaddr *)&sa, sizeof(sa));
	if (err < 0) {
		fprintf(stderr, "Connect error\n");
		exit(1);
	}

return sd;
}

/* closes the given socket descriptor.
 */
extern void tcp_close(int sd)
{
	shutdown(sd, SHUT_RDWR); /* no more receptions */
	close(sd);
}

File: gnutls.info,  Node: Helper functions for UDP connections,  Prev: Helper functions for TCP connections,  Up: More advanced client and servers

7.3.13 Helper functions for UDP connections
-------------------------------------------

The UDP helper functions abstract away UDP connection handling from the
other examples.  It is required to build the examples using UDP.

/* This example code is placed in the public domain. */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <unistd.h>

/* udp.c */
int udp_connect(void);
void udp_close(int sd);

/* Connects to the peer and returns a socket
 * descriptor.
 */
extern int udp_connect(void)
{
	const char *PORT = "5557";
	const char *SERVER = "127.0.0.1";
	int err, sd;
#if defined(IP_DONTFRAG) || defined(IP_MTU_DISCOVER)
	int optval;
#endif
	struct sockaddr_in sa;

/* connects to server
	 */
	sd = socket(AF_INET, SOCK_DGRAM, 0);

memset(&sa, '\0', sizeof(sa));
	sa.sin_family = AF_INET;
	sa.sin_port = htons(atoi(PORT));
	inet_pton(AF_INET, SERVER, &sa.sin_addr);

#if defined(IP_DONTFRAG)
	optval = 1;
	setsockopt(sd, IPPROTO_IP, IP_DONTFRAG, (const void *)&optval,
		   sizeof(optval));
#elif defined(IP_MTU_DISCOVER)
	optval = IP_PMTUDISC_DO;
	setsockopt(sd, IPPROTO_IP, IP_MTU_DISCOVER, (const void *)&optval,
		   sizeof(optval));
#endif

err = connect(sd, (struct sockaddr *)&sa, sizeof(sa));
	if (err < 0) {
		fprintf(stderr, "Connect error\n");
		exit(1);
	}

return sd;
}

/* closes the given socket descriptor.
 */
extern void udp_close(int sd)
{
	close(sd);
}

File: gnutls.info,  Node: OCSP example,  Next: Miscellaneous examples,  Prev: More advanced client and servers,  Up: GnuTLS application examples

7.4 OCSP example
================

Generate OCSP request
---------------------

A small tool to generate OCSP requests.

/* This example code is placed in the public domain. */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <gnutls/gnutls.h>
#include <gnutls/crypto.h>
#include <gnutls/ocsp.h>
#ifndef NO_LIBCURL
#include <curl/curl.h>
#endif
#include "read-file.h"

size_t get_data(void *buffer, size_t size, size_t nmemb, void *userp);
static gnutls_x509_crt_t load_cert(const char *cert_file);
static void _response_info(const gnutls_datum_t *data);
static void _generate_request(gnutls_datum_t *rdata, gnutls_x509_crt_t cert,
			      gnutls_x509_crt_t issuer, gnutls_datum_t *nonce);
static int _verify_response(gnutls_datum_t *data, gnutls_x509_crt_t cert,
			    gnutls_x509_crt_t signer, gnutls_datum_t *nonce);

/* This program queries an OCSP server.
   It expects three files. argv[1] containing the certificate to
   be checked, argv[2] holding the issuer for this certificate,
   and argv[3] holding a trusted certificate to verify OCSP's response.
   argv[4] is optional and should hold the server host name.

For simplicity the libcurl library is used.
 */

int main(int argc, char *argv[])
{
	gnutls_datum_t ud, tmp;
	int ret;
	gnutls_datum_t req;
	gnutls_x509_crt_t cert, issuer, signer;
#ifndef NO_LIBCURL
	CURL *handle;
	struct curl_slist *headers = NULL;
#endif
	int v, seq;
	const char *cert_file = argv[1];
	const char *issuer_file = argv[2];
	const char *signer_file = argv[3];
	char *hostname = NULL;
	unsigned char noncebuf[23];
	gnutls_datum_t nonce = { noncebuf, sizeof(noncebuf) };

gnutls_global_init();

if (argc > 4)
		hostname = argv[4];

ret = gnutls_rnd(GNUTLS_RND_NONCE, nonce.data, nonce.size);
	if (ret < 0)
		exit(1);

cert = load_cert(cert_file);
	issuer = load_cert(issuer_file);
	signer = load_cert(signer_file);

if (hostname == NULL) {
		for (seq = 0;; seq++) {
			ret = gnutls_x509_crt_get_authority_info_access(
				cert, seq, GNUTLS_IA_OCSP_URI, &tmp, NULL);
			if (ret == GNUTLS_E_UNKNOWN_ALGORITHM)
				continue;
			if (ret == GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE) {
				fprintf(stderr,
					"No URI was found in the certificate.\n");
				exit(1);
			}
			if (ret < 0) {
				fprintf(stderr, "error: %s\n",
					gnutls_strerror(ret));
				exit(1);
			}

printf("CA issuers URI: %.*s\n", tmp.size, tmp.data);

hostname = malloc(tmp.size + 1);
			if (!hostname) {
				fprintf(stderr,
					"error: cannot allocate memory\n");
				exit(1);
			}
			memcpy(hostname, tmp.data, tmp.size);
			hostname[tmp.size] = 0;

gnutls_free(tmp.data);
			break;
		}
	}

/* Note that the OCSP servers hostname might be available
	 * using gnutls_x509_crt_get_authority_info_access() in the issuer's
	 * certificate */

memset(&ud, 0, sizeof(ud));
	fprintf(stderr, "Connecting to %s\n", hostname);

_generate_request(&req, cert, issuer, &nonce);

#ifndef NO_LIBCURL
	curl_global_init(CURL_GLOBAL_ALL);

handle = curl_easy_init();
	if (handle == NULL)
		exit(1);

headers = curl_slist_append(headers,
				    "Content-Type: application/ocsp-request");

curl_easy_setopt(handle, CURLOPT_HTTPHEADER, headers);
	curl_easy_setopt(handle, CURLOPT_POSTFIELDS, (void *)req.data);
	curl_easy_setopt(handle, CURLOPT_POSTFIELDSIZE, req.size);
	curl_easy_setopt(handle, CURLOPT_URL, hostname);
	curl_easy_setopt(handle, CURLOPT_WRITEFUNCTION, get_data);
	curl_easy_setopt(handle, CURLOPT_WRITEDATA, &ud);

ret = curl_easy_perform(handle);
	if (ret != 0) {
		fprintf(stderr, "curl[%d] error %d\n", __LINE__, ret);
		exit(1);
	}

curl_easy_cleanup(handle);
#endif

_response_info(&ud);

v = _verify_response(&ud, cert, signer, &nonce);

gnutls_x509_crt_deinit(cert);
	gnutls_x509_crt_deinit(issuer);
	gnutls_x509_crt_deinit(signer);
	gnutls_global_deinit();

return v;
}

static void _response_info(const gnutls_datum_t *data)
{
	gnutls_ocsp_resp_t resp;
	int ret;
	gnutls_datum buf;

ret = gnutls_ocsp_resp_init(&resp);
	if (ret < 0)
		exit(1);

ret = gnutls_ocsp_resp_import(resp, data);
	if (ret < 0)
		exit(1);

ret = gnutls_ocsp_resp_print(resp, GNUTLS_OCSP_PRINT_FULL, &buf);
	if (ret != 0)
		exit(1);

printf("%.*s", buf.size, buf.data);
	gnutls_free(buf.data);

gnutls_ocsp_resp_deinit(resp);
}

static gnutls_x509_crt_t load_cert(const char *cert_file)
{
	gnutls_x509_crt_t crt;
	int ret;
	gnutls_datum_t data;
	size_t size;

ret = gnutls_x509_crt_init(&crt);
	if (ret < 0)
		exit(1);

data.data = (void *)read_file(cert_file, RF_BINARY, &size);
	data.size = size;

if (!data.data) {
		fprintf(stderr, "Cannot open file: %s\n", cert_file);
		exit(1);
	}

ret = gnutls_x509_crt_import(crt, &data, GNUTLS_X509_FMT_PEM);
	free(data.data);
	if (ret < 0) {
		fprintf(stderr, "Cannot import certificate in %s: %s\n",
			cert_file, gnutls_strerror(ret));
		exit(1);
	}

return crt;
}

static void _generate_request(gnutls_datum_t *rdata, gnutls_x509_crt_t cert,
			      gnutls_x509_crt_t issuer, gnutls_datum_t *nonce)
{
	gnutls_ocsp_req_t req;
	int ret;

ret = gnutls_ocsp_req_init(&req);
	if (ret < 0)
		exit(1);

ret = gnutls_ocsp_req_add_cert(req, GNUTLS_DIG_SHA1, issuer, cert);
	if (ret < 0)
		exit(1);

ret = gnutls_ocsp_req_set_nonce(req, 0, nonce);
	if (ret < 0)
		exit(1);

ret = gnutls_ocsp_req_export(req, rdata);
	if (ret != 0)
		exit(1);

gnutls_ocsp_req_deinit(req);

return;
}

static int _verify_response(gnutls_datum_t *data, gnutls_x509_crt_t cert,
			    gnutls_x509_crt_t signer, gnutls_datum_t *nonce)
{
	gnutls_ocsp_resp_t resp;
	int ret;
	unsigned verify, resp_indx;
	gnutls_datum_t rnonce;

ret = gnutls_ocsp_resp_init(&resp);
	if (ret < 0)
		exit(1);

ret = gnutls_ocsp_resp_import(resp, data);
	if (ret < 0)
		exit(1);

for (resp_indx = 0;; resp_indx++) {
		ret = gnutls_ocsp_resp_check_crt(resp, resp_indx, cert);
		if (ret == 0 || ret == GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE)
			break;
	}
	if (ret < 0)
		exit(1);

ret = gnutls_ocsp_resp_get_nonce(resp, NULL, &rnonce);
	if (ret < 0)
		exit(1);

if (rnonce.size != nonce->size ||
	    memcmp(nonce->data, rnonce.data, nonce->size) != 0) {
		exit(1);
	}

ret = gnutls_ocsp_resp_verify_direct(resp, signer, &verify, 0);
	if (ret < 0)
		exit(1);

printf("Verifying OCSP Response: ");
	if (verify == 0)
		printf("Verification success!\n");
	else
		printf("Verification error!\n");

if (verify & GNUTLS_OCSP_VERIFY_SIGNER_NOT_FOUND)
		printf("Signer cert not found\n");

if (verify & GNUTLS_OCSP_VERIFY_SIGNER_KEYUSAGE_ERROR)
		printf("Signer cert keyusage error\n");

if (verify & GNUTLS_OCSP_VERIFY_UNTRUSTED_SIGNER)
		printf("Signer cert is not trusted\n");

if (verify & GNUTLS_OCSP_VERIFY_INSECURE_ALGORITHM)
		printf("Insecure algorithm\n");

if (verify & GNUTLS_OCSP_VERIFY_SIGNATURE_FAILURE)
		printf("Signature failure\n");

if (verify & GNUTLS_OCSP_VERIFY_CERT_NOT_ACTIVATED)
		printf("Signer cert not yet activated\n");

if (verify & GNUTLS_OCSP_VERIFY_CERT_EXPIRED)
		printf("Signer cert expired\n");

gnutls_free(rnonce.data);
	gnutls_ocsp_resp_deinit(resp);

return verify;
}

size_t get_data(void *buffer, size_t size, size_t nmemb, void *userp)
{
	gnutls_datum_t *ud = userp;

size *= nmemb;

ud->data = realloc(ud->data, size + ud->size);
	if (ud->data == NULL) {
		fprintf(stderr, "Not enough memory for the request\n");
		exit(1);
	}

memcpy(&ud->data[ud->size], buffer, size);
	ud->size += size;

return size;
}

File: gnutls.info,  Node: Miscellaneous examples,  Prev: OCSP example,  Up: GnuTLS application examples

7.5 Miscellaneous examples
==========================

* Menu:

* Checking for an alert::
* X.509 certificate parsing example::
* Listing the ciphersuites in a priority string::
* PKCS12 structure generation example::

File: gnutls.info,  Node: Checking for an alert,  Next: X.509 certificate parsing example,  Up: Miscellaneous examples

7.5.1 Checking for an alert
---------------------------

This is a function that checks if an alert has been received in the
current session.

/* This example code is placed in the public domain. */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <stdio.h>
#include <stdlib.h>
#include <gnutls/gnutls.h>

#include "examples.h"

/* This function will check whether the given return code from
 * a gnutls function (recv/send), is an alert, and will print
 * that alert.
 */
void check_alert(gnutls_session_t session, int ret)
{
	int last_alert;

if (ret == GNUTLS_E_WARNING_ALERT_RECEIVED ||
	    ret == GNUTLS_E_FATAL_ALERT_RECEIVED) {
		last_alert = gnutls_alert_get(session);

/* The check for renegotiation is only useful if we are 
		 * a server, and we had requested a rehandshake.
		 */
		if (last_alert == GNUTLS_A_NO_RENEGOTIATION &&
		    ret == GNUTLS_E_WARNING_ALERT_RECEIVED)
			printf("* Received NO_RENEGOTIATION alert. "
			       "Client Does not support renegotiation.\n");
		else
			printf("* Received alert '%d': %s.\n", last_alert,
			       gnutls_alert_get_name(last_alert));
	}
}

File: gnutls.info,  Node: X.509 certificate parsing example,  Next: Listing the ciphersuites in a priority string,  Prev: Checking for an alert,  Up: Miscellaneous examples

7.5.2 X.509 certificate parsing example
---------------------------------------

To demonstrate the X.509 parsing capabilities an example program is
listed below.  That program reads the peer's certificate, and prints
information about it.

/* This example code is placed in the public domain. */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <stdio.h>
#include <stdlib.h>
#include <gnutls/gnutls.h>
#include <gnutls/x509.h>

#include "examples.h"

static const char *bin2hex(const void *bin, size_t bin_size)
{
	static char printable[110];
	const unsigned char *_bin = bin;
	char *print;
	size_t i;

if (bin_size > 50)
		bin_size = 50;

print = printable;
	for (i = 0; i < bin_size; i++) {
		sprintf(print, "%.2x ", _bin[i]);
		print += 2;
	}

return printable;
}

/* This function will print information about this session's peer
 * certificate.
 */
void print_x509_certificate_info(gnutls_session_t session)
{
	char serial[40];
	char dn[256];
	size_t size;
	unsigned int algo, bits;
	time_t expiration_time, activation_time;
	const gnutls_datum_t *cert_list;
	unsigned int cert_list_size = 0;
	gnutls_x509_crt_t cert;
	gnutls_datum_t cinfo;

/* This function only works for X.509 certificates.
	 */
	if (gnutls_certificate_type_get(session) != GNUTLS_CRT_X509)
		return;

cert_list = gnutls_certificate_get_peers(session, &cert_list_size);

printf("Peer provided %d certificates.\n", cert_list_size);

if (cert_list_size > 0) {
		int ret;

/* we only print information about the first certificate.
		 */
		gnutls_x509_crt_init(&cert);

gnutls_x509_crt_import(cert, &cert_list[0],
				       GNUTLS_X509_FMT_DER);

printf("Certificate info:\n");

/* This is the preferred way of printing short information about
		   a certificate. */

ret = gnutls_x509_crt_print(cert, GNUTLS_CRT_PRINT_ONELINE,
					    &cinfo);
		if (ret == 0) {
			printf("\t%s\n", cinfo.data);
			gnutls_free(cinfo.data);
		}

/* If you want to extract fields manually for some other reason,
		   below are popular example calls. */

expiration_time = gnutls_x509_crt_get_expiration_time(cert);
		activation_time = gnutls_x509_crt_get_activation_time(cert);

printf("\tCertificate is valid since: %s",
		       ctime(&activation_time));
		printf("\tCertificate expires: %s", ctime(&expiration_time));

/* Print the serial number of the certificate.
		 */
		size = sizeof(serial);
		gnutls_x509_crt_get_serial(cert, serial, &size);

printf("\tCertificate serial number: %s\n",
		       bin2hex(serial, size));

/* Extract some of the public key algorithm's parameters
		 */
		algo = gnutls_x509_crt_get_pk_algorithm(cert, &bits);

printf("Certificate public key: %s",
		       gnutls_pk_algorithm_get_name(algo));

/* Print the version of the X.509
		 * certificate.
		 */
		printf("\tCertificate version: #%d\n",
		       gnutls_x509_crt_get_version(cert));

size = sizeof(dn);
		gnutls_x509_crt_get_dn(cert, dn, &size);
		printf("\tDN: %s\n", dn);

size = sizeof(dn);
		gnutls_x509_crt_get_issuer_dn(cert, dn, &size);
		printf("\tIssuer's DN: %s\n", dn);

gnutls_x509_crt_deinit(cert);
	}
}

File: gnutls.info,  Node: Listing the ciphersuites in a priority string,  Next: PKCS12 structure generation example,  Prev: X.509 certificate parsing example,  Up: Miscellaneous examples

7.5.3 Listing the ciphersuites in a priority string
---------------------------------------------------

This is a small program to list the enabled ciphersuites by a priority
string.

/* This example code is placed in the public domain. */

#include <config.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <gnutls/gnutls.h>

static void print_cipher_suite_list(const char *priorities)
{
	size_t i;
	int ret;
	unsigned int idx;
	const char *name;
	const char *err;
	unsigned char id[2];
	gnutls_protocol_t version;
	gnutls_priority_t pcache;

if (priorities != NULL) {
		printf("Cipher suites for %s\n", priorities);

ret = gnutls_priority_init(&pcache, priorities, &err);
		if (ret < 0) {
			fprintf(stderr, "Syntax error at: %s\n", err);
			exit(1);
		}

for (i = 0;; i++) {
			ret = gnutls_priority_get_cipher_suite_index(pcache, i,
								     &idx);
			if (ret == GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE)
				break;
			if (ret == GNUTLS_E_UNKNOWN_CIPHER_SUITE)
				continue;

name = gnutls_cipher_suite_info(idx, id, NULL, NULL,
							NULL, &version);

if (name != NULL)
				printf("%-50s\t0x%02x, 0x%02x\t%s\n", name,
				       (unsigned char)id[0],
				       (unsigned char)id[1],
				       gnutls_protocol_get_name(version));
		}

return;
	}
}

int main(int argc, char **argv)
{
	if (argc > 1)
		print_cipher_suite_list(argv[1]);
	return 0;
}

File: gnutls.info,  Node: PKCS12 structure generation example,  Prev: Listing the ciphersuites in a priority string,  Up: Miscellaneous examples

7.5.4 PKCS #12 structure generation example
-------------------------------------------

This small program demonstrates the usage of the PKCS #12 API, by
generating such a structure.

/* This example code is placed in the public domain. */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include <stdio.h>
#include <stdlib.h>
#include <gnutls/gnutls.h>
#include <gnutls/pkcs12.h>

#include "examples.h"

#define OUTFILE "out.p12"

/* This function will write a pkcs12 structure into a file.
 * cert: is a DER encoded certificate
 * pkcs8_key: is a PKCS #8 encrypted key (note that this must be
 *  encrypted using a PKCS #12 cipher, or some browsers will crash)
 * password: is the password used to encrypt the PKCS #12 packet.
 */
int write_pkcs12(const gnutls_datum_t *cert, const gnutls_datum_t *pkcs8_key,
		 const char *password)
{
	gnutls_pkcs12_t pkcs12;
	int ret, bag_index;
	gnutls_pkcs12_bag_t bag, key_bag;
	char pkcs12_struct[10 * 1024];
	size_t pkcs12_struct_size;
	FILE *fp;

/* A good idea might be to use gnutls_x509_privkey_get_key_id()
	 * to obtain a unique ID.
	 */
	gnutls_datum_t key_id = { (void *)"\x00\x00\x07", 3 };

gnutls_global_init();

/* Firstly we create two helper bags, which hold the certificate,
	 * and the (encrypted) key.
	 */

gnutls_pkcs12_bag_init(&bag);
	gnutls_pkcs12_bag_init(&key_bag);

ret = gnutls_pkcs12_bag_set_data(bag, GNUTLS_BAG_CERTIFICATE, cert);
	if (ret < 0) {
		fprintf(stderr, "ret: %s\n", gnutls_strerror(ret));
		return 1;
	}

/* ret now holds the bag's index.
	 */
	bag_index = ret;

/* Associate a friendly name with the given certificate. Used
	 * by browsers.
	 */
	gnutls_pkcs12_bag_set_friendly_name(bag, bag_index, "My name");

/* Associate the certificate with the key using a unique key
	 * ID.
	 */
	gnutls_pkcs12_bag_set_key_id(bag, bag_index, &key_id);

/* use weak encryption for the certificate. 
	 */
	gnutls_pkcs12_bag_encrypt(bag, password, GNUTLS_PKCS_USE_PKCS12_RC2_40);

/* Now the key.
	 */

ret = gnutls_pkcs12_bag_set_data(
		key_bag, GNUTLS_BAG_PKCS8_ENCRYPTED_KEY, pkcs8_key);
	if (ret < 0) {
		fprintf(stderr, "ret: %s\n", gnutls_strerror(ret));
		return 1;
	}

/* Note that since the PKCS #8 key is already encrypted we don't
	 * bother encrypting that bag.
	 */
	bag_index = ret;

gnutls_pkcs12_bag_set_friendly_name(key_bag, bag_index, "My name");

gnutls_pkcs12_bag_set_key_id(key_bag, bag_index, &key_id);

/* The bags were filled. Now create the PKCS #12 structure.
	 */
	gnutls_pkcs12_init(&pkcs12);

/* Insert the two bags in the PKCS #12 structure.
	 */

gnutls_pkcs12_set_bag(pkcs12, bag);
	gnutls_pkcs12_set_bag(pkcs12, key_bag);

/* Generate a message authentication code for the PKCS #12
	 * structure.
	 */
	gnutls_pkcs12_generate_mac(pkcs12, password);

pkcs12_struct_size = sizeof(pkcs12_struct);
	ret = gnutls_pkcs12_export(pkcs12, GNUTLS_X509_FMT_DER, pkcs12_struct,
				   &pkcs12_struct_size);
	if (ret < 0) {
		fprintf(stderr, "ret: %s\n", gnutls_strerror(ret));
		return 1;
	}

fp = fopen(OUTFILE, "w");
	if (fp == NULL) {
		fprintf(stderr, "cannot open file\n");
		return 1;
	}
	fwrite(pkcs12_struct, 1, pkcs12_struct_size, fp);
	fclose(fp);

gnutls_pkcs12_bag_deinit(bag);
	gnutls_pkcs12_bag_deinit(key_bag);
	gnutls_pkcs12_deinit(pkcs12);

return 0;
}

File: gnutls.info,  Node: System-wide configuration of the library,  Next: Using GnuTLS as a cryptographic library,  Prev: GnuTLS application examples,  Up: Top

8 System-wide configuration of the library
******************************************

GnuTLS 3.6.9 introduced a system-wide configuration of the library which
can be used to disable or mark algorithms and protocols as insecure
system-wide, overriding the library defaults.  The format of this
configuration file is of an INI file, with the hash ('#') allowed for
commenting.  It intentionally does not allow switching algorithms or
protocols which were disabled or marked as insecure during compile time
to the secure set.  This is to prevent the feature from being used to
attack the system.  Unknown options or sections in the configuration
file are skipped unless the environment variable
‘GNUTLS_SYSTEM_PRIORITY_FAIL_ON_INVALID’ is set to 1, where it would
cause the library to exit on unknown options.

The location of the default configuration file is
‘/usr/local/etc/gnutls/config’, but its actual location may be
overridden during compile time or at run-time using the
‘GNUTLS_SYSTEM_PRIORITY_FILE’ environment variable.  The file used can
be queried using *note gnutls_get_system_config_file::.

-- Function: const char * gnutls_get_system_config_file ( VOID)

Returns the filename of the system wide configuration file to be
     loaded by the library.

*Returns:* a constant pointer to the config file path

*Since:* 3.6.9

* Menu:

* Application-specific priority strings::
* Disabling algorithms and protocols::
* Querying for disabled algorithms and protocols::
* Overriding the parameter verification profile::
* Overriding the default priority string::
* Enabling/Disabling system/acceleration protocols::
* Enabling/Disabling RSAES-PKCS1-v1_5::

File: gnutls.info,  Node: Application-specific priority strings,  Next: Disabling algorithms and protocols,  Up: System-wide configuration of the library

8.1 Application-specific priority strings
=========================================

It is possible to specify custom cipher priority strings, in addition to
the default priority strings (‘NORMAL’, ‘PERFORMANCE’, etc.).  These can
be used either by individual applications, or even as the default option
if the library is compiled with the configuration option
‘--with-default-priority-string’.  In the latter case the defined
priority string will be used for applications using *note
gnutls_set_default_priority:: or *note
gnutls_set_default_priority_append::.

The priority strings can be specified in the global section of the
configuration file, or in the section named ‘[priorities]’.  The format
is '‘KEYWORD = VALUE’', e.g.,

When used they may be followed by additional options that will be
appended to the system string (e.g., '‘@EXAMPLE-PRIORITY:+SRP’').
'‘EXAMPLE-PRIORITY=NORMAL:+ARCFOUR-128’'.  Since version 3.5.1
applications are allowed to specify fallback keywords such as
@KEYWORD1,@KEYWORD2, and the first valid keyword will be used.

The following example configuration defines a priority string called
‘@SYSTEM’.  When set, its full settings can be queried using ‘gnutls-cli
--priority @SYSTEM --list’.

[priorities]
     SYSTEM = NORMAL:-AES-128-CBC:-AES-256-CBC

File: gnutls.info,  Node: Disabling algorithms and protocols,  Next: Querying for disabled algorithms and protocols,  Prev: Application-specific priority strings,  Up: System-wide configuration of the library

8.2 Disabling algorithms and protocols
======================================

The approach above works well to create consistent system-wide settings
for cooperative GnuTLS applications.  When an application however does
not use the *note gnutls_set_default_priority:: or *note
gnutls_set_default_priority_append:: functions, the method is not
sufficient to prevent applications from using protocols or algorithms
forbidden by a local policy.  The override method described below
enables the deprecation of algorithms and protocols system-wide for all
applications.

The available options must be set in the ‘[overrides]’ section of the
configuration file and can be
   • ‘insecure-sig-for-cert’: to mark the signature algorithm as
     insecure when used in certificates.
   • ‘insecure-sig’: to mark the signature algorithm as insecure for any
     use.
   • ‘insecure-hash’: to mark the hash algorithm as insecure for digital
     signature use (provides a more generic way to disable digital
     signatures for broken hash algorithms).
   • ‘disabled-curve’: to disable the specified elliptic curve.
   • ‘disabled-version’: to disable the specified TLS versions.
   • ‘tls-disabled-cipher’: to disable the specified ciphers for use in
     the TLS or DTLS protocols.
   • ‘tls-disabled-mac’: to disable the specified MAC algorithms for use
     in the TLS or DTLS protocols.
   • ‘tls-disabled-group’: to disable the specified group for use in the
     TLS or DTLS protocols.
   • ‘tls-disabled-kx’: to disable the specified key exchange algorithms
     for use in the TLS or DTLS protocols (applies to TLS1.2 or
     earlier).

Each of the options can be repeated multiple times when multiple values
need to be disabled or enabled.

The valid values for the options above can be found in the 'Protocols',
'Digests' 'PK-signatures', 'Protocols', 'Ciphers', and 'MACs' fields of
the output of ‘gnutls-cli --list’.

Sometimes the system administrator wants to enable only specific
algorithms, despite the library defaults.  GnuTLS provides an
alternative mode of overriding: allowlisting.

As shown below in the examples, it is hard to use this mode correctly,
as it requires understanding of how algorithms are used underneath by
the protocols.  Allowlisting configuration mode is intended to be used
by the operating system vendors that prefer laying out the library
defaults exhaustively from scratch instead on depending on gnutls
presets, such as ‘NORMAL’.  Applications are then expected to optionally
disable or enable only a subset algorithms on top of the vendor-provided
configuration.

In the allowlisting mode, all the algorithms are initially marked as
insecure or disabled, and shall be explicitly turned on by the options
listed below in the ‘[overrides]’ section.  As the allowlisting mode is
mutually exclusive to the blocklisting mode, the options listed above
for the blocklisting mode are forbidden in the allowlisting mode, and
vice versa.

• ‘secure-sig-for-cert’: to mark the signature algorithm as secure
     when used in certificates.
   • ‘secure-sig’: to mark the signature algorithm as secure for any
     use.
   • ‘secure-hash’: to mark the hash algorithm as secure for digital
     signature use (provides a more generic way to enable digital
     signatures for broken hash algorithms).
   • ‘enabled-curve’: to enable the specified elliptic curve.
   • ‘enabled-version’: to enable the specified TLS versions.
   • ‘tls-enabled-cipher’: to enable the specified ciphers for use in
     the TLS or DTLS protocols.
   • ‘tls-enabled-mac’: to enable the specified MAC algorithms for use
     in the TLS or DTLS protocols.
   • ‘tls-enabled-group’: to enable the specified group for use in the
     TLS or DTLS protocols.
   • ‘tls-enabled-kx’: to enable the specified key exchange algorithms
     for use in the TLS or DTLS protocols (applies to TLS1.2 or
     earlier).

The allowlisting mode can be enabled by adding ‘override-mode =
allowlist’ in the ‘[global]’ section.

The following functions allow the applications to modify the setting.

‘INT *note gnutls_ecc_curve_set_enabled:: (gnutls_ecc_curve_t CURVE, unsigned int ENABLED)’
‘INT *note gnutls_sign_set_secure:: (gnutls_sign_algorithm_t SIGN, unsigned int SECURE)’
‘INT *note gnutls_sign_set_secure_for_certs:: (gnutls_sign_algorithm_t SIGN, unsigned int SECURE)’
‘INT *note gnutls_digest_set_secure:: (gnutls_digest_algorithm_t DIG, unsigned int SECURE)’
‘INT *note gnutls_protocol_set_enabled:: (gnutls_protocol_t VERSION, unsigned int ENABLED)’

When the allowlisting mode is in effect, a ‘@SYSTEM’ priority string is
automatically constructed from the options in the ‘[overrides]’ section.
For this reason, the above functions should be called before the
‘@SYSTEM’ priority is used.

8.2.1 Examples
--------------

The following example marks as insecure all digital signature algorithms
which depend on SHA384, as well as the RSA-SHA1 signature algorithm.

[overrides]
     insecure-hash = sha384
     insecure-sig = rsa-sha1

The following example marks RSA-SHA256 as insecure for use in
certificates and disables the TLS1.0 and TLS1.1 protocols.

[overrides]
     insecure-sig-for-cert = rsa-sha256
     disabled-version = tls1.0
     disabled-version = tls1.1

The following example disables the ‘AES-128-CBC’ and ‘AES-256-CBC’
ciphers, the ‘HMAC-SHA1’ MAC algorithm and the ‘GROUP-FFDHE8192’ group
for TLS and DTLS protocols.

[overrides]
     tls-disabled-cipher = aes-128-cbc
     tls-disabled-cipher = aes-256-cbc
     tls-disabled-mac = sha1
     tls-disabled-group = group-ffdhe8192

The following example demonstrates the use of the allowlisting mode.
All the signature algorithms are disabled by default but ‘RSA-SHA256’.
Note that the hash algorithm ‘SHA256’ also needs to be explicitly
enabled.

[global]
     override-mode = allowlist

[overrides]
     secure-hash = sha256
     secure-sig = rsa-sha256

To enable a TLS ciphersuite in the allowlist mode requires a more
verbose configuration, explicitly listing algorithm dependencies.  The
following example enables TLS_AES_128_GCM_SHA256, using the SECP256R1
curve for signing and key exchange.

[global]
     override-mode = allowlist

[overrides]
     secure-hash = sha256
     enabled-curve = secp256r1
     secure-sig = ecdsa-secp256r1-sha256
     enabled-version = tls1.3
     tls-enabled-cipher = aes-128-gcm
     tls-enabled-mac = aead
     tls-enabled-group = secp256r1

File: gnutls.info,  Node: Querying for disabled algorithms and protocols,  Next: Overriding the parameter verification profile,  Prev: Disabling algorithms and protocols,  Up: System-wide configuration of the library

8.3 Querying for disabled algorithms and protocols
==================================================

When necessary applications can query whether a particular algorithm or
protocol has been marked as insecure or disabled system-wide.  Digital
signatures can be queried using the following algorithms.
‘UNSIGNED *note gnutls_sign_is_secure:: (gnutls_sign_algorithm_t ALGORITHM)’
‘UNSIGNED *note gnutls_sign_is_secure2:: (gnutls_sign_algorithm_t ALGORITHM, unsigned int FLAGS)’

Any disabled protocol versions or elliptic curves will not show up in
the lists provided by the following functions.

‘CONST GNUTLS_PROTOCOL_T * *note gnutls_protocol_list:: ( VOID)’
‘CONST GNUTLS_GROUP_T * *note gnutls_group_list:: ( VOID)’
‘CONST GNUTLS_ECC_CURVE_T * *note gnutls_ecc_curve_list:: ( VOID)’

It is not possible to query for insecure hash algorithms directly (only
indirectly through the signature API).

File: gnutls.info,  Node: Overriding the parameter verification profile,  Next: Overriding the default priority string,  Prev: Querying for disabled algorithms and protocols,  Up: System-wide configuration of the library

8.4 Overriding the parameter verification profile
=================================================

When verifying a certificate or TLS session parameters, GnuTLS uses a
set of profiles associated with the session to determine whether the
parameters seen in the session are acceptable.  For example, whether the
RSA public key size as seen on the wire, or the Diffie-Hellman
parameters for the session.  These profiles are normally set using the
‘%PROFILE’ priority string (see *note Priority Strings:: and *note
Selecting cryptographic key sizes::).

It is possible to set the low bar profile that applications cannot
override using the following.

[overrides]

# do not allow applications use the LOW or VERY-WEAK profiles.
     min-verification-profile = legacy

File: gnutls.info,  Node: Overriding the default priority string,  Next: Enabling/Disabling system/acceleration protocols,  Prev: Overriding the parameter verification profile,  Up: System-wide configuration of the library

8.5 Overriding the default priority string
==========================================

GnuTLS uses default priority string which is defined at compiled time.
Usually it is set to ‘NORMAL’.  This override allows to set the default
priority string to something more appropriate for a given deployment.

Below example sets a more specific default priority string.
     [overrides]
     default-priority-string = SECURE128:-VERS-TLS-ALL:+VERS-TLS1.3

File: gnutls.info,  Node: Enabling/Disabling system/acceleration protocols,  Next: Enabling/Disabling RSAES-PKCS1-v1_5,  Prev: Overriding the default priority string,  Up: System-wide configuration of the library

8.6 Enabling/Disabling system/acceleration protocols
====================================================

The following options can overwrite default behavior of protocols
system-wide.
     [global]
     ktls = true

8.6.1 Enabling KTLS
-------------------

When GnuTLS is build with -–enable-ktls configuration, KTLS is disabled
by default.  This can be enabled by setting ‘ktls = true’ in ‘[global]’
section.

File: gnutls.info,  Node: Enabling/Disabling RSAES-PKCS1-v1_5,  Prev: Enabling/Disabling system/acceleration protocols,  Up: System-wide configuration of the library

8.7 Enabling/Disabling RSAES-PKCS1-v1_5
=======================================

This option can be used to enable/disable RSA PKCS1 v1.5 encryption and
decryption in GnuTLS. The RSAES-PKCS1-v1_5 is enabled by default.

Below example shows how to explicitely disable the RSAES-PKCS1-v1_5.
     [overrides]
     allow-rsa-pkcs1-encrypt = false

File: gnutls.info,  Node: Using GnuTLS as a cryptographic library,  Next: Other included programs,  Prev: System-wide configuration of the library,  Up: Top

9 Using GnuTLS as a cryptographic library
*****************************************

GnuTLS is not a low-level cryptographic library, i.e., it does not
provide access to basic cryptographic primitives.  However it abstracts
the internal cryptographic back-end (see *note Cryptographic Backend::),
providing symmetric crypto, hash and HMAC algorithms, as well access to
the random number generation.  For a low-level crypto API the usage of
nettle (1) library is recommended.

* Menu:

* Symmetric algorithms::
* Public key algorithms::
* Cryptographic Message Syntax / PKCS7::
* Hash and MAC functions::
* Random number generation::
* Overriding algorithms::

---------- Footnotes ----------

(1) See <https://www.lysator.liu.se/~nisse/nettle/>.

File: gnutls.info,  Node: Symmetric algorithms,  Next: Public key algorithms,  Up: Using GnuTLS as a cryptographic library

9.1 Symmetric algorithms
========================

The available functions to access symmetric crypto algorithms operations
are listed in the sections below.  The supported algorithms are the
algorithms required by the TLS protocol.  They are listed in *note
Figure 9.1: gnutls_cipher_algorithm_t.  Note that there two types of
ciphers, the ones providing an authenticated-encryption with associated
data (AEAD), and the legacy ciphers which provide raw access to the
ciphers.  We recommend the use of the AEAD ciphers under the AEAD APIs
for new applications as they are designed to minimize the misuse of
cryptographic primitives.

‘GNUTLS_CIPHER_UNKNOWN’
     Value to identify an unknown/unsupported algorithm.
‘GNUTLS_CIPHER_NULL’
     The NULL (identity) encryption algorithm.
‘GNUTLS_CIPHER_ARCFOUR_128’
     ARCFOUR stream cipher with 128-bit keys.
‘GNUTLS_CIPHER_3DES_CBC’
     3DES in CBC mode.
‘GNUTLS_CIPHER_AES_128_CBC’
     AES in CBC mode with 128-bit keys.
‘GNUTLS_CIPHER_AES_256_CBC’
     AES in CBC mode with 256-bit keys.
‘GNUTLS_CIPHER_ARCFOUR_40’
     ARCFOUR stream cipher with 40-bit keys.
‘GNUTLS_CIPHER_CAMELLIA_128_CBC’
     Camellia in CBC mode with 128-bit keys.
‘GNUTLS_CIPHER_CAMELLIA_256_CBC’
     Camellia in CBC mode with 256-bit keys.
‘GNUTLS_CIPHER_AES_192_CBC’
     AES in CBC mode with 192-bit keys.
‘GNUTLS_CIPHER_AES_128_GCM’
     AES in GCM mode with 128-bit keys (AEAD).
‘GNUTLS_CIPHER_AES_256_GCM’
     AES in GCM mode with 256-bit keys (AEAD).
‘GNUTLS_CIPHER_CAMELLIA_192_CBC’
     Camellia in CBC mode with 192-bit keys.
‘GNUTLS_CIPHER_SALSA20_256’
     Salsa20 with 256-bit keys.
‘GNUTLS_CIPHER_ESTREAM_SALSA20_256’
     Estream's Salsa20 variant with 256-bit keys.
‘GNUTLS_CIPHER_CAMELLIA_128_GCM’
     CAMELLIA in GCM mode with 128-bit keys (AEAD).
‘GNUTLS_CIPHER_CAMELLIA_256_GCM’
     CAMELLIA in GCM mode with 256-bit keys (AEAD).
‘GNUTLS_CIPHER_RC2_40_CBC’
     RC2 in CBC mode with 40-bit keys.
‘GNUTLS_CIPHER_DES_CBC’
     DES in CBC mode (56-bit keys).
‘GNUTLS_CIPHER_AES_128_CCM’
     AES in CCM mode with 128-bit keys (AEAD).
‘GNUTLS_CIPHER_AES_256_CCM’
     AES in CCM mode with 256-bit keys (AEAD).
‘GNUTLS_CIPHER_AES_128_CCM_8’
     AES in CCM mode with 64-bit tag and 128-bit keys (AEAD).
‘GNUTLS_CIPHER_AES_256_CCM_8’
     AES in CCM mode with 64-bit tag and 256-bit keys (AEAD).
‘GNUTLS_CIPHER_CHACHA20_POLY1305’
     The Chacha20 cipher with the Poly1305 authenticator (AEAD).
‘GNUTLS_CIPHER_GOST28147_TC26Z_CFB’
     GOST 28147-89 (Magma) cipher in CFB mode with TC26 Z S-box.
‘GNUTLS_CIPHER_GOST28147_CPA_CFB’
     GOST 28147-89 (Magma) cipher in CFB mode with CryptoPro A S-box.
‘GNUTLS_CIPHER_GOST28147_CPB_CFB’
     GOST 28147-89 (Magma) cipher in CFB mode with CryptoPro B S-box.
‘GNUTLS_CIPHER_GOST28147_CPC_CFB’
     GOST 28147-89 (Magma) cipher in CFB mode with CryptoPro C S-box.
‘GNUTLS_CIPHER_GOST28147_CPD_CFB’
     GOST 28147-89 (Magma) cipher in CFB mode with CryptoPro D S-box.
‘GNUTLS_CIPHER_AES_128_CFB8’
     AES in CFB8 mode with 128-bit keys.
‘GNUTLS_CIPHER_AES_192_CFB8’
     AES in CFB8 mode with 192-bit keys.
‘GNUTLS_CIPHER_AES_256_CFB8’
     AES in CFB8 mode with 256-bit keys.
‘GNUTLS_CIPHER_AES_128_XTS’
     AES in XTS mode with 128-bit key + 128bit tweak key.
‘GNUTLS_CIPHER_AES_256_XTS’
     AES in XTS mode with 256-bit key + 256bit tweak key.  Note that the
     XTS ciphers are message oriented.  The whole message needs to be
     provided with a single call, because cipher-stealing requires to
     know where the message actually terminates in order to be able to
     compute where the stealing occurs.
‘GNUTLS_CIPHER_GOST28147_TC26Z_CNT’
     GOST 28147-89 (Magma) cipher in CNT mode with TC26 Z S-box.
‘GNUTLS_CIPHER_CHACHA20_64’
     Chacha20 cipher with 64-bit nonces and 64-bit block counters.
‘GNUTLS_CIPHER_CHACHA20_32’
     Chacha20 cipher with 96-bit nonces and 32-bit block counters.
‘GNUTLS_CIPHER_AES_128_SIV’
     AES in SIV mode with 128-bit key.
‘GNUTLS_CIPHER_AES_256_SIV’
     AES in SIV mode with 256-bit key.  Note that the SIV ciphers can
     only be used with the AEAD interface, and the IV plays a role as
     the authentication tag while it is prepended to the cipher text.
‘GNUTLS_CIPHER_AES_192_GCM’
     AES in GCM mode with 192-bit keys (AEAD).
‘GNUTLS_CIPHER_MAGMA_CTR_ACPKM’
     GOST R 34.12-2015 (Magma) cipher in CTR-ACPKM mode.
‘GNUTLS_CIPHER_KUZNYECHIK_CTR_ACPKM’
     GOST R 34.12-2015 (Kuznyechik) cipher in CTR-ACPKM mode.
‘GNUTLS_CIPHER_AES_128_SIV_GCM’
     AES in SIV-GCM mode with 128-bit key.
‘GNUTLS_CIPHER_AES_256_SIV_GCM’
     AES in SIV-GCM mode with 256-bit key.
‘GNUTLS_CIPHER_IDEA_PGP_CFB’
     IDEA in CFB mode (placeholder - unsupported).
‘GNUTLS_CIPHER_3DES_PGP_CFB’
     3DES in CFB mode (placeholder - unsupported).
‘GNUTLS_CIPHER_CAST5_PGP_CFB’
     CAST5 in CFB mode (placeholder - unsupported).
‘GNUTLS_CIPHER_BLOWFISH_PGP_CFB’
     Blowfish in CFB mode (placeholder - unsupported).
‘GNUTLS_CIPHER_SAFER_SK128_PGP_CFB’
     Safer-SK in CFB mode with 128-bit keys (placeholder - unsupported).
‘GNUTLS_CIPHER_AES128_PGP_CFB’
     AES in CFB mode with 128-bit keys (placeholder - unsupported).
‘GNUTLS_CIPHER_AES192_PGP_CFB’
     AES in CFB mode with 192-bit keys (placeholder - unsupported).
‘GNUTLS_CIPHER_AES256_PGP_CFB’
     AES in CFB mode with 256-bit keys (placeholder - unsupported).
‘GNUTLS_CIPHER_TWOFISH_PGP_CFB’
     Twofish in CFB mode (placeholder - unsupported).

Figure 9.1: The supported ciphers.

Authenticated-encryption API
----------------------------

The AEAD API provides access to all ciphers supported by GnuTLS which
support authenticated encryption with associated data; these ciphers are
marked with the AEAD keyword on the table above.  The AEAD cipher API is
particularly suitable for message or packet-encryption as it provides
authentication and encryption on the same API. See ‘RFC5116’ for more
information on authenticated encryption.

‘INT *note gnutls_aead_cipher_init:: (gnutls_aead_cipher_hd_t * HANDLE, gnutls_cipher_algorithm_t CIPHER, const gnutls_datum_t * KEY)’
‘INT *note gnutls_aead_cipher_encrypt:: (gnutls_aead_cipher_hd_t HANDLE, const void * NONCE, size_t NONCE_LEN, const void * AUTH, size_t AUTH_LEN, size_t TAG_SIZE, const void * PTEXT, size_t PTEXT_LEN, void * CTEXT, size_t * CTEXT_LEN)’
‘INT *note gnutls_aead_cipher_decrypt:: (gnutls_aead_cipher_hd_t HANDLE, const void * NONCE, size_t NONCE_LEN, const void * AUTH, size_t AUTH_LEN, size_t TAG_SIZE, const void * CTEXT, size_t CTEXT_LEN, void * PTEXT, size_t * PTEXT_LEN)’
‘VOID *note gnutls_aead_cipher_deinit:: (gnutls_aead_cipher_hd_t HANDLE)’

Because the encryption function above may be difficult to use with
scattered data, we provide the following API.

-- Function: int gnutls_aead_cipher_encryptv (gnutls_aead_cipher_hd_t
          HANDLE, const void * NONCE, size_t NONCE_LEN, const giovec_t *
          AUTH_IOV, int AUTH_IOVCNT, size_t TAG_SIZE, const giovec_t *
          IOV, int IOVCNT, void * CTEXT, size_t * CTEXT_LEN)
     HANDLE: is a ‘gnutls_aead_cipher_hd_t’ type.

NONCE: the nonce to set

NONCE_LEN: The length of the nonce

AUTH_IOV: additional data to be authenticated

AUTH_IOVCNT: The number of buffers in ‘auth_iov’

TAG_SIZE: The size of the tag to use (use zero for the default)

IOV: the data to be encrypted

IOVCNT: The number of buffers in ‘iov’

CTEXT: the encrypted data including authentication tag

CTEXT_LEN: the length of encrypted data (initially must hold the
     maximum available size, including space for tag)

This function will encrypt the provided data buffers using the
     algorithm specified by the context.  The output data will contain
     the authentication tag.

*Returns:* Zero or a negative error code on error.

*Since:* 3.6.3

Legacy API
----------

The legacy API provides low-level access to all legacy ciphers supported
by GnuTLS, and some of the AEAD ciphers (e.g., AES-GCM and CHACHA20).
The restrictions of the nettle library implementation of the ciphers
apply verbatim to this API(1).

‘INT *note gnutls_cipher_init:: (gnutls_cipher_hd_t * HANDLE, gnutls_cipher_algorithm_t CIPHER, const gnutls_datum_t * KEY, const gnutls_datum_t * IV)’
‘INT *note gnutls_cipher_encrypt2:: (gnutls_cipher_hd_t HANDLE, const void * PTEXT, size_t PTEXT_LEN, void * CTEXT, size_t CTEXT_LEN)’
‘INT *note gnutls_cipher_decrypt2:: (gnutls_cipher_hd_t HANDLE, const void * CTEXT, size_t CTEXT_LEN, void * PTEXT, size_t PTEXT_LEN)’
‘VOID *note gnutls_cipher_set_iv:: (gnutls_cipher_hd_t HANDLE, void * IV, size_t IVLEN)’
‘VOID *note gnutls_cipher_deinit:: (gnutls_cipher_hd_t HANDLE)’

‘INT *note gnutls_cipher_add_auth:: (gnutls_cipher_hd_t HANDLE, const void * PTEXT, size_t PTEXT_SIZE)’
‘INT *note gnutls_cipher_tag:: (gnutls_cipher_hd_t HANDLE, void * TAG, size_t TAG_SIZE)’
While the latter two functions allow the same API can be used with
authenticated encryption ciphers, it is recommended to use the following
functions which are solely for AEAD ciphers.  The latter API is designed
to be simple to use and also hard to misuse, by handling the tag
verification and addition in transparent way.

---------- Footnotes ----------

(1) See the nettle manual
<https://www.lysator.liu.se/~nisse/nettle/nettle.html>

File: gnutls.info,  Node: Public key algorithms,  Next: Cryptographic Message Syntax / PKCS7,  Prev: Symmetric algorithms,  Up: Using GnuTLS as a cryptographic library

9.2 Public key algorithms
=========================

Public key cryptography algorithms such as RSA, DSA and ECDSA, are
accessed using the abstract key API in *note Abstract key types::.  This
is a high level API with the advantage of transparently handling keys
stored in memory and keys present in smart cards.

‘INT *note gnutls_privkey_init:: (gnutls_privkey_t * KEY)’
‘INT *note gnutls_privkey_import_url:: (gnutls_privkey_t KEY, const char * URL, unsigned int FLAGS)’
‘INT *note gnutls_privkey_import_x509_raw:: (gnutls_privkey_t PKEY, const gnutls_datum_t * DATA, gnutls_x509_crt_fmt_t FORMAT, const char * PASSWORD, unsigned int FLAGS)’
‘INT *note gnutls_privkey_sign_data:: (gnutls_privkey_t SIGNER, gnutls_digest_algorithm_t HASH, unsigned int FLAGS, const gnutls_datum_t * DATA, gnutls_datum_t * SIGNATURE)’
‘INT *note gnutls_privkey_sign_hash:: (gnutls_privkey_t SIGNER, gnutls_digest_algorithm_t HASH_ALGO, unsigned int FLAGS, const gnutls_datum_t * HASH_DATA, gnutls_datum_t * SIGNATURE)’
‘VOID *note gnutls_privkey_deinit:: (gnutls_privkey_t KEY)’

‘INT *note gnutls_pubkey_init:: (gnutls_pubkey_t * KEY)’
‘INT *note gnutls_pubkey_import_url:: (gnutls_pubkey_t KEY, const char * URL, unsigned int FLAGS)’
‘INT *note gnutls_pubkey_import_x509:: (gnutls_pubkey_t KEY, gnutls_x509_crt_t CRT, unsigned int FLAGS)’
‘INT *note gnutls_pubkey_verify_data2:: (gnutls_pubkey_t PUBKEY, gnutls_sign_algorithm_t ALGO, unsigned int FLAGS, const gnutls_datum_t * DATA, const gnutls_datum_t * SIGNATURE)’
‘INT *note gnutls_pubkey_verify_hash2:: (gnutls_pubkey_t KEY, gnutls_sign_algorithm_t ALGO, unsigned int FLAGS, const gnutls_datum_t * HASH, const gnutls_datum_t * SIGNATURE)’
‘VOID *note gnutls_pubkey_deinit:: (gnutls_pubkey_t KEY)’

Keys stored in memory can be imported using functions like *note
gnutls_privkey_import_x509_raw::, while keys on smart cards or HSMs
should be imported using their PKCS#11 URL with *note
gnutls_privkey_import_url::.

If any of the smart card operations require PIN, that should be provided
either by setting the global PIN function (*note
gnutls_pkcs11_set_pin_function::), or better with the targeted to
structures functions such as *note gnutls_privkey_set_pin_function::.

9.2.1 Key generation
--------------------

All supported key types (including RSA, DSA, ECDSA, Ed25519, Ed448) can
be generated with GnuTLS. They can be generated with the simpler *note
gnutls_privkey_generate:: or with the more advanced *note
gnutls_privkey_generate2::.

-- Function: int gnutls_privkey_generate2 (gnutls_privkey_t PKEY,
          gnutls_pk_algorithm_t ALGO, unsigned int BITS, unsigned int
          FLAGS, const gnutls_keygen_data_st * DATA, unsigned DATA_SIZE)
     PKEY: The private key

ALGO: is one of the algorithms in ‘gnutls_pk_algorithm_t’ .

BITS: the size of the modulus

FLAGS: Must be zero or flags from ‘gnutls_privkey_flags_t’ .

DATA: Allow specifying ‘gnutls_keygen_data_st’ types such as the
     seed to be used.

DATA_SIZE: The number of ‘data’ available.

This function will generate a random private key.  Note that this
     function must be called on an initialized private key.

The flag ‘GNUTLS_PRIVKEY_FLAG_PROVABLE’ instructs the key
     generation process to use algorithms like Shawe-Taylor (from FIPS
     PUB186-4) which generate provable parameters out of a seed for RSA
     and DSA keys.  On DSA keys the PQG parameters are generated using
     the seed, while on RSA the two primes.  To specify an explicit seed
     (by default a random seed is used), use the ‘data’ with a
     ‘GNUTLS_KEYGEN_SEED’ type.

Note that when generating an elliptic curve key, the curve can be
     substituted in the place of the bits parameter using the
     ‘GNUTLS_CURVE_TO_BITS()’ macro.

To export the generated keys in memory or in files it is
     recommended to use the PKCS‘8’ form as it can handle all key types,
     and can store additional parameters such as the seed, in case of
     provable RSA or DSA keys.  Generated keys can be exported in memory
     using ‘gnutls_privkey_export_x509()’ , and then with
     ‘gnutls_x509_privkey_export2_pkcs8()’ .

If key generation is part of your application, avoid setting the
     number of bits directly, and instead use
     ‘gnutls_sec_param_to_pk_bits()’ .  That way the generated keys will
     adapt to the security levels of the underlying GnuTLS library.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.5.0

File: gnutls.info,  Node: Cryptographic Message Syntax / PKCS7,  Next: Hash and MAC functions,  Prev: Public key algorithms,  Up: Using GnuTLS as a cryptographic library

9.3 Cryptographic Message Syntax / PKCS7
========================================

The CMS or PKCS #7 format is a commonly used format for digital
signatures.  PKCS #7 is the name of the original standard when published
by RSA, though today the standard is adopted by IETF under the name CMS.

The standards include multiple ways of signing a digital document, e.g.,
by embedding the data into the signature, or creating detached
signatures of the data, including a timestamp, additional certificates
etc.  In certain cases the same format is also used to transport lists
of certificates and CRLs.

It is a relatively popular standard to sign structures, and is being
used to sign in PDF files, as well as for signing kernel modules and
other structures.

In GnuTLS, the basic functions to initialize, deinitialize, import,
export or print information about a PKCS #7 structure are listed below.
‘INT *note gnutls_pkcs7_init:: (gnutls_pkcs7_t * PKCS7)’
‘VOID *note gnutls_pkcs7_deinit:: (gnutls_pkcs7_t PKCS7)’
‘INT *note gnutls_pkcs7_export2:: (gnutls_pkcs7_t PKCS7, gnutls_x509_crt_fmt_t FORMAT, gnutls_datum_t * OUT)’
‘INT *note gnutls_pkcs7_import:: (gnutls_pkcs7_t PKCS7, const gnutls_datum_t * DATA, gnutls_x509_crt_fmt_t FORMAT)’
‘INT *note gnutls_pkcs7_print:: (gnutls_pkcs7_t PKCS7, gnutls_certificate_print_formats_t FORMAT, gnutls_datum_t * OUT)’

The following functions allow the verification of a structure using
either a trust list, or individual certificates.  The *note
gnutls_pkcs7_sign:: function is the data signing function.

‘INT *note gnutls_pkcs7_verify_direct:: (gnutls_pkcs7_t PKCS7, gnutls_x509_crt_t SIGNER, unsigned IDX, const gnutls_datum_t * DATA, unsigned FLAGS)’
‘INT *note gnutls_pkcs7_verify:: (gnutls_pkcs7_t PKCS7, gnutls_x509_trust_list_t TL, gnutls_typed_vdata_st * VDATA, unsigned int VDATA_SIZE, unsigned IDX, const gnutls_datum_t * DATA, unsigned FLAGS)’

-- Function: int gnutls_pkcs7_sign (gnutls_pkcs7_t PKCS7,
          gnutls_x509_crt_t SIGNER, gnutls_privkey_t SIGNER_KEY, const
          gnutls_datum_t * DATA, gnutls_pkcs7_attrs_t SIGNED_ATTRS,
          gnutls_pkcs7_attrs_t UNSIGNED_ATTRS, gnutls_digest_algorithm_t
          DIG, unsigned FLAGS)
     PKCS7: should contain a ‘gnutls_pkcs7_t’ type

SIGNER: the certificate to sign the structure

SIGNER_KEY: the key to sign the structure

DATA: The data to be signed or ‘NULL’ if the data are already
     embedded

SIGNED_ATTRS: Any additional attributes to be included in the
     signed ones (or ‘NULL’ )

UNSIGNED_ATTRS: Any additional attributes to be included in the
     unsigned ones (or ‘NULL’ )

DIG: The digest algorithm to use for signing

FLAGS: Should be zero or one of ‘GNUTLS_PKCS7’ flags

This function will add a signature in the provided PKCS ‘7’
     structure for the provided data.  Multiple signatures can be made
     with different signers.

The available flags are: ‘GNUTLS_PKCS7_EMBED_DATA’ ,
     ‘GNUTLS_PKCS7_INCLUDE_TIME’ , ‘GNUTLS_PKCS7_INCLUDE_CERT’ , and
     ‘GNUTLS_PKCS7_WRITE_SPKI’ .  They are explained in the
     ‘gnutls_pkcs7_sign_flags’ definition.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.4.2

‘GNUTLS_PKCS7_EMBED_DATA’
     The signed data will be embedded in the structure.
‘GNUTLS_PKCS7_INCLUDE_TIME’
     The signing time will be included in the structure.
‘GNUTLS_PKCS7_INCLUDE_CERT’
     The signer's certificate will be included in the cert list.
‘GNUTLS_PKCS7_WRITE_SPKI’
     Use the signer's key identifier instead of name.

Figure 9.2: Flags applicable to gnutls_pkcs7_sign()

Other helper functions which allow to access the signatures, or
certificates attached in the structure are listed below.

‘INT *note gnutls_pkcs7_get_signature_count:: (gnutls_pkcs7_t PKCS7)’
‘INT *note gnutls_pkcs7_get_signature_info:: (gnutls_pkcs7_t PKCS7, unsigned IDX, gnutls_pkcs7_signature_info_st * INFO)’
‘INT *note gnutls_pkcs7_get_crt_count:: (gnutls_pkcs7_t PKCS7)’
‘INT *note gnutls_pkcs7_get_crt_raw2:: (gnutls_pkcs7_t PKCS7, unsigned INDX, gnutls_datum_t * CERT)’
‘INT *note gnutls_pkcs7_get_crl_count:: (gnutls_pkcs7_t PKCS7)’
‘INT *note gnutls_pkcs7_get_crl_raw2:: (gnutls_pkcs7_t PKCS7, unsigned INDX, gnutls_datum_t * CRL)’

To append certificates, or CRLs in the structure the following functions
are provided.
‘INT *note gnutls_pkcs7_set_crt_raw:: (gnutls_pkcs7_t PKCS7, const gnutls_datum_t * CRT)’
‘INT *note gnutls_pkcs7_set_crt:: (gnutls_pkcs7_t PKCS7, gnutls_x509_crt_t CRT)’
‘INT *note gnutls_pkcs7_set_crl_raw:: (gnutls_pkcs7_t PKCS7, const gnutls_datum_t * CRL)’
‘INT *note gnutls_pkcs7_set_crl:: (gnutls_pkcs7_t PKCS7, gnutls_x509_crl_t CRL)’

File: gnutls.info,  Node: Hash and MAC functions,  Next: Random number generation,  Prev: Cryptographic Message Syntax / PKCS7,  Up: Using GnuTLS as a cryptographic library

9.4 Hash and MAC functions
==========================

The available operations to access hash functions and hash-MAC (HMAC)
algorithms are shown below.  HMAC algorithms provided keyed hash
functionality.  The supported MAC and HMAC algorithms are listed in
*note Figure 9.3: gnutls_mac_algorithm_t.  Note that, despite the ‘hmac’
part in the name of the MAC functions listed below, they can be used
either for HMAC or MAC operations.

‘GNUTLS_MAC_UNKNOWN’
     Unknown MAC algorithm.
‘GNUTLS_MAC_NULL’
     NULL MAC algorithm (empty output).
‘GNUTLS_MAC_MD5’
     HMAC-MD5 algorithm.
‘GNUTLS_MAC_SHA1’
     HMAC-SHA-1 algorithm.
‘GNUTLS_MAC_RMD160’
     HMAC-RMD160 algorithm.
‘GNUTLS_MAC_MD2’
     HMAC-MD2 algorithm.
‘GNUTLS_MAC_SHA256’
     HMAC-SHA-256 algorithm.
‘GNUTLS_MAC_SHA384’
     HMAC-SHA-384 algorithm.
‘GNUTLS_MAC_SHA512’
     HMAC-SHA-512 algorithm.
‘GNUTLS_MAC_SHA224’
     HMAC-SHA-224 algorithm.
‘GNUTLS_MAC_SHA3_224’
     Reserved; unimplemented.
‘GNUTLS_MAC_SHA3_256’
     Reserved; unimplemented.
‘GNUTLS_MAC_SHA3_384’
     Reserved; unimplemented.
‘GNUTLS_MAC_SHA3_512’
     Reserved; unimplemented.
‘GNUTLS_MAC_MD5_SHA1’
     Combined MD5+SHA1 MAC placeholder.
‘GNUTLS_MAC_GOSTR_94’
     HMAC GOST R 34.11-94 algorithm.
‘GNUTLS_MAC_STREEBOG_256’
     HMAC GOST R 34.11-2001 (Streebog) algorithm, 256 bit.
‘GNUTLS_MAC_STREEBOG_512’
     HMAC GOST R 34.11-2001 (Streebog) algorithm, 512 bit.
‘GNUTLS_MAC_AEAD’
     MAC implicit through AEAD cipher.
‘GNUTLS_MAC_UMAC_96’
     The UMAC-96 MAC algorithm (requires nonce).
‘GNUTLS_MAC_UMAC_128’
     The UMAC-128 MAC algorithm (requires nonce).
‘GNUTLS_MAC_AES_CMAC_128’
     The AES-CMAC-128 MAC algorithm.
‘GNUTLS_MAC_AES_CMAC_256’
     The AES-CMAC-256 MAC algorithm.
‘GNUTLS_MAC_AES_GMAC_128’
     The AES-GMAC-128 MAC algorithm (requires nonce).
‘GNUTLS_MAC_AES_GMAC_192’
     The AES-GMAC-192 MAC algorithm (requires nonce).
‘GNUTLS_MAC_AES_GMAC_256’
     The AES-GMAC-256 MAC algorithm (requires nonce).
‘GNUTLS_MAC_GOST28147_TC26Z_IMIT’
     The GOST 28147-89 working in IMIT mode with TC26 Z S-box.
‘GNUTLS_MAC_SHAKE_128’
     The SHAKE128 extendable output function.
‘GNUTLS_MAC_SHAKE_256’
     The SHAKE256 extendable output function.
‘GNUTLS_MAC_MAGMA_OMAC’
     GOST R 34.12-2015 (Magma) in OMAC (CMAC) mode.
‘GNUTLS_MAC_KUZNYECHIK_OMAC’
     GOST R 34.12-2015 (Kuznyechik) in OMAC (CMAC) mode.
‘GNUTLS_MAC_PBMAC1’
     - undescribed -

Figure 9.3: The supported MAC and HMAC algorithms.

‘INT *note gnutls_hmac_init:: (gnutls_hmac_hd_t * DIG, gnutls_mac_algorithm_t ALGORITHM, const void * KEY, size_t KEYLEN)’
‘INT *note gnutls_hmac:: (gnutls_hmac_hd_t HANDLE, const void * PTEXT, size_t PTEXT_LEN)’
‘VOID *note gnutls_hmac_output:: (gnutls_hmac_hd_t HANDLE, void * DIGEST)’
‘VOID *note gnutls_hmac_deinit:: (gnutls_hmac_hd_t HANDLE, void * DIGEST)’
‘UNSIGNED *note gnutls_hmac_get_len:: (gnutls_mac_algorithm_t ALGORITHM)’
‘INT *note gnutls_hmac_fast:: (gnutls_mac_algorithm_t ALGORITHM, const void * KEY, size_t KEYLEN, const void * PTEXT, size_t PTEXT_LEN, void * DIGEST)’

The available functions to access hash functions are shown below.  The
supported hash functions are shown in *note Figure 9.4:
gnutls_digest_algorithm_t.

‘INT *note gnutls_hash_init:: (gnutls_hash_hd_t * DIG, gnutls_digest_algorithm_t ALGORITHM)’
‘INT *note gnutls_hash:: (gnutls_hash_hd_t HANDLE, const void * PTEXT, size_t PTEXT_LEN)’
‘VOID *note gnutls_hash_output:: (gnutls_hash_hd_t HANDLE, void * DIGEST)’
‘VOID *note gnutls_hash_deinit:: (gnutls_hash_hd_t HANDLE, void * DIGEST)’
‘UNSIGNED *note gnutls_hash_get_len:: (gnutls_digest_algorithm_t ALGORITHM)’
‘INT *note gnutls_hash_fast:: (gnutls_digest_algorithm_t ALGORITHM, const void * PTEXT, size_t PTEXT_LEN, void * DIGEST)’
‘INT *note gnutls_fingerprint:: (gnutls_digest_algorithm_t ALGO, const gnutls_datum_t * DATA, void * RESULT, size_t * RESULT_SIZE)’

‘GNUTLS_DIG_UNKNOWN’
     Unknown hash algorithm.
‘GNUTLS_DIG_NULL’
     NULL hash algorithm (empty output).
‘GNUTLS_DIG_MD5’
     MD5 algorithm.
‘GNUTLS_DIG_SHA1’
     SHA-1 algorithm.
‘GNUTLS_DIG_RMD160’
     RMD160 algorithm.
‘GNUTLS_DIG_MD2’
     MD2 algorithm.
‘GNUTLS_DIG_SHA256’
     SHA-256 algorithm.
‘GNUTLS_DIG_SHA384’
     SHA-384 algorithm.
‘GNUTLS_DIG_SHA512’
     SHA-512 algorithm.
‘GNUTLS_DIG_SHA224’
     SHA-224 algorithm.
‘GNUTLS_DIG_SHA3_224’
     SHA3-224 algorithm.
‘GNUTLS_DIG_SHA3_256’
     SHA3-256 algorithm.
‘GNUTLS_DIG_SHA3_384’
     SHA3-384 algorithm.
‘GNUTLS_DIG_SHA3_512’
     SHA3-512 algorithm.
‘GNUTLS_DIG_MD5_SHA1’
     Combined MD5+SHA1 algorithm.
‘GNUTLS_DIG_GOSTR_94’
     GOST R 34.11-94 algorithm.
‘GNUTLS_DIG_STREEBOG_256’
     GOST R 34.11-2001 (Streebog) algorithm, 256 bit.
‘GNUTLS_DIG_STREEBOG_512’
     GOST R 34.11-2001 (Streebog) algorithm, 512 bit.
‘GNUTLS_DIG_SHAKE_128’
     The SHAKE128 extendable output function.
‘GNUTLS_DIG_SHAKE_256’
     The SHAKE256 extendable output function.

Figure 9.4: The supported hash algorithms.

File: gnutls.info,  Node: Random number generation,  Next: Overriding algorithms,  Prev: Hash and MAC functions,  Up: Using GnuTLS as a cryptographic library

9.5 Random number generation
============================

Access to the random number generator is provided using the *note
gnutls_rnd:: function.  It allows obtaining random data of various
levels.

‘GNUTLS_RND_NONCE’
     Non-predictable random number.  Fatal in parts of session if
     broken, i.e., vulnerable to statistical analysis.
‘GNUTLS_RND_RANDOM’
     Pseudo-random cryptographic random number.  Fatal in session if
     broken.  Example use: temporal keys.
‘GNUTLS_RND_KEY’
     Fatal in many sessions if broken.  Example use: Long-term keys.

Figure 9.5: The random number levels.

-- Function: int gnutls_rnd (gnutls_rnd_level_t LEVEL, void * DATA,
          size_t LEN)
     LEVEL: a security level

DATA: place to store random bytes

LEN: The requested size

This function will generate random data and store it to output
     buffer.  The value of ‘level’ should be one of ‘GNUTLS_RND_NONCE’ ,
     ‘GNUTLS_RND_RANDOM’ and ‘GNUTLS_RND_KEY’ .  See the manual and
     ‘gnutls_rnd_level_t’ for detailed information.

This function is thread-safe and also fork-safe.

*Returns:* Zero on success, or a negative error code on error.

*Since:* 2.12.0

See *note Random Number Generators-internals:: for more information on
the random number generator operation.

File: gnutls.info,  Node: Overriding algorithms,  Prev: Random number generation,  Up: Using GnuTLS as a cryptographic library

9.6 Overriding algorithms
=========================

In systems which provide a hardware accelerated cipher implementation
that is not directly supported by GnuTLS, it is possible to utilize it.
There are functions which allow overriding the default cipher, digest
and MAC implementations.  Those are described below.

To override public key operations see *note Abstract private keys::.

-- Function: int gnutls_crypto_register_cipher
          (gnutls_cipher_algorithm_t ALGORITHM, int PRIORITY,
          gnutls_cipher_init_func INIT, gnutls_cipher_setkey_func
          SETKEY, gnutls_cipher_setiv_func SETIV,
          gnutls_cipher_encrypt_func ENCRYPT, gnutls_cipher_decrypt_func
          DECRYPT, gnutls_cipher_deinit_func DEINIT)
     ALGORITHM: is the gnutls algorithm identifier

PRIORITY: is the priority of the algorithm

INIT: A function which initializes the cipher

SETKEY: A function which sets the key of the cipher

SETIV: A function which sets the nonce/IV of the cipher (non-AEAD)

ENCRYPT: A function which performs encryption (non-AEAD)

DECRYPT: A function which performs decryption (non-AEAD)

DEINIT: A function which deinitializes the cipher

This function will register a cipher algorithm to be used by
     gnutls.  Any algorithm registered will override the included
     algorithms and by convention kernel implemented algorithms have
     priority of 90 and CPU-assisted of 80.  The algorithm with the
     lowest priority will be used by gnutls.

In the case the registered init or setkey functions return
     ‘GNUTLS_E_NEED_FALLBACK’ , GnuTLS will attempt to use the next in
     priority registered cipher.

The functions which are marked as non-AEAD they are not required
     when registering a cipher to be used with the new AEAD API
     introduced in GnuTLS 3.4.0.  Internally GnuTLS uses the new AEAD
     API.

*Deprecated:* since 3.7.0 it is no longer possible to override
     cipher implementation

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, otherwise a negative
     error code.

*Since:* 3.4.0

-- Function: int gnutls_crypto_register_aead_cipher
          (gnutls_cipher_algorithm_t ALGORITHM, int PRIORITY,
          gnutls_cipher_init_func INIT, gnutls_cipher_setkey_func
          SETKEY, gnutls_cipher_aead_encrypt_func AEAD_ENCRYPT,
          gnutls_cipher_aead_decrypt_func AEAD_DECRYPT,
          gnutls_cipher_deinit_func DEINIT)
     ALGORITHM: is the gnutls AEAD cipher identifier

PRIORITY: is the priority of the algorithm

INIT: A function which initializes the cipher

SETKEY: A function which sets the key of the cipher

AEAD_ENCRYPT: Perform the AEAD encryption

AEAD_DECRYPT: Perform the AEAD decryption

DEINIT: A function which deinitializes the cipher

In the case the registered init or setkey functions return
     ‘GNUTLS_E_NEED_FALLBACK’ , GnuTLS will attempt to use the next in
     priority registered cipher.

The functions registered will be used with the new AEAD API
     introduced in GnuTLS 3.4.0.  Internally GnuTLS uses the new AEAD
     API.

*Deprecated:* since 3.7.0 it is no longer possible to override
     cipher implementation

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, otherwise a negative
     error code.

*Since:* 3.4.0

-- Function: int gnutls_crypto_register_mac (gnutls_mac_algorithm_t
          ALGORITHM, int PRIORITY, gnutls_mac_init_func INIT,
          gnutls_mac_setkey_func SETKEY, gnutls_mac_setnonce_func
          SETNONCE, gnutls_mac_hash_func HASH, gnutls_mac_output_func
          OUTPUT, gnutls_mac_deinit_func DEINIT, gnutls_mac_fast_func
          HASH_FAST)
     ALGORITHM: is the gnutls MAC identifier

PRIORITY: is the priority of the algorithm

INIT: A function which initializes the MAC

SETKEY: A function which sets the key of the MAC

SETNONCE: A function which sets the nonce for the mac (may be
     ‘NULL’ for common MAC algorithms)

HASH: Perform the hash operation

OUTPUT: Provide the output of the MAC

DEINIT: A function which deinitializes the MAC

HASH_FAST: Perform the MAC operation in one go

This function will register a MAC algorithm to be used by gnutls.
     Any algorithm registered will override the included algorithms and
     by convention kernel implemented algorithms have priority of 90 and
     CPU-assisted of 80.  The algorithm with the lowest priority will be
     used by gnutls.

*Deprecated:* since 3.7.0 it is no longer possible to override
     cipher implementation

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, otherwise a negative
     error code.

*Since:* 3.4.0

-- Function: int gnutls_crypto_register_digest
          (gnutls_digest_algorithm_t ALGORITHM, int PRIORITY,
          gnutls_digest_init_func INIT, gnutls_digest_hash_func HASH,
          gnutls_digest_output_func OUTPUT, gnutls_digest_deinit_func
          DEINIT, gnutls_digest_fast_func HASH_FAST)
     ALGORITHM: is the gnutls digest identifier

PRIORITY: is the priority of the algorithm

INIT: A function which initializes the digest

HASH: Perform the hash operation

OUTPUT: Provide the output of the digest

DEINIT: A function which deinitializes the digest

HASH_FAST: Perform the digest operation in one go

This function will register a digest algorithm to be used by
     gnutls.  Any algorithm registered will override the included
     algorithms and by convention kernel implemented algorithms have
     priority of 90 and CPU-assisted of 80.  The algorithm with the
     lowest priority will be used by gnutls.

*Deprecated:* since 3.7.0 it is no longer possible to override
     cipher implementation

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, otherwise a negative
     error code.

*Since:* 3.4.0

File: gnutls.info,  Node: Other included programs,  Next: Internal architecture of GnuTLS,  Prev: Using GnuTLS as a cryptographic library,  Up: Top

10 Other included programs
**************************

Included with GnuTLS are also a few command line tools that let you use
the library for common tasks without writing an application.  The
applications are discussed in this chapter.

* Menu:

* gnutls-cli Invocation::          Invoking gnutls-cli
* gnutls-serv Invocation::         Invoking gnutls-serv
* gnutls-cli-debug Invocation::    Invoking gnutls-cli-debug

File: gnutls.info,  Node: gnutls-cli Invocation,  Next: gnutls-serv Invocation,  Up: Other included programs

Invoking gnutls-cli
===================

Simple client program to set up a TLS connection to some other computer.
It sets up a TLS connection and forwards data from the standard input to
the secured socket and vice versa.

gnutls-cli help/usage (‘-?’)
----------------------------

gnutls-cli - GnuTLS client
     Usage:  gnutls-cli [ -<flag> [<val>] | --<name>[{=| }<val>] ]... [hostname]

None:

-d, --debug=num            Enable debugging
     				- it must be in the range:
     				  0 to 9999
        -V, --verbose              More verbose output
            --tofu                 Enable trust on first use authentication
            --strict-tofu          Fail to connect if a certificate is unknown or a known certificate has changed
            --dane                 Enable DANE certificate verification (DNSSEC)
            --local-dns            Use the local DNS server for DNSSEC resolving
            --ca-verification      Enable CA certificate verification
     				- enabled by default
     				- disabled as '--no-ca-verification'
            --ocsp                 Enable OCSP certificate verification
        -r, --resume               Establish a session and resume
            --earlydata=str        Send early data on resumption from the specified file
        -e, --rehandshake          Establish a session and rehandshake
            --sni-hostname=str     Server's hostname for server name indication extension
            --verify-hostname=str  Server's hostname to use for validation
        -s, --starttls             Connect, establish a plain session and start TLS
            --app-proto            an alias for the 'starttls-proto' option
            --starttls-proto=str   The application protocol to be used to obtain the server's certificate (https, ftp, smtp, imap, ldap, xmpp, lmtp, pop3, nntp, sieve, postgres)
     				- prohibits the option 'starttls'
            --starttls-name=str    The hostname presented to the application protocol for STARTTLS (for smtp, xmpp, lmtp)
     				- prohibits the option 'starttls'
     				- requires the option 'starttls-proto'
        -u, --udp                  Use DTLS (datagram TLS) over UDP
            --mtu=num              Set MTU for datagram TLS
     				- it must be in the range:
     				  0 to 17000
            --crlf                 Send CR LF instead of LF
            --fastopen             Enable TCP Fast Open
            --x509fmtder           Use DER format for certificates to read from
            --print-cert           Print peer's certificate in PEM format
            --save-cert=str        Save the peer's certificate chain in the specified file in PEM format
            --save-ocsp=str        Save the peer's OCSP status response in the provided file
     				- prohibits the option 'save-ocsp-multi'
            --save-ocsp-multi=str  Save all OCSP responses provided by the peer in this file
     				- prohibits the option 'save-ocsp'
            --save-server-trace=str Save the server-side TLS message trace in the provided file
            --save-client-trace=str Save the client-side TLS message trace in the provided file
            --dh-bits=num          The minimum number of bits allowed for DH
            --priority=str         Priorities string
            --x509cafile=str       Certificate file or PKCS #11 URL to use
            --x509crlfile=file     CRL file to use
     				- file must pre-exist
            --x509keyfile=str      X.509 key file or PKCS #11 URL to use
            --x509certfile=str     X.509 Certificate file or PKCS #11 URL to use
     				- requires the option 'x509keyfile'
            --rawpkkeyfile=str     Private key file (PKCS #8 or PKCS #12) or PKCS #11 URL to use
            --rawpkfile=str        Raw public-key file to use
     				- requires the option 'rawpkkeyfile'
            --srpusername=str      SRP username to use
            --srppasswd=str        SRP password to use
            --pskusername=str      PSK username to use
            --pskkey=str           PSK key (in hex) to use
        -p, --port=str             The port or service to connect to
            --insecure             Don't abort program if server certificate can't be validated
            --verify-allow-broken  Allow broken algorithms, such as MD5 for certificate verification
            --benchmark-ciphers    Benchmark individual ciphers
            --benchmark-tls-kx     Benchmark TLS key exchange methods
            --benchmark-tls-ciphers  Benchmark TLS ciphers
        -l, --list                 Print a list of the supported algorithms and modes
     				- prohibits the option 'port'
            --priority-list        Print a list of the supported priority strings
            --noticket             Don't allow session tickets
            --srtp-profiles=str    Offer SRTP profiles
            --alpn=str             Application layer protocol
            --compress-cert=str    Compress certificate
        -b, --heartbeat            Activate heartbeat support
            --recordsize=num       The maximum record size to advertise
     				- it must be in the range:
     				  0 to 4096
            --disable-sni          Do not send a Server Name Indication (SNI)
            --single-key-share     Send a single key share under TLS1.3
            --post-handshake-auth  Enable post-handshake authentication under TLS1.3
            --inline-commands      Inline commands of the form ^<cmd>^
            --inline-commands-prefix=str Change the default delimiter for inline commands
            --provider=file        Specify the PKCS #11 provider library
     				- file must pre-exist
            --fips140-mode         Reports the status of the FIPS140-2 mode in gnutls library
            --list-config          Reports the configuration of the library
            --logfile=str          Redirect informational messages to a specific file
            --keymatexport=str     Label used for exporting keying material
            --keymatexportsize=num Size of the exported keying material
            --waitresumption       Block waiting for the resumption data under TLS1.3
            --ca-auto-retrieve     Enable automatic retrieval of missing CA certificates
            --attime=str           Perform validation at the timestamp instead of the system time

Version, usage and configuration options:

Options are specified by doubled hyphens and their name or by a single
     hyphen and the flag character.
     Operands and options may be intermixed.  They will be reordered.

Simple client program to set up a TLS connection to some other computer.
     It sets up a TLS connection and forwards data from the standard input to the secured socket and vice versa.

Please send bug reports to:  <bugs@gnutls.org>

debug option (-d).
------------------

This is the "enable debugging" option.  This option takes a
ArgumentType.NUMBER argument.  Specifies the debug level.

tofu option.
------------

This is the "enable trust on first use authentication" option.  This
option will, in addition to certificate authentication, perform
authentication based on previously seen public keys, a model similar to
SSH authentication.  Note that when tofu is specified (PKI) and DANE
authentication will become advisory to assist the public key acceptance
process.

strict-tofu option.
-------------------

This is the "fail to connect if a certificate is unknown or a known
certificate has changed" option.  This option will perform
authentication as with option -tofu; however, no questions shall be
asked whatsoever, neither to accept an unknown certificate nor a changed
one.

dane option.
------------

This is the "enable dane certificate verification (dnssec)" option.
This option will, in addition to certificate authentication using the
trusted CAs, verify the server certificates using on the DANE
information available via DNSSEC.

local-dns option.
-----------------

This is the "use the local dns server for dnssec resolving" option.
This option will use the local DNS server for DNSSEC. This is disabled
by default due to many servers not allowing DNSSEC.

ca-verification option.
-----------------------

This is the "enable ca certificate verification" option.

This option has some usage constraints.  It:
   • can be disabled with -no-ca-verification.
   • It is enabled by default.

This option can be used to enable or disable CA certificate
verification.  It is to be used with the -dane or -tofu options.

ocsp option.
------------

This is the "enable ocsp certificate verification" option.  This option
will enable verification of the peer's certificate using ocsp

resume option (-r).
-------------------

This is the "establish a session and resume" option.  Connect, establish
a session, reconnect and resume.

rehandshake option (-e).
------------------------

This is the "establish a session and rehandshake" option.  Connect,
establish a session and rehandshake immediately.

sni-hostname option.
--------------------

This is the "server's hostname for server name indication extension"
option.  This option takes a ArgumentType.STRING argument.  Set
explicitly the server name used in the TLS server name indication
extension.  That is useful when testing with servers setup on different
DNS name than the intended.  If not specified, the provided hostname is
used.  Even with this option server certificate verification still uses
the hostname passed on the main commandline.  Use -verify-hostname to
change this.

verify-hostname option.
-----------------------

This is the "server's hostname to use for validation" option.  This
option takes a ArgumentType.STRING argument.  Set explicitly the server
name to be used when validating the server's certificate.

starttls option (-s).
---------------------

This is the "connect, establish a plain session and start tls" option.
The TLS session will be initiated when EOF or a SIGALRM is received.

app-proto option.
-----------------

This is an alias for the ‘starttls-proto’ option, *note the
starttls-proto option documentation: gnutls-cli starttls-proto.

starttls-proto option.
----------------------

This option has some usage constraints.  It:
   • must not appear in combination with any of the following options:
     starttls.

Specify the application layer protocol for STARTTLS. If the protocol is
supported, gnutls-cli will proceed to the TLS negotiation.

starttls-name option.
---------------------

This is the "the hostname presented to the application protocol for
starttls (for smtp, xmpp, lmtp)" option.  This option takes a
ArgumentType.STRING argument.

This option has some usage constraints.  It:
   • must not appear in combination with any of the following options:
     starttls.
   • must appear in combination with the following options:
     starttls-proto.

Specify the hostname presented to the application protocol for STARTTLS.

save-ocsp-multi option.
-----------------------

This is the "save all ocsp responses provided by the peer in this file"
option.  This option takes a ArgumentType.STRING argument.

This option has some usage constraints.  It:
   • must not appear in combination with any of the following options:
     save-ocsp.

The file will contain a list of PEM encoded OCSP status responses if any
were provided by the peer, starting with the one for the peer's server
certificate.

dh-bits option.
---------------

This is the "the minimum number of bits allowed for dh" option.  This
option takes a ArgumentType.NUMBER argument.  This option sets the
minimum number of bits allowed for a Diffie-Hellman key exchange.  You
may want to lower the default value if the peer sends a weak prime and
you get an connection error with unacceptable prime.

priority option.
----------------

This is the "priorities string" option.  This option takes a
ArgumentType.STRING argument.  TLS algorithms and protocols to enable.
You can use predefined sets of ciphersuites such as PERFORMANCE, NORMAL,
PFS, SECURE128, SECURE256.  The default is NORMAL.

Check the GnuTLS manual on section "Priority strings" for more
information on the allowed keywords

rawpkkeyfile option.
--------------------

This is the "private key file (pkcs #8 or pkcs #12) or pkcs #11 url to
use" option.  This option takes a ArgumentType.STRING argument.  In
order to instruct the application to negotiate raw public keys one must
enable the respective certificate types via the priority strings (i.e.
CTYPE-CLI-* and CTYPE-SRV-* flags).

Check the GnuTLS manual on section "Priority strings" for more
information on how to set certificate types.

rawpkfile option.
-----------------

This is the "raw public-key file to use" option.  This option takes a
ArgumentType.STRING argument.

This option has some usage constraints.  It:
   • must appear in combination with the following options:
     rawpkkeyfile.

In order to instruct the application to negotiate raw public keys one
must enable the respective certificate types via the priority strings
(i.e.  CTYPE-CLI-* and CTYPE-SRV-* flags).

Check the GnuTLS manual on section "Priority strings" for more
information on how to set certificate types.

ranges option.
--------------

This is the "use length-hiding padding to prevent traffic analysis"
option.  When possible (e.g., when using CBC ciphersuites), use
length-hiding padding to prevent traffic analysis.

*NOTE**: THIS OPTION IS DEPRECATED*

benchmark-ciphers option.
-------------------------

This is the "benchmark individual ciphers" option.  By default the
benchmarked ciphers will utilize any capabilities of the local CPU to
improve performance.  To test against the raw software implementation
set the environment variable GNUTLS_CPUID_OVERRIDE to 0x1.

benchmark-tls-ciphers option.
-----------------------------

This is the "benchmark tls ciphers" option.  By default the benchmarked
ciphers will utilize any capabilities of the local CPU to improve
performance.  To test against the raw software implementation set the
environment variable GNUTLS_CPUID_OVERRIDE to 0x1.

list option (-l).
-----------------

This is the "print a list of the supported algorithms and modes" option.

This option has some usage constraints.  It:
   • must not appear in combination with any of the following options:
     port.

Print a list of the supported algorithms and modes.  If a priority
string is given then only the enabled ciphersuites are shown.

priority-list option.
---------------------

This is the "print a list of the supported priority strings" option.
Print a list of the supported priority strings.  The ciphersuites
corresponding to each priority string can be examined using -l -p.

noticket option.
----------------

This is the "don't allow session tickets" option.  Disable the request
of receiving of session tickets under TLS1.2 or earlier

alpn option.
------------

This is the "application layer protocol" option.  This option takes a
ArgumentType.STRING argument.  This option will set and enable the
Application Layer Protocol Negotiation (ALPN) in the TLS protocol.

compress-cert option.
---------------------

This is the "compress certificate" option.  This option takes a
ArgumentType.STRING argument.  This option sets a supported compression
method for certificate compression.

disable-extensions option.
--------------------------

This is the "disable all the tls extensions" option.  This option
disables all TLS extensions.  Deprecated option.  Use the priority
string.

*NOTE**: THIS OPTION IS DEPRECATED*

single-key-share option.
------------------------

This is the "send a single key share under tls1.3" option.  This option
switches the default mode of sending multiple key shares, to send a
single one (the top one).

post-handshake-auth option.
---------------------------

This is the "enable post-handshake authentication under tls1.3" option.
This option enables post-handshake authentication when under TLS1.3.

inline-commands option.
-----------------------

This is the "inline commands of the form ^<cmd>^" option.  Enable inline
commands of the form ^<cmd>^.  The inline commands are expected to be in
a line by themselves.  The available commands are: resume, rekey1 (local
rekey), rekey (rekey on both peers) and renegotiate.

inline-commands-prefix option.
------------------------------

This is the "change the default delimiter for inline commands" option.
This option takes a ArgumentType.STRING argument.  Change the default
delimiter (^) used for inline commands.  The delimiter is expected to be
a single US-ASCII character (octets 0 - 127).  This option is only
relevant if inline commands are enabled via the inline-commands option

provider option.
----------------

This is the "specify the pkcs #11 provider library" option.  This option
takes a ArgumentType.FILE argument.  This will override the default
options in /usr/local/etc/gnutls/pkcs11.conf

logfile option.
---------------

This is the "redirect informational messages to a specific file" option.
This option takes a ArgumentType.STRING argument.  Redirect
informational messages to a specific file.  The file may be /dev/null
also to make the gnutls client quiet to use it in piped server
connections where only the server communication may appear on stdout.

waitresumption option.
----------------------

This is the "block waiting for the resumption data under tls1.3" option.
This option makes the client to block waiting for the resumption data
under TLS1.3.  The option has effect only when -resume is provided.

ca-auto-retrieve option.
------------------------

This is the "enable automatic retrieval of missing ca certificates"
option.  This option enables the client to automatically retrieve the
missing intermediate CA certificates in the certificate chain, based on
the Authority Information Access (AIA) extension.

attime option.
--------------

version option (-v).
--------------------

help option (-h).
-----------------

This is the "display extended usage information and exit" option.
Display usage information and exit.

more-help option (-!).
----------------------

This is the "extended usage information passed thru pager" option.  Pass
the extended usage information through a pager.

gnutls-cli exit status
----------------------

One of the following exit values will be returned:
‘0 (EXIT_SUCCESS)’
     Successful program execution.
‘1 (EXIT_FAILURE)’
     The operation failed or the command syntax was not valid.

gnutls-cli See Also
...................

gnutls-cli-debug(1), gnutls-serv(1)

gnutls-cli Examples
...................

Connecting using PSK authentication
-----------------------------------

To connect to a server using PSK authentication, you need to enable the
choice of PSK by using a cipher priority parameter such as in the
example below.
     $ ./gnutls-cli -p 5556 localhost --pskusername psk_identity \
         --pskkey 88f3824b3e5659f52d00e959bacab954b6540344 \
         --priority NORMAL:-KX-ALL:+ECDHE-PSK:+DHE-PSK:+PSK
     Resolving 'localhost'...
     Connecting to '127.0.0.1:5556'...
     - PSK authentication.
     - Version: TLS1.1
     - Key Exchange: PSK
     - Cipher: AES-128-CBC
     - MAC: SHA1
     - Compression: NULL
     - Handshake was completed

- Simple Client Mode:
By keeping the -pskusername parameter and removing the -pskkey
parameter, it will query only for the password during the handshake.

Connecting using raw public-key authentication
----------------------------------------------

To connect to a server using raw public-key authentication, you need to
enable the option to negotiate raw public-keys via the priority strings
such as in the example below.
     $ ./gnutls-cli -p 5556 localhost --priority NORMAL:-CTYPE-CLI-ALL:+CTYPE-CLI-RAWPK \
         --rawpkkeyfile cli.key.pem \
         --rawpkfile cli.rawpk.pem
     Processed 1 client raw public key pair...
     Resolving 'localhost'...
     Connecting to '127.0.0.1:5556'...
     - Successfully sent 1 certificate(s) to server.
     - Server has requested a certificate.
     - Certificate type: X.509
     - Got a certificate list of 1 certificates.
     - Certificate[0] info:
      - skipped
     - Description: (TLS1.3-Raw Public Key-X.509)-(ECDHE-SECP256R1)-(RSA-PSS-RSAE-SHA256)-(AES-256-GCM)
     - Options:
     - Handshake was completed

- Simple Client Mode:

Connecting to STARTTLS services
-------------------------------

You could also use the client to connect to services with starttls
capability.
     $ gnutls-cli --starttls-proto smtp --port 25 localhost

Listing ciphersuites in a priority string
-----------------------------------------

To list the ciphersuites in a priority string:
     $ ./gnutls-cli --priority SECURE192 -l
     Cipher suites for SECURE192
     TLS_ECDHE_ECDSA_AES_256_CBC_SHA384         0xc0, 0x24	TLS1.2
     TLS_ECDHE_ECDSA_AES_256_GCM_SHA384         0xc0, 0x2e	TLS1.2
     TLS_ECDHE_RSA_AES_256_GCM_SHA384           0xc0, 0x30	TLS1.2
     TLS_DHE_RSA_AES_256_CBC_SHA256             0x00, 0x6b	TLS1.2
     TLS_DHE_DSS_AES_256_CBC_SHA256             0x00, 0x6a	TLS1.2
     TLS_RSA_AES_256_CBC_SHA256                 0x00, 0x3d	TLS1.2

Certificate types: CTYPE-X.509
     Protocols: VERS-TLS1.2, VERS-TLS1.1, VERS-TLS1.0, VERS-SSL3.0, VERS-DTLS1.0
     Compression: COMP-NULL
     Elliptic curves: CURVE-SECP384R1, CURVE-SECP521R1
     PK-signatures: SIGN-RSA-SHA384, SIGN-ECDSA-SHA384, SIGN-RSA-SHA512, SIGN-ECDSA-SHA512

Connecting using a PKCS #11 token
---------------------------------

To connect to a server using a certificate and a private key present in
a PKCS #11 token you need to substitute the PKCS 11 URLs in the
x509certfile and x509keyfile parameters.

Those can be found using "p11tool -list-tokens" and then listing all the
objects in the needed token, and using the appropriate.
     $ p11tool --list-tokens

Token 0:
     	URL: pkcs11:model=PKCS15;manufacturer=MyMan;serial=1234;token=Test
     	Label: Test
     	Manufacturer: EnterSafe
     	Model: PKCS15
     	Serial: 1234

$ p11tool --login --list-certs "pkcs11:model=PKCS15;manufacturer=MyMan;serial=1234;token=Test"

Object 0:
     	URL: pkcs11:model=PKCS15;manufacturer=MyMan;serial=1234;token=Test;object=client;type=cert
     	Type: X.509 Certificate
     	Label: client
     	ID: 2a:97:0d:58:d1:51:3c:23:07:ae:4e:0d:72:26:03:7d:99:06:02:6a

$ MYCERT="pkcs11:model=PKCS15;manufacturer=MyMan;serial=1234;token=Test;object=client;type=cert"
     $ MYKEY="pkcs11:model=PKCS15;manufacturer=MyMan;serial=1234;token=Test;object=client;type=private"
     $ export MYCERT MYKEY

$ gnutls-cli www.example.com --x509keyfile $MYKEY --x509certfile $MYCERT
Notice that the private key only differs from the certificate in the
type.

File: gnutls.info,  Node: gnutls-serv Invocation,  Next: gnutls-cli-debug Invocation,  Prev: gnutls-cli Invocation,  Up: Other included programs

Invoking gnutls-serv
====================

Server program that listens to incoming TLS connections.

gnutls-serv help/usage (‘-?’)
-----------------------------

gnutls-serv - GnuTLS server
     Usage:  gnutls-serv [ -<flag> [<val>] | --<name>[{=| }<val>] ]...

None:

-d, --debug=num            Enable debugging
     				- it must be in the range:
     				  0 to 9999
            --sni-hostname=str     Server's hostname for server name extension
            --sni-hostname-fatal   Send fatal alert on sni-hostname mismatch
            --alpn=str             Specify ALPN protocol to be enabled by the server
            --alpn-fatal           Send fatal alert on non-matching ALPN name
            --noticket             Don't accept session tickets
            --earlydata            Accept early data
            --maxearlydata=num     The maximum early data size to accept
     				- it must be in the range:
     				  1 to 2147483648
            --nocookie             Don't require cookie on DTLS sessions
        -g, --generate             Generate Diffie-Hellman parameters
        -q, --quiet                Suppress some messages
            --nodb                 Do not use a resumption database
            --http                 Act as an HTTP server
            --echo                 Act as an Echo server
            --crlf                 Do not replace CRLF by LF in Echo server mode
        -u, --udp                  Use DTLS (datagram TLS) over UDP
            --mtu=num              Set MTU for datagram TLS
     				- it must be in the range:
     				  0 to 17000
            --srtp-profiles=str    Offer SRTP profiles
        -a, --disable-client-cert  Do not request a client certificate
     				- prohibits the option 'require-client-cert'
        -r, --require-client-cert  Require a client certificate
            --verify-client-cert   If a client certificate is sent then verify it
            --compress-cert=str    Compress certificate
        -b, --heartbeat            Activate heartbeat support
            --x509fmtder           Use DER format for certificates to read from
            --priority=str         Priorities string
            --dhparams=file        DH params file to use
     				- file must pre-exist
            --x509cafile=str       Certificate file or PKCS #11 URL to use
            --x509crlfile=file     CRL file to use
     				- file must pre-exist
            --x509keyfile=str      X.509 key file or PKCS #11 URL to use
            --x509certfile=str     X.509 Certificate file or PKCS #11 URL to use
            --rawpkkeyfile=str     Private key file (PKCS #8 or PKCS #12) or PKCS #11 URL to use
            --rawpkfile=str        Raw public-key file to use
     				- requires the option 'rawpkkeyfile'
            --srppasswd=file       SRP password file to use
     				- file must pre-exist
            --srppasswdconf=file   SRP password configuration file to use
     				- file must pre-exist
            --pskpasswd=file       PSK password file to use
     				- file must pre-exist
            --pskhint=str          PSK identity hint to use
            --ocsp-response=str    The OCSP response to send to client
            --ignore-ocsp-response-errors  Ignore any errors when setting the OCSP response
        -p, --port=num             The port to connect to
        -l, --list                 Print a list of the supported algorithms and modes
            --provider=file        Specify the PKCS #11 provider library
     				- file must pre-exist
            --keymatexport=str     Label used for exporting keying material
            --keymatexportsize=num Size of the exported keying material
            --recordsize=num       The maximum record size to advertise
     				- it must be in the range:
     				  0 to 16384
            --httpdata=file        The data used as HTTP response
     				- file must pre-exist
            --timeout=num          The timeout period for server
            --attime=str           Perform validation at the timestamp instead of the system time

Version, usage and configuration options:

Options are specified by doubled hyphens and their name or by a single
     hyphen and the flag character.

Server program that listens to incoming TLS connections.

Please send bug reports to:  <bugs@gnutls.org>

debug option (-d).
------------------

This is the "enable debugging" option.  This option takes a
ArgumentType.NUMBER argument.  Specifies the debug level.

sni-hostname option.
--------------------

This is the "server's hostname for server name extension" option.  This
option takes a ArgumentType.STRING argument.  Server name of type
host_name that the server will recognise as its own.  If the server
receives client hello with different name, it will send a warning-level
unrecognized_name alert.

alpn option.
------------

This is the "specify alpn protocol to be enabled by the server" option.
This option takes a ArgumentType.STRING argument.  Specify the (textual)
ALPN protocol for the server to use.

require-client-cert option (-r).
--------------------------------

This is the "require a client certificate" option.  This option before
3.6.0 used to imply -verify-client-cert.  Since 3.6.0 it will no longer
verify the certificate by default.

verify-client-cert option.
--------------------------

This is the "if a client certificate is sent then verify it" option.  Do
not require, but if a client certificate is sent then verify it and
close the connection if invalid.

compress-cert option.
---------------------

This is the "compress certificate" option.  This option takes a
ArgumentType.STRING argument.  This option sets a supported compression
method for certificate compression.

heartbeat option (-b).
----------------------

This is the "activate heartbeat support" option.  Regularly ping client
via heartbeat extension messages

priority option.
----------------

Check the GnuTLS manual on section "Priority strings" for more
information on allowed keywords

x509keyfile option.
-------------------

This is the "x.509 key file or pkcs #11 url to use" option.  This option
takes a ArgumentType.STRING argument.  Specify the private key file or
URI to use; it must correspond to the certificate specified in
-x509certfile.  Multiple keys and certificates can be specified with
this option and in that case each occurrence of keyfile must be followed
by the corresponding x509certfile or vice-versa.

x509certfile option.
--------------------

This is the "x.509 certificate file or pkcs #11 url to use" option.
This option takes a ArgumentType.STRING argument.  Specify the
certificate file or URI to use; it must correspond to the key specified
in -x509keyfile.  Multiple keys and certificates can be specified with
this option and in that case each occurrence of keyfile must be followed
by the corresponding x509certfile or vice-versa.

x509dsakeyfile option.
----------------------

This is an alias for the ‘x509keyfile’ option, *note the x509keyfile
option documentation: gnutls-serv x509keyfile.

x509dsacertfile option.
-----------------------

This is an alias for the ‘x509certfile’ option, *note the x509certfile
option documentation: gnutls-serv x509certfile.

x509ecckeyfile option.
----------------------

This is an alias for the ‘x509keyfile’ option, *note the x509keyfile
option documentation: gnutls-serv x509keyfile.

x509ecccertfile option.
-----------------------

This is an alias for the ‘x509certfile’ option, *note the x509certfile
option documentation: gnutls-serv x509certfile.

rawpkkeyfile option.
--------------------

This is the "private key file (pkcs #8 or pkcs #12) or pkcs #11 url to
use" option.  This option takes a ArgumentType.STRING argument.  Specify
the private key file or URI to use; it must correspond to the raw
public-key specified in -rawpkfile.  Multiple key pairs can be specified
with this option and in that case each occurrence of keyfile must be
followed by the corresponding rawpkfile or vice-versa.

In order to instruct the application to negotiate raw public keys one
must enable the respective certificate types via the priority strings
(i.e.  CTYPE-CLI-* and CTYPE-SRV-* flags).

Check the GnuTLS manual on section "Priority strings" for more
information on how to set certificate types.

rawpkfile option.
-----------------

This is the "raw public-key file to use" option.  This option takes a
ArgumentType.STRING argument.

This option has some usage constraints.  It:
   • must appear in combination with the following options:
     rawpkkeyfile.

Specify the raw public-key file to use; it must correspond to the
private key specified in -rawpkkeyfile.  Multiple key pairs can be
specified with this option and in that case each occurrence of keyfile
must be followed by the corresponding rawpkfile or vice-versa.

In order to instruct the application to negotiate raw public keys one
must enable the respective certificate types via the priority strings
(i.e.  CTYPE-CLI-* and CTYPE-SRV-* flags).

Check the GnuTLS manual on section "Priority strings" for more
information on how to set certificate types.

ocsp-response option.
---------------------

This is the "the ocsp response to send to client" option.  This option
takes a ArgumentType.STRING argument.  If the client requested an OCSP
response, return data from this file to the client.

ignore-ocsp-response-errors option.
-----------------------------------

This is the "ignore any errors when setting the ocsp response" option.
That option instructs gnutls to not attempt to match the provided OCSP
responses with the certificates.

list option (-l).
-----------------

This is the "print a list of the supported algorithms and modes" option.
Print a list of the supported algorithms and modes.  If a priority
string is given then only the enabled ciphersuites are shown.

provider option.
----------------

This is the "specify the pkcs #11 provider library" option.  This option
takes a ArgumentType.FILE argument.  This will override the default
options in /usr/local/etc/gnutls/pkcs11.conf

attime option.
--------------

version option (-v).
--------------------

help option (-h).
-----------------

This is the "display extended usage information and exit" option.
Display usage information and exit.

more-help option (-!).
----------------------

This is the "extended usage information passed thru pager" option.  Pass
the extended usage information through a pager.

gnutls-serv exit status
-----------------------

One of the following exit values will be returned:
‘0 (EXIT_SUCCESS)’
     Successful program execution.
‘1 (EXIT_FAILURE)’
     The operation failed or the command syntax was not valid.

gnutls-serv See Also
....................

gnutls-cli-debug(1), gnutls-cli(1)

gnutls-serv Examples
....................

Running your own TLS server based on GnuTLS can be useful when debugging
clients and/or GnuTLS itself.  This section describes how to use
‘gnutls-serv’ as a simple HTTPS server.

The most basic server can be started as:

gnutls-serv --http --priority "NORMAL:+ANON-ECDH:+ANON-DH"

It will only support anonymous ciphersuites, which many TLS clients
refuse to use.

The next step is to add support for X.509.  First we generate a CA:

$ certtool --generate-privkey > x509-ca-key.pem
     $ echo 'cn = GnuTLS test CA' > ca.tmpl
     $ echo 'ca' >> ca.tmpl
     $ echo 'cert_signing_key' >> ca.tmpl
     $ certtool --generate-self-signed --load-privkey x509-ca-key.pem \
       --template ca.tmpl --outfile x509-ca.pem

Then generate a server certificate.  Remember to change the dns_name
value to the name of your server host, or skip that command to avoid the
field.

$ certtool --generate-privkey > x509-server-key.pem
     $ echo 'organization = GnuTLS test server' > server.tmpl
     $ echo 'cn = test.gnutls.org' >> server.tmpl
     $ echo 'tls_www_server' >> server.tmpl
     $ echo 'encryption_key' >> server.tmpl
     $ echo 'signing_key' >> server.tmpl
     $ echo 'dns_name = test.gnutls.org' >> server.tmpl
     $ certtool --generate-certificate --load-privkey x509-server-key.pem \
       --load-ca-certificate x509-ca.pem --load-ca-privkey x509-ca-key.pem \
       --template server.tmpl --outfile x509-server.pem

For use in the client, you may want to generate a client certificate as
well.

$ certtool --generate-privkey > x509-client-key.pem
     $ echo 'cn = GnuTLS test client' > client.tmpl
     $ echo 'tls_www_client' >> client.tmpl
     $ echo 'encryption_key' >> client.tmpl
     $ echo 'signing_key' >> client.tmpl
     $ certtool --generate-certificate --load-privkey x509-client-key.pem \
       --load-ca-certificate x509-ca.pem --load-ca-privkey x509-ca-key.pem \
       --template client.tmpl --outfile x509-client.pem

To be able to import the client key/certificate into some applications,
you will need to convert them into a PKCS#12 structure.  This also
encrypts the security sensitive key with a password.

$ certtool --to-p12 --load-ca-certificate x509-ca.pem \
       --load-privkey x509-client-key.pem --load-certificate x509-client.pem \
       --outder --outfile x509-client.p12

For icing, we'll create a proxy certificate for the client too.

$ certtool --generate-privkey > x509-proxy-key.pem
     $ echo 'cn = GnuTLS test client proxy' > proxy.tmpl
     $ certtool --generate-proxy --load-privkey x509-proxy-key.pem \
       --load-ca-certificate x509-client.pem --load-ca-privkey x509-client-key.pem \
       --load-certificate x509-client.pem --template proxy.tmpl \
       --outfile x509-proxy.pem

Then start the server again:

$ gnutls-serv --http \
                 --x509cafile x509-ca.pem \
                 --x509keyfile x509-server-key.pem \
                 --x509certfile x509-server.pem

Try connecting to the server using your web browser.  Note that the
server listens to port 5556 by default.

While you are at it, to allow connections using ECDSA, you can also
create a ECDSA key and certificate for the server.  These credentials
will be used in the final example below.

$ certtool --generate-privkey --ecdsa > x509-server-key-ecc.pem
     $ certtool --generate-certificate --load-privkey x509-server-key-ecc.pem \
       --load-ca-certificate x509-ca.pem --load-ca-privkey x509-ca-key.pem \
       --template server.tmpl --outfile x509-server-ecc.pem

The next step is to add support for SRP authentication.  This requires
an SRP password file created with ‘srptool’.  To start the server with
SRP support:

gnutls-serv --http --priority NORMAL:+SRP-RSA:+SRP \
                 --srppasswdconf srp-tpasswd.conf \
                 --srppasswd srp-passwd.txt

Let's also start a server with support for PSK. This would require a
password file created with ‘psktool’.

gnutls-serv --http --priority NORMAL:+ECDHE-PSK:+PSK \
                 --pskpasswd psk-passwd.txt

If you want a server with support for raw public-keys we can also add
these credentials.  Note however that there is no identity information
linked to these keys as is the case with regular x509 certificates.
Authentication must be done via different means.  Also we need to
explicitly enable raw public-key certificates via the priority strings.

gnutls-serv --http --priority NORMAL:+CTYPE-CLI-RAWPK:+CTYPE-SRV-RAWPK \
                 --rawpkfile srv.rawpk.pem \
                 --rawpkkeyfile srv.key.pem

Finally, we start the server with all the earlier parameters and you get
this command:

gnutls-serv --http --priority NORMAL:+PSK:+SRP:+CTYPE-CLI-RAWPK:+CTYPE-SRV-RAWPK \
                 --x509cafile x509-ca.pem \
                 --x509keyfile x509-server-key.pem \
                 --x509certfile x509-server.pem \
                 --x509keyfile x509-server-key-ecc.pem \
                 --x509certfile x509-server-ecc.pem \
                 --srppasswdconf srp-tpasswd.conf \
                 --srppasswd srp-passwd.txt \
                 --pskpasswd psk-passwd.txt \
                 --rawpkfile srv.rawpk.pem \
                 --rawpkkeyfile srv.key.pem

File: gnutls.info,  Node: gnutls-cli-debug Invocation,  Prev: gnutls-serv Invocation,  Up: Other included programs

Invoking gnutls-cli-debug
=========================

TLS debug client.  It sets up multiple TLS connections to a server and
queries its capabilities.  It was created to assist in debugging GnuTLS,
but it might be useful to extract a TLS server's capabilities.  It
connects to a TLS server, performs tests and print the server's
capabilities.  If called with the '-V' parameter more checks will be
performed.  Can be used to check for servers with special needs or bugs.

gnutls-cli-debug help/usage (‘-?’)
----------------------------------

gnutls-cli-debug - GnuTLS debug client
     Usage:  gnutls-cli-debug [ -<flag> [<val>] | --<name>[{=| }<val>] ]... [hostname]

None:

-d, --debug=num            Enable debugging
     				- it must be in the range:
     				  0 to 9999
        -V, --verbose              More verbose output
        -p, --port=num             The port to connect to
     				- it must be in the range:
     				  0 to 65536
            --app-proto            an alias for the 'starttls-proto' option
            --starttls-proto=str   The application protocol to be used to obtain the server's certificate (https, ftp, smtp, imap, ldap, xmpp, lmtp, pop3, nntp, sieve, postgres)
            --attime=str           Perform validation at the timestamp instead of the system time

Version, usage and configuration options:

Options are specified by doubled hyphens and their name or by a single
     hyphen and the flag character.
     Operands and options may be intermixed.  They will be reordered.

TLS debug client. It sets up multiple TLS connections to
     a server and queries its capabilities. It was created to assist in debugging
     GnuTLS, but it might be useful to extract a TLS server's capabilities.
     It connects to a TLS server, performs tests and print the server's
     capabilities. If called with the `-V' parameter more checks will be performed.
     Can be used to check for servers with special needs or bugs.

Please send bug reports to:  <bugs@gnutls.org>

debug option (-d).
------------------

This is the "enable debugging" option.  This option takes a
ArgumentType.NUMBER argument.  Specifies the debug level.

app-proto option.
-----------------

This is an alias for the ‘starttls-proto’ option, *note the
starttls-proto option documentation: gnutls-cli-debug starttls-proto.

starttls-proto option.
----------------------

This is the "the application protocol to be used to obtain the server's
certificate (https, ftp, smtp, imap, ldap, xmpp, lmtp, pop3, nntp,
sieve, postgres)" option.  This option takes a ArgumentType.STRING
argument.  Specify the application layer protocol for STARTTLS. If the
protocol is supported, gnutls-cli will proceed to the TLS negotiation.

attime option.
--------------

version option (-v).
--------------------

help option (-h).
-----------------

This is the "display extended usage information and exit" option.
Display usage information and exit.

more-help option (-!).
----------------------

This is the "extended usage information passed thru pager" option.  Pass
the extended usage information through a pager.

gnutls-cli-debug exit status
----------------------------

One of the following exit values will be returned:
‘0 (EXIT_SUCCESS)’
     Successful program execution.
‘1 (EXIT_FAILURE)’
     The operation failed or the command syntax was not valid.

gnutls-cli-debug See Also
.........................

gnutls-cli(1), gnutls-serv(1)

gnutls-cli-debug Examples
.........................

$ gnutls-cli-debug localhost
     GnuTLS debug client 3.5.0
     Checking localhost:443
                                  for SSL 3.0 (RFC6101) support... yes
                             whether we need to disable TLS 1.2... no
                             whether we need to disable TLS 1.1... no
                             whether we need to disable TLS 1.0... no
                             whether %NO_EXTENSIONS is required... no
                                    whether %COMPAT is required... no
                                  for TLS 1.0 (RFC2246) support... yes
                                  for TLS 1.1 (RFC4346) support... yes
                                  for TLS 1.2 (RFC5246) support... yes
                                       fallback from TLS 1.6 to... TLS1.2
                             for RFC7507 inappropriate fallback... yes
                                          for HTTPS server name... Local
                                    for certificate chain order... sorted
                       for safe renegotiation (RFC5746) support... yes
                          for Safe renegotiation support (SCSV)... no
                         for encrypt-then-MAC (RFC7366) support... no
                        for ext master secret (RFC7627) support... no
                                for heartbeat (RFC6520) support... no
                            for version rollback bug in RSA PMS... dunno
                       for version rollback bug in Client Hello... no
                 whether the server ignores the RSA PMS version... yes
     whether small records (512 bytes) are tolerated on handshake... yes
         whether cipher suites not in SSL 3.0 spec are accepted... yes
     whether a bogus TLS record version in the client hello is accepted... yes
              whether the server understands TLS closure alerts... partially
                 whether the server supports session resumption... yes
                           for anonymous authentication support... no
                           for ephemeral Diffie-Hellman support... no
                        for ephemeral EC Diffie-Hellman support... yes
                         ephemeral EC Diffie-Hellman group info... SECP256R1
                       for AES-128-GCM cipher (RFC5288) support... yes
                       for AES-128-CCM cipher (RFC6655) support... no
                     for AES-128-CCM-8 cipher (RFC6655) support... no
                       for AES-128-CBC cipher (RFC3268) support... yes
                  for CAMELLIA-128-GCM cipher (RFC6367) support... no
                  for CAMELLIA-128-CBC cipher (RFC5932) support... no
                          for 3DES-CBC cipher (RFC2246) support... yes
                       for ARCFOUR 128 cipher (RFC2246) support... yes
                                            for MD5 MAC support... yes
                                           for SHA1 MAC support... yes
                                         for SHA256 MAC support... yes
                                   for ZLIB compression support... no
                          for max record size (RFC6066) support... no
                     for OCSP status response (RFC6066) support... no
                   for OpenPGP authentication (RFC6091) support... no

You could also use the client to debug services with starttls
capability.
     $ gnutls-cli-debug --starttls-proto smtp --port 25 localhost

File: gnutls.info,  Node: Internal architecture of GnuTLS,  Next: Upgrading from previous versions,  Prev: Other included programs,  Up: Top

11 Internal Architecture of GnuTLS
**********************************

This chapter is to give a brief description of the way GnuTLS works.
The focus is to give an idea to potential developers and those who want
to know what happens inside the black box.

* Menu:

* The TLS Protocol::
* TLS Handshake Protocol::
* TLS Authentication Methods::
* TLS Hello Extension Handling::
* Cryptographic Backend::
* Random Number Generators-internals::
* FIPS140-2 mode::

File: gnutls.info,  Node: The TLS Protocol,  Next: TLS Handshake Protocol,  Up: Internal architecture of GnuTLS

11.1 The TLS Protocol
=====================

The main use case for the TLS protocol is shown in *note Figure 11.1:
fig-client-server.  A user of a library implementing the protocol
expects no less than this functionality, i.e., to be able to set
parameters such as the accepted security level, perform a negotiation
with the peer and be able to exchange data.

�[image src="gnutls-client-server-use-case.png"�]

Figure 11.1: TLS protocol use case.

File: gnutls.info,  Node: TLS Handshake Protocol,  Next: TLS Authentication Methods,  Prev: The TLS Protocol,  Up: Internal architecture of GnuTLS

11.2 TLS Handshake Protocol
===========================

The GnuTLS handshake protocol is implemented as a state machine that
waits for input or returns immediately when the non-blocking transport
layer functions are used.  The main idea is shown in *note Figure 11.2:
fig-gnutls-handshake.

�[image src="gnutls-handshake-state.png"�]

Figure 11.2: GnuTLS handshake state machine.

Also the way the input is processed varies per ciphersuite.  Several
implementations of the internal handlers are available and *note
gnutls_handshake:: only multiplexes the input to the appropriate
handler.  For example a PSK ciphersuite has a different implementation
of the ‘process_client_key_exchange’ than a certificate ciphersuite.  We
illustrate the idea in *note Figure 11.3: fig-gnutls-handshake-sequence.

�[image src="gnutls-handshake-sequence.png"�]

Figure 11.3: GnuTLS handshake process sequence.

File: gnutls.info,  Node: TLS Authentication Methods,  Next: TLS Hello Extension Handling,  Prev: TLS Handshake Protocol,  Up: Internal architecture of GnuTLS

11.3 TLS Authentication Methods
===============================

In GnuTLS authentication methods can be implemented quite easily.  Since
the required changes to add a new authentication method affect only the
handshake protocol, a simple interface is used.  An authentication
method needs to implement the functions shown below.

typedef struct
{
  const char *name;
  int (*gnutls_generate_server_certificate) (gnutls_session_t, gnutls_buffer_st*);
  int (*gnutls_generate_client_certificate) (gnutls_session_t, gnutls_buffer_st*);
  int (*gnutls_generate_server_kx) (gnutls_session_t, gnutls_buffer_st*);
  int (*gnutls_generate_client_kx) (gnutls_session_t, gnutls_buffer_st*);
  int (*gnutls_generate_client_cert_vrfy) (gnutls_session_t, gnutls_buffer_st *);
  int (*gnutls_generate_server_certificate_request) (gnutls_session_t,
                                                     gnutls_buffer_st *);

int (*gnutls_process_server_certificate) (gnutls_session_t, opaque *,
                                            size_t);
  int (*gnutls_process_client_certificate) (gnutls_session_t, opaque *,
                                            size_t);
  int (*gnutls_process_server_kx) (gnutls_session_t, opaque *, size_t);
  int (*gnutls_process_client_kx) (gnutls_session_t, opaque *, size_t);
  int (*gnutls_process_client_cert_vrfy) (gnutls_session_t, opaque *, size_t);
  int (*gnutls_process_server_certificate_request) (gnutls_session_t,
                                                    opaque *, size_t);
} mod_auth_st;

Those functions are responsible for the interpretation of the handshake
protocol messages.  It is common for such functions to read data from
one or more ‘credentials_t’ structures(1) and write data, such as
certificates, usernames etc.  to ‘auth_info_t’ structures.

Simple examples of existing authentication methods can be seen in
‘auth/psk.c’ for PSK ciphersuites and ‘auth/srp.c’ for SRP ciphersuites.
After implementing these functions the structure holding its pointers
has to be registered in ‘gnutls_algorithms.c’ in the
‘_gnutls_kx_algorithms’ structure.

---------- Footnotes ----------

(1) such as the ‘gnutls_certificate_credentials_t’ structures

File: gnutls.info,  Node: TLS Hello Extension Handling,  Next: Cryptographic Backend,  Prev: TLS Authentication Methods,  Up: Internal architecture of GnuTLS

11.4 TLS Extension Handling
===========================

As with authentication methods, adding TLS hello extensions can be done
quite easily by implementing the interface shown below.

typedef int (*gnutls_ext_recv_func) (gnutls_session_t session,
                                     const unsigned char *data, size_t len);
typedef int (*gnutls_ext_send_func) (gnutls_session_t session,
                                     gnutls_buffer_st *extdata);

Here there are two main functions, one for parsing the received
extension data and one for formatting the extension data that must be
send.  These functions have to check internally whether they operate
within a client or a server session.

A simple example of an extension handler can be seen in ‘lib/ext/srp.c’
in GnuTLS' source code.  After implementing these functions, the
extension has to be registered.  Registering an extension can be done in
two ways.  You can create a GnuTLS internal extension and register it in
‘hello_ext.c’ or write an external extension (not inside GnuTLS but
inside an application using GnuTLS) and register it via the exported
functions *note gnutls_session_ext_register:: or *note
gnutls_ext_register::.

Adding a new TLS hello extension
--------------------------------

Adding support for a new TLS hello extension is done from time to time,
and the process to do so is not difficult.  Here are the steps you need
to follow if you wish to do this yourself.  For the sake of discussion,
let's consider adding support for the hypothetical TLS extension
‘foobar’.  The following section is about adding an hello extension to
GnuTLS itself.  For custom application extensions you should check the
exported functions *note gnutls_session_ext_register:: or *note
gnutls_ext_register::.

Add ‘configure’ option like ‘--enable-foobar’ or ‘--disable-foobar’.
....................................................................

This step is useful when the extension code is large and it might be
desirable under some circumstances to be able to leave out the extension
during compilation of GnuTLS. If you don't need this kind of feature
this step can be safely skipped.

Whether to choose enable or disable depends on whether you intend to
make the extension be enabled by default.  Look at existing checks
(i.e., SRP, authz) for how to model the code.  For example:

AC_MSG_CHECKING([whether to disable foobar support])
     AC_ARG_ENABLE(foobar,
     	AS_HELP_STRING([--disable-foobar],
     		[disable foobar support]),
     	ac_enable_foobar=no)
     if test x$ac_enable_foobar != xno; then
      AC_MSG_RESULT(no)
      AC_DEFINE(ENABLE_FOOBAR, 1, [enable foobar])
     else
      ac_full=0
      AC_MSG_RESULT(yes)
     fi
     AM_CONDITIONAL(ENABLE_FOOBAR, test "$ac_enable_foobar" != "no")

These lines should go in ‘lib/m4/hooks.m4’.

Add an extension identifier to ‘extensions_t’ in ‘gnutls_int.h’.
................................................................

A good name for the identifier would be GNUTLS_EXTENSION_FOOBAR. If the
extension that you are implementing is an extension that is officially
registered by IANA then it is recommended to use its official name such
that the extension can be correctly identified by other developers.
Check with <https://www.iana.org/assignments/tls-extensiontype-values>
for registered extensions.

In order for the extension to be executed you need to register it in the
‘static hello_ext_entry_st const *extfunc[]’ list in ‘lib/hello_ext.c’.

A typical entry would be:

#ifdef ENABLE_FOOBAR
     	[GNUTLS_EXTENSION_FOOBAR] = &ext_mod_foobar,
     #endif

Also for every extension you need to create an ‘hello_ext_entry_st’ that
describes the extension.  This structure is placed in the designated c
file for your extension and its name is used in the registration entry
as depicted above.

The structure of ‘hello_ext_entry_st’ is as follows:
       const hello_ext_entry_st ext_mod_foobar = {
         .name = "FOOBAR",
         .tls_id = 255,
         .gid = GNUTLS_EXTENSION_FOOBAR,
         .parse_type = GNUTLS_EXT_TLS,
         .validity = GNUTLS_EXT_FLAG_CLIENT_HELLO |
     	GNUTLS_EXT_FLAG_TLS12_SERVER_HELLO |
     	GNUTLS_EXT_FLAG_TLS13_SERVER_HELLO |
     	GNUTLS_EXT_FLAG_TLS,
         .recv_func = _gnutls_foobar_recv_params,
         .send_func = _gnutls_foobar_send_params,
         .pack_func = _gnutls_foobar_pack,
         .unpack_func = _gnutls_foobar_unpack,
         .deinit_func = _gnutls_foobar_deinit,
         .cannot_be_overriden = 1
       };

The GNUTLS_EXTENSION_FOOBAR is the identifier that you've added to
‘gnutls_int.h’ earlier.  The ‘.tls_id’ should contain the number that
IANA has assigned to this extension, or an unassigned number of your
choice if this is an unregistered extension.  In the rest of this
structure you specify the functions to handle the extension data.  The
‘receive’ function will be called upon reception of the data and will be
used to parse or interpret the extension data.  The ‘send’ function will
be called prior to sending the extension data on the wire and will be
used to format the data such that it can be send over the wire.  The
‘pack’ and ‘unpack’ functions will be used to prepare the data for
storage in case of session resumption (and vice versa).  The ‘deinit’
function will be called to deinitialize the extension's private
parameters, if any.

Look at ‘gnutls_ext_parse_type_t’ and ‘gnutls_ext_flags_t’ for a
complete list of available flags.

Note that the conditional ‘ENABLE_FOOBAR’ definition should only be used
if step 1 with the ‘configure’ options has taken place.

Add new files that implement the hello extension.
.................................................

To keep things structured every extension should have its own files.
The functions that you should (at least) add are those referenced in the
struct from the previous step.  Use descriptive file names such as
‘lib/ext/foobar.c’ and for the corresponding header ‘lib/ext/foobar.h’.
As a starter, you could add this:

int
     _gnutls_foobar_recv_params (gnutls_session_t session, const uint8_t * data,
                          size_t data_size)
     {
       return 0;
     }

int
     _gnutls_foobar_send_params (gnutls_session_t session, gnutls_buffer_st* data)
     {
       return 0;
     }

int
     _gnutls_foobar_pack (extension_priv_data_t epriv, gnutls_buffer_st * ps)
     {
        /* Append the extension's internal state to buffer */
        return 0;
     }

int
     _gnutls_foobar_unpack (gnutls_buffer_st * ps, extension_priv_data_t * epriv)
     {
        /* Read the internal state from buffer */
        return 0;
     }

The ‘_gnutls_foobar_recv_params’ function is responsible for parsing
incoming extension data (both in the client and server).

The ‘_gnutls_foobar_send_params’ function is responsible for formatting
extension data such that it can be send over the wire (both in the
client and server).  It should append data to provided buffer and return
a positive (or zero) number on success or a negative error code.
Previous to 3.6.0 versions of GnuTLS required that function to return
the number of bytes that were written.  If zero is returned and no bytes
are appended the extension will not be sent.  If a zero byte extension
is to be sent this function must return ‘GNUTLS_E_INT_RET_0’.

If you receive length fields that don't match, return
‘GNUTLS_E_UNEXPECTED_PACKET_LENGTH’.  If you receive invalid data,
return ‘GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER’.  You can use other error
codes from the list in *note Error codes::.  Return 0 on success.

An extension typically stores private information in the ‘session’ data
for later usage.  That can be done using the functions
‘_gnutls_hello_ext_set_datum’ and ‘_gnutls_hello_ext_get_datum’.  You
can check simple examples at ‘lib/ext/max_record.c’ and
‘lib/ext/server_name.c’ extensions.  That private information can be
saved and restored across session resumption if the following functions
are set:

The ‘_gnutls_foobar_pack’ function is responsible for packing internal
extension data to save them in the session resumption storage.

The ‘_gnutls_foobar_unpack’ function is responsible for restoring
session data from the session resumption storage.

When the internal data is stored using the
‘_gnutls_hello_ext_set_datum’, then you can rely on the default pack and
unpack functions: ‘_gnutls_hello_ext_default_pack’ and
‘_gnutls_hello_ext_default_unpack’.

Recall that both for the client and server, the send and receive
functions most likely will need to do different things depending on
which mode they are in.  It may be useful to make this distinction
explicit in the code.  Thus, for example, a better template than above
would be:

int
     _gnutls_foobar_recv_params (gnutls_session_t session,
                                 const uint8_t * data,
                                 size_t data_size)
     {
       if (session->security_parameters.entity == GNUTLS_CLIENT)
         return foobar_recv_client (session, data, data_size);
       else
         return foobar_recv_server (session, data, data_size);
     }

int
     _gnutls_foobar_send_params (gnutls_session_t session,
                                 gnutls_buffer_st * data)
     {
       if (session->security_parameters.entity == GNUTLS_CLIENT)
         return foobar_send_client (session, data);
       else
         return foobar_send_server (session, data);
     }

The functions used would be declared as ‘static’ functions, of the
appropriate prototype, in the same file.

When adding the new extension files, you'll need to add them to
‘lib/ext/Makefile.am’ as well, for example:

if ENABLE_FOOBAR
     libgnutls_ext_la_SOURCES += ext/foobar.c ext/foobar.h
     endif

Add API functions to use the extension.
.......................................

It might be desirable to allow users of the extension to request the use
of the extension, or set extension specific data.  This can be
implemented by adding extension specific function calls that can be
added to ‘includes/gnutls/gnutls.h’, as long as the LGPLv2.1+ applies.
The implementation of these functions should lie in the
‘lib/ext/foobar.c’ file.

To make the API available in the shared library you need to add the
added symbols in ‘lib/libgnutls.map’, so that the symbols are exported
properly.

When writing GTK-DOC style documentation for your new APIs, don't forget
to add ‘Since:’ tags to indicate the GnuTLS version the API was
introduced in.

Adding a new Supplemental Data Handshake Message
------------------------------------------------

TLS handshake extensions allow to send so called supplemental data
handshake messages [*note RFC4680::].  This short section explains how
to implement a supplemental data handshake message for a given TLS
extension.

First of all, modify your extension ‘foobar’ in the way, to instruct the
handshake process to send and receive supplemental data, as shown below.

int
     _gnutls_foobar_recv_params (gnutls_session_t session, const opaque * data,
                                      size_t _data_size)
     {
        ...
        gnutls_supplemental_recv(session, 1);
        ...
     }

int
     _gnutls_foobar_send_params (gnutls_session_t session, gnutls_buffer_st *extdata)
     {
        ...
        gnutls_supplemental_send(session, 1);
        ...
     }

Furthermore you'll need two new functions ‘_foobar_supp_recv_params’ and
‘_foobar_supp_send_params’, which must conform to the following
prototypes.

typedef int (*gnutls_supp_recv_func)(gnutls_session_t session,
                                          const unsigned char *data,
                                          size_t data_size);
     typedef int (*gnutls_supp_send_func)(gnutls_session_t session,
                                          gnutls_buffer_t buf);

The following example code shows how to send a "Hello World" string in
the supplemental data handshake message.

int
     _foobar_supp_recv_params(gnutls_session_t session, const opaque *data, size_t _data_size)
     {
        uint8_t len = _data_size;
        unsigned char *msg;

msg = gnutls_malloc(len);
        if (msg == NULL) return GNUTLS_E_MEMORY_ERROR;

memcpy(msg, data, len);
        msg[len]='\0';

/* do something with msg */
        gnutls_free(msg);

return len;
     }

int
     _foobar_supp_send_params(gnutls_session_t session, gnutls_buffer_t buf)
     {
        unsigned char *msg = "hello world";
        int len = strlen(msg);

if (gnutls_buffer_append_data(buf, msg, len) < 0)
            abort();

return len;
     }

Afterwards, register the new supplemental data using *note
gnutls_session_supplemental_register::, or *note
gnutls_supplemental_register:: at some point in your program.

File: gnutls.info,  Node: Cryptographic Backend,  Next: Random Number Generators-internals,  Prev: TLS Hello Extension Handling,  Up: Internal architecture of GnuTLS

11.5 Cryptographic Backend
==========================

Today most new processors, either for embedded or desktop systems
include either instructions intended to speed up cryptographic
operations, or a co-processor with cryptographic capabilities.  Taking
advantage of those is a challenging task for every cryptographic
application or library.  GnuTLS handles the cryptographic provider in a
modular way, following a layered approach to access cryptographic
operations as in *note Figure 11.4: fig-crypto-layers.

�[image src="gnutls-crypto-layers.png"�]

Figure 11.4: GnuTLS cryptographic back-end design.

The TLS layer uses a cryptographic provider layer, that will in turn
either use the default crypto provider - a software crypto library, or
use an external crypto provider, if available in the local system.  The
reason of handling the external cryptographic provider in GnuTLS and not
delegating it to the cryptographic libraries, is that none of the
supported cryptographic libraries support ‘/dev/crypto’ or CPU-optimized
cryptography in an efficient way.

Cryptographic library layer
---------------------------

The Cryptographic library layer, currently supports only libnettle.
Older versions of GnuTLS used to support libgcrypt, but it was switched
with nettle mainly for performance reasons(1) and secondary because it
is a simpler library to use.  In the future other cryptographic
libraries might be supported as well.

External cryptography provider
------------------------------

Systems that include a cryptographic co-processor, typically come with
kernel drivers to utilize the operations from software.  For this reason
GnuTLS provides a layer where each individual algorithm used can be
replaced by another implementation, i.e., the one provided by the
driver.  The FreeBSD, OpenBSD and Linux kernels(2) include already a
number of hardware assisted implementations, and also provide an
interface to access them, called ‘/dev/crypto’.  GnuTLS will take
advantage of this interface if compiled with special options.  That is
because in most systems where hardware-assisted cryptographic operations
are not available, using this interface might actually harm performance.

In systems that include cryptographic instructions with the CPU's
instructions set, using the kernel interface will introduce an unneeded
layer.  For this reason GnuTLS includes such optimizations found in
popular processors such as the AES-NI or VIA PADLOCK instruction sets.
This is achieved using a mechanism that detects CPU capabilities and
overrides parts of crypto back-end at runtime.  The next section
discusses the registration of a detected algorithm optimization.  For
more information please consult the GnuTLS source code in
‘lib/accelerated/’.

Overriding specific algorithms
..............................

When an optimized implementation of a single algorithm is available, say
a hardware assisted version of AES-CBC then the following functions,
from ‘crypto.h’, can be used to register those algorithms.

• *note gnutls_crypto_register_cipher::: To register a cipher
     algorithm.

• *note gnutls_crypto_register_aead_cipher::: To register an AEAD
     cipher algorithm.

• *note gnutls_crypto_register_mac::: To register a MAC algorithm.

• *note gnutls_crypto_register_digest::: To register a hash
     algorithm.

Those registration functions will only replace the specified algorithm
and leave the rest of subsystem intact.

Protecting keys through isolation
---------------------------------

For asymmetric or public keys, GnuTLS supports PKCS #11 which allows
operation without access to long term keys, in addition to CPU
offloading.  For more information see *note Hardware security modules
and abstract key types::.

---------- Footnotes ----------

(1) See
<https://lists.gnu.org/archive/html/gnutls-devel/2011-02/msg00079.html>.

(2) Check <https://home.gna.org/cryptodev-linux/> for the Linux
kernel implementation of ‘/dev/crypto’.

File: gnutls.info,  Node: Random Number Generators-internals,  Next: FIPS140-2 mode,  Prev: Cryptographic Backend,  Up: Internal architecture of GnuTLS

11.6 Random Number Generators
=============================

About the generators
--------------------

GnuTLS provides two random generators.  The default, and the AES-DRBG
random generator which is only used when the library is compiled with
support for FIPS140-2 and the system is in FIPS140-2 mode.

The default generator - inner workings
--------------------------------------

The random number generator levels in ‘gnutls_rnd_level_t’ map to two
CHACHA-based random generators which are initially seeded using the OS
random device, e.g., ‘/dev/urandom’ or ‘getrandom()’.  These random
generators are unique per thread, and are automatically re-seeded when a
fork is detected.

The reason the CHACHA cipher was selected for the GnuTLS' PRNG is the
fact that CHACHA is considered a secure and fast stream cipher, and is
already defined for use in TLS protocol.  As such, the utilization of it
would not stress the CPU caches, and would allow for better performance
on busy servers, irrespective of their architecture (e.g., even if AES
is not available with an optimized instruction set).

The generators are unique per thread to allow lock-free operation.  That
induces a cost of around 140-bytes for the state of the generators per
thread, on threads that would utilize *note gnutls_rnd::.  At the same
time it allows fast and lock-free access to the generators.  The
lock-free access benefits servers which utilize more than 4 threads,
while imposes no cost on single threaded processes.

On the first call to *note gnutls_rnd:: the generators are seeded with
two independent keys obtained from the OS random device.  Their seed is
used to output a fixed amount of bytes before re-seeding; the number of
bytes output varies per generator.

One generator is dedicated for the ‘GNUTLS_RND_NONCE’ level, and the
second is shared for the ‘GNUTLS_RND_KEY’ and ‘GNUTLS_RND_RANDOM’
levels.  For the rest of this section we refer to the first as the nonce
generator and the second as the key generator.

The nonce generator will reseed after outputting a fixed amount of bytes
(typically few megabytes), or after few hours of operation without
reaching the limit has passed.  It is being re-seed using the key
generator to obtain a new key for the CHACHA cipher, which is mixed with
its old one.

Similarly, the key generator, will also re-seed after a fixed amount of
bytes is generated (typically less than the nonce), and will also
re-seed based on time, i.e., after few hours of operation without
reaching the limit for a re-seed.  For its re-seed it mixes mixes data
obtained from the OS random device with the previous key.

Although the key generator used to provide data for the
‘GNUTLS_RND_RANDOM’ and ‘GNUTLS_RND_KEY’ levels is identical, when used
with the ‘GNUTLS_RND_KEY’ level a re-key of the PRNG using its own
output, is additionally performed.  That ensures that the recovery of
the PRNG state will not be sufficient to recover previously generated
values.

The AES-DRBG generator - inner workings
---------------------------------------

Similar with the default generator, the random number generator levels
in ‘gnutls_rnd_level_t’ map to two AES-DRBG random generators which are
initially seeded using the OS random device, e.g., ‘/dev/urandom’ or
‘getrandom()’.  These random generators are unique per thread, and are
automatically re-seeded when a fork is detected.

The AES-DRBG generator is based on the AES cipher in counter mode and is
re-seeded after a fixed amount of bytes are generated.

Defense against PRNG attacks
----------------------------

This section describes the counter-measures available in the
Pseudo-random number generator (PRNG) of GnuTLS for known attacks as
described in [*note PRNGATTACKS::].  Note that, the attacks on a PRNG
such as state-compromise, assume a quite powerful adversary which has in
practice access to the PRNG state.

Cryptanalytic
.............

To defend against cryptanalytic attacks GnuTLS' PRNG is a stream cipher
designed to defend against the same attacks.  As such, GnuTLS' PRNG
strength with regards to this attack relies on the underlying crypto
block, which at the time of writing is CHACHA. That is easily
replaceable in the future if attacks are found to be possible in that
cipher.

Input-based attacks
...................

These attacks assume that the attacker can influence the input that is
used to form the state of the PRNG. To counter these attacks GnuTLS does
not gather input from the system environment but rather relies on the OS
provided random generator.  That is the ‘/dev/urandom’ or
‘getentropy’/‘getrandom’ system calls.  As such, GnuTLS' PRNG is as
strong as the system random generator can assure with regards to
input-based attacks.

State-compromise: Backtracking
..............................

A backtracking attack, assumes that an adversary obtains at some point
of time access to the generator state, and wants to recover past bytes.
As the GnuTLS generator is fine-tuned to provide multiple levels, such
an attack mainly concerns levels ‘GNUTLS_RND_RANDOM’ and
‘GNUTLS_RND_KEY’, since ‘GNUTLS_RND_NONCE’ is intended to output
non-secret data.  The ‘GNUTLS_RND_RANDOM’ generator at the time of
writing can output 2MB prior to being re-seeded thus this is its upper
bound for previously generated data recovered using this attack.  That
assumes that the state of the operating system random generator is
unknown to the attacker, and we carry that assumption on the next
paragraphs.  The usage of ‘GNUTLS_RND_KEY’ level ensures that no
backtracking is possible for all output data, by re-keying the PRNG
using its own output.

Such an attack reflects the real world scenario where application's
memory is temporarily compromised, while the kernel's memory is
inaccessible.

State-compromise: Permanent Compromise Attack
.............................................

A permanent compromise attack implies that once an attacker compromises
the state of GnuTLS' random generator at a specific time, future and
past outputs from the generator are compromised.  For past outputs the
previous paragraph applies.  For future outputs, both the
‘GNUTLS_RND_RANDOM’ and the ‘GNUTLS_RND_KEY’ will recover after 2MB of
data have been generated or few hours have passed (two at the time of
writing).  Similarly the ‘GNUTLS_RND_NONCE’ level generator will recover
after several megabytes of output is generated, or its re-key time is
reached.

State-compromise: Iterative guessing
....................................

This attack assumes that after an attacker obtained the PRNG state at
some point, is able to recover the state at a later time by observing
outputs of the PRNG. That is countered by switching the key to
generators using a combination of a fresh key and the old one (using
XOR), at re-seed time.  All levels are immune to such attack after a
re-seed.

State-compromise: Meet-in-the-Middle
....................................

This attack assumes that the attacker obtained the PRNG state at two
distinct times, and being able to recover the state at the third time
after observing the output of the PRNG. Given the approach described on
the above paragraph, all levels are immune to such attack.

File: gnutls.info,  Node: FIPS140-2 mode,  Prev: Random Number Generators-internals,  Up: Internal architecture of GnuTLS

11.7 FIPS140-2 mode
===================

GnuTLS can operate in a special mode for FIPS140-2.  That mode of
operation is for the conformance to NIST's FIPS140-2 publication, which
consists of policies for cryptographic modules (such as software
libraries).  Its implementation in GnuTLS is designed for Red Hat
Enterprise Linux, and can only be enabled when the library is explicitly
compiled with the '-enable-fips140-mode' configure option.

There are two distinct library states with regard to FIPS140-2: the
FIPS140-2 mode is _installed_ if ‘/etc/system-fips’ is present, and the
FIPS140-2 mode is _enabled_ if ‘/proc/sys/crypto/fips_enabled’ contains
'1', which is typically set with the "fips=1" kernel command line
option.

When the FIPS140-2 mode is installed, the operation of the library is
modified as follows.

• The random generator used switches to DRBG-AES
   • The integrity of the GnuTLS and dependent libraries is checked on
     startup
   • Algorithm self-tests are run on library load

When the FIPS140-2 mode is enabled, The operation of the library is in
addition modified as follows.

• Only approved by FIPS140-2 algorithms are enabled
   • Only approved by FIPS140-2 key lengths are allowed for key
     generation
   • Any cryptographic operation will be refused if any of the
     self-tests failed

There are also few environment variables which modify that operation.
The environment variable ‘GNUTLS_SKIP_FIPS_INTEGRITY_CHECKS’ will
disable the library integrity tests on startup, and the variable
‘GNUTLS_FORCE_FIPS_MODE’ can be set to force a value from *note Figure
11.5: gnutls_fips_mode_t, i.e., '1' will enable the FIPS140-2 mode,
while '0' will disable it.

The integrity checks for the dependent libraries and GnuTLS are
performed using '.hmac' files which are present at the same path as the
library.  The key for the operations can be provided on compile-time
with the configure option '-with-fips140-key'.  The MAC algorithm used
is HMAC-SHA256.

On runtime an application can verify whether the library is in FIPS140-2
mode using the *note gnutls_fips140_mode_enabled:: function.

Relaxing FIPS140-2 requirements
-------------------------------

The library by default operates in a strict enforcing mode, ensuring
that all constraints imposed by the FIPS140-2 specification are
enforced.  However the application can relax these requirements via
*note gnutls_fips140_set_mode:: which can switch to alternative modes as
in *note Figure 11.5: gnutls_fips_mode_t.

‘GNUTLS_FIPS140_DISABLED’
     The FIPS140-2 mode is disabled.
‘GNUTLS_FIPS140_STRICT’
     The default mode; all forbidden operations will cause an operation
     failure via error code.
‘GNUTLS_FIPS140_SELFTESTS’
     A transient state during library initialization.  That state cannot
     be set or seen by applications.
‘GNUTLS_FIPS140_LAX’
     The library still uses the FIPS140-2 relevant algorithms but all
     forbidden by FIPS140-2 operations are allowed; this is useful when
     the application is aware of the followed security policy, and needs
     to utilize disallowed operations for other reasons (e.g.,
     compatibility).
‘GNUTLS_FIPS140_LOG’
     Similarly to ‘GNUTLS_FIPS140_LAX’ , it allows forbidden operations;
     any use of them results to a message to the audit callback
     functions.

Figure 11.5: The ‘gnutls_fips_mode_t’ enumeration.

The intention of this API is to be used by applications which may run in
FIPS140-2 mode, while they utilize few algorithms not in the allowed
set, e.g., for non-security related purposes.  In these cases
applications should wrap the non-compliant code within blocks like the
following.

GNUTLS_FIPS140_SET_LAX_MODE();

_gnutls_hash_fast(GNUTLS_DIG_MD5, buffer, sizeof(buffer), output);

GNUTLS_FIPS140_SET_STRICT_MODE();

The ‘GNUTLS_FIPS140_SET_LAX_MODE’ and ‘GNUTLS_FIPS140_SET_STRICT_MODE’
are macros to simplify the following sequence of calls.

if (gnutls_fips140_mode_enabled())
       gnutls_fips140_set_mode(GNUTLS_FIPS140_LAX, GNUTLS_FIPS140_SET_MODE_THREAD);

_gnutls_hash_fast(GNUTLS_DIG_MD5, buffer, sizeof(buffer), output);

if (gnutls_fips140_mode_enabled())
       gnutls_fips140_set_mode(GNUTLS_FIPS140_STRICT, GNUTLS_FIPS140_SET_MODE_THREAD);

The reason of the ‘GNUTLS_FIPS140_SET_MODE_THREAD’ flag in the previous
calls is to localize the change in the mode.  Note also, that such a
block has no effect when the library is not operating under FIPS140-2
mode, and thus it can be considered a no-op.

Applications could also switch FIPS140-2 mode explicitly off, by calling
     gnutls_fips140_set_mode(GNUTLS_FIPS140_LAX, 0);

Service indicator
-----------------

The above restrictions may not cover all the requirements in every usage
context, and as the FIPS140 standard evolves (like FIPS140-3), GnuTLS
may not be able to add new restrictions without breaking compatibility.

Therefore an additional set of API functions is provided to communicate
with the user whether any approved mode of operations is performed
within a given context.

‘INT *note gnutls_fips140_context_init:: (gnutls_fips140_context_t * CONTEXT)’
‘VOID *note gnutls_fips140_context_deinit:: (gnutls_fips140_context_t CONTEXT)’
‘INT *note gnutls_fips140_push_context:: (gnutls_fips140_context_t CONTEXT)’
‘INT *note gnutls_fips140_pop_context:: ( VOID)’

The ‘gnutls_fips140_context_t’ represents the FIPS140-2 mode of
operation.  It can be attached to the current execution thread with
*note gnutls_fips140_push_context:: and its internal state will be
updated until it is detached with *note gnutls_fips140_pop_context::.
Afterwards *note gnutls_fips140_get_operation_state:: allows the user to
examine whether any approved (or non-approved) security function is
invoked.

-- Function: gnutls_fips140_operation_state_t
          gnutls_fips140_get_operation_state (gnutls_fips140_context_t
          CONTEXT)
     CONTEXT: a ‘gnutls_fips140_context_t’

Get the previous operation state of ‘context’ in terms of FIPS.

*Returns:* a ‘gnutls_fips140_operation_state_t’

*Since:* 3.7.3

File: gnutls.info,  Node: Upgrading from previous versions,  Next: Support,  Prev: Internal architecture of GnuTLS,  Up: Top

Appendix A Upgrading from previous versions
*******************************************

The GnuTLS library typically maintains binary and source code
compatibility across versions.  The releases that have the major version
increased break binary compatibility but source compatibility is
provided.  This section lists exceptional cases where changes to
existing code are required due to library changes.

Upgrading to 2.12.x from previous versions
==========================================

GnuTLS 2.12.x is binary compatible with previous versions but changes
the semantics of ‘gnutls_transport_set_lowat’, which might cause
breakage in applications that relied on its default value be 1.  Two
fixes are proposed:
   • Quick fix.  Explicitly call ‘gnutls_transport_set_lowat (session,
     1);’ after *note gnutls_init::.
   • Long term fix.  Because later versions of gnutls abolish the
     functionality of using the system call ‘select’ to check for gnutls
     pending data, the function *note gnutls_record_check_pending:: has
     to be used to achieve the same functionality as described in *note
     Asynchronous operation::.

Upgrading to 3.0.x from 2.12.x
==============================

GnuTLS 3.0.x is source compatible with previous versions except for the
functions listed below.

Old function           Replacement
                       
-------------------------------------------------------------------
‘gnutls_transport_set_lowat’To replace its functionality the function
                       *note gnutls_record_check_pending:: has
                       to be used, as described in
                       *note Asynchronous operation::
                       
‘gnutls_session_get_server_random’,They are replaced by the safer function
‘gnutls_session_get_client_random’*note gnutls_session_get_random::
                       
‘gnutls_session_get_master_secret’Replaced by the keying material exporters
                       discussed in
                       *note Deriving keys for other applications/protocols::
                       
‘gnutls_transport_set_global_errno’Replaced by using the system's errno
                       facility or
                       *note gnutls_transport_set_errno::.
                       
‘gnutls_x509_privkey_verify_data’Replaced by
                       *note gnutls_pubkey_verify_data2::.
                       
‘gnutls_certificate_verify_peers’Replaced by
                       *note gnutls_certificate_verify_peers2::.
                       
‘gnutls_psk_netconf_derive_key’Removed.  The key derivation function was
                       never standardized.
                       
‘gnutls_session_set_finished_function’Removed.
                       
‘gnutls_ext_register’  Removed.  Extension registration API is
                       now internal to allow easier changes in
                       the API.
                       
‘gnutls_certificate_get_x509_crls’,Removed to allow updating the internal
‘gnutls_certificate_get_x509_cas’structures.  Replaced by
                       *note gnutls_certificate_get_issuer::.
                       
‘gnutls_certificate_get_openpgp_keyring’Removed.
                       
‘gnutls_ia_’           Removed.  The inner application
                       extensions were completely removed (they
                       failed to be standardized).

Upgrading to 3.1.x from 3.0.x
=============================

GnuTLS 3.1.x is source and binary compatible with GnuTLS 3.0.x releases.
Few functions have been deprecated and are listed below.

Old function           Replacement
                       
-------------------------------------------------------------------
‘gnutls_pubkey_verify_hash’The function
                       *note gnutls_pubkey_verify_hash2:: is
                       provided and is functionally equivalent
                       and safer to use.
                       
‘gnutls_pubkey_verify_data’The function
                       *note gnutls_pubkey_verify_data2:: is
                       provided and is functionally equivalent
                       and safer to use.

Upgrading to 3.2.x from 3.1.x
=============================

GnuTLS 3.2.x is source and binary compatible with GnuTLS 3.1.x releases.
Few functions have been deprecated and are listed below.

Old function           Replacement
                       
-------------------------------------------------------------------
‘gnutls_privkey_sign_raw_data’The function
                       *note gnutls_privkey_sign_hash:: is
                       equivalent when the flag
                       ‘GNUTLS_PRIVKEY_SIGN_FLAG_TLS1_RSA’ is
                       specified.

Upgrading to 3.3.x from 3.2.x
=============================

GnuTLS 3.3.x is source and binary compatible with GnuTLS 3.2.x releases;
however there few changes in semantics which are listed below.

Old function           Replacement
                       
-------------------------------------------------------------------
‘gnutls_global_init’   No longer required.  The library is
                       initialized using a constructor.
                       
‘gnutls_global_deinit’ No longer required.  The library is
                       deinitialized using a destructor.

Upgrading to 3.4.x from 3.3.x
=============================

GnuTLS 3.4.x is source compatible with GnuTLS 3.3.x releases; however,
several deprecated functions were removed, and are listed below.

Old function           Replacement
                       
-------------------------------------------------------------------
Priority string        The following string emulates the 3.3.x
"NORMAL" has been      behavior
modified               "NORMAL:+VERS-SSL3.0:+ARCFOUR-128:+DHE-DSS:+SIGN-DSA-SHA512:+SIGN-DSA-SHA256:+SIGN-DSA-SHA1"
                       
‘gnutls_certificate_client_set_retrieve_function’,*note gnutls_certificate_set_retrieve_function::
‘gnutls_certificate_server_set_retrieve_function’
‘gnutls_certificate_set_rsa_export_params’,No replacement; the library does not
‘gnutls_rsa_export_get_modulus_bits’,support the RSA-EXPORT ciphersuites.
‘gnutls_rsa_export_get_pubkey’,
‘gnutls_rsa_params_cpy’,
‘gnutls_rsa_params_deinit’,
‘gnutls_rsa_params_export_pkcs1’,
‘gnutls_rsa_params_export_raw’,
‘gnutls_rsa_params_generate2’,
‘gnutls_rsa_params_import_pkcs1’,
‘gnutls_rsa_params_import_raw’,
‘gnutls_rsa_params_init’
‘gnutls_pubkey_verify_hash’,*note gnutls_pubkey_verify_hash2::.
                       
‘gnutls_pubkey_verify_data’,*note gnutls_pubkey_verify_data2::.
                       
‘gnutls_x509_crt_get_verify_algorithm’,No replacement; a similar function is
                       *note gnutls_x509_crt_get_signature_algorithm::.
                       
‘gnutls_pubkey_get_verify_algorithm’,No replacement; a similar function is
                       *note gnutls_pubkey_get_preferred_hash_algorithm::.
                       
‘gnutls_certificate_type_set_priority’,*note gnutls_priority_set_direct::.
‘gnutls_cipher_set_priority’,
‘gnutls_compression_set_priority’,
‘gnutls_kx_set_priority’,
‘gnutls_mac_set_priority’,
‘gnutls_protocol_set_priority’
‘gnutls_sign_callback_get’,*note gnutls_privkey_import_ext3::
‘gnutls_sign_callback_set’
‘gnutls_x509_crt_verify_hash’*note gnutls_pubkey_verify_hash2::
                       
‘gnutls_x509_crt_verify_data’*note gnutls_pubkey_verify_data2::
                       
‘gnutls_privkey_sign_raw_data’*note gnutls_privkey_sign_hash:: with the
                       flag GNUTLS_PRIVKEY_SIGN_FLAG_TLS1_RSA

Upgrading to 3.6.x from 3.5.x
=============================

GnuTLS 3.6.x is source and binary compatible with GnuTLS 3.5.x releases;
however, there are minor differences, listed below.

Old functionality      Replacement
                       
-------------------------------------------------------------------
The priority strings   TLS compression is no longer available.
"+COMP" are a no-op    
The SSL 3.0 protocol   SSL 3.0 is no longer compiled in by
is a no-op             default.  It is a legacy protocol which
                       is completely eliminated from public
                       internet.  As such it was removed to
                       reduce the attack vector for applications
                       using the library.
                       
The hash function      TLS 1.3 no longer uses SHA2-224, and it
SHA2-224 is a no-op    was never a widespread hash algorithm.
for TLS1.2             As such it was removed for simplicity.
                       
The SRP key exchange   The SRP key exchange is restricted to
accepted parameters    [*note TLSSRP::] spec parameters to
outside the            protect clients from MitM attacks.
[*note TLSSRP::]       
spec
The                    No longer use ‘gnutls_compression_get’,
compression-related    ‘gnutls_compression_get_name’,
functions are          ‘gnutls_compression_list’, and
deprecated             ‘gnutls_compression_get_id’.
                       
*note gnutls_x509_crt_sign::,These signing functions will no longer
*note gnutls_x509_crl_sign::,sign using SHA1, but with a secure hash
*note gnutls_x509_crq_sign::algorithm.
                       
*note gnutls_certificate_set_ocsp_status_request_file::This function will return an error if the
                       loaded response doesn't match any of the
                       present certificates.  To revert to
                       previous semantics set the
                       ‘GNUTLS_CERTIFICATE_SKIP_OCSP_RESPONSE_CHECK’
                       flag using
                       *note gnutls_certificate_set_flags::.
                       
The callback           It is replaced with
*note gnutls_privkey_import_ext3::*note gnutls_privkey_import_ext4::
is not flexible        
enough for new
signature algorithms
such as RSA-PSS
Re-handshake           It is replaced by separate key update and
functionality is not   re-authentication functionality which can
applicable under TLS   be accessed directly via
1.3.                   *note gnutls_session_key_update:: and
                       *note gnutls_reauth::.
                       
TLS session            The TLS session identifiers are
identifiers are not    persistent across resumption only on
shared with the        server side and can be obtained as before
server under TLS       via *note gnutls_session_get_id2::.
1.3.                   
*note gnutls_pkcs11_privkey_generate3::,These functions no longer create an
*note gnutls_pkcs11_copy_secret_key::,exportable key by default; they require
*note gnutls_pkcs11_copy_x509_privkey2::the flag
                       ‘GNUTLS_PKCS11_OBJ_FLAG_MARK_NOT_SENSITIVE’
                       to do so.
                       
*note gnutls_db_set_retrieve_function::,These functions are no longer relevant
*note gnutls_db_set_store_function::,under TLS 1.3; resumption under TLS 1.3
*note gnutls_db_set_remove_function::is done via session tickets, c.f.
                       *note gnutls_session_ticket_enable_server::.
                       
*note gnutls_session_get_data2::,These functions may introduce a slight
*note gnutls_session_get_data::delay under TLS 1.3 for few milliseconds.
                       Check output of
                       *note gnutls_session_get_flags:: for
                       GNUTLS_SFLAGS_SESSION_TICKET before
                       calling this function to avoid delays.
                       To work efficiently under TLS 1.3 this
                       function requires the application setting
                       *note gnutls_transport_set_pull_timeout_function::.
                       
SRP and RSA-PSK key    SRP and RSA-PSK key exchanges are not
exchanges are not      supported in TLS 1.3, so when these key
supported under TLS    exchanges are present in a priority
1.3                    string, TLS 1.3 is disabled.
                       
Anonymous key          There is no anonymous key exchange
exchange is not        supported under TLS 1.3, so if an
supported under TLS    anonymous key exchange method is set in a
1.3                    priority string, and no certificate
                       credentials are set in the client or
                       server, TLS 1.3 will not be negotiated.
                       
ECDHE-PSK and          In the priority strings, both ‘ECDHEPSK’
DHE-PSK keywords       and ‘DHEPSK’ indicate the intent to
have the same          support an ephemeral key exchange with
meaning under TLS      the pre-shared key.  The parameters of
1.3                    the key exchange are negotiated with the
                       supported groups specified in the
                       priority string.
                       
Authentication-only    Ciphersuites with the ‘NULL’ cipher
ciphersuites are not   (i.e., authentication-only) are not
supported under TLS    supported in TLS 1.3, so when they are
1.3                    specified in a priority string, TLS 1.3
                       is disabled.
                       
Supplemental data is   The TLS supplemental data handshake
not supported under    message (RFC 4680) is not supported under
TLS 1.3                TLS 1.3, so if the application calls
                       *note gnutls_supplemental_register:: or
                       *note gnutls_session_supplemental_register::,
                       TLS 1.3 is disabled.
                       
The                    The macro was non-functional and because
GNUTLS_X509_NO_WELL_DEFINED_EXPIRATIONof the nature of the definition of the
macro is a no-op       no-well-defined date for certificates (a
                       real date), it will not be fixed or
                       re-introduced.

File: gnutls.info,  Node: Support,  Next: Error codes,  Prev: Upgrading from previous versions,  Up: Top

Appendix B Support
******************

* Menu:

* Getting help::
* Commercial Support::
* Bug Reports::
* Contributing::
* Certification::

File: gnutls.info,  Node: Getting help,  Next: Commercial Support,  Up: Support

B.1 Getting Help
================

A mailing list where users may help each other exists, and you can reach
it by sending e-mail to <gnutls-help@gnutls.org>.  Archives of the
mailing list discussions, and an interface to manage subscriptions, is
available through the World Wide Web at
<https://lists.gnutls.org/pipermail/gnutls-help/>.

A mailing list for developers are also available, see
<https://www.gnutls.org/lists.html>.  Bug reports should be sent to
<bugs@gnutls.org>, see *note Bug Reports::.

File: gnutls.info,  Node: Commercial Support,  Next: Bug Reports,  Prev: Getting help,  Up: Support

B.2 Commercial Support
======================

Commercial support is available for users of GnuTLS. See
<https://www.gnutls.org/commercial.html> for more information.

File: gnutls.info,  Node: Bug Reports,  Next: Contributing,  Prev: Commercial Support,  Up: Support

B.3 Bug Reports
===============

If you think you have found a bug in GnuTLS, please investigate it and
report it.

• Please make sure that the bug is really in GnuTLS, and preferably
     also check that it hasn't already been fixed in the latest version.

• You have to send us a test case that makes it possible for us to
     reproduce the bug.

• You also have to explain what is wrong; if you get a crash, or if
     the results printed are not good and in that case, in what way.
     Make sure that the bug report includes all information you would
     need to fix this kind of bug for someone else.

Please make an effort to produce a self-contained report, with something
definite that can be tested or debugged.  Vague queries or piecemeal
messages are difficult to act on and don't help the development effort.

If your bug report is good, we will do our best to help you to get a
corrected version of the software; if the bug report is poor, we won't
do anything about it (apart from asking you to send better bug reports).

If you think something in this manual is unclear, or downright
incorrect, or if the language needs to be improved, please also send a
note.

Send your bug report to:

‘bugs@gnutls.org’

File: gnutls.info,  Node: Contributing,  Next: Certification,  Prev: Bug Reports,  Up: Support

B.4 Contributing
================

If you want to submit a patch for inclusion - from solving a typo you
discovered, up to adding support for a new feature - you should submit
it as a bug report, using the process in *note Bug Reports::.  There are
some things that you can do to increase the chances for it to be
included in the official package.

Unless your patch is very small (say, under 10 lines) we require that
you assign the copyright of your work to the Free Software Foundation.
This is to protect the freedom of the project.  If you have not already
signed papers, we will send you the necessary information when you
submit your contribution.

For contributions that doesn't consist of actual programming code, the
only guidelines are common sense.  For code contributions, a number of
style guides will help you:

• Coding Style.  Follow the Linux kernel coding style(1).

If you normally code using another coding standard, there is no
     problem, but you should run the ‘indent-gnutls’ script found in the
     ‘devel’ directory to reformat the code before submitting your work.

• Use the unified diff format ‘diff -u’.

• Return errors.  No reason whatsoever should abort the execution of
     the library.  Even memory allocation errors, e.g.  when malloc
     return NULL, should work although result in an error code.

• Design with thread safety in mind.  Don't use global variables.
     Don't even write to per-handle global variables unless the
     documented behaviour of the function you write is to write to the
     per-handle global variable.

• Avoid using the C math library.  It causes problems for embedded
     implementations, and in most situations it is very easy to avoid
     using it.

• Document your functions.  Use comments before each function
     headers, that, if properly formatted, are extracted into Texinfo
     manuals and GTK-DOC web pages.

• Supply a ChangeLog and NEWS entries, where appropriate.

---------- Footnotes ----------

(1) see
<https://www.kernel.org/doc/html/latest/process/coding-style.html>.

File: gnutls.info,  Node: Certification,  Prev: Contributing,  Up: Support

B.5 Certification
=================

There are certifications from national or international bodies which
"prove" to an auditor that the crypto component follows some best
practices, such as unit testing and reliance on well known crypto
primitives.

GnuTLS has support for the FIPS 140-2 certification under Red Hat
Enterprise Linux.  See *note FIPS140-2 mode:: for more information.

File: gnutls.info,  Node: Error codes,  Next: Supported ciphersuites,  Prev: Support,  Up: Top

Appendix C Error Codes and Descriptions
***************************************

The error codes used throughout the library are described below.  The
return code ‘GNUTLS_E_SUCCESS’ indicates a successful operation, and is
guaranteed to have the value 0, so you can use it in logical
expressions.

0           GNUTLS_E_SUCCESS              Success.
-3          GNUTLS_E_UNKNOWN_COMPRESSION_ALGORITHMCould not negotiate a
                                          supported compression
                                          method.
-6          GNUTLS_E_UNKNOWN_CIPHER_TYPE  The cipher type is
                                          unsupported.
-7          GNUTLS_E_LARGE_PACKET         The transmitted packet is
                                          too large (EMSGSIZE).
-8          GNUTLS_E_UNSUPPORTED_VERSION_PACKETA packet with illegal or
                                          unsupported version was
                                          received.
-9          GNUTLS_E_UNEXPECTED_PACKET_LENGTHError decoding the
                                          received TLS packet.
-10         GNUTLS_E_INVALID_SESSION      The specified session has
                                          been invalidated for some
                                          reason.
-12         GNUTLS_E_FATAL_ALERT_RECEIVED A TLS fatal alert has
                                          been received.
-15         GNUTLS_E_UNEXPECTED_PACKET    An unexpected TLS packet
                                          was received.
-16         GNUTLS_E_WARNING_ALERT_RECEIVEDA TLS warning alert has
                                          been received.
-18         GNUTLS_E_ERROR_IN_FINISHED_PACKETAn error was encountered
                                          at the TLS Finished
                                          packet calculation.
-19         GNUTLS_E_UNEXPECTED_HANDSHAKE_PACKETAn unexpected TLS
                                          handshake packet was
                                          received.
-21         GNUTLS_E_UNKNOWN_CIPHER_SUITE Could not negotiate a
                                          supported cipher suite.
-22         GNUTLS_E_UNWANTED_ALGORITHM   An algorithm that is not
                                          enabled was negotiated.
-23         GNUTLS_E_MPI_SCAN_FAILED      The scanning of a large
                                          integer has failed.
-24         GNUTLS_E_DECRYPTION_FAILED    Decryption has failed.
-25         GNUTLS_E_MEMORY_ERROR         Internal error in memory
                                          allocation.
-26         GNUTLS_E_DECOMPRESSION_FAILED Decompression of the TLS
                                          record packet has failed.
-27         GNUTLS_E_COMPRESSION_FAILED   Compression of the TLS
                                          record packet has failed.
-28         GNUTLS_E_AGAIN                Resource temporarily
                                          unavailable, try again.
-29         GNUTLS_E_EXPIRED              The session or
                                          certificate has expired.
-30         GNUTLS_E_DB_ERROR             Error in Database
                                          backend.
-31         GNUTLS_E_SRP_PWD_ERROR        Error in password/key
                                          file.
-32         GNUTLS_E_INSUFFICIENT_CREDENTIALSInsufficient credentials
                                          for that request.
-33         GNUTLS_E_HASH_FAILED          Hashing has failed.
-34         GNUTLS_E_BASE64_DECODING_ERRORBase64 decoding error.
-35         GNUTLS_E_MPI_PRINT_FAILED     Could not export a large
                                          integer.
-37         GNUTLS_E_REHANDSHAKE          Rehandshake was requested
                                          by the peer.
-38         GNUTLS_E_GOT_APPLICATION_DATA TLS Application data were
                                          received, while expecting
                                          handshake data.
-39         GNUTLS_E_RECORD_LIMIT_REACHED The upper limit of record
                                          packet sequence numbers
                                          has been reached.  Wow!
-40         GNUTLS_E_ENCRYPTION_FAILED    Encryption has failed.
-43         GNUTLS_E_CERTIFICATE_ERROR    Error in the certificate.
-44         GNUTLS_E_PK_ENCRYPTION_FAILED Public key encryption has
                                          failed.
-45         GNUTLS_E_PK_DECRYPTION_FAILED Public key decryption has
                                          failed.
-46         GNUTLS_E_PK_SIGN_FAILED       Public key signing has
                                          failed.
-47         GNUTLS_E_X509_UNSUPPORTED_CRITICAL_EXTENSIONUnsupported critical
                                          extension in X.509
                                          certificate.
-48         GNUTLS_E_KEY_USAGE_VIOLATION  Key usage violation in
                                          certificate has been
                                          detected.
-49         GNUTLS_E_NO_CERTIFICATE_FOUND No certificate was found.
-50         GNUTLS_E_INVALID_REQUEST      The request is invalid.
-51         GNUTLS_E_SHORT_MEMORY_BUFFER  The given memory buffer
                                          is too short to hold
                                          parameters.
-52         GNUTLS_E_INTERRUPTED          Function was interrupted.
-53         GNUTLS_E_PUSH_ERROR           Error in the push
                                          function.
-54         GNUTLS_E_PULL_ERROR           Error in the pull
                                          function.
-55         GNUTLS_E_RECEIVED_ILLEGAL_PARAMETERAn illegal parameter has
                                          been received.
-56         GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLEThe requested data were
                                          not available.
-57         GNUTLS_E_PKCS1_WRONG_PAD      Wrong padding in PKCS1
                                          packet.
-58         GNUTLS_E_RECEIVED_ILLEGAL_EXTENSIONAn illegal TLS extension
                                          was received.
-59         GNUTLS_E_INTERNAL_ERROR       GnuTLS internal error.
-60         GNUTLS_E_CERTIFICATE_KEY_MISMATCHThe certificate and the
                                          given key do not match.
-61         GNUTLS_E_UNSUPPORTED_CERTIFICATE_TYPEThe certificate type is
                                          not supported.
-62         GNUTLS_E_X509_UNKNOWN_SAN     Unknown Subject
                                          Alternative name in X.509
                                          certificate.
-63         GNUTLS_E_DH_PRIME_UNACCEPTABLEThe Diffie-Hellman prime
                                          sent by the server is not
                                          acceptable (not long
                                          enough).
-64         GNUTLS_E_FILE_ERROR           Error while reading file.
-67         GNUTLS_E_ASN1_ELEMENT_NOT_FOUNDASN1 parser: Element was
                                          not found.
-68         GNUTLS_E_ASN1_IDENTIFIER_NOT_FOUNDASN1 parser: Identifier
                                          was not found
-69         GNUTLS_E_ASN1_DER_ERROR       ASN1 parser: Error in DER
                                          parsing.
-70         GNUTLS_E_ASN1_VALUE_NOT_FOUND ASN1 parser: Value was
                                          not found.
-71         GNUTLS_E_ASN1_GENERIC_ERROR   ASN1 parser: Generic
                                          parsing error.
-72         GNUTLS_E_ASN1_VALUE_NOT_VALID ASN1 parser: Value is not
                                          valid.
-73         GNUTLS_E_ASN1_TAG_ERROR       ASN1 parser: Error in
                                          TAG.
-74         GNUTLS_E_ASN1_TAG_IMPLICIT    ASN1 parser: error in
                                          implicit tag
-75         GNUTLS_E_ASN1_TYPE_ANY_ERROR  ASN1 parser: Error in
                                          type 'ANY'.
-76         GNUTLS_E_ASN1_SYNTAX_ERROR    ASN1 parser: Syntax
                                          error.
-77         GNUTLS_E_ASN1_DER_OVERFLOW    ASN1 parser: Overflow in
                                          DER parsing.
-78         GNUTLS_E_TOO_MANY_EMPTY_PACKETSToo many empty record
                                          packets have been
                                          received.
-79         GNUTLS_E_OPENPGP_UID_REVOKED  The OpenPGP User ID is
                                          revoked.
-80         GNUTLS_E_UNKNOWN_PK_ALGORITHM An unknown public key
                                          algorithm was
                                          encountered.
-81         GNUTLS_E_TOO_MANY_HANDSHAKE_PACKETSToo many handshake
                                          packets have been
                                          received.
-82         GNUTLS_E_RECEIVED_DISALLOWED_NAMEA disallowed SNI server
                                          name has been received.
-84         GNUTLS_E_NO_TEMPORARY_RSA_PARAMSNo temporary RSA
                                          parameters were found.
-86         GNUTLS_E_NO_COMPRESSION_ALGORITHMSNo supported compression
                                          algorithms have been
                                          found.
-87         GNUTLS_E_NO_CIPHER_SUITES     No supported cipher
                                          suites have been found.
-88         GNUTLS_E_OPENPGP_GETKEY_FAILEDCould not get OpenPGP
                                          key.
-89         GNUTLS_E_PK_SIG_VERIFY_FAILED Public key signature
                                          verification has failed.
-90         GNUTLS_E_ILLEGAL_SRP_USERNAME The SRP username supplied
                                          is illegal.
-91         GNUTLS_E_SRP_PWD_PARSING_ERRORParsing error in
                                          password/key file.
-93         GNUTLS_E_NO_TEMPORARY_DH_PARAMSNo temporary DH
                                          parameters were found.
-94         GNUTLS_E_OPENPGP_FINGERPRINT_UNSUPPORTEDThe OpenPGP fingerprint
                                          is not supported.
-95         GNUTLS_E_X509_UNSUPPORTED_ATTRIBUTEThe certificate has
                                          unsupported attributes.
-96         GNUTLS_E_UNKNOWN_HASH_ALGORITHMThe hash algorithm is
                                          unknown.
-97         GNUTLS_E_UNKNOWN_PKCS_CONTENT_TYPEThe PKCS structure's
                                          content type is unknown.
-98         GNUTLS_E_UNKNOWN_PKCS_BAG_TYPEThe PKCS structure's bag
                                          type is unknown.
-99         GNUTLS_E_INVALID_PASSWORD     The given password
                                          contains invalid
                                          characters.
-100        GNUTLS_E_MAC_VERIFY_FAILED    The Message
                                          Authentication Code
                                          verification failed.
-101        GNUTLS_E_CONSTRAINT_ERROR     Some constraint limits
                                          were reached.
-104        GNUTLS_E_IA_VERIFY_FAILED     Verifying TLS/IA phase
                                          checksum failed
-105        GNUTLS_E_UNKNOWN_ALGORITHM    The specified algorithm
                                          or protocol is unknown.
-106        GNUTLS_E_UNSUPPORTED_SIGNATURE_ALGORITHMThe signature algorithm
                                          is not supported.
-107        GNUTLS_E_SAFE_RENEGOTIATION_FAILEDSafe renegotiation
                                          failed.
-108        GNUTLS_E_UNSAFE_RENEGOTIATION_DENIEDUnsafe renegotiation
                                          denied.
-109        GNUTLS_E_UNKNOWN_SRP_USERNAME The username supplied is
                                          unknown.
-110        GNUTLS_E_PREMATURE_TERMINATIONThe TLS connection was
                                          non-properly terminated.
-111        GNUTLS_E_MALFORMED_CIDR       CIDR name constraint is
                                          malformed in size or
                                          structure.
-112        GNUTLS_E_CERTIFICATE_REQUIRED Certificate is required.
-113        GNUTLS_E_UNSUPPORTED_ENCRYPTION_ALGORITHMThe encryption algorithm
                                          is not supported.
-201        GNUTLS_E_BASE64_ENCODING_ERRORBase64 encoding error.
-202        GNUTLS_E_INCOMPATIBLE_GCRYPT_LIBRARYThe crypto library
                                          version is too old.
-203        GNUTLS_E_INCOMPATIBLE_LIBTASN1_LIBRARYThe tasn1 library version
                                          is too old.
-204        GNUTLS_E_OPENPGP_KEYRING_ERRORError loading the
                                          keyring.
-205        GNUTLS_E_X509_UNSUPPORTED_OID The OID is not supported.
-206        GNUTLS_E_RANDOM_FAILED        Failed to acquire random
                                          data.
-207        GNUTLS_E_BASE64_UNEXPECTED_HEADER_ERRORBase64 unexpected header
                                          error.
-208        GNUTLS_E_OPENPGP_SUBKEY_ERROR Could not find OpenPGP
                                          subkey.
-209        GNUTLS_E_CRYPTO_ALREADY_REGISTEREDThere is already a crypto
                                          algorithm with lower
                                          priority.
-210        GNUTLS_E_HANDSHAKE_TOO_LARGE  The handshake data size
                                          is too large.
-211        GNUTLS_E_CRYPTODEV_IOCTL_ERRORError interfacing with
                                          /dev/crypto
-212        GNUTLS_E_CRYPTODEV_DEVICE_ERRORError opening /dev/crypto
-213        GNUTLS_E_CHANNEL_BINDING_NOT_AVAILABLEChannel binding data not
                                          available
-214        GNUTLS_E_BAD_COOKIE           The cookie was bad.
-215        GNUTLS_E_OPENPGP_PREFERRED_KEY_ERRORThe OpenPGP key has not a
                                          preferred key set.
-216        GNUTLS_E_INCOMPAT_DSA_KEY_WITH_TLS_PROTOCOLThe given DSA key is
                                          incompatible with the
                                          selected TLS protocol.
-217        GNUTLS_E_INSUFFICIENT_SECURITYOne of the involved
                                          algorithms has
                                          insufficient security
                                          level.
-292        GNUTLS_E_HEARTBEAT_PONG_RECEIVEDA heartbeat pong message
                                          was received.
-293        GNUTLS_E_HEARTBEAT_PING_RECEIVEDA heartbeat ping message
                                          was received.
-294        GNUTLS_E_UNRECOGNIZED_NAME    The SNI host name not
                                          recognised.
-300        GNUTLS_E_PKCS11_ERROR         PKCS #11 error.
-301        GNUTLS_E_PKCS11_LOAD_ERROR    PKCS #11 initialization
                                          error.
-302        GNUTLS_E_PARSING_ERROR        Error in parsing.
-303        GNUTLS_E_PKCS11_PIN_ERROR     Error in provided PIN.
-305        GNUTLS_E_PKCS11_SLOT_ERROR    PKCS #11 error in slot
-306        GNUTLS_E_LOCKING_ERROR        Thread locking error
-307        GNUTLS_E_PKCS11_ATTRIBUTE_ERRORPKCS #11 error in
                                          attribute
-308        GNUTLS_E_PKCS11_DEVICE_ERROR  PKCS #11 error in device
-309        GNUTLS_E_PKCS11_DATA_ERROR    PKCS #11 error in data
-310        GNUTLS_E_PKCS11_UNSUPPORTED_FEATURE_ERRORPKCS #11 unsupported
                                          feature
-311        GNUTLS_E_PKCS11_KEY_ERROR     PKCS #11 error in key
-312        GNUTLS_E_PKCS11_PIN_EXPIRED   PKCS #11 PIN expired
-313        GNUTLS_E_PKCS11_PIN_LOCKED    PKCS #11 PIN locked
-314        GNUTLS_E_PKCS11_SESSION_ERROR PKCS #11 error in session
-315        GNUTLS_E_PKCS11_SIGNATURE_ERRORPKCS #11 error in
                                          signature
-316        GNUTLS_E_PKCS11_TOKEN_ERROR   PKCS #11 error in token
-317        GNUTLS_E_PKCS11_USER_ERROR    PKCS #11 user error
-318        GNUTLS_E_CRYPTO_INIT_FAILED   The initialization of
                                          crypto backend has
                                          failed.
-319        GNUTLS_E_TIMEDOUT             The operation timed out
-320        GNUTLS_E_USER_ERROR           The operation was
                                          cancelled due to user
                                          error
-321        GNUTLS_E_ECC_NO_SUPPORTED_CURVESNo supported ECC curves
                                          were found
-322        GNUTLS_E_ECC_UNSUPPORTED_CURVEThe curve is unsupported
-323        GNUTLS_E_PKCS11_REQUESTED_OBJECT_NOT_AVAILBLEThe requested PKCS #11
                                          object is not available
-324        GNUTLS_E_CERTIFICATE_LIST_UNSORTEDThe provided X.509
                                          certificate list is not
                                          sorted (in subject to
                                          issuer order)
-325        GNUTLS_E_ILLEGAL_PARAMETER    An illegal parameter was
                                          found.
-326        GNUTLS_E_NO_PRIORITIES_WERE_SETNo or insufficient
                                          priorities were set.
-327        GNUTLS_E_X509_UNSUPPORTED_EXTENSIONUnsupported extension in
                                          X.509 certificate.
-328        GNUTLS_E_SESSION_EOF          Peer has terminated the
                                          connection
-329        GNUTLS_E_TPM_ERROR            TPM error.
-330        GNUTLS_E_TPM_KEY_PASSWORD_ERRORError in provided
                                          password for key to be
                                          loaded in TPM.
-331        GNUTLS_E_TPM_SRK_PASSWORD_ERRORError in provided SRK
                                          password for TPM.
-332        GNUTLS_E_TPM_SESSION_ERROR    Cannot initialize a
                                          session with the TPM.
-333        GNUTLS_E_TPM_KEY_NOT_FOUND    TPM key was not found in
                                          persistent storage.
-334        GNUTLS_E_TPM_UNINITIALIZED    TPM is not initialized.
-335        GNUTLS_E_TPM_NO_LIB           The TPM library
                                          (trousers) cannot be
                                          found.
-340        GNUTLS_E_NO_CERTIFICATE_STATUSThere is no certificate
                                          status (OCSP).
-341        GNUTLS_E_OCSP_RESPONSE_ERROR  The OCSP response is
                                          invalid
-342        GNUTLS_E_RANDOM_DEVICE_ERROR  Error in the system's
                                          randomness device.
-343        GNUTLS_E_AUTH_ERROR           Could not authenticate
                                          peer.
-344        GNUTLS_E_NO_APPLICATION_PROTOCOLNo common application
                                          protocol could be
                                          negotiated.
-345        GNUTLS_E_SOCKETS_INIT_ERROR   Error in sockets
                                          initialization.
-346        GNUTLS_E_KEY_IMPORT_FAILED    Failed to import the key
                                          into store.
-347        GNUTLS_E_INAPPROPRIATE_FALLBACKA connection with
                                          inappropriate fallback
                                          was attempted.
-348        GNUTLS_E_CERTIFICATE_VERIFICATION_ERRORError in the certificate
                                          verification.
-349        GNUTLS_E_PRIVKEY_VERIFICATION_ERRORError in the private key
                                          verification; seed
                                          doesn't match.
-350        GNUTLS_E_UNEXPECTED_EXTENSIONS_LENGTHInvalid TLS extensions
                                          length field.
-351        GNUTLS_E_ASN1_EMBEDDED_NULL_IN_STRINGThe provided string has
                                          an embedded null.
-400        GNUTLS_E_SELF_TEST_ERROR      Error while performing
                                          self checks.
-401        GNUTLS_E_NO_SELF_TEST         There is no self test for
                                          this algorithm.
-402        GNUTLS_E_LIB_IN_ERROR_STATE   An error has been
                                          detected in the library
                                          and cannot continue
                                          operations.
-403        GNUTLS_E_PK_GENERATION_ERROR  Error in public key
                                          generation.
-404        GNUTLS_E_IDNA_ERROR           There was an issue
                                          converting to or from
                                          UTF8.
-406        GNUTLS_E_SESSION_USER_ID_CHANGEDPeer's certificate or
                                          username has changed
                                          during a rehandshake.
-407        GNUTLS_E_HANDSHAKE_DURING_FALSE_STARTAttempted handshake
                                          during false start.
-408        GNUTLS_E_UNAVAILABLE_DURING_HANDSHAKECannot perform this
                                          action while handshake is
                                          in progress.
-409        GNUTLS_E_PK_INVALID_PUBKEY    The public key is
                                          invalid.
-410        GNUTLS_E_PK_INVALID_PRIVKEY   The private key is
                                          invalid.
-411        GNUTLS_E_NOT_YET_ACTIVATED    The certificate is not
                                          yet activated.
-412        GNUTLS_E_INVALID_UTF8_STRING  The given string contains
                                          invalid UTF-8 characters.
-413        GNUTLS_E_NO_EMBEDDED_DATA     There are no embedded
                                          data in the structure.
-414        GNUTLS_E_INVALID_UTF8_EMAIL   The given email string
                                          contains non-ASCII
                                          characters before '.́
-415        GNUTLS_E_INVALID_PASSWORD_STRINGThe given password
                                          contains invalid
                                          characters.
-416        GNUTLS_E_CERTIFICATE_TIME_ERRORError in the time fields
                                          of certificate.
-417        GNUTLS_E_RECORD_OVERFLOW      A TLS record packet with
                                          invalid length was
                                          received.
-418        GNUTLS_E_ASN1_TIME_ERROR      The DER time encoding is
                                          invalid.
-419        GNUTLS_E_INCOMPATIBLE_SIG_WITH_KEYThe signature is
                                          incompatible with the
                                          public key.
-420        GNUTLS_E_PK_INVALID_PUBKEY_PARAMSThe public key parameters
                                          are invalid.
-421        GNUTLS_E_PK_NO_VALIDATION_PARAMSThere are no validation
                                          parameters present.
-422        GNUTLS_E_OCSP_MISMATCH_WITH_CERTSThe OCSP response
                                          provided doesn't match
                                          the available
                                          certificates
-423        GNUTLS_E_NO_COMMON_KEY_SHARE  No common key share with
                                          peer.
-424        GNUTLS_E_REAUTH_REQUEST       Re-authentication was
                                          requested by the peer.
-425        GNUTLS_E_TOO_MANY_MATCHES     More than a single object
                                          matches the criteria.
-426        GNUTLS_E_CRL_VERIFICATION_ERRORError in the CRL
                                          verification.
-427        GNUTLS_E_MISSING_EXTENSION    An required TLS extension
                                          was received.
-428        GNUTLS_E_DB_ENTRY_EXISTS      The Database entry
                                          already exists.
-429        GNUTLS_E_EARLY_DATA_REJECTED  The early data were
                                          rejected.
-430        GNUTLS_E_X509_DUPLICATE_EXTENSIONDuplicate extension in
                                          X.509 certificate.

File: gnutls.info,  Node: Supported ciphersuites,  Next: API reference,  Prev: Error codes,  Up: Top

Appendix D Supported Ciphersuites
*********************************

Ciphersuites
============

Ciphersuite name                            TLS ID         Since
--------------------------------------------------------------------------
TLS_AES_128_GCM_SHA256                      0x13 0x01      TLS1.3
TLS_AES_256_GCM_SHA384                      0x13 0x02      TLS1.3
TLS_CHACHA20_POLY1305_SHA256                0x13 0x03      TLS1.3
TLS_AES_128_CCM_SHA256                      0x13 0x04      TLS1.3
TLS_AES_128_CCM_8_SHA256                    0x13 0x05      TLS1.3
TLS_RSA_NULL_MD5                            0x00 0x01      TLS1.0
TLS_RSA_NULL_SHA1                           0x00 0x02      TLS1.0
TLS_RSA_NULL_SHA256                         0x00 0x3B      TLS1.2
TLS_RSA_ARCFOUR_128_SHA1                    0x00 0x05      TLS1.0
TLS_RSA_ARCFOUR_128_MD5                     0x00 0x04      TLS1.0
TLS_RSA_3DES_EDE_CBC_SHA1                   0x00 0x0A      TLS1.0
TLS_RSA_AES_128_CBC_SHA1                    0x00 0x2F      TLS1.0
TLS_RSA_AES_256_CBC_SHA1                    0x00 0x35      TLS1.0
TLS_RSA_CAMELLIA_128_CBC_SHA256             0x00 0xBA      TLS1.2
TLS_RSA_CAMELLIA_256_CBC_SHA256             0x00 0xC0      TLS1.2
TLS_RSA_CAMELLIA_128_CBC_SHA1               0x00 0x41      TLS1.0
TLS_RSA_CAMELLIA_256_CBC_SHA1               0x00 0x84      TLS1.0
TLS_RSA_AES_128_CBC_SHA256                  0x00 0x3C      TLS1.2
TLS_RSA_AES_256_CBC_SHA256                  0x00 0x3D      TLS1.2
TLS_RSA_AES_128_GCM_SHA256                  0x00 0x9C      TLS1.2
TLS_RSA_AES_256_GCM_SHA384                  0x00 0x9D      TLS1.2
TLS_RSA_CAMELLIA_128_GCM_SHA256             0xC0 0x7A      TLS1.2
TLS_RSA_CAMELLIA_256_GCM_SHA384             0xC0 0x7B      TLS1.2
TLS_RSA_AES_128_CCM                         0xC0 0x9C      TLS1.2
TLS_RSA_AES_256_CCM                         0xC0 0x9D      TLS1.2
TLS_RSA_AES_128_CCM_8                       0xC0 0xA0      TLS1.2
TLS_RSA_AES_256_CCM_8                       0xC0 0xA1      TLS1.2
TLS_DHE_DSS_ARCFOUR_128_SHA1                0x00 0x66      TLS1.0
TLS_DHE_DSS_3DES_EDE_CBC_SHA1               0x00 0x13      TLS1.0
TLS_DHE_DSS_AES_128_CBC_SHA1                0x00 0x32      TLS1.0
TLS_DHE_DSS_AES_256_CBC_SHA1                0x00 0x38      TLS1.0
TLS_DHE_DSS_CAMELLIA_128_CBC_SHA256         0x00 0xBD      TLS1.2
TLS_DHE_DSS_CAMELLIA_256_CBC_SHA256         0x00 0xC3      TLS1.2
TLS_DHE_DSS_CAMELLIA_128_CBC_SHA1           0x00 0x44      TLS1.0
TLS_DHE_DSS_CAMELLIA_256_CBC_SHA1           0x00 0x87      TLS1.0
TLS_DHE_DSS_AES_128_CBC_SHA256              0x00 0x40      TLS1.2
TLS_DHE_DSS_AES_256_CBC_SHA256              0x00 0x6A      TLS1.2
TLS_DHE_DSS_AES_128_GCM_SHA256              0x00 0xA2      TLS1.2
TLS_DHE_DSS_AES_256_GCM_SHA384              0x00 0xA3      TLS1.2
TLS_DHE_DSS_CAMELLIA_128_GCM_SHA256         0xC0 0x80      TLS1.2
TLS_DHE_DSS_CAMELLIA_256_GCM_SHA384         0xC0 0x81      TLS1.2
TLS_DHE_RSA_3DES_EDE_CBC_SHA1               0x00 0x16      TLS1.0
TLS_DHE_RSA_AES_128_CBC_SHA1                0x00 0x33      TLS1.0
TLS_DHE_RSA_AES_256_CBC_SHA1                0x00 0x39      TLS1.0
TLS_DHE_RSA_CAMELLIA_128_CBC_SHA256         0x00 0xBE      TLS1.2
TLS_DHE_RSA_CAMELLIA_256_CBC_SHA256         0x00 0xC4      TLS1.2
TLS_DHE_RSA_CAMELLIA_128_CBC_SHA1           0x00 0x45      TLS1.0
TLS_DHE_RSA_CAMELLIA_256_CBC_SHA1           0x00 0x88      TLS1.0
TLS_DHE_RSA_AES_128_CBC_SHA256              0x00 0x67      TLS1.2
TLS_DHE_RSA_AES_256_CBC_SHA256              0x00 0x6B      TLS1.2
TLS_DHE_RSA_AES_128_GCM_SHA256              0x00 0x9E      TLS1.2
TLS_DHE_RSA_AES_256_GCM_SHA384              0x00 0x9F      TLS1.2
TLS_DHE_RSA_CAMELLIA_128_GCM_SHA256         0xC0 0x7C      TLS1.2
TLS_DHE_RSA_CAMELLIA_256_GCM_SHA384         0xC0 0x7D      TLS1.2
TLS_DHE_RSA_CHACHA20_POLY1305               0xCC 0xAA      TLS1.2
TLS_DHE_RSA_AES_128_CCM                     0xC0 0x9E      TLS1.2
TLS_DHE_RSA_AES_256_CCM                     0xC0 0x9F      TLS1.2
TLS_DHE_RSA_AES_128_CCM_8                   0xC0 0xA2      TLS1.2
TLS_DHE_RSA_AES_256_CCM_8                   0xC0 0xA3      TLS1.2
TLS_ECDHE_RSA_NULL_SHA1                     0xC0 0x10      TLS1.0
TLS_ECDHE_RSA_3DES_EDE_CBC_SHA1             0xC0 0x12      TLS1.0
TLS_ECDHE_RSA_AES_128_CBC_SHA1              0xC0 0x13      TLS1.0
TLS_ECDHE_RSA_AES_256_CBC_SHA1              0xC0 0x14      TLS1.0
TLS_ECDHE_RSA_AES_256_CBC_SHA384            0xC0 0x28      TLS1.2
TLS_ECDHE_RSA_ARCFOUR_128_SHA1              0xC0 0x11      TLS1.0
TLS_ECDHE_RSA_CAMELLIA_128_CBC_SHA256       0xC0 0x76      TLS1.2
TLS_ECDHE_RSA_CAMELLIA_256_CBC_SHA384       0xC0 0x77      TLS1.2
TLS_ECDHE_ECDSA_NULL_SHA1                   0xC0 0x06      TLS1.0
TLS_ECDHE_ECDSA_3DES_EDE_CBC_SHA1           0xC0 0x08      TLS1.0
TLS_ECDHE_ECDSA_AES_128_CBC_SHA1            0xC0 0x09      TLS1.0
TLS_ECDHE_ECDSA_AES_256_CBC_SHA1            0xC0 0x0A      TLS1.0
TLS_ECDHE_ECDSA_ARCFOUR_128_SHA1            0xC0 0x07      TLS1.0
TLS_ECDHE_ECDSA_CAMELLIA_128_CBC_SHA256     0xC0 0x72      TLS1.2
TLS_ECDHE_ECDSA_CAMELLIA_256_CBC_SHA384     0xC0 0x73      TLS1.2
TLS_ECDHE_ECDSA_AES_128_CBC_SHA256          0xC0 0x23      TLS1.2
TLS_ECDHE_RSA_AES_128_CBC_SHA256            0xC0 0x27      TLS1.2
TLS_ECDHE_ECDSA_CAMELLIA_128_GCM_SHA256     0xC0 0x86      TLS1.2
TLS_ECDHE_ECDSA_CAMELLIA_256_GCM_SHA384     0xC0 0x87      TLS1.2
TLS_ECDHE_ECDSA_AES_128_GCM_SHA256          0xC0 0x2B      TLS1.2
TLS_ECDHE_ECDSA_AES_256_GCM_SHA384          0xC0 0x2C      TLS1.2
TLS_ECDHE_RSA_AES_128_GCM_SHA256            0xC0 0x2F      TLS1.2
TLS_ECDHE_RSA_AES_256_GCM_SHA384            0xC0 0x30      TLS1.2
TLS_ECDHE_ECDSA_AES_256_CBC_SHA384          0xC0 0x24      TLS1.2
TLS_ECDHE_RSA_CAMELLIA_128_GCM_SHA256       0xC0 0x8A      TLS1.2
TLS_ECDHE_RSA_CAMELLIA_256_GCM_SHA384       0xC0 0x8B      TLS1.2
TLS_ECDHE_RSA_CHACHA20_POLY1305             0xCC 0xA8      TLS1.2
TLS_ECDHE_ECDSA_CHACHA20_POLY1305           0xCC 0xA9      TLS1.2
TLS_ECDHE_ECDSA_AES_128_CCM                 0xC0 0xAC      TLS1.2
TLS_ECDHE_ECDSA_AES_256_CCM                 0xC0 0xAD      TLS1.2
TLS_ECDHE_ECDSA_AES_128_CCM_8               0xC0 0xAE      TLS1.2
TLS_ECDHE_ECDSA_AES_256_CCM_8               0xC0 0xAF      TLS1.2
TLS_ECDHE_PSK_3DES_EDE_CBC_SHA1             0xC0 0x34      TLS1.0
TLS_ECDHE_PSK_AES_128_CBC_SHA1              0xC0 0x35      TLS1.0
TLS_ECDHE_PSK_AES_256_CBC_SHA1              0xC0 0x36      TLS1.0
TLS_ECDHE_PSK_AES_128_CBC_SHA256            0xC0 0x37      TLS1.2
TLS_ECDHE_PSK_AES_256_CBC_SHA384            0xC0 0x38      TLS1.2
TLS_ECDHE_PSK_ARCFOUR_128_SHA1              0xC0 0x33      TLS1.0
TLS_ECDHE_PSK_NULL_SHA1                     0xC0 0x39      TLS1.0
TLS_ECDHE_PSK_NULL_SHA256                   0xC0 0x3A      TLS1.2
TLS_ECDHE_PSK_NULL_SHA384                   0xC0 0x3B      TLS1.0
TLS_ECDHE_PSK_CAMELLIA_128_CBC_SHA256       0xC0 0x9A      TLS1.2
TLS_ECDHE_PSK_CAMELLIA_256_CBC_SHA384       0xC0 0x9B      TLS1.2
TLS_PSK_ARCFOUR_128_SHA1                    0x00 0x8A      TLS1.0
TLS_PSK_3DES_EDE_CBC_SHA1                   0x00 0x8B      TLS1.0
TLS_PSK_AES_128_CBC_SHA1                    0x00 0x8C      TLS1.0
TLS_PSK_AES_256_CBC_SHA1                    0x00 0x8D      TLS1.0
TLS_PSK_AES_128_CBC_SHA256                  0x00 0xAE      TLS1.2
TLS_PSK_AES_256_GCM_SHA384                  0x00 0xA9      TLS1.2
TLS_PSK_CAMELLIA_128_GCM_SHA256             0xC0 0x8E      TLS1.2
TLS_PSK_CAMELLIA_256_GCM_SHA384             0xC0 0x8F      TLS1.2
TLS_PSK_AES_128_GCM_SHA256                  0x00 0xA8      TLS1.2
TLS_PSK_NULL_SHA1                           0x00 0x2C      TLS1.0
TLS_PSK_NULL_SHA256                         0x00 0xB0      TLS1.2
TLS_PSK_CAMELLIA_128_CBC_SHA256             0xC0 0x94      TLS1.2
TLS_PSK_CAMELLIA_256_CBC_SHA384             0xC0 0x95      TLS1.2
TLS_PSK_AES_256_CBC_SHA384                  0x00 0xAF      TLS1.2
TLS_PSK_NULL_SHA384                         0x00 0xB1      TLS1.2
TLS_RSA_PSK_ARCFOUR_128_SHA1                0x00 0x92      TLS1.0
TLS_RSA_PSK_3DES_EDE_CBC_SHA1               0x00 0x93      TLS1.0
TLS_RSA_PSK_AES_128_CBC_SHA1                0x00 0x94      TLS1.0
TLS_RSA_PSK_AES_256_CBC_SHA1                0x00 0x95      TLS1.0
TLS_RSA_PSK_CAMELLIA_128_GCM_SHA256         0xC0 0x92      TLS1.2
TLS_RSA_PSK_CAMELLIA_256_GCM_SHA384         0xC0 0x93      TLS1.2
TLS_RSA_PSK_AES_128_GCM_SHA256              0x00 0xAC      TLS1.2
TLS_RSA_PSK_AES_128_CBC_SHA256              0x00 0xB6      TLS1.2
TLS_RSA_PSK_NULL_SHA1                       0x00 0x2E      TLS1.0
TLS_RSA_PSK_NULL_SHA256                     0x00 0xB8      TLS1.2
TLS_RSA_PSK_AES_256_GCM_SHA384              0x00 0xAD      TLS1.2
TLS_RSA_PSK_AES_256_CBC_SHA384              0x00 0xB7      TLS1.2
TLS_RSA_PSK_NULL_SHA384                     0x00 0xB9      TLS1.2
TLS_RSA_PSK_CAMELLIA_128_CBC_SHA256         0xC0 0x98      TLS1.2
TLS_RSA_PSK_CAMELLIA_256_CBC_SHA384         0xC0 0x99      TLS1.2
TLS_DHE_PSK_ARCFOUR_128_SHA1                0x00 0x8E      TLS1.0
TLS_DHE_PSK_3DES_EDE_CBC_SHA1               0x00 0x8F      TLS1.0
TLS_DHE_PSK_AES_128_CBC_SHA1                0x00 0x90      TLS1.0
TLS_DHE_PSK_AES_256_CBC_SHA1                0x00 0x91      TLS1.0
TLS_DHE_PSK_AES_128_CBC_SHA256              0x00 0xB2      TLS1.2
TLS_DHE_PSK_AES_128_GCM_SHA256              0x00 0xAA      TLS1.2
TLS_DHE_PSK_NULL_SHA1                       0x00 0x2D      TLS1.0
TLS_DHE_PSK_NULL_SHA256                     0x00 0xB4      TLS1.2
TLS_DHE_PSK_NULL_SHA384                     0x00 0xB5      TLS1.2
TLS_DHE_PSK_AES_256_CBC_SHA384              0x00 0xB3      TLS1.2
TLS_DHE_PSK_AES_256_GCM_SHA384              0x00 0xAB      TLS1.2
TLS_DHE_PSK_CAMELLIA_128_CBC_SHA256         0xC0 0x96      TLS1.2
TLS_DHE_PSK_CAMELLIA_256_CBC_SHA384         0xC0 0x97      TLS1.2
TLS_DHE_PSK_CAMELLIA_128_GCM_SHA256         0xC0 0x90      TLS1.2
TLS_DHE_PSK_CAMELLIA_256_GCM_SHA384         0xC0 0x91      TLS1.2
TLS_PSK_AES_128_CCM                         0xC0 0xA4      TLS1.2
TLS_PSK_AES_256_CCM                         0xC0 0xA5      TLS1.2
TLS_DHE_PSK_AES_128_CCM                     0xC0 0xA6      TLS1.2
TLS_DHE_PSK_AES_256_CCM                     0xC0 0xA7      TLS1.2
TLS_PSK_AES_128_CCM_8                       0xC0 0xA8      TLS1.2
TLS_PSK_AES_256_CCM_8                       0xC0 0xA9      TLS1.2
TLS_DHE_PSK_AES_128_CCM_8                   0xC0 0xAA      TLS1.2
TLS_DHE_PSK_AES_256_CCM_8                   0xC0 0xAB      TLS1.2
TLS_DHE_PSK_CHACHA20_POLY1305               0xCC 0xAD      TLS1.2
TLS_ECDHE_PSK_CHACHA20_POLY1305             0xCC 0xAC      TLS1.2
TLS_RSA_PSK_CHACHA20_POLY1305               0xCC 0xAE      TLS1.2
TLS_PSK_CHACHA20_POLY1305                   0xCC 0xAB      TLS1.2
TLS_DH_ANON_ARCFOUR_128_MD5                 0x00 0x18      TLS1.0
TLS_DH_ANON_3DES_EDE_CBC_SHA1               0x00 0x1B      TLS1.0
TLS_DH_ANON_AES_128_CBC_SHA1                0x00 0x34      TLS1.0
TLS_DH_ANON_AES_256_CBC_SHA1                0x00 0x3A      TLS1.0
TLS_DH_ANON_CAMELLIA_128_CBC_SHA256         0x00 0xBF      TLS1.2
TLS_DH_ANON_CAMELLIA_256_CBC_SHA256         0x00 0xC5      TLS1.2
TLS_DH_ANON_CAMELLIA_128_CBC_SHA1           0x00 0x46      TLS1.0
TLS_DH_ANON_CAMELLIA_256_CBC_SHA1           0x00 0x89      TLS1.0
TLS_DH_ANON_AES_128_CBC_SHA256              0x00 0x6C      TLS1.2
TLS_DH_ANON_AES_256_CBC_SHA256              0x00 0x6D      TLS1.2
TLS_DH_ANON_AES_128_GCM_SHA256              0x00 0xA6      TLS1.2
TLS_DH_ANON_AES_256_GCM_SHA384              0x00 0xA7      TLS1.2
TLS_DH_ANON_CAMELLIA_128_GCM_SHA256         0xC0 0x84      TLS1.2
TLS_DH_ANON_CAMELLIA_256_GCM_SHA384         0xC0 0x85      TLS1.2
TLS_ECDH_ANON_NULL_SHA1                     0xC0 0x15      TLS1.0
TLS_ECDH_ANON_3DES_EDE_CBC_SHA1             0xC0 0x17      TLS1.0
TLS_ECDH_ANON_AES_128_CBC_SHA1              0xC0 0x18      TLS1.0
TLS_ECDH_ANON_AES_256_CBC_SHA1              0xC0 0x19      TLS1.0
TLS_ECDH_ANON_ARCFOUR_128_SHA1              0xC0 0x16      TLS1.0
TLS_GOSTR341112_256_28147_CNT_IMIT          0xC1 0x02      TLS1.2

Certificate types
=================

‘X.509’
‘Raw Public Key’

Protocols
=========

‘TLS1.0’
‘TLS1.1’
‘TLS1.2’
‘TLS1.3’
‘DTLS0.9’
‘DTLS1.0’
‘DTLS1.2’

Ciphers
=======

‘AES-256-CBC’
‘AES-192-CBC’
‘AES-128-CBC’
‘AES-128-GCM’
‘AES-192-GCM’
‘AES-256-GCM’
‘AES-128-CCM’
‘AES-256-CCM’
‘AES-128-CCM-8’
‘AES-256-CCM-8’
‘ARCFOUR-128’
‘ESTREAM-SALSA20-256’
‘SALSA20-256’
‘CHACHA20-32’
‘CHACHA20-64’
‘CAMELLIA-256-CBC’
‘CAMELLIA-192-CBC’
‘CAMELLIA-128-CBC’
‘CHACHA20-POLY1305’
‘CAMELLIA-128-GCM’
‘CAMELLIA-256-GCM’
‘GOST28147-TC26Z-CFB’
‘GOST28147-CPA-CFB’
‘GOST28147-CPB-CFB’
‘GOST28147-CPC-CFB’
‘GOST28147-CPD-CFB’
‘AES-128-CFB8’
‘AES-192-CFB8’
‘AES-256-CFB8’
‘AES-128-XTS’
‘AES-256-XTS’
‘AES-128-SIV’
‘AES-256-SIV’
‘AES-128-SIV-GCM’
‘AES-256-SIV-GCM’
‘GOST28147-TC26Z-CNT’
‘MAGMA-CTR-ACPKM’
‘KUZNYECHIK-CTR-ACPKM’
‘3DES-CBC’
‘DES-CBC’
‘RC2-40’
‘NULL’

MAC algorithms
==============

‘SHA1’
‘SHA256’
‘SHA384’
‘SHA512’
‘SHA224’
‘UMAC-96’
‘UMAC-128’
‘AEAD’
‘MD5’
‘GOSTR341194’
‘STREEBOG-256’
‘STREEBOG-512’
‘AES-CMAC-128’
‘AES-CMAC-256’
‘AES-GMAC-128’
‘AES-GMAC-192’
‘AES-GMAC-256’
‘GOST28147-TC26Z-IMIT’
‘OMAC-MAGMA’
‘OMAC-KUZNYECHIK’
‘PBMAC1’

Key exchange methods
====================

‘ECDHE-RSA’
‘ECDHE-ECDSA’
‘RSA’
‘DHE-RSA’
‘DHE-DSS’
‘PSK’
‘RSA-PSK’
‘DHE-PSK’
‘ECDHE-PSK’
‘ANON-DH’
‘ANON-ECDH’
‘VKO-GOST-12’
‘RSA-EXPORT’

Public key algorithms
=====================

‘RSA’
‘RSA-PSS’
‘RSA-OAEP’
‘RSA’
‘DSA’
‘GOST R 34.10-2012-512’
‘GOST R 34.10-2012-256’
‘GOST R 34.10-2001’
‘EC/ECDSA’
‘EdDSA (Ed25519)’
‘EdDSA (Ed448)’
‘DH’
‘ECDH (X25519)’
‘ECDH (X448)’

Public key signature algorithms
===============================

‘RSA-SHA256’
‘RSA-SHA384’
‘RSA-SHA512’
‘RSA-PSS-SHA256’
‘RSA-PSS-RSAE-SHA256’
‘RSA-PSS-SHA384’
‘RSA-PSS-RSAE-SHA384’
‘RSA-PSS-SHA512’
‘RSA-PSS-RSAE-SHA512’
‘EdDSA-Ed25519’
‘EdDSA-Ed448’
‘ECDSA-SHA256’
‘ECDSA-SHA384’
‘ECDSA-SHA512’
‘ECDSA-SECP256R1-SHA256’
‘ECDSA-SECP384R1-SHA384’
‘ECDSA-SECP521R1-SHA512’
‘ECDSA-SHA3-224’
‘ECDSA-SHA3-256’
‘ECDSA-SHA3-384’
‘ECDSA-SHA3-512’
‘RSA-SHA3-224’
‘RSA-SHA3-256’
‘RSA-SHA3-384’
‘RSA-SHA3-512’
‘DSA-SHA3-224’
‘DSA-SHA3-256’
‘DSA-SHA3-384’
‘DSA-SHA3-512’
‘RSA-RAW’
‘RSA-SHA1’
‘RSA-SHA1’
‘RSA-SHA224’
‘RSA-RMD160’
‘DSA-SHA1’
‘DSA-SHA1’
‘DSA-SHA224’
‘DSA-SHA256’
‘RSA-MD5’
‘RSA-MD5’
‘RSA-MD2’
‘ECDSA-SHA1’
‘ECDSA-SHA224’
‘GOSTR341012-512’
‘GOSTR341012-256’
‘GOSTR341001’
‘DSA-SHA384’
‘DSA-SHA512’

Groups
======

‘SECP256R1’
‘SECP384R1’
‘SECP521R1’
‘X25519’
‘GC256B’
‘GC512A’
‘X448’
‘FFDHE2048’
‘FFDHE3072’
‘FFDHE4096’
‘FFDHE6144’
‘FFDHE8192’

File: gnutls.info,  Node: API reference,  Next: Copying Information,  Prev: Supported ciphersuites,  Up: Top

Appendix E API reference
************************

* Menu:

* Core TLS API::
* Datagram TLS API::
* X509 certificate API::
* PKCS 7 API::
* OCSP API::
* PKCS 12 API::
* PKCS 11 API::
* TPM API::
* Abstract key API::
* Socket specific API::
* DANE API::
* Cryptographic API::
* Compatibility API::

File: gnutls.info,  Node: Core TLS API,  Next: Datagram TLS API,  Up: API reference

E.1 Core TLS API
================

The prototypes for the following functions lie in ‘gnutls/gnutls.h’.

gnutls_alert_get
----------------

-- Function: gnutls_alert_description_t gnutls_alert_get
          (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

*Returns:* the last alert received, a ‘gnutls_alert_description_t’
     value.

gnutls_alert_get_name
---------------------

-- Function: const char * gnutls_alert_get_name
          (gnutls_alert_description_t ALERT)
     ALERT: is an alert number.

This function will return a string that describes the given alert
     number, or ‘NULL’ .  See ‘gnutls_alert_get()’ .

*Returns:* string corresponding to ‘gnutls_alert_description_t’
     value.

gnutls_alert_get_strname
------------------------

-- Function: const char * gnutls_alert_get_strname
          (gnutls_alert_description_t ALERT)
     ALERT: is an alert number.

This function will return a string of the name of the alert.

*Returns:* string corresponding to ‘gnutls_alert_description_t’
     value.

*Since:* 3.0

gnutls_alert_send
-----------------

-- Function: int gnutls_alert_send (gnutls_session_t SESSION,
          gnutls_alert_level_t LEVEL, gnutls_alert_description_t DESC)
     SESSION: is a ‘gnutls_session_t’ type.

LEVEL: is the level of the alert

DESC: is the alert description

The error code of the underlying record send function will be
     returned, so you may also receive ‘GNUTLS_E_INTERRUPTED’ or
     ‘GNUTLS_E_AGAIN’ as well.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise an error code is returned.

gnutls_alert_send_appropriate
-----------------------------

-- Function: int gnutls_alert_send_appropriate (gnutls_session_t
          SESSION, int ERR)
     SESSION: is a ‘gnutls_session_t’ type.

ERR: is an error code returned by another GnuTLS function

Sends an alert to the peer depending on the error code returned by
     a gnutls function.  This function will call
     ‘gnutls_error_to_alert()’ to determine the appropriate alert to
     send.

This function may also return ‘GNUTLS_E_AGAIN’ , or
     ‘GNUTLS_E_INTERRUPTED’ .

This function historically was always sending an alert to the peer,
     even if ‘err’ was inappropriate to respond with an alert (e.g.,
     ‘GNUTLS_E_SUCCESS’ ).  Since 3.6.6 this function returns success
     without transmitting any data on error codes that should not result
     to an alert.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise an error code is returned.

gnutls_alert_set_read_function
------------------------------

-- Function: void gnutls_alert_set_read_function (gnutls_session_t
          SESSION, gnutls_alert_read_func FUNC)
     SESSION: is ‘gnutls_session_t’ type

FUNC: is the function to be called

This function will set a callback to be called when an alert
     message is being sent.

*Since:* 3.7.0

gnutls_alpn_get_selected_protocol
---------------------------------

-- Function: int gnutls_alpn_get_selected_protocol (gnutls_session_t
          SESSION, gnutls_datum_t * PROTOCOL)
     SESSION: is a ‘gnutls_session_t’ type.

PROTOCOL: will hold the protocol name

This function allows you to get the negotiated protocol name.  The
     returned protocol should be treated as opaque, constant value and
     only valid during the session life.

The selected protocol is the first supported by the list sent by
     the client.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

Since 3.2.0

gnutls_alpn_set_protocols
-------------------------

-- Function: int gnutls_alpn_set_protocols (gnutls_session_t SESSION,
          const gnutls_datum_t * PROTOCOLS, unsigned PROTOCOLS_SIZE,
          unsigned int FLAGS)
     SESSION: is a ‘gnutls_session_t’ type.

PROTOCOLS: is the protocol names to add.

PROTOCOLS_SIZE: the number of protocols to add.

FLAGS: zero or a sequence of ‘gnutls_alpn_flags_t’

This function is to be used by both clients and servers, to declare
     the supported ALPN protocols, which are used during negotiation
     with peer.

See ‘gnutls_alpn_flags_t’ description for the documentation of
     available flags.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

Since 3.2.0

gnutls_anon_allocate_client_credentials
---------------------------------------

-- Function: int gnutls_anon_allocate_client_credentials
          (gnutls_anon_client_credentials_t * SC)
     SC: is a pointer to a ‘gnutls_anon_client_credentials_t’ type.

Allocate a gnutls_anon_client_credentials_t structure.

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, or an error code.

gnutls_anon_allocate_server_credentials
---------------------------------------

-- Function: int gnutls_anon_allocate_server_credentials
          (gnutls_anon_server_credentials_t * SC)
     SC: is a pointer to a ‘gnutls_anon_server_credentials_t’ type.

Allocate a gnutls_anon_server_credentials_t structure.

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, or an error code.

gnutls_anon_free_client_credentials
-----------------------------------

-- Function: void gnutls_anon_free_client_credentials
          (gnutls_anon_client_credentials_t SC)
     SC: is a ‘gnutls_anon_client_credentials_t’ type.

Free a gnutls_anon_client_credentials_t structure.

gnutls_anon_free_server_credentials
-----------------------------------

-- Function: void gnutls_anon_free_server_credentials
          (gnutls_anon_server_credentials_t SC)
     SC: is a ‘gnutls_anon_server_credentials_t’ type.

Free a gnutls_anon_server_credentials_t structure.

gnutls_anon_set_params_function
-------------------------------

-- Function: void gnutls_anon_set_params_function
          (gnutls_anon_server_credentials_t RES, gnutls_params_function
          * FUNC)
     RES: is a gnutls_anon_server_credentials_t type

FUNC: is the function to be called

This function will set a callback in order for the server to get
     the Diffie-Hellman or RSA parameters for anonymous authentication.
     The callback should return ‘GNUTLS_E_SUCCESS’ (0) on success.

*Deprecated:* This function is unnecessary and discouraged on
     GnuTLS 3.6.0 or later.  Since 3.6.0, DH parameters are negotiated
     following RFC7919.

gnutls_anon_set_server_dh_params
--------------------------------

-- Function: void gnutls_anon_set_server_dh_params
          (gnutls_anon_server_credentials_t RES, gnutls_dh_params_t
          DH_PARAMS)
     RES: is a gnutls_anon_server_credentials_t type

DH_PARAMS: The Diffie-Hellman parameters.

This function will set the Diffie-Hellman parameters for an
     anonymous server to use.  These parameters will be used in
     Anonymous Diffie-Hellman cipher suites.

*Deprecated:* This function is unnecessary and discouraged on
     GnuTLS 3.6.0 or later.  Since 3.6.0, DH parameters are negotiated
     following RFC7919.

gnutls_anon_set_server_known_dh_params
--------------------------------------

-- Function: int gnutls_anon_set_server_known_dh_params
          (gnutls_anon_server_credentials_t RES, gnutls_sec_param_t
          SEC_PARAM)
     RES: is a gnutls_anon_server_credentials_t type

SEC_PARAM: is an option of the ‘gnutls_sec_param_t’ enumeration

This function will set the Diffie-Hellman parameters for an
     anonymous server to use.  These parameters will be used in
     Anonymous Diffie-Hellman cipher suites and will be selected from
     the FFDHE set of RFC7919 according to the security level provided.

*Deprecated:* This function is unnecessary and discouraged on
     GnuTLS 3.6.0 or later.  Since 3.6.0, DH parameters are negotiated
     following RFC7919.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.5.6

gnutls_anon_set_server_params_function
--------------------------------------

-- Function: void gnutls_anon_set_server_params_function
          (gnutls_anon_server_credentials_t RES, gnutls_params_function
          * FUNC)
     RES: is a gnutls_certificate_credentials_t type

FUNC: is the function to be called

This function will set a callback in order for the server to get
     the Diffie-Hellman parameters for anonymous authentication.  The
     callback should return ‘GNUTLS_E_SUCCESS’ (0) on success.

*Deprecated:* This function is unnecessary and discouraged on
     GnuTLS 3.6.0 or later.  Since 3.6.0, DH parameters are negotiated
     following RFC7919.

gnutls_anti_replay_deinit
-------------------------

-- Function: void gnutls_anti_replay_deinit (gnutls_anti_replay_t
          ANTI_REPLAY)
     ANTI_REPLAY: is a ‘gnutls_anti_replay’ type

This function will deinitialize all resources occupied by the given
     anti-replay context.

*Since:* 3.6.5

gnutls_anti_replay_enable
-------------------------

-- Function: void gnutls_anti_replay_enable (gnutls_session_t SESSION,
          gnutls_anti_replay_t ANTI_REPLAY)
     SESSION: is a ‘gnutls_session_t’ type.

ANTI_REPLAY: is a ‘gnutls_anti_replay_t’ type.

Request that the server should use anti-replay mechanism.

*Since:* 3.6.5

gnutls_anti_replay_init
-----------------------

-- Function: int gnutls_anti_replay_init (gnutls_anti_replay_t *
          ANTI_REPLAY)
     ANTI_REPLAY: is a pointer to ‘gnutls_anti_replay_t’ type

This function will allocate and initialize the ‘anti_replay’
     context to be usable for detect replay attacks.  The context can
     then be attached to a ‘gnutls_session_t’ with
     ‘gnutls_anti_replay_enable()’ .

*Returns:* Zero or a negative error code on error.

*Since:* 3.6.5

gnutls_anti_replay_set_add_function
-----------------------------------

-- Function: void gnutls_anti_replay_set_add_function
          (gnutls_anti_replay_t ANTI_REPLAY, gnutls_db_add_func
          ADD_FUNC)
     ANTI_REPLAY: is a ‘gnutls_anti_replay_t’ type.

ADD_FUNC: is the function.

Sets the function that will be used to store an entry if it is not
     already present in the resumed sessions database.  This function
     returns 0 if the entry is successfully stored, and a negative error
     code otherwise.  In particular, if the entry is found in the
     database, it returns ‘GNUTLS_E_DB_ENTRY_EXISTS’ .

The arguments to the ‘add_func’ are: - ‘ptr’ : the pointer set with
     ‘gnutls_anti_replay_set_ptr()’ - ‘exp_time’ : the expiration time
     of the entry - ‘key’ : a pointer to the key - ‘data’ : a pointer to
     data to store

The data set by this function can be examined using
     ‘gnutls_db_check_entry_expire_time()’ and
     ‘gnutls_db_check_entry_time()’ .

*Since:* 3.6.5

gnutls_anti_replay_set_ptr
--------------------------

-- Function: void gnutls_anti_replay_set_ptr (gnutls_anti_replay_t
          ANTI_REPLAY, void * PTR)
     ANTI_REPLAY: is a ‘gnutls_anti_replay_t’ type.

PTR: is the pointer

Sets the pointer that will be provided to db add function as the
     first argument.

gnutls_anti_replay_set_window
-----------------------------

-- Function: void gnutls_anti_replay_set_window (gnutls_anti_replay_t
          ANTI_REPLAY, unsigned int WINDOW)
     ANTI_REPLAY: is a ‘gnutls_anti_replay_t’ type.

WINDOW: is the time window recording ClientHello, in milliseconds

Sets the time window used for ClientHello recording.  In order to
     protect against replay attacks, the server records ClientHello
     messages within this time period from the last update, and
     considers it a replay when a ClientHello outside of the period; if
     a ClientHello arrives within this period, the server checks the
     database and detects duplicates.

For the details of the algorithm, see RFC 8446, section 8.2.

*Since:* 3.6.5

gnutls_auth_client_get_type
---------------------------

-- Function: gnutls_credentials_type_t gnutls_auth_client_get_type
          (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Returns the type of credentials that were used for client
     authentication.  The returned information is to be used to
     distinguish the function used to access authentication data.

Note that on resumed sessions, this function returns the schema
     used in the original session authentication.

*Returns:* The type of credentials for the client authentication
     schema, a ‘gnutls_credentials_type_t’ type.

gnutls_auth_get_type
--------------------

-- Function: gnutls_credentials_type_t gnutls_auth_get_type
          (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Returns type of credentials for the current authentication schema.
     The returned information is to be used to distinguish the function
     used to access authentication data.

Eg.  for CERTIFICATE ciphersuites (key exchange algorithms:
     ‘GNUTLS_KX_RSA’ , ‘GNUTLS_KX_DHE_RSA’ ), the same function are to
     be used to access the authentication data.

Note that on resumed sessions, this function returns the schema
     used in the original session authentication.

*Returns:* The type of credentials for the current authentication
     schema, a ‘gnutls_credentials_type_t’ type.

gnutls_auth_server_get_type
---------------------------

-- Function: gnutls_credentials_type_t gnutls_auth_server_get_type
          (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Returns the type of credentials that were used for server
     authentication.  The returned information is to be used to
     distinguish the function used to access authentication data.

Note that on resumed sessions, this function returns the schema
     used in the original session authentication.

*Returns:* The type of credentials for the server authentication
     schema, a ‘gnutls_credentials_type_t’ type.

gnutls_base64_decode2
---------------------

-- Function: int gnutls_base64_decode2 (const gnutls_datum_t * BASE64,
          gnutls_datum_t * RESULT)
     BASE64: contains the encoded data

RESULT: the location of decoded data

This function will decode the given base64 encoded data.  The
     decoded data will be allocated, and stored into result.

You should use ‘gnutls_free()’ to free the returned data.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise an error code is returned.

*Since:* 3.6.0

gnutls_base64_encode2
---------------------

-- Function: int gnutls_base64_encode2 (const gnutls_datum_t * DATA,
          gnutls_datum_t * RESULT)
     DATA: contains the raw data

RESULT: will hold the newly allocated encoded data

This function will convert the given data to printable data, using
     the base64 encoding.  This function will allocate the required
     memory to hold the encoded data.

You should use ‘gnutls_free()’ to free the returned data.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise an error code is returned.

*Since:* 3.6.0

gnutls_buffer_append_data
-------------------------

-- Function: int gnutls_buffer_append_data (gnutls_buffer_t DEST, const
          void * DATA, size_t DATA_SIZE)
     DEST: the buffer to append to

DATA: the data

DATA_SIZE: the size of ‘data’

Appends the provided ‘data’ to the destination buffer.

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, otherwise a negative
     error code.

*Since:* 3.4.0

gnutls_bye
----------

-- Function: int gnutls_bye (gnutls_session_t SESSION,
          gnutls_close_request_t HOW)
     SESSION: is a ‘gnutls_session_t’ type.

HOW: is an integer

This function may also return ‘GNUTLS_E_AGAIN’ or
     ‘GNUTLS_E_INTERRUPTED’ ; cf.  ‘gnutls_record_get_direction()’ .

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, or an error code, see
     function documentation for entire semantics.

gnutls_certificate_activation_time_peers
----------------------------------------

-- Function: time_t gnutls_certificate_activation_time_peers
          (gnutls_session_t SESSION)
     SESSION: is a gnutls session

This function will return the peer's certificate activation time.

*Returns:* (time_t)-1 on error.

*Deprecated:* ‘gnutls_certificate_verify_peers2()’ now verifies
     activation times.

gnutls_certificate_allocate_credentials
---------------------------------------

-- Function: int gnutls_certificate_allocate_credentials
          (gnutls_certificate_credentials_t * RES)
     RES: is a pointer to a ‘gnutls_certificate_credentials_t’ type.

Allocate a gnutls_certificate_credentials_t structure.

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, or an error code.

gnutls_certificate_client_get_request_status
--------------------------------------------

-- Function: unsigned gnutls_certificate_client_get_request_status
          (gnutls_session_t SESSION)
     SESSION: is a gnutls session

Get whether client certificate was requested on the last handshake
     or not.

*Returns:* 0 if the peer (server) did not request client
     authentication or 1 otherwise.

gnutls_certificate_expiration_time_peers
----------------------------------------

-- Function: time_t gnutls_certificate_expiration_time_peers
          (gnutls_session_t SESSION)
     SESSION: is a gnutls session

This function will return the peer's certificate expiration time.

*Returns:* (time_t)-1 on error.

*Deprecated:* ‘gnutls_certificate_verify_peers2()’ now verifies
     expiration times.

gnutls_certificate_free_ca_names
--------------------------------

-- Function: void gnutls_certificate_free_ca_names
          (gnutls_certificate_credentials_t SC)
     SC: is a ‘gnutls_certificate_credentials_t’ type.

This function will delete all the CA name in the given credentials.
     Clients may call this to save some memory since in client side the
     CA names are not used.  Servers might want to use this function if
     a large list of trusted CAs is present and sending the names of it
     would just consume bandwidth without providing information to
     client.

CA names are used by servers to advertise the CAs they support to
     clients.

gnutls_certificate_free_cas
---------------------------

-- Function: void gnutls_certificate_free_cas
          (gnutls_certificate_credentials_t SC)
     SC: is a ‘gnutls_certificate_credentials_t’ type.

This function was operational on very early versions of gnutls.
     Due to internal refactorings and the fact that this was hardly ever
     used, it is currently a no-op.

gnutls_certificate_free_credentials
-----------------------------------

-- Function: void gnutls_certificate_free_credentials
          (gnutls_certificate_credentials_t SC)
     SC: is a ‘gnutls_certificate_credentials_t’ type.

Free a gnutls_certificate_credentials_t structure.

This function does not free any temporary parameters associated
     with this structure (ie RSA and DH parameters are not freed by this
     function).

gnutls_certificate_free_crls
----------------------------

-- Function: void gnutls_certificate_free_crls
          (gnutls_certificate_credentials_t SC)
     SC: is a ‘gnutls_certificate_credentials_t’ type.

This function will delete all the CRLs associated with the given
     credentials.

gnutls_certificate_free_keys
----------------------------

-- Function: void gnutls_certificate_free_keys
          (gnutls_certificate_credentials_t SC)
     SC: is a ‘gnutls_certificate_credentials_t’ type.

This function will delete all the keys and the certificates
     associated with the given credentials.  This function must not be
     called when a TLS negotiation that uses the credentials is in
     progress.

gnutls_certificate_get_crt_raw
------------------------------

-- Function: int gnutls_certificate_get_crt_raw
          (gnutls_certificate_credentials_t SC, unsigned IDX1, unsigned
          IDX2, gnutls_datum_t * CERT)
     SC: is a ‘gnutls_certificate_credentials_t’ type.

IDX1: the index of the certificate chain if multiple are present

IDX2: the index of the certificate in the chain.  Zero gives the
     server's certificate.

CERT: Will hold the DER encoded certificate.

This function will return the DER encoded certificate of the server
     or any other certificate on its certificate chain (based on ‘idx2’
     ).  The returned data should be treated as constant and only
     accessible during the lifetime of ‘sc’ .  The ‘idx1’ matches the
     value ‘gnutls_certificate_set_x509_key()’ and friends functions.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.  In case the indexes are out of
     bounds ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ is returned.

*Since:* 3.2.5

gnutls_certificate_get_issuer
-----------------------------

-- Function: int gnutls_certificate_get_issuer
          (gnutls_certificate_credentials_t SC, gnutls_x509_crt_t CERT,
          gnutls_x509_crt_t * ISSUER, unsigned int FLAGS)
     SC: is a ‘gnutls_certificate_credentials_t’ type.

CERT: is the certificate to find issuer for

ISSUER: Will hold the issuer if any.  Should be treated as
     constant.

FLAGS: Use zero or ‘GNUTLS_TL_GET_COPY’

This function will return the issuer of a given certificate.  If
     the flag ‘GNUTLS_TL_GET_COPY’ is specified a copy of the issuer
     will be returned which must be freed using
     ‘gnutls_x509_crt_deinit()’ .  In that case the provided ‘issuer’
     must not be initialized.

As with ‘gnutls_x509_trust_list_get_issuer()’ this function
     requires the ‘GNUTLS_TL_GET_COPY’ flag in order to operate with
     PKCS‘11’ trust lists in a thread-safe way.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.0

gnutls_certificate_get_ocsp_expiration
--------------------------------------

-- Function: time_t gnutls_certificate_get_ocsp_expiration
          (gnutls_certificate_credentials_t SC, unsigned IDX, int OIDX,
          unsigned FLAGS)
     SC: is a credentials structure.

IDX: is a certificate chain index as returned by
     ‘gnutls_certificate_set_key()’ and friends

OIDX: is an OCSP response index

FLAGS: should be zero

This function returns the validity of the loaded OCSP responses, to
     provide information on when to reload/refresh them.

*Returns:* On success, the expiration time of the OCSP response.
     Otherwise (time_t)(-1) on error, or (time_t)-2 on out of bounds.

*Since:* 3.6.3

gnutls_certificate_get_ours
---------------------------

-- Function: const gnutls_datum_t * gnutls_certificate_get_ours
          (gnutls_session_t SESSION)
     SESSION: is a gnutls session

Gets the certificate as sent to the peer in the last handshake.
     The certificate is in raw (DER) format.  No certificate list is
     being returned.  Only the first certificate.

This function returns the certificate that was sent in the current
     handshake.  In subsequent resumed sessions this function will
     return ‘NULL’ .  That differs from ‘gnutls_certificate_get_peers()’
     which always returns the peer's certificate used in the original
     session.

*Returns:* a pointer to a ‘gnutls_datum_t’ containing our
     certificate, or ‘NULL’ in case of an error or if no certificate was
     used.

gnutls_certificate_get_peers
----------------------------

-- Function: const gnutls_datum_t * gnutls_certificate_get_peers
          (gnutls_session_t SESSION, unsigned int * LIST_SIZE)
     SESSION: is a gnutls session

LIST_SIZE: is the length of the certificate list (may be ‘NULL’ )

Get the peer's raw certificate (chain) as sent by the peer.  These
     certificates are in raw format (DER encoded for X.509).  In case of
     a X.509 then a certificate list may be present.  The list is
     provided as sent by the server; the server must send as first
     certificate in the list its own certificate, following the issuer's
     certificate, then the issuer's issuer etc.  However, there are
     servers which violate this principle and thus on certain occasions
     this may be an unsorted list.

In resumed sessions, this function will return the peer's
     certificate list as used in the first/original session.

*Returns:* a pointer to a ‘gnutls_datum_t’ containing the peer's
     certificates, or ‘NULL’ in case of an error or if no certificate
     was used.

gnutls_certificate_get_peers_subkey_id
--------------------------------------

-- Function: int gnutls_certificate_get_peers_subkey_id
          (gnutls_session_t SESSION, gnutls_datum_t * ID)
     SESSION: is a gnutls session

ID: will contain the ID

This function is no-op.

*Returns:* ‘GNUTLS_E_UNIMPLEMENTED_FEATURE’ .

*Since:* 3.1.3

gnutls_certificate_get_verify_flags
-----------------------------------

-- Function: unsigned int gnutls_certificate_get_verify_flags
          (gnutls_certificate_credentials_t RES)
     RES: is a gnutls_certificate_credentials_t type

Returns the verification flags set with
     ‘gnutls_certificate_set_verify_flags()’ .

*Returns:* The certificate verification flags used by ‘res’ .

*Since:* 3.4.0

gnutls_certificate_get_x509_crt
-------------------------------

-- Function: int gnutls_certificate_get_x509_crt
          (gnutls_certificate_credentials_t RES, unsigned INDEX,
          gnutls_x509_crt_t ** CRT_LIST, unsigned * CRT_LIST_SIZE)
     RES: is a ‘gnutls_certificate_credentials_t’ type.

INDEX: The index of the certificate list to obtain.

CRT_LIST: Where to store the certificate list.

CRT_LIST_SIZE: Will hold the number of certificates.

Obtains a X.509 certificate list that has been stored in ‘res’ with
     one of ‘gnutls_certificate_set_x509_key()’ ,
     ‘gnutls_certificate_set_key()’ ,
     ‘gnutls_certificate_set_x509_key_file()’ ,
     ‘gnutls_certificate_set_x509_key_file2()’ ,
     ‘gnutls_certificate_set_x509_key_mem()’ , or
     ‘gnutls_certificate_set_x509_key_mem2()’ .  Each certificate in the
     returned certificate list must be deallocated with
     ‘gnutls_x509_crt_deinit()’ , and the list itself must be freed with
     ‘gnutls_free()’ .

The ‘index’ matches the return value of
     ‘gnutls_certificate_set_x509_key()’ and friends functions, when the
     ‘GNUTLS_CERTIFICATE_API_V2’ flag is set.

If there is no certificate with the given index,
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ is returned.  If the
     certificate with the given index is not a X.509 certificate,
     ‘GNUTLS_E_INVALID_REQUEST’ is returned.  The returned certificates
     must be deinitialized after use, and the ‘crt_list’ pointer must be
     freed using ‘gnutls_free()’ .

*Returns:* ‘GNUTLS_E_SUCCESS’ (0) on success, or a negative error
     code.

*Since:* 3.4.0

gnutls_certificate_get_x509_key
-------------------------------

-- Function: int gnutls_certificate_get_x509_key
          (gnutls_certificate_credentials_t RES, unsigned INDEX,
          gnutls_x509_privkey_t * KEY)
     RES: is a ‘gnutls_certificate_credentials_t’ type.

INDEX: The index of the key to obtain.

KEY: Location to store the key.

Obtains a X.509 private key that has been stored in ‘res’ with one
     of ‘gnutls_certificate_set_x509_key()’ ,
     ‘gnutls_certificate_set_key()’ ,
     ‘gnutls_certificate_set_x509_key_file()’ ,
     ‘gnutls_certificate_set_x509_key_file2()’ ,
     ‘gnutls_certificate_set_x509_key_mem()’ , or
     ‘gnutls_certificate_set_x509_key_mem2()’ .  The returned key must
     be deallocated with ‘gnutls_x509_privkey_deinit()’ when no longer
     needed.

The ‘index’ matches the return value of
     ‘gnutls_certificate_set_x509_key()’ and friends functions, when the
     ‘GNUTLS_CERTIFICATE_API_V2’ flag is set.

If there is no key with the given index,
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ is returned.  If the key
     with the given index is not a X.509 key, ‘GNUTLS_E_INVALID_REQUEST’
     is returned.

*Returns:* ‘GNUTLS_E_SUCCESS’ (0) on success, or a negative error
     code.

*Since:* 3.4.0

gnutls_certificate_send_x509_rdn_sequence
-----------------------------------------

-- Function: void gnutls_certificate_send_x509_rdn_sequence
          (gnutls_session_t SESSION, int STATUS)
     SESSION: a ‘gnutls_session_t’ type.

STATUS: is 0 or 1

This function has no effect in clients, and in authentication
     methods other than certificate with X.509 certificates.

gnutls_certificate_server_set_request
-------------------------------------

-- Function: void gnutls_certificate_server_set_request
          (gnutls_session_t SESSION, gnutls_certificate_request_t REQ)
     SESSION: is a ‘gnutls_session_t’ type.

REQ: is one of GNUTLS_CERT_REQUEST, GNUTLS_CERT_REQUIRE,
     GNUTLS_CERT_IGNORE

gnutls_certificate_set_dh_params
--------------------------------

-- Function: void gnutls_certificate_set_dh_params
          (gnutls_certificate_credentials_t RES, gnutls_dh_params_t
          DH_PARAMS)
     RES: is a gnutls_certificate_credentials_t type

DH_PARAMS: the Diffie-Hellman parameters.

This function will set the Diffie-Hellman parameters for a
     certificate server to use.  These parameters will be used in
     Ephemeral Diffie-Hellman cipher suites.  Note that only a pointer
     to the parameters are stored in the certificate handle, so you must
     not deallocate the parameters before the certificate is
     deallocated.

*Deprecated:* This function is unnecessary and discouraged on
     GnuTLS 3.6.0 or later.  Since 3.6.0, DH parameters are negotiated
     following RFC7919.

gnutls_certificate_set_flags
----------------------------

-- Function: void gnutls_certificate_set_flags
          (gnutls_certificate_credentials_t RES, unsigned int FLAGS)
     RES: is a gnutls_certificate_credentials_t type

FLAGS: are the flags of ‘gnutls_certificate_flags’ type

This function will set flags to tweak the operation of the
     credentials structure.  See the ‘gnutls_certificate_flags’
     enumerations for more information on the available flags.

*Since:* 3.4.7

gnutls_certificate_set_known_dh_params
--------------------------------------

-- Function: int gnutls_certificate_set_known_dh_params
          (gnutls_certificate_credentials_t RES, gnutls_sec_param_t
          SEC_PARAM)
     RES: is a gnutls_certificate_credentials_t type

SEC_PARAM: is an option of the ‘gnutls_sec_param_t’ enumeration

This function will set the Diffie-Hellman parameters for a
     certificate server to use.  These parameters will be used in
     Ephemeral Diffie-Hellman cipher suites and will be selected from
     the FFDHE set of RFC7919 according to the security level provided.

*Deprecated:* This function is unnecessary and discouraged on
     GnuTLS 3.6.0 or later.  Since 3.6.0, DH parameters are negotiated
     following RFC7919.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.5.6

gnutls_certificate_set_ocsp_status_request_file
-----------------------------------------------

-- Function: int gnutls_certificate_set_ocsp_status_request_file
          (gnutls_certificate_credentials_t SC, const char *
          RESPONSE_FILE, unsigned IDX)
     SC: is a credentials structure.

RESPONSE_FILE: a filename of the OCSP response

IDX: is a certificate index as returned by
     ‘gnutls_certificate_set_key()’ and friends

This function loads the provided OCSP response.  It will be sent to
     the client if requests an OCSP certificate status for the
     certificate chain specified by ‘idx’ .

*Note:* the ability to set multiple OCSP responses per credential
     structure via the index ‘idx’ was added in version 3.5.6.  To keep
     backwards compatibility, it requires using
     ‘gnutls_certificate_set_flags()’ with the
     ‘GNUTLS_CERTIFICATE_API_V2’ flag to make the set certificate
     functions return an index usable by this function.

This function can be called multiple times since GnuTLS 3.6.3 when
     multiple responses which apply to the chain are available.  If the
     response provided does not match any certificates present in the
     chain, the code ‘GNUTLS_E_OCSP_MISMATCH_WITH_CERTS’ is returned.
     To revert to the previous behavior set the flag
     ‘GNUTLS_CERTIFICATE_SKIP_OCSP_RESPONSE_CHECK’ in the certificate
     credentials structure.  In that case, only the end-certificate's
     OCSP response can be set.  If the response is already expired at
     the time of loading the code ‘GNUTLS_E_EXPIRED’ is returned.

To revert to the previous behavior of this function which does not
     return any errors, set the flag
     ‘GNUTLS_CERTIFICATE_SKIP_OCSP_RESPONSE_CHECK’

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

*Since:* 3.1.3

gnutls_certificate_set_ocsp_status_request_file2
------------------------------------------------

-- Function: int gnutls_certificate_set_ocsp_status_request_file2
          (gnutls_certificate_credentials_t SC, const char *
          RESPONSE_FILE, unsigned IDX, gnutls_x509_crt_fmt_t FMT)
     SC: is a credentials structure.

RESPONSE_FILE: a filename of the OCSP response

IDX: is a certificate index as returned by
     ‘gnutls_certificate_set_key()’ and friends

FMT: is PEM or DER

This function loads the OCSP responses to be sent to the peer for
     the certificate chain specified by ‘idx’ .  When ‘fmt’ is set to
     PEM, multiple responses can be loaded.

This function must be called after setting any certificates, and
     cannot be used for certificates that are provided via a callback -
     that is when ‘gnutls_certificate_set_retrieve_function()’ is used.
     In that case consider using
     ‘gnutls_certificate_set_retrieve_function3()’ .

This function can be called multiple times when multiple responses
     applicable to the certificate chain are available.  If the response
     provided does not match any certificates present in the chain, the
     code ‘GNUTLS_E_OCSP_MISMATCH_WITH_CERTS’ is returned.  If the
     response is already expired at the time of loading the code
     ‘GNUTLS_E_EXPIRED’ is returned.

*Returns:* On success, the number of loaded responses is returned,
     otherwise a negative error code.

*Since:* 3.1.3

gnutls_certificate_set_ocsp_status_request_function
---------------------------------------------------

-- Function: void gnutls_certificate_set_ocsp_status_request_function
          (gnutls_certificate_credentials_t SC,
          gnutls_status_request_ocsp_func OCSP_FUNC, void * PTR)
     SC: is a ‘gnutls_certificate_credentials_t’ type.

OCSP_FUNC: function pointer to OCSP status request callback.

PTR: opaque pointer passed to callback function

This function is to be used by server to register a callback to
     handle OCSP status requests from the client.  The callback will be
     invoked if the client supplied a status-request OCSP extension.
     The callback function prototype is:

typedef int (*gnutls_status_request_ocsp_func) (gnutls_session_t
     session, void *ptr, gnutls_datum_t *ocsp_response);

The callback will be invoked if the client requests an OCSP
     certificate status.  The callback may return
     ‘GNUTLS_E_NO_CERTIFICATE_STATUS’ , if there is no recent OCSP
     response.  If the callback returns ‘GNUTLS_E_SUCCESS’ , it is
     expected to have the ‘ocsp_response’ field set with a valid
     (DER-encoded) OCSP response.  The response must be a value
     allocated using ‘gnutls_malloc()’ , and will be deinitialized by
     the caller.

It is possible to set a specific callback for each provided
     certificate using
     ‘gnutls_certificate_set_ocsp_status_request_function2()’ .

*Since:* 3.1.3

gnutls_certificate_set_ocsp_status_request_function2
----------------------------------------------------

-- Function: int gnutls_certificate_set_ocsp_status_request_function2
          (gnutls_certificate_credentials_t SC, unsigned IDX,
          gnutls_status_request_ocsp_func OCSP_FUNC, void * PTR)
     SC: is a ‘gnutls_certificate_credentials_t’ type.

IDX: is a certificate index as returned by
     ‘gnutls_certificate_set_key()’ and friends

OCSP_FUNC: function pointer to OCSP status request callback.

PTR: opaque pointer passed to callback function

This function is to be used by server to register a callback to
     provide OCSP status requests that correspond to the indexed
     certificate chain from the client.  The callback will be invoked if
     the client supplied a status-request OCSP extension.

The callback function prototype is:

typedef int (*gnutls_status_request_ocsp_func) (gnutls_session_t
     session, void *ptr, gnutls_datum_t *ocsp_response);

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

*Since:* 3.5.5

gnutls_certificate_set_ocsp_status_request_mem
----------------------------------------------

-- Function: int gnutls_certificate_set_ocsp_status_request_mem
          (gnutls_certificate_credentials_t SC, const gnutls_datum_t *
          RESP_DATA, unsigned IDX, gnutls_x509_crt_fmt_t FMT)
     SC: is a credentials structure.

RESP_DATA: a memory buffer holding an OCSP response

IDX: is a certificate index as returned by
     ‘gnutls_certificate_set_key()’ and friends

FMT: is PEM or DER

This function sets the OCSP responses to be sent to the peer for
     the certificate chain specified by ‘idx’ .  When ‘fmt’ is set to
     PEM, multiple responses can be loaded.

This function can be called multiple times when multiple responses
     which apply to the certificate chain are available.  If the
     response provided does not match any certificates present in the
     chain, the code ‘GNUTLS_E_OCSP_MISMATCH_WITH_CERTS’ is returned.
     If the response is already expired at the time of loading the code
     ‘GNUTLS_E_EXPIRED’ is returned.

*Returns:* On success, the number of loaded responses is returned,
     otherwise a negative error code.

*Since:* 3.6.3

gnutls_certificate_set_params_function
--------------------------------------

-- Function: void gnutls_certificate_set_params_function
          (gnutls_certificate_credentials_t RES, gnutls_params_function
          * FUNC)
     RES: is a gnutls_certificate_credentials_t type

FUNC: is the function to be called

This function will set a callback in order for the server to get
     the Diffie-Hellman or RSA parameters for certificate
     authentication.  The callback should return ‘GNUTLS_E_SUCCESS’ (0)
     on success.

*Deprecated:* This function is unnecessary and discouraged on
     GnuTLS 3.6.0 or later.  Since 3.6.0, DH parameters are negotiated
     following RFC7919.

gnutls_certificate_set_pin_function
-----------------------------------

FN: A PIN callback

USERDATA: Data to be passed in the callback

This function will set a callback function to be used when required
     to access a protected object.  This function overrides any other
     global PIN functions.

Note that this function must be called right after initialization
     to have effect.

*Since:* 3.1.0

gnutls_certificate_set_rawpk_key_file
-------------------------------------

-- Function: int gnutls_certificate_set_rawpk_key_file
          (gnutls_certificate_credentials_t CRED, const char *
          RAWPKFILE, const char * PRIVKEYFILE, gnutls_x509_crt_fmt_t
          FORMAT, const char * PASS, unsigned int KEY_USAGE, const char
          ** NAMES, unsigned int NAMES_LENGTH, unsigned int
          PRIVKEY_FLAGS, unsigned int PKCS11_FLAGS)
     CRED: is a ‘gnutls_certificate_credentials_t’ type.

RAWPKFILE: contains a raw public key in PKIX.SubjectPublicKeyInfo
     format.

PRIVKEYFILE: contains a file path to a private key.

FORMAT: encoding of the keys.  DER or PEM.

PASS: an optional password to unlock the private key privkeyfile.

KEY_USAGE: an ORed sequence of ‘GNUTLS_KEY_’ * flags.

NAMES: is an array of DNS names belonging to the public-key (NULL
     if none).

NAMES_LENGTH: holds the length of the names list.

PRIVKEY_FLAGS: an ORed sequence of ‘gnutls_pkcs_encrypt_flags_t’ .
     These apply to the private key pkey.

PKCS11_FLAGS: one of gnutls_pkcs11_obj_flags.  These apply to URLs.

This function sets a public/private keypair read from file in the
     ‘gnutls_certificate_credentials_t’ type to be used for
     authentication and/or encryption.  ‘spki’ and ‘privkey’ should
     match otherwise set signatures cannot be validated.  In case of no
     match this function returns ‘GNUTLS_E_CERTIFICATE_KEY_MISMATCH’ .
     This function should be called once for the client because there is
     currently no mechanism to determine which raw public-key to select
     for the peer when there are multiple present.  Multiple raw public
     keys for the server can be distinghuished by setting the ‘names’ .

Note here that ‘spki’ is a raw public-key as defined in RFC7250.
     It means that there is no surrounding certificate that holds the
     public key and that there is therefore no direct mechanism to prove
     the authenticity of this key.  The keypair can be used during a TLS
     handshake but its authenticity should be established via a
     different mechanism (e.g.  TOFU or known fingerprint).

The supported formats are basic unencrypted key, PKCS8, PKCS12, and
     the openssl format and will be autodetected.

If the raw public-key and the private key are given in PEM encoding
     then the strings that hold their values must be null terminated.

Key usage (as defined by X.509 extension (2.5.29.15)) can be
     explicitly set because there is no certificate structure around the
     key to define this value.  See for more info
     ‘gnutls_x509_crt_get_key_usage()’ .

Note that, this function by default returns zero on success and a
     negative value on error.  Since 3.5.6, when the flag
     ‘GNUTLS_CERTIFICATE_API_V2’ is set using
     ‘gnutls_certificate_set_flags()’ it returns an index (greater or
     equal to zero).  That index can be used in other functions to refer
     to the added key-pair.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned, in case
     the key pair does not match ‘GNUTLS_E_CERTIFICATE_KEY_MISMATCH’ is
     returned, in other erroneous cases a different negative error code
     is returned.

*Since:* 3.6.6

gnutls_certificate_set_rawpk_key_mem
------------------------------------

-- Function: int gnutls_certificate_set_rawpk_key_mem
          (gnutls_certificate_credentials_t CRED, const gnutls_datum_t *
          SPKI, const gnutls_datum_t * PKEY, gnutls_x509_crt_fmt_t
          FORMAT, const char * PASS, unsigned int KEY_USAGE, const char
          ** NAMES, unsigned int NAMES_LENGTH, unsigned int FLAGS)
     CRED: is a ‘gnutls_certificate_credentials_t’ type.

SPKI: contains a raw public key in PKIX.SubjectPublicKeyInfo
     format.

PKEY: contains a raw private key.

FORMAT: encoding of the keys.  DER or PEM.

PASS: an optional password to unlock the private key pkey.

KEY_USAGE: An ORed sequence of ‘GNUTLS_KEY_’ * flags.

NAMES: is an array of DNS names belonging to the public-key (NULL
     if none).

NAMES_LENGTH: holds the length of the names list.

FLAGS: an ORed sequence of ‘gnutls_pkcs_encrypt_flags_t’ .  These
     apply to the private key pkey.

This function sets a public/private keypair in the
     ‘gnutls_certificate_credentials_t’ type to be used for
     authentication and/or encryption.  ‘spki’ and ‘privkey’ should
     match otherwise set signatures cannot be validated.  In case of no
     match this function returns ‘GNUTLS_E_CERTIFICATE_KEY_MISMATCH’ .
     This function should be called once for the client because there is
     currently no mechanism to determine which raw public-key to select
     for the peer when there are multiple present.  Multiple raw public
     keys for the server can be distinghuished by setting the ‘names’ .

The supported formats are basic unencrypted key, PKCS8, PKCS12, and
     the openssl format and will be autodetected.

If the raw public-key and the private key are given in PEM encoding
     then the strings that hold their values must be null terminated.

Note that, this function by default returns zero on success and a
     negative value on error.  Since 3.5.6, when the flag
     ‘GNUTLS_CERTIFICATE_API_V2’ is set using
     ‘gnutls_certificate_set_flags()’ it returns an index (greater or
     equal to zero).  That index can be used in other functions to refer
     to the added key-pair.

*Since:* 3.6.6

gnutls_certificate_set_retrieve_function
----------------------------------------

-- Function: void gnutls_certificate_set_retrieve_function
          (gnutls_certificate_credentials_t CRED,
          gnutls_certificate_retrieve_function * FUNC)
     CRED: is a ‘gnutls_certificate_credentials_t’ type.

FUNC: is the callback function

This function sets a callback to be called in order to retrieve the
     certificate to be used in the handshake.  The callback will take
     control only if a certificate is requested by the peer.  You are
     advised to use ‘gnutls_certificate_set_retrieve_function2()’
     because it is much more efficient in the processing it requires
     from gnutls.

The callback's function prototype is: int
     (*callback)(gnutls_session_t, const gnutls_datum_t* req_ca_dn, int
     nreqs, const gnutls_pk_algorithm_t* pk_algos, int pk_algos_length,
     gnutls_retr2_st* st);

‘req_ca_dn’ is only used in X.509 certificates.  Contains a list
     with the CA names that the server considers trusted.  This is a
     hint and typically the client should send a certificate that is
     signed by one of these CAs.  These names, when available, are DER
     encoded.  To get a more meaningful value use the function
     ‘gnutls_x509_rdn_get()’ .

‘pk_algos’ contains a list with server's acceptable public key
     algorithms.  The certificate returned should support the server's
     given algorithms.

‘st’ should contain the certificates and private keys.

If the callback function is provided then gnutls will call it, in
     the handshake, after the certificate request message has been
     received.

In server side pk_algos and req_ca_dn are NULL.

The callback function should set the certificate list to be sent,
     and return 0 on success.  If no certificate was selected then the
     number of certificates should be set to zero.  The value (-1)
     indicates error and the handshake will be terminated.  If both
     certificates are set in the credentials and a callback is
     available, the callback takes predence.

*Since:* 3.0

gnutls_certificate_set_verify_flags
-----------------------------------

-- Function: void gnutls_certificate_set_verify_flags
          (gnutls_certificate_credentials_t RES, unsigned int FLAGS)
     RES: is a gnutls_certificate_credentials_t type

FLAGS: are the flags

This function will set the flags to be used for verification of
     certificates and override any defaults.  The provided flags must be
     an OR of the ‘gnutls_certificate_verify_flags’ enumerations.

gnutls_certificate_set_verify_function
--------------------------------------

-- Function: void gnutls_certificate_set_verify_function
          (gnutls_certificate_credentials_t CRED,
          gnutls_certificate_verify_function * FUNC)
     CRED: is a ‘gnutls_certificate_credentials_t’ type.

FUNC: is the callback function

This function sets a callback to be called when peer's certificate
     has been received in order to verify it on receipt rather than
     doing after the handshake is completed.

The callback's function prototype is: int
     (*callback)(gnutls_session_t);

If the callback function is provided then gnutls will call it, in
     the handshake, just after the certificate message has been
     received.  To verify or obtain the certificate the
     ‘gnutls_certificate_verify_peers2()’ ,
     ‘gnutls_certificate_type_get()’ , ‘gnutls_certificate_get_peers()’
     functions can be used.

The callback function should return 0 for the handshake to continue
     or non-zero to terminate.

*Since:* 2.10.0

gnutls_certificate_set_verify_limits
------------------------------------

-- Function: void gnutls_certificate_set_verify_limits
          (gnutls_certificate_credentials_t RES, unsigned int MAX_BITS,
          unsigned int MAX_DEPTH)
     RES: is a gnutls_certificate_credentials type

MAX_BITS: is the number of bits of an acceptable certificate
     (default 8200)

MAX_DEPTH: is maximum depth of the verification of a certificate
     chain (default 5)

This function will set some upper limits for the default
     verification function, ‘gnutls_certificate_verify_peers2()’ , to
     avoid denial of service attacks.  You can set them to zero to
     disable limits.

gnutls_certificate_set_x509_crl
-------------------------------

-- Function: int gnutls_certificate_set_x509_crl
          (gnutls_certificate_credentials_t RES, gnutls_x509_crl_t *
          CRL_LIST, int CRL_LIST_SIZE)
     RES: is a ‘gnutls_certificate_credentials_t’ type.

CRL_LIST: is a list of trusted CRLs.  They should have been
     verified before.

CRL_LIST_SIZE: holds the size of the crl_list

This function adds the trusted CRLs in order to verify client or
     server certificates.  In case of a client this is not required to
     be called if the certificates are not verified using
     ‘gnutls_certificate_verify_peers2()’ .  This function may be called
     multiple times.

*Returns:* number of CRLs processed, or a negative error code on
     error.

*Since:* 2.4.0

gnutls_certificate_set_x509_crl_file
------------------------------------

-- Function: int gnutls_certificate_set_x509_crl_file
          (gnutls_certificate_credentials_t RES, const char * CRLFILE,
          gnutls_x509_crt_fmt_t TYPE)
     RES: is a ‘gnutls_certificate_credentials_t’ type.

CRLFILE: is a file containing the list of verified CRLs (DER or PEM
     list)

TYPE: is PEM or DER

*Returns:* number of CRLs processed or a negative error code on
     error.

gnutls_certificate_set_x509_crl_mem
-----------------------------------

-- Function: int gnutls_certificate_set_x509_crl_mem
          (gnutls_certificate_credentials_t RES, const gnutls_datum_t *
          CRL, gnutls_x509_crt_fmt_t TYPE)
     RES: is a ‘gnutls_certificate_credentials_t’ type.

CRL: is a list of trusted CRLs.  They should have been verified
     before.

TYPE: is DER or PEM

*Returns:* number of CRLs processed, or a negative error code on
     error.

gnutls_certificate_set_x509_key
-------------------------------

-- Function: int gnutls_certificate_set_x509_key
          (gnutls_certificate_credentials_t RES, gnutls_x509_crt_t *
          CERT_LIST, int CERT_LIST_SIZE, gnutls_x509_privkey_t KEY)
     RES: is a ‘gnutls_certificate_credentials_t’ type.

CERT_LIST: contains a certificate list (path) for the specified
     private key

CERT_LIST_SIZE: holds the size of the certificate list

KEY: is a ‘gnutls_x509_privkey_t’ key

This function sets a certificate/private key pair in the
     gnutls_certificate_credentials_t type.  This function may be called
     more than once, in case multiple keys/certificates exist for the
     server.  For clients that wants to send more than their own end
     entity certificate (e.g., also an intermediate CA cert) then put
     the certificate chain in ‘cert_list’ .

Note that the certificates and keys provided, can be safely
     deinitialized after this function is called.

If that function fails to load the ‘res’ type is at an undefined
     state, it must not be reused to load other keys or certificates.

Note that, this function by default returns zero on success and a
     negative value on error.  Since 3.5.6, when the flag
     ‘GNUTLS_CERTIFICATE_API_V2’ is set using
     ‘gnutls_certificate_set_flags()’ it returns an index (greater or
     equal to zero).  That index can be used to other functions to refer
     to the added key-pair.

*Returns:* On success this functions returns zero, and otherwise a
     negative value on error (see above for modifying that behavior).

*Since:* 2.4.0

gnutls_certificate_set_x509_key_file
------------------------------------

-- Function: int gnutls_certificate_set_x509_key_file
          (gnutls_certificate_credentials_t RES, const char * CERTFILE,
          const char * KEYFILE, gnutls_x509_crt_fmt_t TYPE)
     RES: is a ‘gnutls_certificate_credentials_t’ type.

CERTFILE: is a file that containing the certificate list (path) for
     the specified private key, in PKCS7 format, or a list of
     certificates

KEYFILE: is a file that contains the private key

TYPE: is PEM or DER

This function sets a certificate/private key pair in the
     gnutls_certificate_credentials_t type.  This function may be called
     more than once, in case multiple keys/certificates exist for the
     server.  For clients that need to send more than its own end entity
     certificate, e.g., also an intermediate CA cert, then the
     ‘certfile’ must contain the ordered certificate chain.

Note that the names in the certificate provided will be considered
     when selecting the appropriate certificate to use (in case of
     multiple certificate/key pairs).

In case the ‘certfile’ is provided as a PKCS ‘11’ URL, then the
     certificate, and its present issuers in the token are imported
     (i.e., forming the required trust chain).

If that function fails to load the ‘res’ structure is at an
     undefined state, it must not be reused to load other keys or
     certificates.

Note that, this function by default returns zero on success and a
     negative value on error.  Since 3.5.6, when the flag
     ‘GNUTLS_CERTIFICATE_API_V2’ is set using
     ‘gnutls_certificate_set_flags()’ it returns an index (greater or
     equal to zero).  That index can be used to other functions to refer
     to the added key-pair.

*Returns:* On success this functions returns zero, and otherwise a
     negative value on error (see above for modifying that behavior).

*Since:* 3.1.11

gnutls_certificate_set_x509_key_file2
-------------------------------------

-- Function: int gnutls_certificate_set_x509_key_file2
          (gnutls_certificate_credentials_t RES, const char * CERTFILE,
          const char * KEYFILE, gnutls_x509_crt_fmt_t TYPE, const char *
          PASS, unsigned int FLAGS)
     RES: is a ‘gnutls_certificate_credentials_t’ type.

CERTFILE: is a file that containing the certificate list (path) for
     the specified private key, in PKCS7 format, or a list of
     certificates

KEYFILE: is a file that contains the private key

TYPE: is PEM or DER

PASS: is the password of the key

FLAGS: an ORed sequence of gnutls_pkcs_encrypt_flags_t

This function sets a certificate/private key pair in the
     gnutls_certificate_credentials_t type.  This function may be called
     more than once, in case multiple keys/certificates exist for the
     server.  For clients that need to send more than its own end entity
     certificate, e.g., also an intermediate CA cert, then the
     ‘certfile’ must contain the ordered certificate chain.

Note that the names in the certificate provided will be considered
     when selecting the appropriate certificate to use (in case of
     multiple certificate/key pairs).

This function can also accept URLs at ‘keyfile’ and ‘certfile’ .
     In that case it will use the private key and certificate indicated
     by the URLs.  Note that the supported URLs are the ones indicated
     by ‘gnutls_url_is_supported()’ .  Before GnuTLS 3.4.0 when a URL
     was specified, the ‘pass’ part was ignored and a PIN callback had
     to be registered, this is no longer the case in current releases.

In case the ‘certfile’ is provided as a PKCS ‘11’ URL, then the
     certificate, and its present issuers in the token are imported
     (i.e., forming the required trust chain).

If that function fails to load the ‘res’ structure is at an
     undefined state, it must not be reused to load other keys or
     certificates.

Note that, this function by default returns zero on success and a
     negative value on error.  Since 3.5.6, when the flag
     ‘GNUTLS_CERTIFICATE_API_V2’ is set using
     ‘gnutls_certificate_set_flags()’ it returns an index (greater or
     equal to zero).  That index can be used to other functions to refer
     to the added key-pair.

*Returns:* On success this functions returns zero, and otherwise a
     negative value on error (see above for modifying that behavior).

gnutls_certificate_set_x509_key_mem
-----------------------------------

-- Function: int gnutls_certificate_set_x509_key_mem
          (gnutls_certificate_credentials_t RES, const gnutls_datum_t *
          CERT, const gnutls_datum_t * KEY, gnutls_x509_crt_fmt_t TYPE)
     RES: is a ‘gnutls_certificate_credentials_t’ type.

CERT: contains a certificate list (path) for the specified private
     key

KEY: is the private key, or ‘NULL’

TYPE: is PEM or DER

Note that the keyUsage (2.5.29.15) PKIX extension in X.509
     certificates is supported.  This means that certificates intended
     for signing cannot be used for ciphersuites that require
     encryption.

If the certificate and the private key are given in PEM encoding
     then the strings that hold their values must be null terminated.

The ‘key’ may be ‘NULL’ if you are using a sign callback, see
     ‘gnutls_sign_callback_set()’ .

Note that, this function by default returns zero on success and a
     negative value on error.  Since 3.5.6, when the flag
     ‘GNUTLS_CERTIFICATE_API_V2’ is set using
     ‘gnutls_certificate_set_flags()’ it returns an index (greater or
     equal to zero).  That index can be used to other functions to refer
     to the added key-pair.

*Returns:* On success this functions returns zero, and otherwise a
     negative value on error (see above for modifying that behavior).

gnutls_certificate_set_x509_key_mem2
------------------------------------

-- Function: int gnutls_certificate_set_x509_key_mem2
          (gnutls_certificate_credentials_t RES, const gnutls_datum_t *
          CERT, const gnutls_datum_t * KEY, gnutls_x509_crt_fmt_t TYPE,
          const char * PASS, unsigned int FLAGS)
     RES: is a ‘gnutls_certificate_credentials_t’ type.

CERT: contains a certificate list (path) for the specified private
     key

KEY: is the private key, or ‘NULL’

TYPE: is PEM or DER

PASS: is the key's password

FLAGS: an ORed sequence of gnutls_pkcs_encrypt_flags_t

If the certificate and the private key are given in PEM encoding
     then the strings that hold their values must be null terminated.

The ‘key’ may be ‘NULL’ if you are using a sign callback, see
     ‘gnutls_sign_callback_set()’ .

Note that, this function by default returns zero on success and a
     negative value on error.  Since 3.5.6, when the flag
     ‘GNUTLS_CERTIFICATE_API_V2’ is set using
     ‘gnutls_certificate_set_flags()’ it returns an index (greater or
     equal to zero).  That index can be used to other functions to refer
     to the added key-pair.

*Returns:* On success this functions returns zero, and otherwise a
     negative value on error (see above for modifying that behavior).

gnutls_certificate_set_x509_simple_pkcs12_file
----------------------------------------------

-- Function: int gnutls_certificate_set_x509_simple_pkcs12_file
          (gnutls_certificate_credentials_t RES, const char *
          PKCS12FILE, gnutls_x509_crt_fmt_t TYPE, const char * PASSWORD)
     RES: is a ‘gnutls_certificate_credentials_t’ type.

PKCS12FILE: filename of file containing PKCS‘12’ blob.

TYPE: is PEM or DER of the ‘pkcs12file’ .

PASSWORD: optional password used to decrypt PKCS‘12’ file, bags and
     keys.

This function sets a certificate/private key pair and/or a CRL in
     the gnutls_certificate_credentials_t type.  This function may be
     called more than once (in case multiple keys/certificates exist for
     the server).

PKCS‘12’ files with a MAC, encrypted bags and PKCS ‘8’ private keys
     are supported.  However, only password based security, and the same
     password for all operations, are supported.

PKCS‘12’ file may contain many keys and/or certificates, and this
     function will try to auto-detect based on the key ID the
     certificate and key pair to use.  If the PKCS‘12’ file contain the
     issuer of the selected certificate, it will be appended to the
     certificate to form a chain.

If more than one private keys are stored in the PKCS‘12’ file, then
     only one key will be read (and it is undefined which one).

It is believed that the limitations of this function is acceptable
     for most usage, and that any more flexibility would introduce
     complexity that would make it harder to use this functionality at
     all.

Note that, this function by default returns zero on success and a
     negative value on error.  Since 3.5.6, when the flag
     ‘GNUTLS_CERTIFICATE_API_V2’ is set using
     ‘gnutls_certificate_set_flags()’ it returns an index (greater or
     equal to zero).  That index can be used to other functions to refer
     to the added key-pair.

*Returns:* On success this functions returns zero, and otherwise a
     negative value on error (see above for modifying that behavior).

gnutls_certificate_set_x509_simple_pkcs12_mem
---------------------------------------------

-- Function: int gnutls_certificate_set_x509_simple_pkcs12_mem
          (gnutls_certificate_credentials_t RES, const gnutls_datum_t *
          P12BLOB, gnutls_x509_crt_fmt_t TYPE, const char * PASSWORD)
     RES: is a ‘gnutls_certificate_credentials_t’ type.

P12BLOB: the PKCS‘12’ blob.

TYPE: is PEM or DER of the ‘pkcs12file’ .

PASSWORD: optional password used to decrypt PKCS‘12’ file, bags and
     keys.

Encrypted PKCS‘12’ bags and PKCS‘8’ private keys are supported.
     However, only password based security, and the same password for
     all operations, are supported.

If more than one private keys are stored in the PKCS‘12’ file, then
     only one key will be read (and it is undefined which one).

Note that, this function by default returns zero on success and a
     negative value on error.  Since 3.5.6, when the flag
     ‘GNUTLS_CERTIFICATE_API_V2’ is set using
     ‘gnutls_certificate_set_flags()’ it returns an index (greater or
     equal to zero).  That index can be used to other functions to refer
     to the added key-pair.

*Returns:* On success this functions returns zero, and otherwise a
     negative value on error (see above for modifying that behavior).

*Since:* 2.8.0

gnutls_certificate_set_x509_system_trust
----------------------------------------

-- Function: int gnutls_certificate_set_x509_system_trust
          (gnutls_certificate_credentials_t CRED)
     CRED: is a ‘gnutls_certificate_credentials_t’ type.

This function adds the system's default trusted CAs in order to
     verify client or server certificates.

In the case the system is currently unsupported
     ‘GNUTLS_E_UNIMPLEMENTED_FEATURE’ is returned.

*Returns:* the number of certificates processed or a negative error
     code on error.

*Since:* 3.0.20

gnutls_certificate_set_x509_trust
---------------------------------

-- Function: int gnutls_certificate_set_x509_trust
          (gnutls_certificate_credentials_t RES, gnutls_x509_crt_t *
          CA_LIST, int CA_LIST_SIZE)
     RES: is a ‘gnutls_certificate_credentials_t’ type.

CA_LIST: is a list of trusted CAs

CA_LIST_SIZE: holds the size of the CA list

This function adds the trusted CAs in order to verify client or
     server certificates.  In case of a client this is not required to
     be called if the certificates are not verified using
     ‘gnutls_certificate_verify_peers2()’ .  This function may be called
     multiple times.

In case of a server the CAs set here will be sent to the client if
     a certificate request is sent.  This can be disabled using
     ‘gnutls_certificate_send_x509_rdn_sequence()’ .

*Returns:* the number of certificates processed or a negative error
     code on error.

*Since:* 2.4.0

gnutls_certificate_set_x509_trust_dir
-------------------------------------

-- Function: int gnutls_certificate_set_x509_trust_dir
          (gnutls_certificate_credentials_t CRED, const char * CA_DIR,
          gnutls_x509_crt_fmt_t TYPE)
     CRED: is a ‘gnutls_certificate_credentials_t’ type.

CA_DIR: is a directory containing the list of trusted CAs (DER or
     PEM list)

TYPE: is PEM or DER

This function adds the trusted CAs present in the directory in
     order to verify client or server certificates.  This function is
     identical to ‘gnutls_certificate_set_x509_trust_file()’ but loads
     all certificates in a directory.

*Returns:* the number of certificates processed

*Since:* 3.3.6

gnutls_certificate_set_x509_trust_file
--------------------------------------

-- Function: int gnutls_certificate_set_x509_trust_file
          (gnutls_certificate_credentials_t CRED, const char * CAFILE,
          gnutls_x509_crt_fmt_t TYPE)
     CRED: is a ‘gnutls_certificate_credentials_t’ type.

CAFILE: is a file containing the list of trusted CAs (DER or PEM
     list)

TYPE: is PEM or DER

In case of a server the names of the CAs set here will be sent to
     the client if a certificate request is sent.  This can be disabled
     using ‘gnutls_certificate_send_x509_rdn_sequence()’ .

This function can also accept URLs.  In that case it will import
     all certificates that are marked as trusted.  Note that the
     supported URLs are the ones indicated by
     ‘gnutls_url_is_supported()’ .

*Returns:* the number of certificates processed

gnutls_certificate_set_x509_trust_mem
-------------------------------------

-- Function: int gnutls_certificate_set_x509_trust_mem
          (gnutls_certificate_credentials_t RES, const gnutls_datum_t *
          CA, gnutls_x509_crt_fmt_t TYPE)
     RES: is a ‘gnutls_certificate_credentials_t’ type.

CA: is a list of trusted CAs or a DER certificate

TYPE: is DER or PEM

In case of a server the CAs set here will be sent to the client if
     a certificate request is sent.  This can be disabled using
     ‘gnutls_certificate_send_x509_rdn_sequence()’ .

*Returns:* the number of certificates processed or a negative error
     code on error.

gnutls_certificate_type_get
---------------------------

-- Function: gnutls_certificate_type_t gnutls_certificate_type_get
          (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

This function returns the type of the certificate that is
     negotiated for this side to send to the peer.  The certificate type
     is by default X.509, unless an alternative certificate type is
     enabled by ‘gnutls_init()’ and negotiated during the session.

Resumed sessions will return the certificate type that was
     negotiated and used in the original session.

As of version 3.6.4 it is recommended to use
     ‘gnutls_certificate_type_get2()’ which is more fine-grained.

*Returns:* the currently used ‘gnutls_certificate_type_t’
     certificate type as negotiated for 'our' side of the connection.

gnutls_certificate_type_get2
----------------------------

-- Function: gnutls_certificate_type_t gnutls_certificate_type_get2
          (gnutls_session_t SESSION, gnutls_ctype_target_t TARGET)
     SESSION: is a ‘gnutls_session_t’ type.

TARGET: is a ‘gnutls_ctype_target_t’ type.

This function returns the type of the certificate that a side is
     negotiated to use.  The certificate type is by default X.509,
     unless an alternative certificate type is enabled by
     ‘gnutls_init()’ and negotiated during the session.

The ‘target’ parameter specifies whether to request the negotiated
     certificate type for the client (‘GNUTLS_CTYPE_CLIENT’ ), or for
     the server (‘GNUTLS_CTYPE_SERVER’ ).  Additionally, in P2P mode
     connection set up where you don't know in advance who will be
     client and who will be server you can use the flag
     (‘GNUTLS_CTYPE_OURS’ ) and (‘GNUTLS_CTYPE_PEERS’ ) to retrieve the
     corresponding certificate types.

Resumed sessions will return the certificate type that was
     negotiated and used in the original session.  That is, this
     function can be used to reliably determine the type of the
     certificate returned by ‘gnutls_certificate_get_peers()’ .

*Returns:* the currently used ‘gnutls_certificate_type_t’
     certificate type for the client or the server.

*Since:* 3.6.4

gnutls_certificate_type_get_id
------------------------------

-- Function: gnutls_certificate_type_t gnutls_certificate_type_get_id
          (const char * NAME)
     NAME: is a certificate type name

The names are compared in a case insensitive way.

*Returns:* a ‘gnutls_certificate_type_t’ for the specified in a
     string certificate type, or ‘GNUTLS_CRT_UNKNOWN’ on error.

gnutls_certificate_type_get_name
--------------------------------

-- Function: const char * gnutls_certificate_type_get_name
          (gnutls_certificate_type_t TYPE)
     TYPE: is a certificate type

Convert a ‘gnutls_certificate_type_t’ type to a string.

*Returns:* a string that contains the name of the specified
     certificate type, or ‘NULL’ in case of unknown types.

gnutls_certificate_type_list
----------------------------

-- Function: const gnutls_certificate_type_t *
          gnutls_certificate_type_list ( VOID)

Get a list of certificate types.

*Returns:* a (0)-terminated list of ‘gnutls_certificate_type_t’
     integers indicating the available certificate types.

gnutls_certificate_verification_status_print
--------------------------------------------

-- Function: int gnutls_certificate_verification_status_print (unsigned
          int STATUS, gnutls_certificate_type_t TYPE, gnutls_datum_t *
          OUT, unsigned int FLAGS)
     STATUS: The status flags to be printed

TYPE: The certificate type

OUT: Newly allocated datum with (0) terminated string.

FLAGS: should be zero

This function will pretty print the status of a verification
     process - eg.  the one obtained by
     ‘gnutls_certificate_verify_peers3()’ .

The output ‘out’ needs to be deallocated using ‘gnutls_free()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.1.4

gnutls_certificate_verify_peers
-------------------------------

-- Function: int gnutls_certificate_verify_peers (gnutls_session_t
          SESSION, gnutls_typed_vdata_st * DATA, unsigned int ELEMENTS,
          unsigned int * STATUS)
     SESSION: is a gnutls session

DATA: an array of typed data

ELEMENTS: the number of data elements

STATUS: is the output of the verification

This function will verify the peer's certificate and store the the
     status in the ‘status’ variable as a bitwise OR of
     gnutls_certificate_status_t values or zero if the certificate is
     trusted.  Note that value in ‘status’ is set only when the return
     value of this function is success (i.e, failure to trust a
     certificate does not imply a negative return value).  The default
     verification flags used by this function can be overridden using
     ‘gnutls_certificate_set_verify_flags()’ .  See the documentation of
     ‘gnutls_certificate_verify_peers2()’ for details in the
     verification process.

This function will take into account the stapled OCSP responses
     sent by the server, as well as the following X.509 certificate
     extensions: Name Constraints, Key Usage, and Basic Constraints
     (pathlen).

The acceptable ‘data’ types are ‘GNUTLS_DT_DNS_HOSTNAME’ ,
     ‘GNUTLS_DT_RFC822NAME’ and ‘GNUTLS_DT_KEY_PURPOSE_OID’ .  The
     former two accept as data a null-terminated hostname or email
     address, and the latter a null-terminated object identifier (e.g.,
     ‘GNUTLS_KP_TLS_WWW_SERVER’ ).

If a DNS hostname is provided then this function will compare the
     hostname in the certificate against the given.  If names do not
     match the ‘GNUTLS_CERT_UNEXPECTED_OWNER’ status flag will be set.
     If a key purpose OID is provided and the end-certificate contains
     the extended key usage PKIX extension, it will be required to be
     have the provided key purpose or be marked for any purpose,
     otherwise verification status will have the
     ‘GNUTLS_CERT_SIGNER_CONSTRAINTS_FAILURE’ flag set.

To avoid denial of service attacks some default upper limits
     regarding the certificate key size and chain size are set.  To
     override them use ‘gnutls_certificate_set_verify_limits()’ .

Note that when using raw public-keys verification will not work
     because there is no corresponding certificate body belonging to the
     raw key that can be verified.  In that case this function will
     return ‘GNUTLS_E_INVALID_REQUEST’ .

*Returns:* ‘GNUTLS_E_SUCCESS’ (0) when the validation is performed,
     or a negative error code otherwise.  A successful error code means
     that the ‘status’ parameter must be checked to obtain the
     validation status.

*Since:* 3.3.0

gnutls_certificate_verify_peers2
--------------------------------

-- Function: int gnutls_certificate_verify_peers2 (gnutls_session_t
          SESSION, unsigned int * STATUS)
     SESSION: is a gnutls session

STATUS: is the output of the verification

This function will verify the peer's certificate and store the
     status in the ‘status’ variable as a bitwise OR of
     gnutls_certificate_status_t values or zero if the certificate is
     trusted.  Note that value in ‘status’ is set only when the return
     value of this function is success (i.e, failure to trust a
     certificate does not imply a negative return value).  The default
     verification flags used by this function can be overridden using
     ‘gnutls_certificate_set_verify_flags()’ .

Note that you must also check the peer's name in order to check if
     the verified certificate belongs to the actual peer, see
     ‘gnutls_x509_crt_check_hostname()’ , or use
     ‘gnutls_certificate_verify_peers3()’ .

To avoid denial of service attacks some default upper limits
     regarding the certificate key size and chain size are set.  To
     override them use ‘gnutls_certificate_set_verify_limits()’ .

gnutls_certificate_verify_peers3
--------------------------------

-- Function: int gnutls_certificate_verify_peers3 (gnutls_session_t
          SESSION, const char * HOSTNAME, unsigned int * STATUS)
     SESSION: is a gnutls session

HOSTNAME: is the expected name of the peer; may be ‘NULL’

STATUS: is the output of the verification

If the ‘hostname’ provided is non-NULL then this function will
     compare the hostname in the certificate against it.  The comparison
     will follow the RFC6125 recommendations.  If names do not match the
     ‘GNUTLS_CERT_UNEXPECTED_OWNER’ status flag will be set.

In order to verify the purpose of the end-certificate (by checking
     the extended key usage), use ‘gnutls_certificate_verify_peers()’ .

To avoid denial of service attacks some default upper limits
     regarding the certificate key size and chain size are set.  To
     override them use ‘gnutls_certificate_set_verify_limits()’ .

*Since:* 3.1.4

gnutls_check_version
--------------------

-- Function: const char * gnutls_check_version (const char *
          REQ_VERSION)
     REQ_VERSION: version string to compare with, or ‘NULL’ .

Check the GnuTLS Library version against the provided string.  See
     ‘GNUTLS_VERSION’ for a suitable ‘req_version’ string.

See also ‘gnutls_check_version_numeric()’ , which provides this
     functionality as a macro.

*Returns:* Check that the version of the library is at minimum the
     one given as a string in ‘req_version’ and return the actual
     version string of the library; return ‘NULL’ if the condition is
     not met.  If ‘NULL’ is passed to this function no check is done and
     only the version string is returned.

gnutls_cipher_get
-----------------

-- Function: gnutls_cipher_algorithm_t gnutls_cipher_get
          (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Get the currently used cipher.

*Returns:* the currently used cipher, a ‘gnutls_cipher_algorithm_t’
     type.

gnutls_cipher_get_id
--------------------

-- Function: gnutls_cipher_algorithm_t gnutls_cipher_get_id (const char
          * NAME)
     NAME: is a cipher algorithm name

The names are compared in a case insensitive way.

*Returns:* return a ‘gnutls_cipher_algorithm_t’ value corresponding
     to the specified cipher, or ‘GNUTLS_CIPHER_UNKNOWN’ on error.

gnutls_cipher_get_key_size
--------------------------

-- Function: size_t gnutls_cipher_get_key_size
          (gnutls_cipher_algorithm_t ALGORITHM)
     ALGORITHM: is an encryption algorithm

This function returns the key size of the provided algorithm.

*Returns:* length (in bytes) of the given cipher's key size, or 0
     if the given cipher is invalid.

gnutls_cipher_get_name
----------------------

-- Function: const char * gnutls_cipher_get_name
          (gnutls_cipher_algorithm_t ALGORITHM)
     ALGORITHM: is an encryption algorithm

Convert a ‘gnutls_cipher_algorithm_t’ type to a string.

*Returns:* a pointer to a string that contains the name of the
     specified cipher, or ‘NULL’ .

gnutls_cipher_list
------------------

-- Function: const gnutls_cipher_algorithm_t * gnutls_cipher_list (
          VOID)

Get a list of supported cipher algorithms.  Note that not
     necessarily all ciphers are supported as TLS cipher suites.  For
     example, DES is not supported as a cipher suite, but is supported
     for other purposes (e.g., PKCS‘8’ or similar).

This function is not thread safe.

*Returns:* a (0)-terminated list of ‘gnutls_cipher_algorithm_t’
     integers indicating the available ciphers.

gnutls_cipher_suite_get_name
----------------------------

-- Function: const char * gnutls_cipher_suite_get_name
          (gnutls_kx_algorithm_t KX_ALGORITHM, gnutls_cipher_algorithm_t
          CIPHER_ALGORITHM, gnutls_mac_algorithm_t MAC_ALGORITHM)
     KX_ALGORITHM: is a Key exchange algorithm

CIPHER_ALGORITHM: is a cipher algorithm

MAC_ALGORITHM: is a MAC algorithm

This function returns the ciphersuite name under TLS1.2 or earlier
     versions when provided with individual algorithms.  The full cipher
     suite name must be prepended by TLS or SSL depending of the
     protocol in use.

To get a description of the current ciphersuite across versions, it
     is recommended to use ‘gnutls_session_get_desc()’ .

*Returns:* a string that contains the name of a TLS cipher suite,
     specified by the given algorithms, or ‘NULL’ .

gnutls_cipher_suite_info
------------------------

-- Function: const char * gnutls_cipher_suite_info (size_t IDX,
          unsigned char * CS_ID, gnutls_kx_algorithm_t * KX,
          gnutls_cipher_algorithm_t * CIPHER, gnutls_mac_algorithm_t *
          MAC, gnutls_protocol_t * MIN_VERSION)
     IDX: index of cipher suite to get information about, starts on 0.

CS_ID: output buffer with room for 2 bytes, indicating cipher suite
     value

KX: output variable indicating key exchange algorithm, or ‘NULL’ .

CIPHER: output variable indicating cipher, or ‘NULL’ .

MAC: output variable indicating MAC algorithm, or ‘NULL’ .

MIN_VERSION: output variable indicating TLS protocol version, or
     ‘NULL’ .

Get information about supported cipher suites.  Use the function
     iteratively to get information about all supported cipher suites.
     Call with idx=0 to get information about first cipher suite, then
     idx=1 and so on until the function returns NULL.

*Returns:* the name of ‘idx’ cipher suite, and set the information
     about the cipher suite in the output variables.  If ‘idx’ is out of
     bounds, ‘NULL’ is returned.

gnutls_ciphersuite_get
----------------------

-- Function: const char * gnutls_ciphersuite_get (gnutls_session_t
          SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Get the canonical name of negotiated TLS ciphersuite.  The names
     returned by this function match the IANA registry, with one
     exception:

TLS_DHE_DSS_RC4_128_SHA { 0x00, 0x66 }

which is reserved for compatibility.

To get a detailed description of the current ciphersuite, it is
     recommended to use ‘gnutls_session_get_desc()’ .

*Returns:* a string that contains the canonical name of a TLS
     ciphersuite, or ‘NULL’ if the handshake is not completed.

*Since:* 3.7.4

gnutls_compress_certificate_get_selected_method
-----------------------------------------------

-- Function: gnutls_compression_method_t
          gnutls_compress_certificate_get_selected_method
          (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

This function returns the certificate compression method that has
     been selected to compress the certificate before sending it to the
     peer.  The selection is done based on the local list of supported
     compression methods and the peer's requested compression methods.

*Returns:* selected certificate compression method.

Since 3.7.4

gnutls_compress_certificate_set_methods
---------------------------------------

-- Function: int gnutls_compress_certificate_set_methods
          (gnutls_session_t SESSION, const gnutls_compression_method_t *
          METHODS, size_t METHODS_LEN)
     SESSION: is a ‘gnutls_session_t’ type.

METHODS: is a list of supported compression methods.

METHODS_LEN: number of compression methods in ‘methods’

This function sets the supported compression methods for
     certificate compression for the given session.  The list of
     supported compression methods will be used for a) requesting the
     compression of peer's certificate and b) selecting the method to
     compress the local certificate before sending it to the peer.  The
     order of compression methods inside the list does matter as the
     method that appears earlier in the list will be preferred before
     the later ones.  Note that even if you set the list of supported
     compression methods, the compression might not be used if the peer
     does not support any of your chosen compression methods.

The list of supported compression methods must meet the following
     criteria: Argument ‘methods’ must be an array of valid compression
     methods of type ‘gnutls_compression_method_t’ .  Argument
     ‘methods_len’ must contain the number of compression methods stored
     in the ‘methods’ array and must be within range <1, 127>.  The
     length constraints are defined by
     ‘MIN_COMPRESS_CERTIFICATE_METHODS’ and
     ‘MAX_COMPRESS_CERTIFICATE_METHODS’ macros located in the header
     file compress_certificate.h.

If either ‘methods’ or ‘methods_len’ is equal to 0, current list of
     supported compression methods will be unset.

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, otherwise a negative
     error code.

Since 3.7.4

gnutls_credentials_clear
------------------------

-- Function: void gnutls_credentials_clear (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Clears all the credentials previously set in this session.

gnutls_credentials_get
----------------------

-- Function: int gnutls_credentials_get (gnutls_session_t SESSION,
          gnutls_credentials_type_t TYPE, void ** CRED)
     SESSION: is a ‘gnutls_session_t’ type.

TYPE: is the type of the credentials to return

CRED: will contain the credentials.

Returns the previously provided credentials structures.

For ‘GNUTLS_CRD_ANON’ , ‘cred’ will be
     ‘gnutls_anon_client_credentials_t’ in case of a client.  In case of
     a server it should be ‘gnutls_anon_server_credentials_t’ .

For ‘GNUTLS_CRD_SRP’ , ‘cred’ will be
     ‘gnutls_srp_client_credentials_t’ in case of a client, and
     ‘gnutls_srp_server_credentials_t’ , in case of a server.

For ‘GNUTLS_CRD_PSK’ , ‘cred’ will be
     ‘gnutls_psk_client_credentials_t’ in case of a client, and
     ‘gnutls_psk_server_credentials_t’ , in case of a server.

For ‘GNUTLS_CRD_CERTIFICATE’ , ‘cred’ will be
     ‘gnutls_certificate_credentials_t’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

*Since:* 3.3.3

gnutls_credentials_set
----------------------

-- Function: int gnutls_credentials_set (gnutls_session_t SESSION,
          gnutls_credentials_type_t TYPE, void * CRED)
     SESSION: is a ‘gnutls_session_t’ type.

TYPE: is the type of the credentials

CRED: the credentials to set

For ‘GNUTLS_CRD_ANON’ , ‘cred’ should be
     ‘gnutls_anon_client_credentials_t’ in case of a client.  In case of
     a server it should be ‘gnutls_anon_server_credentials_t’ .

For ‘GNUTLS_CRD_SRP’ , ‘cred’ should be
     ‘gnutls_srp_client_credentials_t’ in case of a client, and
     ‘gnutls_srp_server_credentials_t’ , in case of a server.

For ‘GNUTLS_CRD_CERTIFICATE’ , ‘cred’ should be
     ‘gnutls_certificate_credentials_t’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

gnutls_db_check_entry
---------------------

-- Function: int gnutls_db_check_entry (gnutls_session_t SESSION,
          gnutls_datum_t SESSION_ENTRY)
     SESSION: is a ‘gnutls_session_t’ type.

SESSION_ENTRY: is the session data (not key)

This function has no effect.

*Returns:* Returns ‘GNUTLS_E_EXPIRED’ , if the database entry has
     expired or 0 otherwise.

*Deprecated:* This function is deprecated.

gnutls_db_check_entry_expire_time
---------------------------------

-- Function: time_t gnutls_db_check_entry_expire_time (gnutls_datum_t *
          ENTRY)
     ENTRY: is a pointer to a ‘gnutls_datum_t’ type.

This function returns the time that this entry will expire.  It can
     be used for database entry expiration.

*Returns:* The time this entry will expire, or zero on error.

*Since:* 3.6.5

gnutls_db_check_entry_time
--------------------------

-- Function: time_t gnutls_db_check_entry_time (gnutls_datum_t * ENTRY)
     ENTRY: is a pointer to a ‘gnutls_datum_t’ type.

This function returns the time that this entry was active.  It can
     be used for database entry expiration.

*Returns:* The time this entry was created, or zero on error.

gnutls_db_get_default_cache_expiration
--------------------------------------

-- Function: unsigned gnutls_db_get_default_cache_expiration ( VOID)

Returns the expiration time (in seconds) of stored sessions for
     resumption.

gnutls_db_get_ptr
-----------------

-- Function: void * gnutls_db_get_ptr (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Get db function pointer.

*Returns:* the pointer that will be sent to db store, retrieve and
     delete functions, as the first argument.

gnutls_db_remove_session
------------------------

-- Function: void gnutls_db_remove_session (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

This function will remove the current session data from the session
     database.  This will prevent future handshakes reusing these
     session data.  This function should be called if a session was
     terminated abnormally, and before ‘gnutls_deinit()’ is called.

Normally ‘gnutls_deinit()’ will remove abnormally terminated
     sessions.

gnutls_db_set_cache_expiration
------------------------------

-- Function: void gnutls_db_set_cache_expiration (gnutls_session_t
          SESSION, int SECONDS)
     SESSION: is a ‘gnutls_session_t’ type.

SECONDS: is the number of seconds.

Set the expiration time for resumed sessions.  The default is 21600
     (6 hours) at the time of writing.

The maximum value that can be set using this function is 604800 (7
     days).

gnutls_db_set_ptr
-----------------

-- Function: void gnutls_db_set_ptr (gnutls_session_t SESSION, void *
          PTR)
     SESSION: is a ‘gnutls_session_t’ type.

PTR: is the pointer

Sets the pointer that will be provided to db store, retrieve and
     delete functions, as the first argument.

gnutls_db_set_remove_function
-----------------------------

-- Function: void gnutls_db_set_remove_function (gnutls_session_t
          SESSION, gnutls_db_remove_func REM_FUNC)
     SESSION: is a ‘gnutls_session_t’ type.

REM_FUNC: is the function.

Sets the function that will be used to remove data from the resumed
     sessions database.  This function must return 0 on success.

The first argument to ‘rem_func’ will be null unless
     ‘gnutls_db_set_ptr()’ has been called.

gnutls_db_set_retrieve_function
-------------------------------

-- Function: void gnutls_db_set_retrieve_function (gnutls_session_t
          SESSION, gnutls_db_retr_func RETR_FUNC)
     SESSION: is a ‘gnutls_session_t’ type.

RETR_FUNC: is the function.

Sets the function that will be used to retrieve data from the
     resumed sessions database.  This function must return a
     gnutls_datum_t containing the data on success, or a gnutls_datum_t
     containing null and 0 on failure.

The datum's data must be allocated using the function
     ‘gnutls_malloc()’ .

The first argument to ‘retr_func’ will be null unless
     ‘gnutls_db_set_ptr()’ has been called.

gnutls_db_set_store_function
----------------------------

-- Function: void gnutls_db_set_store_function (gnutls_session_t
          SESSION, gnutls_db_store_func STORE_FUNC)
     SESSION: is a ‘gnutls_session_t’ type.

STORE_FUNC: is the function

Sets the function that will be used to store data in the resumed
     sessions database.  This function must return 0 on success.

The first argument to ‘store_func’ will be null unless
     ‘gnutls_db_set_ptr()’ has been called.

gnutls_deinit
-------------

-- Function: void gnutls_deinit (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

This function clears all buffers associated with the ‘session’ .
     This function will also remove session data from the session
     database if the session was terminated abnormally.

gnutls_dh_get_group
-------------------

-- Function: int gnutls_dh_get_group (gnutls_session_t SESSION,
          gnutls_datum_t * RAW_GEN, gnutls_datum_t * RAW_PRIME)
     SESSION: is a gnutls session

RAW_GEN: will hold the generator.

RAW_PRIME: will hold the prime.

This function will return the group parameters used in the last
     Diffie-Hellman key exchange with the peer.  These are the prime and
     the generator used.  This function should be used for both
     anonymous and ephemeral Diffie-Hellman.  The output parameters must
     be freed with ‘gnutls_free()’ .

Note, that the prime and generator are exported as non-negative
     integers and may include a leading zero byte.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise an error code is returned.

gnutls_dh_get_peers_public_bits
-------------------------------

-- Function: int gnutls_dh_get_peers_public_bits (gnutls_session_t
          SESSION)
     SESSION: is a gnutls session

Get the Diffie-Hellman public key bit size.  Can be used for both
     anonymous and ephemeral Diffie-Hellman.

*Returns:* The public key bit size used in the last Diffie-Hellman
     key exchange with the peer, or a negative error code in case of
     error.

gnutls_dh_get_prime_bits
------------------------

-- Function: int gnutls_dh_get_prime_bits (gnutls_session_t SESSION)
     SESSION: is a gnutls session

This function will return the bits of the prime used in the last
     Diffie-Hellman key exchange with the peer.  Should be used for both
     anonymous and ephemeral Diffie-Hellman.  Note that some ciphers,
     like RSA and DSA without DHE, do not use a Diffie-Hellman key
     exchange, and then this function will return 0.

*Returns:* The Diffie-Hellman bit strength is returned, or 0 if no
     Diffie-Hellman key exchange was done, or a negative error code on
     failure.

gnutls_dh_get_pubkey
--------------------

-- Function: int gnutls_dh_get_pubkey (gnutls_session_t SESSION,
          gnutls_datum_t * RAW_KEY)
     SESSION: is a gnutls session

RAW_KEY: will hold the public key.

This function will return the peer's public key used in the last
     Diffie-Hellman key exchange.  This function should be used for both
     anonymous and ephemeral Diffie-Hellman.  The output parameters must
     be freed with ‘gnutls_free()’ .

Note, that public key is exported as non-negative integer and may
     include a leading zero byte.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise an error code is returned.

gnutls_dh_get_secret_bits
-------------------------

-- Function: int gnutls_dh_get_secret_bits (gnutls_session_t SESSION)
     SESSION: is a gnutls session

This function will return the bits used in the last Diffie-Hellman
     key exchange with the peer.  Should be used for both anonymous and
     ephemeral Diffie-Hellman.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise an error code is returned.

gnutls_dh_params_cpy
--------------------

-- Function: int gnutls_dh_params_cpy (gnutls_dh_params_t DST,
          gnutls_dh_params_t SRC)
     DST: Is the destination parameters, which should be initialized.

SRC: Is the source parameters

This function will copy the DH parameters structure from source to
     destination.  The destination should be already initialized.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

gnutls_dh_params_deinit
-----------------------

-- Function: void gnutls_dh_params_deinit (gnutls_dh_params_t
          DH_PARAMS)
     DH_PARAMS: The parameters

This function will deinitialize the DH parameters type.

gnutls_dh_params_export2_pkcs3
------------------------------

-- Function: int gnutls_dh_params_export2_pkcs3 (gnutls_dh_params_t
          PARAMS, gnutls_x509_crt_fmt_t FORMAT, gnutls_datum_t * OUT)
     PARAMS: Holds the DH parameters

FORMAT: the format of output params.  One of PEM or DER.

OUT: will contain a PKCS3 DHParams structure PEM or DER encoded

This function will export the given dh parameters to a PKCS3
     DHParams structure.  This is the format generated by "openssl
     dhparam" tool.  The data in ‘out’ will be allocated using
     ‘gnutls_malloc()’ .

If the structure is PEM encoded, it will have a header of "BEGIN DH
     PARAMETERS".

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

*Since:* 3.1.3

gnutls_dh_params_export_pkcs3
-----------------------------

-- Function: int gnutls_dh_params_export_pkcs3 (gnutls_dh_params_t
          PARAMS, gnutls_x509_crt_fmt_t FORMAT, unsigned char *
          PARAMS_DATA, size_t * PARAMS_DATA_SIZE)
     PARAMS: Holds the DH parameters

FORMAT: the format of output params.  One of PEM or DER.

PARAMS_DATA: will contain a PKCS3 DHParams structure PEM or DER
     encoded

PARAMS_DATA_SIZE: holds the size of params_data (and will be
     replaced by the actual size of parameters)

This function will export the given dh parameters to a PKCS3
     DHParams structure.  This is the format generated by "openssl
     dhparam" tool.  If the buffer provided is not long enough to hold
     the output, then GNUTLS_E_SHORT_MEMORY_BUFFER will be returned.

If the structure is PEM encoded, it will have a header of "BEGIN DH
     PARAMETERS".

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

gnutls_dh_params_export_raw
---------------------------

-- Function: int gnutls_dh_params_export_raw (gnutls_dh_params_t
          PARAMS, gnutls_datum_t * PRIME, gnutls_datum_t * GENERATOR,
          unsigned int * BITS)
     PARAMS: Holds the DH parameters

PRIME: will hold the new prime

GENERATOR: will hold the new generator

BITS: if non null will hold the secret key's number of bits

This function will export the pair of prime and generator for use
     in the Diffie-Hellman key exchange.  The new parameters will be
     allocated using ‘gnutls_malloc()’ and will be stored in the
     appropriate datum.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

gnutls_dh_params_generate2
--------------------------

-- Function: int gnutls_dh_params_generate2 (gnutls_dh_params_t
          DPARAMS, unsigned int BITS)
     DPARAMS: The parameters

BITS: is the prime's number of bits

This function will generate a new pair of prime and generator for
     use in the Diffie-Hellman key exchange.  This may take long time.

It is recommended not to set the number of bits directly, but use
     ‘gnutls_sec_param_to_pk_bits()’ instead.  Also note that the DH
     parameters are only useful to servers.  Since clients use the
     parameters sent by the server, it's of no use to call this in
     client side.

The parameters generated are of the DSA form.  It also is possible
     to generate provable parameters (following the Shawe-Taylor
     algorithm), using ‘gnutls_x509_privkey_generate2()’ with DSA option
     and the ‘GNUTLS_PRIVKEY_FLAG_PROVABLE’ flag set.  These can the be
     imported with ‘gnutls_dh_params_import_dsa()’ .

It is no longer recommended for applications to generate
     parameters.  See the "Parameter generation" section in the manual.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

gnutls_dh_params_import_dsa
---------------------------

-- Function: int gnutls_dh_params_import_dsa (gnutls_dh_params_t
          DH_PARAMS, gnutls_x509_privkey_t KEY)
     DH_PARAMS: The parameters

KEY: holds a DSA private key

This function will import the prime and generator of the DSA key
     for use in the Diffie-Hellman key exchange.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

gnutls_dh_params_import_pkcs3
-----------------------------

-- Function: int gnutls_dh_params_import_pkcs3 (gnutls_dh_params_t
          PARAMS, const gnutls_datum_t * PKCS3_PARAMS,
          gnutls_x509_crt_fmt_t FORMAT)
     PARAMS: The parameters

PKCS3_PARAMS: should contain a PKCS3 DHParams structure PEM or DER
     encoded

FORMAT: the format of params.  PEM or DER.

This function will extract the DHParams found in a PKCS3 formatted
     structure.  This is the format generated by "openssl dhparam" tool.

If the structure is PEM encoded, it should have a header of "BEGIN
     DH PARAMETERS".

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

gnutls_dh_params_import_raw
---------------------------

-- Function: int gnutls_dh_params_import_raw (gnutls_dh_params_t
          DH_PARAMS, const gnutls_datum_t * PRIME, const gnutls_datum_t
          * GENERATOR)
     DH_PARAMS: The parameters

PRIME: holds the new prime

GENERATOR: holds the new generator

This function will replace the pair of prime and generator for use
     in the Diffie-Hellman key exchange.  The new parameters should be
     stored in the appropriate gnutls_datum.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

gnutls_dh_params_import_raw2
----------------------------

-- Function: int gnutls_dh_params_import_raw2 (gnutls_dh_params_t
          DH_PARAMS, const gnutls_datum_t * PRIME, const gnutls_datum_t
          * GENERATOR, unsigned KEY_BITS)
     DH_PARAMS: The parameters

PRIME: holds the new prime

GENERATOR: holds the new generator

KEY_BITS: the private key bits (set to zero when unknown)

This function will replace the pair of prime and generator for use
     in the Diffie-Hellman key exchange.  The new parameters should be
     stored in the appropriate gnutls_datum.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

gnutls_dh_params_import_raw3
----------------------------

-- Function: int gnutls_dh_params_import_raw3 (gnutls_dh_params_t
          DH_PARAMS, const gnutls_datum_t * PRIME, const gnutls_datum_t
          * Q, const gnutls_datum_t * GENERATOR)
     DH_PARAMS: The parameters

PRIME: holds the new prime

Q: holds the subgroup if available, otherwise NULL

GENERATOR: holds the new generator

This function will replace the pair of prime and generator for use
     in the Diffie-Hellman key exchange.  The new parameters should be
     stored in the appropriate gnutls_datum.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

gnutls_dh_params_init
---------------------

-- Function: int gnutls_dh_params_init (gnutls_dh_params_t * DH_PARAMS)
     DH_PARAMS: The parameters

This function will initialize the DH parameters type.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

gnutls_dh_set_prime_bits
------------------------

-- Function: void gnutls_dh_set_prime_bits (gnutls_session_t SESSION,
          unsigned int BITS)
     SESSION: is a ‘gnutls_session_t’ type.

BITS: is the number of bits

This function sets the number of bits, for use in a Diffie-Hellman
     key exchange.  This is used both in DH ephemeral and DH anonymous
     cipher suites.  This will set the minimum size of the prime that
     will be used for the handshake.

In the client side it sets the minimum accepted number of bits.  If
     a server sends a prime with less bits than that
     ‘GNUTLS_E_DH_PRIME_UNACCEPTABLE’ will be returned by the handshake.

Note that this function will warn via the audit log for value that
     are believed to be weak.

The function has no effect in server side.

Note that since 3.1.7 this function is deprecated.  The minimum
     number of bits is set by the priority string level.  Also this
     function must be called after ‘gnutls_priority_set_direct()’ or the
     set value may be overridden by the selected priority options.

gnutls_digest_get_id
--------------------

-- Function: gnutls_digest_algorithm_t gnutls_digest_get_id (const char
          * NAME)
     NAME: is a digest algorithm name

Convert a string to a ‘gnutls_digest_algorithm_t’ value.  The names
     are compared in a case insensitive way.

*Returns:* a ‘gnutls_digest_algorithm_t’ id of the specified MAC
     algorithm string, or ‘GNUTLS_DIG_UNKNOWN’ on failure.

gnutls_digest_get_name
----------------------

-- Function: const char * gnutls_digest_get_name
          (gnutls_digest_algorithm_t ALGORITHM)
     ALGORITHM: is a digest algorithm

Convert a ‘gnutls_digest_algorithm_t’ value to a string.

*Returns:* a string that contains the name of the specified digest
     algorithm, or ‘NULL’ .

gnutls_digest_get_oid
---------------------

-- Function: const char * gnutls_digest_get_oid
          (gnutls_digest_algorithm_t ALGORITHM)
     ALGORITHM: is a digest algorithm

Convert a ‘gnutls_digest_algorithm_t’ value to its object
     identifier.

*Returns:* a string that contains the object identifier of the
     specified digest algorithm, or ‘NULL’ .

*Since:* 3.4.3

gnutls_digest_list
------------------

-- Function: const gnutls_digest_algorithm_t * gnutls_digest_list (
          VOID)

Get a list of hash (digest) algorithms supported by GnuTLS.

This function is not thread safe.

*Returns:* Return a (0)-terminated list of
     ‘gnutls_digest_algorithm_t’ integers indicating the available
     digests.

gnutls_digest_set_secure
------------------------

-- Function: int gnutls_digest_set_secure (gnutls_digest_algorithm_t
          DIG, unsigned int SECURE)
     DIG: is a digest algorithm

SECURE: whether to mark the digest algorithm secure

Modify the previous system wide setting that marked ‘dig’ as secure
     or insecure.  This only has effect when the algorithm is enabled
     through the allowlisting mode in the configuration file, or when
     the setting is modified with a prior call to this function.

*Since:* 3.7.3

gnutls_early_cipher_get
-----------------------

-- Function: gnutls_cipher_algorithm_t gnutls_early_cipher_get
          (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Get the cipher algorithm used for encrypting early data.

*Returns:* the cipher used for early data, a
     ‘gnutls_cipher_algorithm_t’ type.

*Since:* 3.7.2

gnutls_early_prf_hash_get
-------------------------

-- Function: gnutls_digest_algorithm_t gnutls_early_prf_hash_get (const
          gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Get the hash algorithm used as a PRF to derive keys for encrypting
     early data in TLS 1.3.

*Returns:* the hash algorithm used for early data, a
     ‘gnutls_digest_algorithm_t’ value.

*Since:* 3.7.2

gnutls_ecc_curve_get
--------------------

-- Function: gnutls_ecc_curve_t gnutls_ecc_curve_get (gnutls_session_t
          SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Returns the currently used elliptic curve for key exchange.  Only
     valid when using an elliptic curve ciphersuite.

*Returns:* the currently used curve, a ‘gnutls_ecc_curve_t’ type.

*Since:* 3.0

gnutls_ecc_curve_get_id
-----------------------

-- Function: gnutls_ecc_curve_t gnutls_ecc_curve_get_id (const char *
          NAME)
     NAME: is a curve name

The names are compared in a case insensitive way.

*Returns:* return a ‘gnutls_ecc_curve_t’ value corresponding to the
     specified curve, or ‘GNUTLS_ECC_CURVE_INVALID’ on error.

*Since:* 3.4.3

gnutls_ecc_curve_get_name
-------------------------

-- Function: const char * gnutls_ecc_curve_get_name (gnutls_ecc_curve_t
          CURVE)
     CURVE: is an ECC curve

Convert a ‘gnutls_ecc_curve_t’ value to a string.

*Returns:* a string that contains the name of the specified curve
     or ‘NULL’ .

*Since:* 3.0

gnutls_ecc_curve_get_oid
------------------------

-- Function: const char * gnutls_ecc_curve_get_oid (gnutls_ecc_curve_t
          CURVE)
     CURVE: is an ECC curve

Convert a ‘gnutls_ecc_curve_t’ value to its object identifier.

*Returns:* a string that contains the OID of the specified curve or
     ‘NULL’ .

*Since:* 3.4.3

gnutls_ecc_curve_get_pk
-----------------------

-- Function: gnutls_pk_algorithm_t gnutls_ecc_curve_get_pk
          (gnutls_ecc_curve_t CURVE)
     CURVE: is an ECC curve

*Returns:* the public key algorithm associated with the named curve
     or ‘GNUTLS_PK_UNKNOWN’ .

*Since:* 3.5.0

gnutls_ecc_curve_get_size
-------------------------

-- Function: int gnutls_ecc_curve_get_size (gnutls_ecc_curve_t CURVE)
     CURVE: is an ECC curve

*Returns:* the size in bytes of the curve or 0 on failure.

*Since:* 3.0

gnutls_ecc_curve_list
---------------------

-- Function: const gnutls_ecc_curve_t * gnutls_ecc_curve_list ( VOID)

Get the list of supported elliptic curves.

This function is not thread safe.

*Returns:* Return a (0)-terminated list of ‘gnutls_ecc_curve_t’
     integers indicating the available curves.

gnutls_ecc_curve_set_enabled
----------------------------

-- Function: int gnutls_ecc_curve_set_enabled (gnutls_ecc_curve_t
          CURVE, unsigned int ENABLED)
     CURVE: is an ECC curve

ENABLED: whether to enable the curve

Modify the previous system wide setting that marked ‘curve’ as
     enabled or disabled.  Calling this function is allowed only if
     allowlisting mode is set in the configuration file, and only if the
     system-wide TLS priority string has not been initialized yet.  The
     intended usage is to provide applications with a way to expressly
     deviate from the distribution or site defaults inherited from the
     configuration file.  The modification is composable with further
     modifications performed through the priority string mechanism.

This function is not thread-safe and is intended to be called in
     the main thread at the beginning of the process execution.

*Returns:* 0 on success or negative error code otherwise.

*Since:* 3.7.3

gnutls_error_is_fatal
---------------------

-- Function: int gnutls_error_is_fatal (int ERROR)
     ERROR: is a GnuTLS error code, a negative error code

If a GnuTLS function returns a negative error code you may feed
     that value to this function to see if the error condition is fatal
     to a TLS session (i.e., must be terminated).

Note that you may also want to check the error code manually, since
     some non-fatal errors to the protocol (such as a warning alert or a
     rehandshake request) may be fatal for your program.

This function is only useful if you are dealing with errors from
     functions that relate to a TLS session (e.g., record layer or
     handshake layer handling functions).

*Returns:* Non-zero value on fatal errors or zero on non-fatal.

gnutls_error_to_alert
---------------------

-- Function: int gnutls_error_to_alert (int ERR, int * LEVEL)
     ERR: is a negative integer

LEVEL: the alert level will be stored there

If there is no mapping to a valid alert the alert to indicate
     internal error (‘GNUTLS_A_INTERNAL_ERROR’ ) is returned.

*Returns:* the alert code to use for a particular error code.

gnutls_est_record_overhead_size
-------------------------------

-- Function: size_t gnutls_est_record_overhead_size (gnutls_protocol_t
          VERSION, gnutls_cipher_algorithm_t CIPHER,
          gnutls_mac_algorithm_t MAC, gnutls_compression_method_t COMP,
          unsigned int FLAGS)
     VERSION: is a ‘gnutls_protocol_t’ value

CIPHER: is a ‘gnutls_cipher_algorithm_t’ value

MAC: is a ‘gnutls_mac_algorithm_t’ value

COMP: is a ‘gnutls_compression_method_t’ value (ignored)

FLAGS: must be zero

This function will return the set size in bytes of the overhead due
     to TLS (or DTLS) per record.

Note that this function may provide inaccurate values when TLS
     extensions that modify the record format are negotiated.  In these
     cases a more accurate value can be obtained using
     ‘gnutls_record_overhead_size()’ after a completed handshake.

*Since:* 3.2.2

gnutls_ext_get_current_msg
--------------------------

-- Function: unsigned gnutls_ext_get_current_msg (gnutls_session_t
          SESSION)
     SESSION: a ‘gnutls_session_t’ opaque pointer

This function allows an extension handler to obtain the message
     this extension is being called from.  The returned value is a
     single entry of the ‘gnutls_ext_flags_t’ enumeration.  That is, if
     an extension was registered with the ‘GNUTLS_EXT_FLAG_HRR’ and
     ‘GNUTLS_EXT_FLAG_EE’ flags, the value when called during parsing of
     the encrypted extensions message will be ‘GNUTLS_EXT_FLAG_EE’ .

If not called under an extension handler, its value is undefined.

*Since:* 3.6.3

gnutls_ext_get_data
-------------------

-- Function: int gnutls_ext_get_data (gnutls_session_t SESSION,
          unsigned TLS_ID, gnutls_ext_priv_data_t * DATA)
     SESSION: a ‘gnutls_session_t’ opaque pointer

TLS_ID: the numeric id of the extension

DATA: a pointer to the private data to retrieve

This function retrieves any data previously stored with
     ‘gnutls_ext_set_data()’ .

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, otherwise a negative
     error code.

*Since:* 3.4.0

gnutls_ext_get_name
-------------------

-- Function: const char * gnutls_ext_get_name (unsigned int EXT)
     EXT: is a TLS extension numeric ID

Convert a TLS extension numeric ID to a printable string.

*Returns:* a pointer to a string that contains the name of the
     specified cipher, or ‘NULL’ .

gnutls_ext_get_name2
--------------------

-- Function: const char * gnutls_ext_get_name2 (gnutls_session_t
          SESSION, unsigned int TLS_ID, gnutls_ext_parse_type_t
          PARSE_POINT)
     SESSION: a ‘gnutls_session_t’ opaque pointer

TLS_ID: is a TLS extension numeric ID

PARSE_POINT: the parse type of the extension

Convert a TLS extension numeric ID to a printable string.

*Returns:* a pointer to a string that contains the name of the
     specified cipher, or ‘NULL’ .

gnutls_ext_raw_parse
--------------------

-- Function: int gnutls_ext_raw_parse (void * CTX,
          gnutls_ext_raw_process_func CB, const gnutls_datum_t * DATA,
          unsigned int FLAGS)
     CTX: a pointer to pass to callback function

CB: callback function to process each extension found

DATA: TLS extension data

FLAGS: should be zero or ‘GNUTLS_EXT_RAW_FLAG_TLS_CLIENT_HELLO’ or
     ‘GNUTLS_EXT_RAW_FLAG_DTLS_CLIENT_HELLO’

This function iterates through the TLS extensions as passed in
     ‘data’ , passing the individual extension data to callback.  The
     ‘data’ must conform to Extension extensions<0..2^16-1> format.

If flags is ‘GNUTLS_EXT_RAW_TLS_FLAG_CLIENT_HELLO’ then this
     function will parse the extension data from the position, as if the
     packet in ‘data’ is a client hello (without record or handshake
     headers) - as provided by ‘gnutls_handshake_set_hook_function()’ .

The return value of the callback will be propagated.

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, or an error code.  On
     unknown flags it returns ‘GNUTLS_E_INVALID_REQUEST’ .

*Since:* 3.6.3

gnutls_ext_register
-------------------

-- Function: int gnutls_ext_register (const char * NAME, int ID,
          gnutls_ext_parse_type_t PARSE_POINT, gnutls_ext_recv_func
          RECV_FUNC, gnutls_ext_send_func SEND_FUNC,
          gnutls_ext_deinit_data_func DEINIT_FUNC, gnutls_ext_pack_func
          PACK_FUNC, gnutls_ext_unpack_func UNPACK_FUNC)
     NAME: the name of the extension to register

ID: the numeric TLS id of the extension

PARSE_POINT: the parse type of the extension (see
     gnutls_ext_parse_type_t)

RECV_FUNC: a function to receive the data

SEND_FUNC: a function to send the data

DEINIT_FUNC: a function deinitialize any private data

PACK_FUNC: a function which serializes the extension's private data
     (used on session packing for resumption)

UNPACK_FUNC: a function which will deserialize the extension's
     private data

This function will register a new extension type.  The extension
     will remain registered until ‘gnutls_global_deinit()’ is called.
     If the extension type is already registered then
     ‘GNUTLS_E_ALREADY_REGISTERED’ will be returned.

Each registered extension can store temporary data into the
     gnutls_session_t structure using ‘gnutls_ext_set_data()’ , and they
     can be retrieved using ‘gnutls_ext_get_data()’ .

Any extensions registered with this function are valid for the
     client and TLS1.2 server hello (or encrypted extensions for
     TLS1.3).

This function is not thread safe.

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, otherwise a negative
     error code.

*Since:* 3.4.0

gnutls_ext_set_data
-------------------

-- Function: void gnutls_ext_set_data (gnutls_session_t SESSION,
          unsigned TLS_ID, gnutls_ext_priv_data_t DATA)
     SESSION: a ‘gnutls_session_t’ opaque pointer

TLS_ID: the numeric id of the extension

DATA: the private data to set

This function allows an extension handler to store data in the
     current session and retrieve them later on.  The set data will be
     deallocated using the gnutls_ext_deinit_data_func.

*Since:* 3.4.0

gnutls_fingerprint
------------------

-- Function: int gnutls_fingerprint (gnutls_digest_algorithm_t ALGO,
          const gnutls_datum_t * DATA, void * RESULT, size_t *
          RESULT_SIZE)
     ALGO: is a digest algorithm

DATA: is the data

RESULT: is the place where the result will be copied (may be null).

RESULT_SIZE: should hold the size of the result.  The actual size
     of the returned result will also be copied there.

This function will calculate a fingerprint (actually a hash), of
     the given data.  The result is not printable data.  You should
     convert it to hex, or to something else printable.

This is the usual way to calculate a fingerprint of an X.509 DER
     encoded certificate.  Note however that the fingerprint of an
     OpenPGP certificate is not just a hash and cannot be calculated
     with this function.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise an error code is returned.

gnutls_fips140_context_deinit
-----------------------------

-- Function: void gnutls_fips140_context_deinit
          (gnutls_fips140_context_t CONTEXT)
     CONTEXT: a ‘gnutls_fips140_context_t’

Uninitialize and release the FIPS context ‘context’ .

*Since:* 3.7.3

gnutls_fips140_context_init
---------------------------

-- Function: int gnutls_fips140_context_init (gnutls_fips140_context_t
          * CONTEXT)
     CONTEXT: location to store ‘gnutls_fips140_context_t’

Create and initialize the FIPS context object.

*Returns:* 0 upon success, a negative error code otherwise

*Since:* 3.7.3

gnutls_fips140_get_operation_state
----------------------------------

-- Function: gnutls_fips140_operation_state_t
          gnutls_fips140_get_operation_state (gnutls_fips140_context_t
          CONTEXT)
     CONTEXT: a ‘gnutls_fips140_context_t’

Get the previous operation state of ‘context’ in terms of FIPS.

*Returns:* a ‘gnutls_fips140_operation_state_t’

*Since:* 3.7.3

gnutls_fips140_mode_enabled
---------------------------

-- Function: unsigned gnutls_fips140_mode_enabled ( VOID)

Checks whether this library is in FIPS140 mode.  The returned value
     corresponds to the library mode as set with
     ‘gnutls_fips140_set_mode()’ .

If ‘gnutls_fips140_set_mode()’ was called with
     ‘GNUTLS_FIPS140_SET_MODE_THREAD’ then this function will return the
     current thread's FIPS140 mode, otherwise the global value is
     returned.

*Returns:* return non-zero if true or zero if false.

*Since:* 3.3.0

gnutls_fips140_pop_context
--------------------------

-- Function: int gnutls_fips140_pop_context ( VOID)

Dissociate the FIPS context currently active on the current thread,
     reverting to the previously active context.  If a cryptographic
     operation is ongoing in the current thread, e.g.,
     ‘gnutls_aead_cipher_init()’ is called but
     ‘gnutls_aead_cipher_deinit()’ is not yet called, it returns an
     error ‘GNUTLS_E_INVALID_REQUEST’ .

This function is no-op if FIPS140 is not compiled in nor enabled at
     run-time.

*Returns:* 0 upon success, a negative error code otherwise

*Since:* 3.7.3

gnutls_fips140_push_context
---------------------------

-- Function: int gnutls_fips140_push_context (gnutls_fips140_context_t
          CONTEXT)
     CONTEXT: a ‘gnutls_fips140_context_t’

Associate the FIPS ‘context’ to the current thread, diverting the
     currently active context.  If a cryptographic operation is ongoing
     in the current thread, e.g., ‘gnutls_aead_cipher_init()’ is called
     but ‘gnutls_aead_cipher_deinit()’ is not yet called, it returns an
     error ‘GNUTLS_E_INVALID_REQUEST’ .

The operation state of ‘context’ will be reset to
     ‘GNUTLS_FIPS140_OP_INITIAL’ .

This function is no-op if FIPS140 is not compiled in nor enabled at
     run-time.

*Returns:* 0 upon success, a negative error code otherwise

*Since:* 3.7.3

gnutls_fips140_run_self_tests
-----------------------------

-- Function: int gnutls_fips140_run_self_tests ( VOID)

Manually perform the second round of the FIPS140 self-tests,
     including:

- Known answer tests (KAT) for the selected set of symmetric
     cipher, MAC, public key, KDF, and DRBG - Library integrity checks

Upon failure with FIPS140 mode enabled, it makes the library
     unusable.  This function is not thread-safe.

*Returns:* 0 upon success, a negative error code otherwise

*Since:* 3.7.7

gnutls_fips140_set_mode
-----------------------

-- Function: void gnutls_fips140_set_mode (gnutls_fips_mode_t MODE,
          unsigned FLAGS)
     MODE: the FIPS140-2 mode to switch to

FLAGS: should be zero or ‘GNUTLS_FIPS140_SET_MODE_THREAD’

That function is not thread-safe when changing the mode with no
     flags (globally), and should be called prior to creating any
     threads.  Its behavior with no flags after threads are created is
     undefined.

When the flag ‘GNUTLS_FIPS140_SET_MODE_THREAD’ is specified then
     this call will change the FIPS140-2 mode for this particular thread
     and not for the whole process.  That way an application can utilize
     this function to set and reset mode for specific operations.

This function never fails but will be a no-op if used when the
     library is not in FIPS140-2 mode.  When asked to switch to unknown
     values for ‘mode’ or to ‘GNUTLS_FIPS140_SELFTESTS’ mode, the
     library switches to ‘GNUTLS_FIPS140_STRICT’ mode.

*Since:* 3.6.2

gnutls_get_library_config
-------------------------

-- Function: const gnutls_library_config_st * gnutls_get_library_config
          ( VOID)

Returns the library configuration as key value pairs.  Currently
     defined keys are:

- fips-module-name: the name of the FIPS140 module

- fips-module-version: the version of the FIPS140 module

- libgnutls-soname: the SONAME of the library itself

- libnettle-soname: the library SONAME of linked libnettle

- libhogweed-soname: the library SONAME of linked libhogweed

- libgmp-soname: the library SONAME of linked libgmp

- hardware-features: enabled hardware support features

- tls-features: enabled TLS protocol features

*Returns:* a NUL-terminated ‘gnutls_library_config_st’ array

*Since:* 3.7.3

gnutls_get_system_config_file
-----------------------------

-- Function: const char * gnutls_get_system_config_file ( VOID)

Returns the filename of the system wide configuration file to be
     loaded by the library.

*Returns:* a constant pointer to the config file path

*Since:* 3.6.9

gnutls_global_deinit
--------------------

-- Function: void gnutls_global_deinit ( VOID)

This function deinitializes the global data, that were initialized
     using ‘gnutls_global_init()’ .

Since GnuTLS 3.3.0 this function is no longer necessary to be
     explicitly called.  GnuTLS will automatically deinitialize on
     library destructor.  See ‘gnutls_global_init()’ for disabling the
     implicit initialization/deinitialization.

gnutls_global_init
------------------

-- Function: int gnutls_global_init ( VOID)

Since GnuTLS 3.3.0 this function is no longer necessary to be
     explicitly called.  To disable the implicit call (in a library
     constructor) of this function set the environment variable
     ‘GNUTLS_NO_IMPLICIT_INIT’ to 1.

This function performs any required precalculations, detects the
     supported CPU capabilities and initializes the underlying
     cryptographic backend.  In order to free any resources taken by
     this call you should ‘gnutls_global_deinit()’ when gnutls usage is
     no longer needed.

This function increments a global counter, so that
     ‘gnutls_global_deinit()’ only releases resources when it has been
     called as many times as ‘gnutls_global_init()’ .  This is useful
     when GnuTLS is used by more than one library in an application.
     This function can be called many times, but will only do something
     the first time.  It is thread safe since GnuTLS 3.3.0.

A subsequent call of this function if the initial has failed will
     return the same error code.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

gnutls_global_set_audit_log_function
------------------------------------

-- Function: void gnutls_global_set_audit_log_function
          (gnutls_audit_log_func LOG_FUNC)
     LOG_FUNC: it is the audit log function

‘gnutls_audit_log_func’ is of the form, void
     (*gnutls_audit_log_func)( gnutls_session_t, const char*);

*Since:* 3.0

gnutls_global_set_log_function
------------------------------

-- Function: void gnutls_global_set_log_function (gnutls_log_func
          LOG_FUNC)
     LOG_FUNC: it's a log function

This is the function where you set the logging function gnutls is
     going to use.  This function only accepts a character array.
     Normally you may not use this function since it is only used for
     debugging purposes.

‘gnutls_log_func’ is of the form, void (*gnutls_log_func)( int
     level, const char*);

gnutls_global_set_log_level
---------------------------

-- Function: void gnutls_global_set_log_level (int LEVEL)
     LEVEL: it's an integer from 0 to 99.

This is the function that allows you to set the log level.  The
     level is an integer between 0 and 9.  Higher values mean more
     verbosity.  The default value is 0.  Larger values should only be
     used with care, since they may reveal sensitive information.

Use a log level over 10 to enable all debugging options.

gnutls_global_set_mutex
-----------------------

-- Function: void gnutls_global_set_mutex (mutex_init_func INIT,
          mutex_deinit_func DEINIT, mutex_lock_func LOCK,
          mutex_unlock_func UNLOCK)
     INIT: mutex initialization function

DEINIT: mutex deinitialization function

LOCK: mutex locking function

UNLOCK: mutex unlocking function

With this function you are allowed to override the default mutex
     locks used in some parts of gnutls and dependent libraries.  This
     function should be used if you have complete control of your
     program and libraries.  Do not call this function from a library,
     or preferably from any application unless really needed to.  GnuTLS
     will use the appropriate locks for the running system.

This function must be called prior to any other GnuTLS function;
     otherwise the behavior is undefined.

*Deprecated:* This function is discouraged on GnuTLS 3.7.3 or
     later.

*Since:* 2.12.0

gnutls_global_set_time_function
-------------------------------

-- Function: void gnutls_global_set_time_function (gnutls_time_func
          TIME_FUNC)
     TIME_FUNC: it's the system time function, a ‘gnutls_time_func()’
     callback.

This is the function where you can override the default system time
     function.  The application provided function should behave the same
     as the standard function.

*Since:* 2.12.0

gnutls_gost_paramset_get_name
-----------------------------

-- Function: const char * gnutls_gost_paramset_get_name
          (gnutls_gost_paramset_t PARAM)
     PARAM: is a GOST 28147 param set

Convert a ‘gnutls_gost_paramset_t’ value to a string.

*Returns:* a string that contains the name of the specified GOST
     param set, or ‘NULL’ .

*Since:* 3.6.3

gnutls_gost_paramset_get_oid
----------------------------

-- Function: const char * gnutls_gost_paramset_get_oid
          (gnutls_gost_paramset_t PARAM)
     PARAM: is a GOST 28147 param set

Convert a ‘gnutls_gost_paramset_t’ value to its object identifier.

*Returns:* a string that contains the object identifier of the
     specified GOST param set, or ‘NULL’ .

*Since:* 3.6.3

gnutls_group_get
----------------

-- Function: gnutls_group_t gnutls_group_get (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Returns the currently used group for key exchange.  Only valid when
     using an elliptic curve or DH ciphersuite.

*Returns:* the currently used group, a ‘gnutls_group_t’ type.

*Since:* 3.6.0

gnutls_group_get_id
-------------------

-- Function: gnutls_group_t gnutls_group_get_id (const char * NAME)
     NAME: is a group name

The names are compared in a case insensitive way.

*Returns:* return a ‘gnutls_group_t’ value corresponding to the
     specified group, or ‘GNUTLS_GROUP_INVALID’ on error.

*Since:* 3.6.0

gnutls_group_get_name
---------------------

-- Function: const char * gnutls_group_get_name (gnutls_group_t GROUP)
     GROUP: is an element from ‘gnutls_group_t’

Convert a ‘gnutls_group_t’ value to a string.

*Returns:* a string that contains the name of the specified group
     or ‘NULL’ .

*Since:* 3.6.0

gnutls_group_list
-----------------

-- Function: const gnutls_group_t * gnutls_group_list ( VOID)

Get the list of supported elliptic curves.

This function is not thread safe.

*Returns:* Return a (0)-terminated list of ‘gnutls_group_t’
     integers indicating the available groups.

*Since:* 3.6.0

gnutls_handshake
----------------

-- Function: int gnutls_handshake (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

This function performs the handshake of the TLS/SSL protocol, and
     initializes the TLS session parameters.

*Returns:* ‘GNUTLS_E_SUCCESS’ on a successful handshake, otherwise
     a negative error code.

gnutls_handshake_description_get_name
-------------------------------------

-- Function: const char * gnutls_handshake_description_get_name
          (gnutls_handshake_description_t TYPE)
     TYPE: is a handshake message description

Convert a ‘gnutls_handshake_description_t’ value to a string.

*Returns:* a string that contains the name of the specified
     handshake message or ‘NULL’ .

gnutls_handshake_get_last_in
----------------------------

-- Function: gnutls_handshake_description_t
          gnutls_handshake_get_last_in (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

This function is only useful to check where the last performed
     handshake failed.  If the previous handshake succeed or was not
     performed at all then no meaningful value will be returned.

Check ‘gnutls_handshake_description_t’ in gnutls.h for the
     available handshake descriptions.

*Returns:* the last handshake message type received, a
     ‘gnutls_handshake_description_t’ .

gnutls_handshake_get_last_out
-----------------------------

-- Function: gnutls_handshake_description_t
          gnutls_handshake_get_last_out (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

This function is only useful to check where the last performed
     handshake failed.  If the previous handshake succeed or was not
     performed at all then no meaningful value will be returned.

Check ‘gnutls_handshake_description_t’ in gnutls.h for the
     available handshake descriptions.

*Returns:* the last handshake message type sent, a
     ‘gnutls_handshake_description_t’ .

gnutls_handshake_set_hook_function
----------------------------------

HTYPE: the ‘gnutls_handshake_description_t’ of the message to hook
     at

WHEN: ‘GNUTLS_HOOK_’ * depending on when the hook function should
     be called

FUNC: is the function to be called

This callback must return 0 on success or a gnutls error code to
     terminate the handshake.

To hook at all handshake messages use an ‘htype’ of
     ‘GNUTLS_HANDSHAKE_ANY’ .

gnutls_handshake_set_max_packet_length
--------------------------------------

-- Function: void gnutls_handshake_set_max_packet_length
          (gnutls_session_t SESSION, size_t MAX)
     SESSION: is a ‘gnutls_session_t’ type.

MAX: is the maximum number.

This function will set the maximum size of all handshake messages.
     Handshakes over this size are rejected with
     ‘GNUTLS_E_HANDSHAKE_TOO_LARGE’ error code.  The default value is
     128kb which is typically large enough.  Set this to 0 if you do not
     want to set an upper limit.

The reason for restricting the handshake message sizes are to limit
     Denial of Service attacks.

Note that the maximum handshake size was increased to 128kb from
     48kb in GnuTLS 3.5.5.

gnutls_handshake_set_post_client_hello_function
-----------------------------------------------

-- Function: void gnutls_handshake_set_post_client_hello_function
          (gnutls_session_t SESSION, gnutls_handshake_simple_hook_func
          FUNC)
     SESSION: is a ‘gnutls_session_t’ type.

FUNC: is the function to be called

This function will set a callback to be called after the client
     hello has been received (callback valid in server side only).  This
     allows the server to adjust settings based on received extensions.

Those settings could be ciphersuites, requesting certificate, or
     anything else except for version negotiation (this is done before
     the hello message is parsed).

This callback must return 0 on success or a gnutls error code to
     terminate the handshake.

Since GnuTLS 3.3.5 the callback is allowed to return
     ‘GNUTLS_E_AGAIN’ or ‘GNUTLS_E_INTERRUPTED’ to put the handshake on
     hold.  In that case ‘gnutls_handshake()’ will return
     ‘GNUTLS_E_INTERRUPTED’ and can be resumed when needed.

gnutls_handshake_set_private_extensions
---------------------------------------

-- Function: void gnutls_handshake_set_private_extensions
          (gnutls_session_t SESSION, int ALLOW)
     SESSION: is a ‘gnutls_session_t’ type.

ALLOW: is an integer (0 or 1)

This function will enable or disable the use of private cipher
     suites (the ones that start with 0xFF). By default or if ‘allow’ is
     0 then these cipher suites will not be advertised nor used.

Currently GnuTLS does not include such cipher-suites or compression
     algorithms.

Enabling the private ciphersuites when talking to other than gnutls
     servers and clients may cause interoperability problems.

gnutls_handshake_set_random
---------------------------

-- Function: int gnutls_handshake_set_random (gnutls_session_t SESSION,
          const gnutls_datum_t * RANDOM)
     SESSION: is a ‘gnutls_session_t’ type.

RANDOM: a random value of 32-bytes

This function will explicitly set the server or client hello random
     value in the subsequent TLS handshake.  The random value should be
     a 32-byte value.

Note that this function should not normally be used as gnutls will
     select automatically a random value for the handshake.

This function should not be used when resuming a session.

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, or an error code.

Since 3.1.9

gnutls_handshake_set_read_function
----------------------------------

-- Function: void gnutls_handshake_set_read_function (gnutls_session_t
          SESSION, gnutls_handshake_read_func FUNC)
     SESSION: is ‘gnutls_session_t’ type

FUNC: is the function to be called

This function will set a callback to be called when a handshake
     message is being sent.

*Since:* 3.7.0

gnutls_handshake_set_secret_function
------------------------------------

-- Function: void gnutls_handshake_set_secret_function
          (gnutls_session_t SESSION, gnutls_handshake_secret_func FUNC)
     SESSION: is a ‘gnutls_session_t’ type.

FUNC: the secret func

This function will set a callback to be called when a new traffic
     secret is installed.

*Since:* 3.7.0

gnutls_handshake_set_timeout
----------------------------

-- Function: void gnutls_handshake_set_timeout (gnutls_session_t
          SESSION, unsigned int MS)
     SESSION: is a ‘gnutls_session_t’ type.

MS: is a timeout value in milliseconds

This function requires to set a pull timeout callback.  See
     ‘gnutls_transport_set_pull_timeout_function()’ .

*Since:* 3.1.0

gnutls_handshake_write
----------------------

-- Function: int gnutls_handshake_write (gnutls_session_t SESSION,
          gnutls_record_encryption_level_t LEVEL, const void * DATA,
          size_t DATA_SIZE)
     SESSION: is a ‘gnutls_session_t’ type.

LEVEL: the current encryption level for reading a handshake message

DATA: the (const) handshake data to be processed

DATA_SIZE: the size of data

This function processes a handshake message in the encryption level
     specified with ‘level’ .  Prior to calling this function, a
     handshake read callback must be set on ‘session’ .  Use
     ‘gnutls_handshake_set_read_function()’ to do this.

*Since:* 3.7.0

gnutls_heartbeat_allowed
------------------------

-- Function: unsigned gnutls_heartbeat_allowed (gnutls_session_t
          SESSION, unsigned int TYPE)
     SESSION: is a ‘gnutls_session_t’ type.

TYPE: one of ‘GNUTLS_HB_LOCAL_ALLOWED_TO_SEND’ and
     ‘GNUTLS_HB_PEER_ALLOWED_TO_SEND’

This function will check whether heartbeats are allowed to be sent
     or received in this session.

*Returns:* Non zero if heartbeats are allowed.

*Since:* 3.1.2

gnutls_heartbeat_enable
-----------------------

-- Function: void gnutls_heartbeat_enable (gnutls_session_t SESSION,
          unsigned int TYPE)
     SESSION: is a ‘gnutls_session_t’ type.

TYPE: one of the GNUTLS_HB_* flags

If this function is called with the
     ‘GNUTLS_HB_PEER_ALLOWED_TO_SEND’ ‘type’ , GnuTLS will allow
     heartbeat messages to be received.  Moreover it also request the
     peer to accept heartbeat messages.  This function must be called
     prior to TLS handshake.

If the ‘type’ used is ‘GNUTLS_HB_LOCAL_ALLOWED_TO_SEND’ , then the
     peer will be asked to accept heartbeat messages but not send ones.

The function ‘gnutls_heartbeat_allowed()’ can be used to test
     Whether locally generated heartbeat messages can be accepted by the
     peer.

*Since:* 3.1.2

gnutls_heartbeat_get_timeout
----------------------------

-- Function: unsigned int gnutls_heartbeat_get_timeout
          (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

This function will return the milliseconds remaining for a
     retransmission of the previously sent ping message.  This function
     is useful when ping is used in non-blocking mode, to estimate when
     to call ‘gnutls_heartbeat_ping()’ if no packets have been received.

*Returns:* the remaining time in milliseconds.

*Since:* 3.1.2

gnutls_heartbeat_ping
---------------------

-- Function: int gnutls_heartbeat_ping (gnutls_session_t SESSION,
          size_t DATA_SIZE, unsigned int MAX_TRIES, unsigned int FLAGS)
     SESSION: is a ‘gnutls_session_t’ type.

DATA_SIZE: is the length of the ping payload.

MAX_TRIES: if flags is ‘GNUTLS_HEARTBEAT_WAIT’ then this sets the
     number of retransmissions.  Use zero for indefinite (until
     timeout).

FLAGS: if ‘GNUTLS_HEARTBEAT_WAIT’ then wait for pong or timeout
     instead of returning immediately.

This function sends a ping to the peer.  If the ‘flags’ is set to
     ‘GNUTLS_HEARTBEAT_WAIT’ then it waits for a reply from the peer.

Note that it is highly recommended to use this function with the
     flag ‘GNUTLS_HEARTBEAT_WAIT’ , or you need to handle
     retransmissions and timeouts manually.

The total TLS data transmitted as part of the ping message are
     given by the following formula: MAX(16, ‘data_size’
     )+‘gnutls_record_overhead_size()’ +3.

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, otherwise a negative
     error code.

*Since:* 3.1.2

gnutls_heartbeat_pong
---------------------

-- Function: int gnutls_heartbeat_pong (gnutls_session_t SESSION,
          unsigned int FLAGS)
     SESSION: is a ‘gnutls_session_t’ type.

FLAGS: should be zero

This function replies to a ping by sending a pong to the peer.

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, otherwise a negative
     error code.

*Since:* 3.1.2

gnutls_heartbeat_set_timeouts
-----------------------------

-- Function: void gnutls_heartbeat_set_timeouts (gnutls_session_t
          SESSION, unsigned int RETRANS_TIMEOUT, unsigned int
          TOTAL_TIMEOUT)
     SESSION: is a ‘gnutls_session_t’ type.

RETRANS_TIMEOUT: The time at which a retransmission will occur in
     milliseconds

TOTAL_TIMEOUT: The time at which the connection will be aborted, in
     milliseconds.

This function will override the timeouts for the DTLS heartbeat
     protocol.  The retransmission timeout is the time after which a
     message from the peer is not received, the previous request will be
     retransmitted.  The total timeout is the time after which the
     handshake will be aborted with ‘GNUTLS_E_TIMEDOUT’ .

*Since:* 3.1.2

gnutls_hex2bin
--------------

-- Function: int gnutls_hex2bin (const char * HEX_DATA, size_t
          HEX_SIZE, void * BIN_DATA, size_t * BIN_SIZE)
     HEX_DATA: string with data in hex format

HEX_SIZE: size of hex data

BIN_DATA: output array with binary data

BIN_SIZE: when calling should hold maximum size of ‘bin_data’ , on
     return will hold actual length of ‘bin_data’ .

Convert a buffer with hex data to binary data.  This function
     unlike ‘gnutls_hex_decode()’ can parse hex data with separators
     between numbers.  That is, it ignores any non-hex characters.

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, otherwise a negative
     error code.

*Since:* 2.4.0

gnutls_hex_decode
-----------------

-- Function: int gnutls_hex_decode (const gnutls_datum_t * HEX_DATA,
          void * RESULT, size_t * RESULT_SIZE)
     HEX_DATA: contain the encoded data

RESULT: the place where decoded data will be copied

RESULT_SIZE: holds the size of the result

This function will decode the given encoded data, using the hex
     encoding used by PSK password files.

Initially ‘result_size’ must hold the maximum size available in
     ‘result’ , and on return it will contain the number of bytes
     written.

*Returns:* ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ if the buffer given is
     not long enough, ‘GNUTLS_E_PARSING_ERROR’ on invalid hex data, or 0
     on success.

gnutls_hex_decode2
------------------

-- Function: int gnutls_hex_decode2 (const gnutls_datum_t * HEX_DATA,
          gnutls_datum_t * RESULT)
     HEX_DATA: contain the encoded data

RESULT: the result in an allocated string

This function will decode the given encoded data, using the hex
     encoding used by PSK password files.

*Returns:* ‘GNUTLS_E_PARSING_ERROR’ on invalid hex data, or 0 on
     success.

gnutls_hex_encode
-----------------

-- Function: int gnutls_hex_encode (const gnutls_datum_t * DATA, char *
          RESULT, size_t * RESULT_SIZE)
     DATA: contain the raw data

RESULT: the place where hex data will be copied

RESULT_SIZE: holds the size of the result

This function will convert the given data to printable data, using
     the hex encoding, as used in the PSK password files.

Note that the size of the result includes the null terminator.

*Returns:* ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ if the buffer given is
     not long enough, or 0 on success.

gnutls_hex_encode2
------------------

-- Function: int gnutls_hex_encode2 (const gnutls_datum_t * DATA,
          gnutls_datum_t * RESULT)
     DATA: contain the raw data

RESULT: the result in an allocated string

This function will convert the given data to printable data, using
     the hex encoding, as used in the PSK password files.

Note that the size of the result does NOT include the null
     terminator.

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, otherwise a negative
     error code.

gnutls_idna_map
---------------

-- Function: int gnutls_idna_map (const char * INPUT, unsigned ILEN,
          gnutls_datum_t * OUT, unsigned FLAGS)
     INPUT: contain the UTF-8 formatted domain name

ILEN: the length of the provided string

OUT: the result in an null-terminated allocated string

FLAGS: should be zero

This function will convert the provided UTF-8 domain name, to its
     IDNA mapping in an allocated variable.  Note that depending on the
     flags the used gnutls library was compiled with, the output of this
     function may vary (i.e., may be IDNA2008, or IDNA2003).

To force IDNA2008 specify the flag ‘GNUTLS_IDNA_FORCE_2008’ .  In
     the case GnuTLS is not compiled with the necessary dependencies,
     ‘GNUTLS_E_UNIMPLEMENTED_FEATURE’ will be returned to indicate that
     gnutls is unable to perform the requested conversion.

Note also, that this function will return an empty string if an
     empty string is provided as input.

*Returns:* ‘GNUTLS_E_INVALID_UTF8_STRING’ on invalid UTF-8 data, or
     0 on success.

*Since:* 3.5.8

gnutls_idna_reverse_map
-----------------------

-- Function: int gnutls_idna_reverse_map (const char * INPUT, unsigned
          ILEN, gnutls_datum_t * OUT, unsigned FLAGS)
     INPUT: contain the ACE (IDNA) formatted domain name

ILEN: the length of the provided string

OUT: the result in an null-terminated allocated UTF-8 string

FLAGS: should be zero

This function will convert an ACE (ASCII-encoded) domain name to a
     UTF-8 domain name.

If GnuTLS is compiled without IDNA support, then this function will
     return ‘GNUTLS_E_UNIMPLEMENTED_FEATURE’ .

Note also, that this function will return an empty string if an
     empty string is provided as input.

*Returns:* A negative error code on error, or 0 on success.

*Since:* 3.5.8

gnutls_init
-----------

-- Function: int gnutls_init (gnutls_session_t * SESSION, unsigned int
          FLAGS)
     SESSION: is a pointer to a ‘gnutls_session_t’ type.

FLAGS: indicate if this session is to be used for server or client.

‘flags’ can be any combination of flags from ‘gnutls_init_flags_t’
     .

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, or an error code.

gnutls_key_generate
-------------------

-- Function: int gnutls_key_generate (gnutls_datum_t * KEY, unsigned
          int KEY_SIZE)
     KEY: is a pointer to a ‘gnutls_datum_t’ which will contain a newly
     created key

KEY_SIZE: the number of bytes of the key

Generates a random key of ‘key_size’ bytes.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned, or an
     error code.

*Since:* 3.0

gnutls_kx_get
-------------

-- Function: gnutls_kx_algorithm_t gnutls_kx_get (gnutls_session_t
          SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Get the currently used key exchange algorithm.

This function will return ‘GNUTLS_KX_ECDHE_RSA’ , or
     ‘GNUTLS_KX_DHE_RSA’ under TLS 1.3, to indicate an elliptic curve DH
     key exchange or a finite field one.  The precise group used is
     available by calling ‘gnutls_group_get()’ instead.

*Returns:* the key exchange algorithm used in the last handshake, a
     ‘gnutls_kx_algorithm_t’ value.

gnutls_kx_get_id
----------------

-- Function: gnutls_kx_algorithm_t gnutls_kx_get_id (const char * NAME)
     NAME: is a KX name

Convert a string to a ‘gnutls_kx_algorithm_t’ value.  The names are
     compared in a case insensitive way.

*Returns:* an id of the specified KX algorithm, or
     ‘GNUTLS_KX_UNKNOWN’ on error.

gnutls_kx_get_name
------------------

-- Function: const char * gnutls_kx_get_name (gnutls_kx_algorithm_t
          ALGORITHM)
     ALGORITHM: is a key exchange algorithm

Convert a ‘gnutls_kx_algorithm_t’ value to a string.

*Returns:* a pointer to a string that contains the name of the
     specified key exchange algorithm, or ‘NULL’ .

gnutls_kx_list
--------------

-- Function: const gnutls_kx_algorithm_t * gnutls_kx_list ( VOID)

Get a list of supported key exchange algorithms.

This function is not thread safe.

*Returns:* a (0)-terminated list of ‘gnutls_kx_algorithm_t’
     integers indicating the available key exchange algorithms.

gnutls_load_file
----------------

-- Function: int gnutls_load_file (const char * FILENAME,
          gnutls_datum_t * DATA)
     FILENAME: the name of the file to load

DATA: Where the file will be stored

This function will load a file into a datum.  The data are zero
     terminated but the terminating null is not included in length.  The
     returned data are allocated using ‘gnutls_malloc()’ .

Note that this function is not designed for reading sensitive
     materials, such as private keys, on practical applications.  When
     the reading fails in the middle, the partially loaded content might
     remain on memory.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise an error code is returned.

Since 3.1.0

gnutls_mac_get
--------------

-- Function: gnutls_mac_algorithm_t gnutls_mac_get (gnutls_session_t
          SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Get the currently used MAC algorithm.

*Returns:* the currently used mac algorithm, a
     ‘gnutls_mac_algorithm_t’ value.

gnutls_mac_get_id
-----------------

-- Function: gnutls_mac_algorithm_t gnutls_mac_get_id (const char *
          NAME)
     NAME: is a MAC algorithm name

Convert a string to a ‘gnutls_mac_algorithm_t’ value.  The names
     are compared in a case insensitive way.

*Returns:* a ‘gnutls_mac_algorithm_t’ id of the specified MAC
     algorithm string, or ‘GNUTLS_MAC_UNKNOWN’ on failure.

gnutls_mac_get_key_size
-----------------------

-- Function: size_t gnutls_mac_get_key_size (gnutls_mac_algorithm_t
          ALGORITHM)
     ALGORITHM: is an encryption algorithm

Returns the size of the MAC key used in TLS.

*Returns:* length (in bytes) of the given MAC key size, or 0 if the
     given MAC algorithm is invalid.

gnutls_mac_get_name
-------------------

-- Function: const char * gnutls_mac_get_name (gnutls_mac_algorithm_t
          ALGORITHM)
     ALGORITHM: is a MAC algorithm

Convert a ‘gnutls_mac_algorithm_t’ value to a string.

*Returns:* a string that contains the name of the specified MAC
     algorithm, or ‘NULL’ .

gnutls_mac_list
---------------

-- Function: const gnutls_mac_algorithm_t * gnutls_mac_list ( VOID)

Get a list of hash algorithms for use as MACs.  Note that not
     necessarily all MACs are supported in TLS cipher suites.  This
     function is not thread safe.

*Returns:* Return a (0)-terminated list of ‘gnutls_mac_algorithm_t’
     integers indicating the available MACs.

gnutls_memcmp
-------------

-- Function: int gnutls_memcmp (const void * S1, const void * S2,
          size_t N)
     S1: the first address to compare

S2: the second address to compare

N: the size of memory to compare

This function will operate similarly to ‘memcmp()’ , but will
     operate on time that depends only on the size of the string.  That
     is will not return early if the strings don't match on the first
     byte.

*Returns:* non zero on difference and zero if the buffers are
     identical.

*Since:* 3.4.0

gnutls_memset
-------------

-- Function: void gnutls_memset (void * DATA, int C, size_t SIZE)
     DATA: the memory to set

C: the constant byte to fill the memory with

SIZE: the size of memory

This function will operate similarly to ‘memset()’ , but will not
     be optimized out by the compiler.

*Since:* 3.4.0

gnutls_ocsp_status_request_enable_client
----------------------------------------

-- Function: int gnutls_ocsp_status_request_enable_client
          (gnutls_session_t SESSION, gnutls_datum_t * RESPONDER_ID,
          size_t RESPONDER_ID_SIZE, gnutls_datum_t * EXTENSIONS)
     SESSION: is a ‘gnutls_session_t’ type.

RESPONDER_ID: ignored, must be ‘NULL’

RESPONDER_ID_SIZE: ignored, must be zero

EXTENSIONS: ignored, must be ‘NULL’

This function is to be used by clients to request OCSP response
     from the server, using the "status_request" TLS extension.  Only
     OCSP status type is supported.

Previous versions of GnuTLS supported setting ‘responder_id’ and
     ‘extensions’ fields, but due to the difficult semantics of the
     parameter usage, and other issues, this support was removed since
     3.6.0 and these parameters must be set to ‘NULL’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

*Since:* 3.1.3

gnutls_ocsp_status_request_get
------------------------------

-- Function: int gnutls_ocsp_status_request_get (gnutls_session_t
          SESSION, gnutls_datum_t * RESPONSE)
     SESSION: is a ‘gnutls_session_t’ type.

RESPONSE: a ‘gnutls_datum_t’ with DER encoded OCSP response

This function returns the OCSP status response received from the
     TLS server.  The ‘response’ should be treated as constant.  If no
     OCSP response is available then
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ is returned.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

*Since:* 3.1.3

gnutls_ocsp_status_request_get2
-------------------------------

-- Function: int gnutls_ocsp_status_request_get2 (gnutls_session_t
          SESSION, unsigned IDX, gnutls_datum_t * RESPONSE)
     SESSION: is a ‘gnutls_session_t’ type.

IDX: the index of peer's certificate

RESPONSE: a ‘gnutls_datum_t’ with DER encoded OCSP response

This function returns the OCSP status response received from the
     TLS server for the certificate index provided.  The index
     corresponds to certificates as returned by
     gnutls_certificate_get_peers.  When index is zero this function
     operates identically to ‘gnutls_ocsp_status_request_get()’ .

The returned ‘response’ should be treated as constant.  If no OCSP
     response is available for the given index then
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ is returned.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

*Since:* 3.6.3

gnutls_ocsp_status_request_is_checked
-------------------------------------

-- Function: unsigned gnutls_ocsp_status_request_is_checked
          (gnutls_session_t SESSION, unsigned int FLAGS)
     SESSION: is a gnutls session

FLAGS: should be zero or ‘GNUTLS_OCSP_SR_IS_AVAIL’

When flags are zero this function returns non-zero if a valid OCSP
     status response was included in the TLS handshake.  That is, an
     OCSP status response which is not too old, superseded or marks the
     certificate as revoked.  It returns zero otherwise.

When the flag ‘GNUTLS_OCSP_SR_IS_AVAIL’ is specified, the function
     returns non-zero if an OCSP status response was included in the
     handshake even if it was invalid.  Otherwise, if no OCSP status
     response was included, it returns zero.  The
     ‘GNUTLS_OCSP_SR_IS_AVAIL’ flag was introduced in GnuTLS 3.4.0.

This is a helper function when needing to decide whether to perform
     an explicit OCSP validity check on the peer's certificate.  Should
     be called after any of gnutls_certificate_verify_peers*() are
     called.

This function is always usable on client side, but on server side
     only under TLS 1.3, which is the first version of TLS that allows
     clients to send OCSP responses.

*Returns:* Non-zero if the response was valid, or a zero if it
     wasn't sent, or sent and was invalid.

*Since:* 3.1.4

gnutls_oid_to_digest
--------------------

-- Function: gnutls_digest_algorithm_t gnutls_oid_to_digest (const char
          * OID)
     OID: is an object identifier

Converts a textual object identifier to a
     ‘gnutls_digest_algorithm_t’ value.

*Returns:* a ‘gnutls_digest_algorithm_t’ id of the specified digest
     algorithm, or ‘GNUTLS_DIG_UNKNOWN’ on failure.

*Since:* 3.4.3

gnutls_oid_to_ecc_curve
-----------------------

-- Function: gnutls_ecc_curve_t gnutls_oid_to_ecc_curve (const char *
          OID)
     OID: is a curve's OID

*Returns:* return a ‘gnutls_ecc_curve_t’ value corresponding to the
     specified OID, or ‘GNUTLS_ECC_CURVE_INVALID’ on error.

*Since:* 3.4.3

gnutls_oid_to_gost_paramset
---------------------------

-- Function: gnutls_gost_paramset_t gnutls_oid_to_gost_paramset (const
          char * OID)
     OID: is an object identifier

Converts a textual object identifier to a ‘gnutls_gost_paramset_t’
     value.

*Returns:* a ‘gnutls_gost_paramset_get_oid’ of the specified GOST
     28147 param st, or ‘GNUTLS_GOST_PARAMSET_UNKNOWN’ on failure.

*Since:* 3.6.3

gnutls_oid_to_mac
-----------------

-- Function: gnutls_mac_algorithm_t gnutls_oid_to_mac (const char *
          OID)
     OID: is an object identifier

Converts a textual object identifier typically from PKCS‘5’ values
     to a ‘gnutls_mac_algorithm_t’ value.

*Returns:* a ‘gnutls_mac_algorithm_t’ id of the specified digest
     algorithm, or ‘GNUTLS_MAC_UNKNOWN’ on failure.

*Since:* 3.5.4

gnutls_oid_to_pk
----------------

-- Function: gnutls_pk_algorithm_t gnutls_oid_to_pk (const char * OID)
     OID: is an object identifier

Converts a textual object identifier to a ‘gnutls_pk_algorithm_t’
     value.

*Returns:* a ‘gnutls_pk_algorithm_t’ id of the specified digest
     algorithm, or ‘GNUTLS_PK_UNKNOWN’ on failure.

*Since:* 3.4.3

gnutls_oid_to_sign
------------------

-- Function: gnutls_sign_algorithm_t gnutls_oid_to_sign (const char *
          OID)
     OID: is an object identifier

Converts a textual object identifier to a ‘gnutls_sign_algorithm_t’
     value.

*Returns:* a ‘gnutls_sign_algorithm_t’ id of the specified digest
     algorithm, or ‘GNUTLS_SIGN_UNKNOWN’ on failure.

*Since:* 3.4.3

gnutls_openpgp_send_cert
------------------------

-- Function: void gnutls_openpgp_send_cert (gnutls_session_t SESSION,
          gnutls_openpgp_crt_status_t STATUS)
     SESSION: is a gnutls session

STATUS: is ignored

This function is no-op.

*Returns:* ‘GNUTLS_E_UNIMPLEMENTED_FEATURE’ .

gnutls_packet_deinit
--------------------

-- Function: void gnutls_packet_deinit (gnutls_packet_t PACKET)
     PACKET: is a pointer to a ‘gnutls_packet_st’ structure.

This function will deinitialize all data associated with the
     received packet.

*Since:* 3.3.5

gnutls_packet_get
-----------------

-- Function: void gnutls_packet_get (gnutls_packet_t PACKET,
          gnutls_datum_t * DATA, unsigned char * SEQUENCE)
     PACKET: is a ‘gnutls_packet_t’ type.

DATA: will contain the data present in the ‘packet’ structure (may
     be ‘NULL’ )

SEQUENCE: the 8-bytes of the packet sequence number (may be ‘NULL’
     )

This function returns the data and sequence number associated with
     the received packet.

*Since:* 3.3.5

gnutls_pem_base64_decode
------------------------

-- Function: int gnutls_pem_base64_decode (const char * HEADER, const
          gnutls_datum_t * B64_DATA, unsigned char * RESULT, size_t *
          RESULT_SIZE)
     HEADER: A null terminated string with the PEM header (eg.
     CERTIFICATE)

B64_DATA: contain the encoded data

RESULT: the place where decoded data will be copied

RESULT_SIZE: holds the size of the result

This function will decode the given encoded data.  If the header
     given is non ‘NULL’ this function will search for "---BEGIN header"
     and decode only this part.  Otherwise it will decode the first PEM
     packet found.

*Returns:* On success ‘GNUTLS_E_SUCCESS’ (0) is returned,
     ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ is returned if the buffer given is
     not long enough, or 0 on success.

gnutls_pem_base64_decode2
-------------------------

-- Function: int gnutls_pem_base64_decode2 (const char * HEADER, const
          gnutls_datum_t * B64_DATA, gnutls_datum_t * RESULT)
     HEADER: The PEM header (eg.  CERTIFICATE)

B64_DATA: contains the encoded data

RESULT: the location of decoded data

This function will decode the given encoded data.  The decoded data
     will be allocated, and stored into result.  If the header given is
     non null this function will search for "---BEGIN header" and decode
     only this part.  Otherwise it will decode the first PEM packet
     found.

You should use ‘gnutls_free()’ to free the returned data.

Note, that prior to GnuTLS 3.4.0 this function was available under
     the name ‘gnutls_pem_base64_decode_alloc()’ .  There is
     compatibility macro pointing to this function.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise an error code is returned.

*Since:* 3.4.0

gnutls_pem_base64_encode
------------------------

-- Function: int gnutls_pem_base64_encode (const char * MSG, const
          gnutls_datum_t * DATA, char * RESULT, size_t * RESULT_SIZE)
     MSG: is a message to be put in the header (may be ‘NULL’ )

DATA: contain the raw data

RESULT: the place where base64 data will be copied

RESULT_SIZE: holds the size of the result

This function will convert the given data to printable data, using
     the base64 encoding.  This is the encoding used in PEM messages.

The output string will be null terminated, although the output size
     will not include the terminating null.

*Returns:* On success ‘GNUTLS_E_SUCCESS’ (0) is returned,
     ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ is returned if the buffer given is
     not long enough, or 0 on success.

gnutls_pem_base64_encode2
-------------------------

-- Function: int gnutls_pem_base64_encode2 (const char * HEADER, const
          gnutls_datum_t * DATA, gnutls_datum_t * RESULT)
     HEADER: is a message to be put in the encoded header (may be ‘NULL’
     )

DATA: contains the raw data

RESULT: will hold the newly allocated encoded data

This function will convert the given data to printable data, using
     the base64 encoding.  This is the encoding used in PEM messages.
     This function will allocate the required memory to hold the encoded
     data.

You should use ‘gnutls_free()’ to free the returned data.

Note, that prior to GnuTLS 3.4.0 this function was available under
     the name ‘gnutls_pem_base64_encode_alloc()’ .  There is
     compatibility macro pointing to this function.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise an error code is returned.

*Since:* 3.4.0

gnutls_perror
-------------

-- Function: void gnutls_perror (int ERROR)
     ERROR: is a GnuTLS error code, a negative error code

This function is like ‘perror()’ .  The only difference is that it
     accepts an error number returned by a gnutls function.

gnutls_pk_algorithm_get_name
----------------------------

-- Function: const char * gnutls_pk_algorithm_get_name
          (gnutls_pk_algorithm_t ALGORITHM)
     ALGORITHM: is a pk algorithm

Convert a ‘gnutls_pk_algorithm_t’ value to a string.

*Returns:* a string that contains the name of the specified public
     key algorithm, or ‘NULL’ .

gnutls_pk_bits_to_sec_param
---------------------------

-- Function: gnutls_sec_param_t gnutls_pk_bits_to_sec_param
          (gnutls_pk_algorithm_t ALGO, unsigned int BITS)
     ALGO: is a public key algorithm

BITS: is the number of bits

This is the inverse of ‘gnutls_sec_param_to_pk_bits()’ .  Given an
     algorithm and the number of bits, it will return the security
     parameter.  This is a rough indication.

*Returns:* The security parameter.

*Since:* 2.12.0

gnutls_pk_get_id
----------------

-- Function: gnutls_pk_algorithm_t gnutls_pk_get_id (const char * NAME)
     NAME: is a string containing a public key algorithm name.

Convert a string to a ‘gnutls_pk_algorithm_t’ value.  The names are
     compared in a case insensitive way.  For example,
     gnutls_pk_get_id("RSA") will return ‘GNUTLS_PK_RSA’ .

*Returns:* a ‘gnutls_pk_algorithm_t’ id of the specified public key
     algorithm string, or ‘GNUTLS_PK_UNKNOWN’ on failures.

*Since:* 2.6.0

gnutls_pk_get_name
------------------

-- Function: const char * gnutls_pk_get_name (gnutls_pk_algorithm_t
          ALGORITHM)
     ALGORITHM: is a public key algorithm

Convert a ‘gnutls_pk_algorithm_t’ value to a string.

*Returns:* a pointer to a string that contains the name of the
     specified public key algorithm, or ‘NULL’ .

*Since:* 2.6.0

gnutls_pk_get_oid
-----------------

-- Function: const char * gnutls_pk_get_oid (gnutls_pk_algorithm_t
          ALGORITHM)
     ALGORITHM: is a public key algorithm

Convert a ‘gnutls_pk_algorithm_t’ value to its object identifier
     string.

*Returns:* a pointer to a string that contains the object
     identifier of the specified public key algorithm, or ‘NULL’ .

*Since:* 3.4.3

gnutls_pk_list
--------------

-- Function: const gnutls_pk_algorithm_t * gnutls_pk_list ( VOID)

Get a list of supported public key algorithms.

This function is not thread safe.

*Returns:* a (0)-terminated list of ‘gnutls_pk_algorithm_t’
     integers indicating the available ciphers.

*Since:* 2.6.0

gnutls_pk_to_sign
-----------------

-- Function: gnutls_sign_algorithm_t gnutls_pk_to_sign
          (gnutls_pk_algorithm_t PK, gnutls_digest_algorithm_t HASH)
     PK: is a public key algorithm

HASH: a hash algorithm

This function maps public key and hash algorithms combinations to
     signature algorithms.

*Returns:* return a ‘gnutls_sign_algorithm_t’ value, or
     ‘GNUTLS_SIGN_UNKNOWN’ on error.

gnutls_prf
----------

-- Function: int gnutls_prf (gnutls_session_t SESSION, size_t
          LABEL_SIZE, const char * LABEL, int SERVER_RANDOM_FIRST,
          size_t EXTRA_SIZE, const char * EXTRA, size_t OUTSIZE, char *
          OUT)
     SESSION: is a ‘gnutls_session_t’ type.

LABEL_SIZE: length of the ‘label’ variable.

LABEL: label used in PRF computation, typically a short string.

SERVER_RANDOM_FIRST: non-zero if server random field should be
     first in seed

EXTRA_SIZE: length of the ‘extra’ variable.

EXTRA: optional extra data to seed the PRF with.

OUTSIZE: size of pre-allocated output buffer to hold the output.

OUT: pre-allocated buffer to hold the generated data.

Applies the TLS Pseudo-Random-Function (PRF) on the master secret
     and the provided data, seeded with the client and server random
     fields.  For the key expansion specified in RFC5705 see
     ‘gnutls_prf_rfc5705()’ .

The ‘label’ variable usually contains a string denoting the purpose
     for the generated data.  The ‘server_random_first’ indicates
     whether the client random field or the server random field should
     be first in the seed.  Non-zero indicates that the server random
     field is first, 0 that the client random field is first.

The ‘extra’ variable can be used to add more data to the seed,
     after the random variables.  It can be used to make sure the
     generated output is strongly connected to some additional data
     (e.g., a string used in user authentication).

The output is placed in ‘out’ , which must be pre-allocated.

*Note:* This function produces identical output with
     ‘gnutls_prf_rfc5705()’ when ‘server_random_first’ is set to 0 and
     ‘extra’ is ‘NULL’ .  Under TLS1.3 this function will only operate
     when these conditions are true, or otherwise return
     ‘GNUTLS_E_INVALID_REQUEST’ .

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, or an error code.

gnutls_prf_early
----------------

-- Function: int gnutls_prf_early (gnutls_session_t SESSION, size_t
          LABEL_SIZE, const char * LABEL, size_t CONTEXT_SIZE, const
          char * CONTEXT, size_t OUTSIZE, char * OUT)
     SESSION: is a ‘gnutls_session_t’ type.

LABEL_SIZE: length of the ‘label’ variable.

LABEL: label used in PRF computation, typically a short string.

CONTEXT_SIZE: length of the ‘extra’ variable.

CONTEXT: optional extra data to seed the PRF with.

OUTSIZE: size of pre-allocated output buffer to hold the output.

OUT: pre-allocated buffer to hold the generated data.

This function is similar to ‘gnutls_prf_rfc5705()’ , but only works
     in TLS 1.3 or later to export early keying material.

Note that the keying material is only available after the
     ClientHello message is processed and before the application traffic
     keys are established.  Therefore this function shall be called in a
     handshake hook function for ‘GNUTLS_HANDSHAKE_CLIENT_HELLO’ .

The ‘label’ variable usually contains a string denoting the purpose
     for the generated data.

The output is placed in ‘out’ , which must be pre-allocated.

Note that, to provide the RFC5705 context, the ‘context’ variable
     must be non-null.

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, or an error code.

*Since:* 3.6.8

gnutls_prf_hash_get
-------------------

-- Function: gnutls_digest_algorithm_t gnutls_prf_hash_get (const
          gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Get the currently used hash algorithm.  In TLS 1.3, the hash
     algorithm is used for both the key derivation function and
     handshake message authentication code.  In TLS 1.2, it matches the
     hash algorithm used for PRF.

*Returns:* the currently used hash algorithm, a
     ‘gnutls_digest_algorithm_t’ value.

*Since:* 3.6.13

gnutls_prf_raw
--------------

-- Function: int gnutls_prf_raw (gnutls_session_t SESSION, size_t
          LABEL_SIZE, const char * LABEL, size_t SEED_SIZE, const char *
          SEED, size_t OUTSIZE, char * OUT)
     SESSION: is a ‘gnutls_session_t’ type.

LABEL_SIZE: length of the ‘label’ variable.

LABEL: label used in PRF computation, typically a short string.

SEED_SIZE: length of the ‘seed’ variable.

SEED: optional extra data to seed the PRF with.

OUTSIZE: size of pre-allocated output buffer to hold the output.

OUT: pre-allocated buffer to hold the generated data.

Apply the TLS Pseudo-Random-Function (PRF) on the master secret and
     the provided data.

The ‘label’ variable usually contains a string denoting the purpose
     for the generated data.  The ‘seed’ usually contains data such as
     the client and server random, perhaps together with some additional
     data that is added to guarantee uniqueness of the output for a
     particular purpose.

Because the output is not guaranteed to be unique for a particular
     session unless ‘seed’ includes the client random and server random
     fields (the PRF would output the same data on another connection
     resumed from the first one), it is not recommended to use this
     function directly.  The ‘gnutls_prf()’ function seeds the PRF with
     the client and server random fields directly, and is recommended if
     you want to generate pseudo random data unique for each session.

*Note:* This function will only operate under TLS versions prior to
     1.3.  In TLS1.3 the use of PRF is replaced with HKDF and the
     generic exporters like ‘gnutls_prf_rfc5705()’ should be used
     instead.  Under TLS1.3 this function returns
     ‘GNUTLS_E_INVALID_REQUEST’ .

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, or an error code.

gnutls_prf_rfc5705
------------------

LABEL_SIZE: length of the ‘label’ variable.

LABEL: label used in PRF computation, typically a short string.

CONTEXT_SIZE: length of the ‘extra’ variable.

CONTEXT: optional extra data to seed the PRF with.

OUTSIZE: size of pre-allocated output buffer to hold the output.

OUT: pre-allocated buffer to hold the generated data.

Exports keying material from TLS/DTLS session to an application, as
     specified in RFC5705.

In the TLS versions prior to 1.3, it applies the TLS
     Pseudo-Random-Function (PRF) on the master secret and the provided
     data, seeded with the client and server random fields.

In TLS 1.3, it applies HKDF on the exporter master secret derived
     from the master secret.

The ‘label’ variable usually contains a string denoting the purpose
     for the generated data.

The output is placed in ‘out’ , which must be pre-allocated.

Note that, to provide the RFC5705 context, the ‘context’ variable
     must be non-null.

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, or an error code.

*Since:* 3.4.4

gnutls_priority_certificate_type_list
-------------------------------------

-- Function: int gnutls_priority_certificate_type_list
          (gnutls_priority_t PCACHE, const unsigned int ** LIST)
     PCACHE: is a ‘gnutls_priority_t’ type.

LIST: will point to an integer list

Get a list of available certificate types in the priority
     structure.

As of version 3.6.4 this function is an alias for
     gnutls_priority_certificate_type_list2 with the target parameter
     set to: - GNUTLS_CTYPE_SERVER, if the ‘SERVER_PRECEDENCE’ option is
     set - GNUTLS_CTYPE_CLIENT, otherwise.

*Returns:* the number of certificate types, or an error code.

*Since:* 3.0

gnutls_priority_certificate_type_list2
--------------------------------------

-- Function: int gnutls_priority_certificate_type_list2
          (gnutls_priority_t PCACHE, const unsigned int ** LIST,
          gnutls_ctype_target_t TARGET)
     PCACHE: is a ‘gnutls_priority_t’ type.

LIST: will point to an integer list.

TARGET: is a ‘gnutls_ctype_target_t’ type.  Valid arguments are
     GNUTLS_CTYPE_CLIENT and GNUTLS_CTYPE_SERVER

Get a list of available certificate types for the given target in
     the priority structure.

*Returns:* the number of certificate types, or an error code.

*Since:* 3.6.4

gnutls_priority_cipher_list
---------------------------

-- Function: int gnutls_priority_cipher_list (gnutls_priority_t PCACHE,
          const unsigned int ** LIST)
     PCACHE: is a ‘gnutls_priority_t’ type.

LIST: will point to an integer list

Get a list of available ciphers in the priority structure.

*Returns:* the number of items, or an error code.

*Since:* 3.2.3

gnutls_priority_deinit
----------------------

-- Function: void gnutls_priority_deinit (gnutls_priority_t
          PRIORITY_CACHE)
     PRIORITY_CACHE: is a ‘gnutls_priority_t’ type.

Deinitializes the priority cache.

gnutls_priority_ecc_curve_list
------------------------------

-- Function: int gnutls_priority_ecc_curve_list (gnutls_priority_t
          PCACHE, const unsigned int ** LIST)
     PCACHE: is a ‘gnutls_priority_t’ type.

LIST: will point to an integer list

Get a list of available elliptic curves in the priority structure.

*Deprecated:* This function has been replaced by
     ‘gnutls_priority_group_list()’ since 3.6.0.

*Returns:* the number of items, or an error code.

*Since:* 3.0

gnutls_priority_get_cipher_suite_index
--------------------------------------

-- Function: int gnutls_priority_get_cipher_suite_index
          (gnutls_priority_t PCACHE, unsigned int IDX, unsigned int *
          SIDX)
     PCACHE: is a ‘gnutls_priority_t’ type.

IDX: is an index number.

SIDX: internal index of cipher suite to get information about.

Provides the internal ciphersuite index to be used with
     ‘gnutls_cipher_suite_info()’ .  The index ‘idx’ provided is an
     index kept at the priorities structure.  It might be that a valid
     priorities index does not correspond to a ciphersuite and in that
     case ‘GNUTLS_E_UNKNOWN_CIPHER_SUITE’ will be returned.  Once the
     last available index is crossed then
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ will be returned.

*Returns:* On success it returns ‘GNUTLS_E_SUCCESS’ (0), or a
     negative error value otherwise.

*Since:* 3.0.9

gnutls_priority_group_list
--------------------------

-- Function: int gnutls_priority_group_list (gnutls_priority_t PCACHE,
          const unsigned int ** LIST)
     PCACHE: is a ‘gnutls_priority_t’ type.

LIST: will point to an integer list

Get a list of available groups in the priority structure.

*Returns:* the number of items, or an error code.

*Since:* 3.6.0

gnutls_priority_init
--------------------

-- Function: int gnutls_priority_init (gnutls_priority_t *
          PRIORITY_CACHE, const char * PRIORITIES, const char **
          ERR_POS)
     PRIORITY_CACHE: is a ‘gnutls_priority_t’ type.

PRIORITIES: is a string describing priorities (may be ‘NULL’ )

ERR_POS: In case of an error this will have the position in the
     string the error occurred

For applications that do not modify their crypto settings per
     release, consider using ‘gnutls_priority_init2()’ with
     ‘GNUTLS_PRIORITY_INIT_DEF_APPEND’ flag instead.  We suggest to use
     centralized crypto settings handled by the GnuTLS library, and
     applications modifying the default settings to their needs.

This function is identical to ‘gnutls_priority_init2()’ with zero
     flags.

A ‘NULL’ ‘priorities’ string indicates the default priorities to be
     used (this is available since GnuTLS 3.3.0).

*Returns:* On syntax error ‘GNUTLS_E_INVALID_REQUEST’ is returned,
     ‘GNUTLS_E_SUCCESS’ on success, or an error code.

gnutls_priority_init2
---------------------

-- Function: int gnutls_priority_init2 (gnutls_priority_t *
          PRIORITY_CACHE, const char * PRIORITIES, const char **
          ERR_POS, unsigned FLAGS)
     PRIORITY_CACHE: is a ‘gnutls_priority_t’ type.

PRIORITIES: is a string describing priorities (may be ‘NULL’ )

ERR_POS: In case of an error this will have the position in the
     string the error occurred

FLAGS: zero or ‘GNUTLS_PRIORITY_INIT_DEF_APPEND’

Sets priorities for the ciphers, key exchange methods, and macs.
     The ‘priority_cache’ should be deinitialized using
     ‘gnutls_priority_deinit()’ .

The ‘priorities’ option allows you to specify a colon separated
     list of the cipher priorities to enable.  Some keywords are defined
     to provide quick access to common preferences.

When ‘flags’ is set to ‘GNUTLS_PRIORITY_INIT_DEF_APPEND’ then the
     ‘priorities’ specified will be appended to the default options.

Unless there is a special need, use the "NORMAL" keyword to apply a
     reasonable security level, or "NORMAL:%COMPAT" for compatibility.

"PERFORMANCE" means all the "secure" ciphersuites are enabled,
     limited to 128 bit ciphers and sorted by terms of speed
     performance.

"LEGACY" the NORMAL settings for GnuTLS 3.2.x or earlier.  There is
     no verification profile set, and the allowed DH primes are
     considered weak today.

"NORMAL" means all "secure" ciphersuites.  The 256-bit ciphers are
     included as a fallback only.  The ciphers are sorted by security
     margin.

"PFS" means all "secure" ciphersuites that support perfect forward
     secrecy.  The 256-bit ciphers are included as a fallback only.  The
     ciphers are sorted by security margin.

"SECURE128" means all "secure" ciphersuites of security level
     128-bit or more.

"SECURE192" means all "secure" ciphersuites of security level
     192-bit or more.

"SUITEB128" means all the NSA SuiteB ciphersuites with security
     level of 128.

"SUITEB192" means all the NSA SuiteB ciphersuites with security
     level of 192.

"NONE" means nothing is enabled.  This disables everything,
     including protocols.

"@KEYWORD1,KEYWORD2,..."  The system administrator imposed
     settings.  The provided keyword(s) will be expanded from a
     configuration-time provided file - default is:
     /usr/local/etc/gnutls/config.  Any attributes that follow it, will
     be appended to the expanded string.  If multiple keywords are
     provided, separated by commas, then the first keyword that exists
     in the configuration file will be used.  At least one of the
     keywords must exist, or this function will return an error.
     Typical usage would be to specify an application specified keyword
     first, followed by "SYSTEM" as a default fallback.  e.g., "
     ‘LIBVIRT’ ,SYSTEM:!-VERS-SSL3.0" will first try to find a config
     file entry matching "LIBVIRT", but if that does not exist will use
     the entry for "SYSTEM". If "SYSTEM" does not exist either, an error
     will be returned.  In all cases, the SSL3.0 protocol will be
     disabled.  The system priority file entries should be formatted as
     "KEYWORD=VALUE", e.g., "SYSTEM=NORMAL:+ARCFOUR-128".

Special keywords are "!", "-" and "+".  "!"  or "-" appended with
     an algorithm will remove this algorithm.  "+" appended with an
     algorithm will add this algorithm.

Check the GnuTLS manual section "Priority strings" for detailed
     information.

*Examples:*
     "NONE:+VERS-TLS-ALL:+MAC-ALL:+RSA:+AES-128-CBC:+SIGN-ALL:+COMP-NULL"

"NORMAL:+ARCFOUR-128" means normal ciphers plus ARCFOUR-128.

"SECURE128:-VERS-SSL3.0" means that only secure ciphers are and
     enabled, SSL3.0 is disabled.

"NONE:+VERS-TLS-ALL:+AES-128-CBC:+RSA:+SHA1:+COMP-NULL:+SIGN-RSA-SHA1",

"NONE:+VERS-TLS-ALL:+AES-128-CBC:+ECDHE-RSA:+SHA1:+COMP-NULL:+SIGN-RSA-SHA1:+CURVE-SECP256R1",

"SECURE256:+SECURE128",

Note that "NORMAL:%COMPAT" is the most compatible mode.

A ‘NULL’ ‘priorities’ string indicates the default priorities to be
     used (this is available since GnuTLS 3.3.0).

*Returns:* On syntax error ‘GNUTLS_E_INVALID_REQUEST’ is returned,
     ‘GNUTLS_E_SUCCESS’ on success, or an error code.

*Since:* 3.6.3

gnutls_priority_kx_list
-----------------------

-- Function: int gnutls_priority_kx_list (gnutls_priority_t PCACHE,
          const unsigned int ** LIST)
     PCACHE: is a ‘gnutls_priority_t’ type.

LIST: will point to an integer list

Get a list of available key exchange methods in the priority
     structure.

*Returns:* the number of items, or an error code.

*Since:* 3.2.3

gnutls_priority_mac_list
------------------------

-- Function: int gnutls_priority_mac_list (gnutls_priority_t PCACHE,
          const unsigned int ** LIST)
     PCACHE: is a ‘gnutls_priority_t’ type.

LIST: will point to an integer list

Get a list of available MAC algorithms in the priority structure.

*Returns:* the number of items, or an error code.

*Since:* 3.2.3

gnutls_priority_protocol_list
-----------------------------

-- Function: int gnutls_priority_protocol_list (gnutls_priority_t
          PCACHE, const unsigned int ** LIST)
     PCACHE: is a ‘gnutls_priority_t’ type.

LIST: will point to an integer list

Get a list of available TLS version numbers in the priority
     structure.

*Returns:* the number of protocols, or an error code.

*Since:* 3.0

gnutls_priority_set
-------------------

-- Function: int gnutls_priority_set (gnutls_session_t SESSION,
          gnutls_priority_t PRIORITY)
     SESSION: is a ‘gnutls_session_t’ type.

PRIORITY: is a ‘gnutls_priority_t’ type.

Sets the priorities to use on the ciphers, key exchange methods,
     and macs.  Note that this function is expected to be called once
     per session; when called multiple times (e.g., before a
     re-handshake, the caller should make sure that any new settings are
     not incompatible with the original session).

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, or an error code on
     error.

gnutls_priority_set_direct
--------------------------

-- Function: int gnutls_priority_set_direct (gnutls_session_t SESSION,
          const char * PRIORITIES, const char ** ERR_POS)
     SESSION: is a ‘gnutls_session_t’ type.

PRIORITIES: is a string describing priorities

ERR_POS: In case of an error this will have the position in the
     string the error occurred

Sets the priorities to use on the ciphers, key exchange methods,
     and macs.  This function avoids keeping a priority cache and is
     used to directly set string priorities to a TLS session.  For
     documentation check the ‘gnutls_priority_init()’ .

To use a reasonable default, consider using
     ‘gnutls_set_default_priority()’ , or
     ‘gnutls_set_default_priority_append()’ instead of this function.

*Returns:* On syntax error ‘GNUTLS_E_INVALID_REQUEST’ is returned,
     ‘GNUTLS_E_SUCCESS’ on success, or an error code.

gnutls_priority_sign_list
-------------------------

-- Function: int gnutls_priority_sign_list (gnutls_priority_t PCACHE,
          const unsigned int ** LIST)
     PCACHE: is a ‘gnutls_priority_t’ type.

LIST: will point to an integer list

Get a list of available signature algorithms in the priority
     structure.

*Returns:* the number of algorithms, or an error code.

*Since:* 3.0

gnutls_priority_string_list
---------------------------

-- Function: const char * gnutls_priority_string_list (unsigned ITER,
          unsigned int FLAGS)
     ITER: an integer counter starting from zero

FLAGS: one of ‘GNUTLS_PRIORITY_LIST_INIT_KEYWORDS’ ,
     ‘GNUTLS_PRIORITY_LIST_SPECIAL’

Can be used to iterate all available priority strings.  Due to
     internal implementation details, there are cases where this
     function can return the empty string.  In that case that string
     should be ignored.  When no strings are available it returns ‘NULL’
     .

*Returns:* a priority string

*Since:* 3.4.0

gnutls_protocol_get_id
----------------------

-- Function: gnutls_protocol_t gnutls_protocol_get_id (const char *
          NAME)
     NAME: is a protocol name

The names are compared in a case insensitive way.

*Returns:* an id of the specified protocol, or
     ‘GNUTLS_VERSION_UNKNOWN’ on error.

gnutls_protocol_get_name
------------------------

-- Function: const char * gnutls_protocol_get_name (gnutls_protocol_t
          VERSION)
     VERSION: is a (gnutls) version number

Convert a ‘gnutls_protocol_t’ value to a string.

*Returns:* a string that contains the name of the specified TLS
     version (e.g., "TLS1.0"), or ‘NULL’ .

gnutls_protocol_get_version
---------------------------

-- Function: gnutls_protocol_t gnutls_protocol_get_version
          (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Get TLS version, a ‘gnutls_protocol_t’ value.

*Returns:* The version of the currently used protocol.

gnutls_protocol_list
--------------------

-- Function: const gnutls_protocol_t * gnutls_protocol_list ( VOID)

Get a list of supported protocols, e.g.  SSL 3.0, TLS 1.0 etc.

This function is not thread safe.

*Returns:* a (0)-terminated list of ‘gnutls_protocol_t’ integers
     indicating the available protocols.

gnutls_protocol_set_enabled
---------------------------

-- Function: int gnutls_protocol_set_enabled (gnutls_protocol_t
          VERSION, unsigned int ENABLED)
     VERSION: is a (gnutls) version number

ENABLED: whether to enable the protocol

Control the previous system-wide setting that marked ‘version’ as
     enabled or disabled.  Calling this function is allowed only if
     allowlisting mode is set in the configuration file, and only if the
     system-wide TLS priority string has not been initialized yet.  The
     intended usage is to provide applications with a way to expressly
     deviate from the distribution or site defaults inherited from the
     configuration file.  The modification is composable with further
     modifications performed through the priority string mechanism.

This function is not thread-safe and is intended to be called in
     the main thread at the beginning of the process execution.

*Returns:* 0 on success or negative error code otherwise.

*Since:* 3.7.3

gnutls_psk_allocate_client_credentials
--------------------------------------

-- Function: int gnutls_psk_allocate_client_credentials
          (gnutls_psk_client_credentials_t * SC)
     SC: is a pointer to a ‘gnutls_psk_client_credentials_t’ type.

Allocate a gnutls_psk_client_credentials_t structure.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise an error code is returned.

gnutls_psk_allocate_server_credentials
--------------------------------------

-- Function: int gnutls_psk_allocate_server_credentials
          (gnutls_psk_server_credentials_t * SC)
     SC: is a pointer to a ‘gnutls_psk_server_credentials_t’ type.

Allocate a gnutls_psk_server_credentials_t structure.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise an error code is returned.

gnutls_psk_client_get_hint
--------------------------

-- Function: const char * gnutls_psk_client_get_hint (gnutls_session_t
          SESSION)
     SESSION: is a gnutls session

The PSK identity hint may give the client help in deciding which
     username to use.  This should only be called in case of PSK
     authentication and in case of a client.

*Note:* there is no hint in TLS 1.3, so this function will return
     ‘NULL’ if TLS 1.3 has been negotiated.

*Returns:* the identity hint of the peer, or ‘NULL’ in case of an
     error or if TLS 1.3 is being used.

*Since:* 2.4.0

gnutls_psk_format_imported_identity
-----------------------------------

-- Function: int gnutls_psk_format_imported_identity (const
          gnutls_datum_t * IDENTITY, const gnutls_datum_t * CONTEXT,
          gnutls_protocol_t VERSION, gnutls_digest_algorithm_t HASH,
          gnutls_datum_t * IMPORTED_IDENTITY)
     IDENTITY: external identity

CONTEXT: optional contextual information

VERSION: protocol version to which the PSK is imported

HASH: hash algorithm used for KDF

IMPORTED_IDENTITY: where the imported identity is stored

This formats an external PSK identity ‘identity’ into an imported
     form, described in RFC 9258 as ImportedIdentity.

Upon success, the data field of ‘imported_identity’ is allocated
     using ‘gnutls_malloc()’ and the caller must free the memory after
     use.

*Returns:* ‘GNUTLS_E_SUCCESS’ (0) on success, otherwise a negative
     error code.

*Since:* 3.8.1

gnutls_psk_free_client_credentials
----------------------------------

-- Function: void gnutls_psk_free_client_credentials
          (gnutls_psk_client_credentials_t SC)
     SC: is a ‘gnutls_psk_client_credentials_t’ type.

Free a gnutls_psk_client_credentials_t structure.

gnutls_psk_free_server_credentials
----------------------------------

-- Function: void gnutls_psk_free_server_credentials
          (gnutls_psk_server_credentials_t SC)
     SC: is a ‘gnutls_psk_server_credentials_t’ type.

Free a gnutls_psk_server_credentials_t structure.

gnutls_psk_server_get_username
------------------------------

-- Function: const char * gnutls_psk_server_get_username
          (gnutls_session_t SESSION)
     SESSION: is a gnutls session

This should only be called in case of PSK authentication and in
     case of a server.

The returned pointer should be considered constant (do not free)
     and valid for the lifetime of the session.

This function will return ‘NULL’ if the username has embedded NULL
     bytes.  In that case, ‘gnutls_psk_server_get_username2()’ should be
     used to retrieve the username.

*Returns:* the username of the peer, or ‘NULL’ in case of an error,
     or if the username has embedded NULLs.

gnutls_psk_server_get_username2
-------------------------------

-- Function: int gnutls_psk_server_get_username2 (gnutls_session_t
          SESSION, gnutls_datum_t * USERNAME)
     SESSION: is a gnutls session

USERNAME: a datum that will be filled in by this function

Return a pointer to the username of the peer in the supplied datum.
     Does not need to be null-terminated.

This should only be called in case of PSK authentication and in
     case of a server.

The returned pointer should be considered constant (do not free)
     and valid for the lifetime of the session.

*Returns:* ‘GNUTLS_E_SUCCESS’ , or a negative value in case of an
     error.

gnutls_psk_set_client_credentials
---------------------------------

-- Function: int gnutls_psk_set_client_credentials
          (gnutls_psk_client_credentials_t RES, const char * USERNAME,
          const gnutls_datum_t * KEY, gnutls_psk_key_flags FLAGS)
     RES: is a ‘gnutls_psk_client_credentials_t’ type.

USERNAME: is the user's zero-terminated userid

KEY: is the user's key

FLAGS: indicate the format of the key, either ‘GNUTLS_PSK_KEY_RAW’
     or ‘GNUTLS_PSK_KEY_HEX’ .

This function sets the username and password, in a
     gnutls_psk_client_credentials_t type.  Those will be used in PSK
     authentication.  ‘username’ should be an ASCII string or UTF-8
     string.  In case of a UTF-8 string it is recommended to be
     following the PRECIS framework for usernames (rfc8265).  The key
     can be either in raw byte format or in Hex format (without the 0x
     prefix).

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise an error code is returned.

gnutls_psk_set_client_credentials2
----------------------------------

-- Function: int gnutls_psk_set_client_credentials2
          (gnutls_psk_client_credentials_t RES, const gnutls_datum_t *
          USERNAME, const gnutls_datum_t * KEY, gnutls_psk_key_flags
          FLAGS)
     RES: is a ‘gnutls_psk_client_credentials_t’ type.

USERNAME: is the userid

KEY: is the user's key

FLAGS: indicate the format of the key, either ‘GNUTLS_PSK_KEY_RAW’
     or ‘GNUTLS_PSK_KEY_HEX’ .

This function is identical to ‘gnutls_psk_set_client_credentials()’
     , except that it allows a non-null-terminated username to be
     introduced.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise an error code is returned.

gnutls_psk_set_client_credentials_function
------------------------------------------

FUNC: is the callback function

The callback function will be called once per handshake.

The callback function should return 0 on success.  -1 indicates an
     error.

gnutls_psk_set_client_credentials_function2
-------------------------------------------

-- Function: void gnutls_psk_set_client_credentials_function2
          (gnutls_psk_client_credentials_t CRED,
          gnutls_psk_client_credentials_function2 * FUNC)
     CRED: is a ‘gnutls_psk_server_credentials_t’ type.

FUNC: is the callback function

This callback function has the same semantics as that of
     ‘gnutls_psk_set_client_credentials_function()’ , but it allows
     non-string usernames to be used.

The callback function will be called once per handshake.

The callback function should return 0 on success.  -1 indicates an
     error.

gnutls_psk_set_client_credentials_function3
-------------------------------------------

-- Function: void gnutls_psk_set_client_credentials_function3
          (gnutls_psk_client_credentials_t CRED,
          gnutls_psk_client_credentials_function3 * FUNC)
     CRED: is a ‘gnutls_psk_server_credentials_t’ type.

FUNC: is the callback function

This callback function has the same semantics as that of
     ‘gnutls_psk_set_client_credentials_function2()’ , but it returns
     flags associated with the key.  The callback may import external
     PSK using the method described in RFC 9258 by using
     ‘gnutls_psk_format_imported_identity()’ .

The data field of ‘username’ , ‘key’ , and ‘context’ must be
     allocated using ‘gnutls_malloc()’ .  The ‘username’ should be an
     ASCII string or UTF-8 string.  In case of a UTF-8 string it is
     recommended to be following the PRECIS framework for usernames
     (rfc8265).

The callback function will be called once per handshake.

The callback function should return 0 on success.  -1 indicates an
     error.

gnutls_psk_set_params_function
------------------------------

-- Function: void gnutls_psk_set_params_function
          (gnutls_psk_server_credentials_t RES, gnutls_params_function *
          FUNC)
     RES: is a gnutls_psk_server_credentials_t type

FUNC: is the function to be called

This function will set a callback in order for the server to get
     the Diffie-Hellman or RSA parameters for PSK authentication.  The
     callback should return ‘GNUTLS_E_SUCCESS’ (0) on success.

*Deprecated:* This function is unnecessary and discouraged on
     GnuTLS 3.6.0 or later.  Since 3.6.0, DH parameters are negotiated
     following RFC7919.

gnutls_psk_set_server_credentials_file
--------------------------------------

PASSWORD_FILE: is the PSK password file (passwd.psk)

This function sets the password file, in a
     ‘gnutls_psk_server_credentials_t’ type.  This password file holds
     usernames and keys and will be used for PSK authentication.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise an error code is returned.

gnutls_psk_set_server_credentials_function
------------------------------------------

-- Function: void gnutls_psk_set_server_credentials_function
          (gnutls_psk_server_credentials_t CRED,
          gnutls_psk_server_credentials_function * FUNC)
     CRED: is a ‘gnutls_psk_server_credentials_t’ type.

FUNC: is the callback function

This function can be used to set a callback to retrieve the user's
     PSK credentials.  The callback's function form is: int
     (*callback)(gnutls_session_t, const char* username, gnutls_datum_t*
     key);

‘username’ contains the actual username.  The ‘key’ must be filled
     in using the ‘gnutls_malloc()’ .

In case the callback returned a negative number then gnutls will
     assume that the username does not exist.

The callback function will only be called once per handshake.  The
     callback function should return 0 on success, while -1 indicates an
     error.

gnutls_psk_set_server_credentials_function2
-------------------------------------------

-- Function: void gnutls_psk_set_server_credentials_function2
          (gnutls_psk_server_credentials_t CRED,
          gnutls_psk_server_credentials_function2 FUNC)
     CRED: is a ‘gnutls_psk_server_credentials_t’ type.

FUNC: is the callback function

This function can be used to set a callback to retrieve the user's
     PSK credentials.  The callback's function form is: int
     (*callback)(gnutls_session_t, const gnutls_datum_t* username,
     gnutls_datum_t* key);

This callback function has the same semantics as that of
     ‘gnutls_psk_set_server_credentials_function()’ , but it allows
     non-string usernames to be used.

‘username’ contains the actual username.  The ‘key’ must be filled
     in using the ‘gnutls_malloc()’ .

In case the callback returned a negative number then gnutls will
     assume that the username does not exist.

The callback function will only be called once per handshake.  The
     callback function should return 0 on success, while -1 indicates an
     error.

gnutls_psk_set_server_credentials_function3
-------------------------------------------

-- Function: void gnutls_psk_set_server_credentials_function3
          (gnutls_psk_server_credentials_t CRED,
          gnutls_psk_server_credentials_function3 FUNC)
     CRED: is a ‘gnutls_psk_server_credentials_t’ type.

FUNC: is the callback function

This callback function has the same semantics as that of
     ‘gnutls_psk_set_server_credentials_function2()’ , but it returns
     flags associated with the key.  The callback may import external
     PSK using the method described in RFC 9258 by using
     ‘gnutls_psk_format_imported_identity()’ .

‘username’ contains the actual username.  The ‘key’ must be filled
     in using the ‘gnutls_malloc()’ .

In case the callback returned a negative number then gnutls will
     assume that the username does not exist.

The callback function will only be called once per handshake.  The
     callback function should return 0 on success, while -1 indicates an
     error.

gnutls_psk_set_server_credentials_hint
--------------------------------------

-- Function: int gnutls_psk_set_server_credentials_hint
          (gnutls_psk_server_credentials_t RES, const char * HINT)
     RES: is a ‘gnutls_psk_server_credentials_t’ type.

HINT: is the PSK identity hint string

This function sets the identity hint, in a
     ‘gnutls_psk_server_credentials_t’ type.  This hint is sent to the
     client to help it chose a good PSK credential (i.e., username and
     password).

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise an error code is returned.

*Since:* 2.4.0

gnutls_psk_set_server_dh_params
-------------------------------

-- Function: void gnutls_psk_set_server_dh_params
          (gnutls_psk_server_credentials_t RES, gnutls_dh_params_t
          DH_PARAMS)
     RES: is a gnutls_psk_server_credentials_t type

DH_PARAMS: is a structure that holds Diffie-Hellman parameters.

This function will set the Diffie-Hellman parameters for an
     anonymous server to use.  These parameters will be used in
     Diffie-Hellman exchange with PSK cipher suites.

*Deprecated:* This function is unnecessary and discouraged on
     GnuTLS 3.6.0 or later.  Since 3.6.0, DH parameters are negotiated
     following RFC7919.

gnutls_psk_set_server_known_dh_params
-------------------------------------

-- Function: int gnutls_psk_set_server_known_dh_params
          (gnutls_psk_server_credentials_t RES, gnutls_sec_param_t
          SEC_PARAM)
     RES: is a gnutls_psk_server_credentials_t type

SEC_PARAM: is an option of the ‘gnutls_sec_param_t’ enumeration

This function will set the Diffie-Hellman parameters for a PSK
     server to use.  These parameters will be used in Ephemeral
     Diffie-Hellman cipher suites and will be selected from the FFDHE
     set of RFC7919 according to the security level provided.

*Deprecated:* This function is unnecessary and discouraged on
     GnuTLS 3.6.0 or later.  Since 3.6.0, DH parameters are negotiated
     following RFC7919.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.5.6

gnutls_psk_set_server_params_function
-------------------------------------

-- Function: void gnutls_psk_set_server_params_function
          (gnutls_psk_server_credentials_t RES, gnutls_params_function *
          FUNC)
     RES: is a ‘gnutls_certificate_credentials_t’ type

FUNC: is the function to be called

This function will set a callback in order for the server to get
     the Diffie-Hellman parameters for PSK authentication.  The callback
     should return ‘GNUTLS_E_SUCCESS’ (0) on success.

*Deprecated:* This function is unnecessary and discouraged on
     GnuTLS 3.6.0 or later.  Since 3.6.0, DH parameters are negotiated
     following RFC7919.

gnutls_random_art
-----------------

-- Function: int gnutls_random_art (gnutls_random_art_t TYPE, const
          char * KEY_TYPE, unsigned int KEY_SIZE, void * FPR, size_t
          FPR_SIZE, gnutls_datum_t * ART)
     TYPE: The type of the random art (for now only
     ‘GNUTLS_RANDOM_ART_OPENSSH’ is supported)

KEY_TYPE: The type of the key (RSA, DSA etc.)

KEY_SIZE: The size of the key in bits

FPR: The fingerprint of the key

FPR_SIZE: The size of the fingerprint

ART: The returned random art

This function will convert a given fingerprint to an "artistic"
     image.  The returned image is allocated using ‘gnutls_malloc()’ ,
     is null-terminated but art->size will not account the terminating
     null.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise an error code is returned.

gnutls_range_split
------------------

-- Function: int gnutls_range_split (gnutls_session_t SESSION, const
          gnutls_range_st * ORIG, gnutls_range_st * NEXT,
          gnutls_range_st * REMAINDER)
     SESSION: is a ‘gnutls_session_t’ type

ORIG: is the original range provided by the user

NEXT: is the returned range that can be conveyed in a TLS record

REMAINDER: is the returned remaining range

This function should be used when it is required to hide the length
     of very long data that cannot be directly provided to
     ‘gnutls_record_send_range()’ .  In that case this function should
     be called with the desired length hiding range in ‘orig’ .  The
     returned ‘next’ value should then be used in the next call to
     ‘gnutls_record_send_range()’ with the partial data.  That process
     should be repeated until ‘remainder’ is (0,0).

*Returns:* 0 in case splitting succeeds, non zero in case of error.
     Note that ‘orig’ is not changed, while the values of ‘next’ and
     ‘remainder’ are modified to store the resulting values.

gnutls_reauth
-------------

-- Function: int gnutls_reauth (gnutls_session_t SESSION, unsigned int
          FLAGS)
     SESSION: is a ‘gnutls_session_t’ type.

FLAGS: must be zero

This function performs the post-handshake authentication for TLS
     1.3.  The post-handshake authentication is initiated by the server
     by calling this function.  Clients respond when
     ‘GNUTLS_E_REAUTH_REQUEST’ has been seen while receiving data.

The non-fatal errors expected by this function are:
     ‘GNUTLS_E_INTERRUPTED’ , ‘GNUTLS_E_AGAIN’ , as well as
     ‘GNUTLS_E_GOT_APPLICATION_DATA’ when called on server side.

The former two interrupt the authentication procedure due to the
     transport layer being interrupted, and the latter because there
     were pending data prior to peer initiating the re-authentication.
     The server should read/process that data as unauthenticated and
     retry calling ‘gnutls_reauth()’ .

When this function is called under TLS1.2 or earlier or the peer
     didn't advertise post-handshake auth, it always fails with
     ‘GNUTLS_E_INVALID_REQUEST’ .  The verification of the received
     peers certificate is delegated to the session or credentials
     verification callbacks.  A server can check whether post handshake
     authentication is supported by the client by checking the session
     flags with ‘gnutls_session_get_flags()’ .

Prior to calling this function in server side, the function
     ‘gnutls_certificate_server_set_request()’ must be called setting
     expectations for the received certificate (request or require).  If
     none are set this function will return with
     ‘GNUTLS_E_INVALID_REQUEST’ .

Note that post handshake authentication is available irrespective
     of the initial negotiation type (PSK or certificate).  In all cases
     however, certificate credentials must be set to the session prior
     to calling this function.

*Returns:* ‘GNUTLS_E_SUCCESS’ on a successful authentication,
     otherwise a negative error code.

gnutls_record_can_use_length_hiding
-----------------------------------

-- Function: unsigned gnutls_record_can_use_length_hiding
          (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

If the session supports length-hiding padding, you can invoke
     ‘gnutls_record_send_range()’ to send a message whose length is
     hidden in the given range.  If the session does not support length
     hiding padding, you can use the standard ‘gnutls_record_send()’
     function, or ‘gnutls_record_send_range()’ making sure that the
     range is the same as the length of the message you are trying to
     send.

*Returns:* true (1) if the current session supports length-hiding
     padding, false (0) if the current session does not.

gnutls_record_check_corked
--------------------------

-- Function: size_t gnutls_record_check_corked (gnutls_session_t
          SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

This function checks if there pending corked data in the gnutls
     buffers -see ‘gnutls_record_cork()’ .

*Returns:* Returns the size of the corked data or zero.

*Since:* 3.2.8

gnutls_record_check_pending
---------------------------

-- Function: size_t gnutls_record_check_pending (gnutls_session_t
          SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

This function checks if there are unread data in the gnutls
     buffers.  If the return value is non-zero the next call to
     ‘gnutls_record_recv()’ is guaranteed not to block.

*Returns:* Returns the size of the data or zero.

gnutls_record_cork
------------------

-- Function: void gnutls_record_cork (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

If called, ‘gnutls_record_send()’ will no longer send any records.
     Any sent records will be cached until ‘gnutls_record_uncork()’ is
     called.

This function is safe to use with DTLS after GnuTLS 3.3.0.

*Since:* 3.1.9

gnutls_record_disable_padding
-----------------------------

-- Function: void gnutls_record_disable_padding (gnutls_session_t
          SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Used to disabled padding in TLS 1.0 and above.  Normally you do not
     need to use this function, but there are buggy clients that
     complain if a server pads the encrypted data.  This of course will
     disable protection against statistical attacks on the data.

This function is defunct since 3.1.7.  Random padding is disabled
     by default unless requested using ‘gnutls_record_send_range()’ .

gnutls_record_discard_queued
----------------------------

-- Function: size_t gnutls_record_discard_queued (gnutls_session_t
          SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

This function discards all queued to be sent packets in a DTLS
     session.  These are the packets queued after an interrupted
     ‘gnutls_record_send()’ .

This function can only be used with transports where ‘send()’ is an
     all-or-nothing operation (e.g., UDP). When partial writes are
     allowed this function will cause session errors.

*Returns:* The number of bytes discarded.

*Since:* 3.4.0

gnutls_record_get_direction
---------------------------

-- Function: int gnutls_record_get_direction (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

This function is useful to determine whether a GnuTLS function was
     interrupted while sending or receiving, so that ‘select()’ or
     ‘poll()’ may be called appropriately.

This function's output is unreliable if you are using the same
     ‘session’ in different threads for sending and receiving.

*Returns:* 0 if interrupted while trying to read data, or 1 while
     trying to write data.

gnutls_record_get_max_early_data_size
-------------------------------------

-- Function: size_t gnutls_record_get_max_early_data_size
          (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

This function returns the maximum early data size in this
     connection.  This property can only be set to servers.  The client
     may be provided with the maximum allowed size through the
     "early_data" extension of the NewSessionTicket handshake message.

*Returns:* The maximum early data size in this connection.

*Since:* 3.6.5

gnutls_record_get_max_size
--------------------------

-- Function: size_t gnutls_record_get_max_size (gnutls_session_t
          SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Get the record size.  The maximum record size is negotiated by the
     client after the first handshake message.

*Returns:* The maximum record packet size in this connection.

gnutls_record_get_state
-----------------------

-- Function: int gnutls_record_get_state (gnutls_session_t SESSION,
          unsigned READ, gnutls_datum_t * MAC_KEY, gnutls_datum_t * IV,
          gnutls_datum_t * CIPHER_KEY, unsigned char [8] SEQ_NUMBER)
     SESSION: is a ‘gnutls_session_t’ type

READ: if non-zero the read parameters are returned, otherwise the
     write

MAC_KEY: the key used for MAC (if a MAC is used)

IV: the initialization vector or nonce used

CIPHER_KEY: the cipher key

SEQ_NUMBER: A 64-bit sequence number

This function will return the parameters of the current record
     state.  These are only useful to be provided to an external
     off-loading device or subsystem.  The returned values should be
     considered constant and valid for the lifetime of the session.

In that case, to sync the state back you must call
     ‘gnutls_record_set_state()’ .

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, or an error code.

Since 3.4.0

gnutls_record_overhead_size
---------------------------

-- Function: size_t gnutls_record_overhead_size (gnutls_session_t
          SESSION)
     SESSION: is ‘gnutls_session_t’

This function will return the size in bytes of the overhead due to
     TLS (or DTLS) per record.  On certain occasions (e.g., CBC ciphers)
     the returned value is the maximum possible overhead.

*Since:* 3.2.2

gnutls_record_recv
------------------

-- Function: ssize_t gnutls_record_recv (gnutls_session_t SESSION, void
          * DATA, size_t DATA_SIZE)
     SESSION: is a ‘gnutls_session_t’ type.

DATA: the buffer that the data will be read into

DATA_SIZE: the number of requested bytes

gnutls_record_recv_early_data
-----------------------------

-- Function: ssize_t gnutls_record_recv_early_data (gnutls_session_t
          SESSION, void * DATA, size_t DATA_SIZE)
     SESSION: is a ‘gnutls_session_t’ type.

DATA: the buffer that the data will be read into

DATA_SIZE: the number of requested bytes

This function can be used by a server to retrieve data sent early
     in the handshake processes when resuming a session.  This is used
     to implement a zero-roundtrip (0-RTT) mode.  It has the same
     semantics as ‘gnutls_record_recv()’ .

This function can be called either in a handshake hook, or after
     the handshake is complete.

*Returns:* The number of bytes received and zero when early data
     reading is complete.  A negative error code is returned in case of
     an error.  If no early data is received during the handshake, this
     function returns ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ .  The
     number of bytes received might be less than the requested
     ‘data_size’ .

*Since:* 3.6.5

gnutls_record_recv_packet
-------------------------

-- Function: ssize_t gnutls_record_recv_packet (gnutls_session_t
          SESSION, gnutls_packet_t * PACKET)
     SESSION: is a ‘gnutls_session_t’ type.

PACKET: the structure that will hold the packet data

This is a lower-level function than ‘gnutls_record_recv()’ and
     allows to directly receive the whole decrypted packet.  That avoids
     a memory copy, and is intended to be used by applications seeking
     high performance.

The received packet is accessed using ‘gnutls_packet_get()’ and
     must be deinitialized using ‘gnutls_packet_deinit()’ .  The
     returned packet will be ‘NULL’ if the return value is zero (EOF).

*Returns:* The number of bytes received and zero on EOF (for stream
     connections).  A negative error code is returned in case of an
     error.

*Since:* 3.3.5

gnutls_record_recv_seq
----------------------

-- Function: ssize_t gnutls_record_recv_seq (gnutls_session_t SESSION,
          void * DATA, size_t DATA_SIZE, unsigned char * SEQ)
     SESSION: is a ‘gnutls_session_t’ type.

DATA: the buffer that the data will be read into

DATA_SIZE: the number of requested bytes

SEQ: is the packet's 64-bit sequence number.  Should have space for
     8 bytes.

*Returns:* The number of bytes received and zero on EOF. A negative
     error code is returned in case of an error.  The number of bytes
     received might be less than ‘data_size’ .

*Since:* 3.0

gnutls_record_send
------------------

-- Function: ssize_t gnutls_record_send (gnutls_session_t SESSION,
          const void * DATA, size_t DATA_SIZE)
     SESSION: is a ‘gnutls_session_t’ type.

DATA: contains the data to send

DATA_SIZE: is the length of the data

You can replace the default push function which is ‘send()’ , by
     using ‘gnutls_transport_set_push_function()’ .

gnutls_record_send2
-------------------

DATA: contains the data to send

DATA_SIZE: is the length of the data

PAD: padding to be added to the record

FLAGS: must be zero

Note that in order for GnuTLS to provide constant time processing
     of padding and data in TLS1.3, the flag ‘GNUTLS_SAFE_PADDING_CHECK’
     must be used in ‘gnutls_init()’ .

*Since:* 3.6.3

gnutls_record_send_early_data
-----------------------------

-- Function: ssize_t gnutls_record_send_early_data (gnutls_session_t
          SESSION, const void * DATA, size_t DATA_SIZE)
     SESSION: is a ‘gnutls_session_t’ type.

DATA: contains the data to send

DATA_SIZE: is the length of the data

This function can be used by a client to send data early in the
     handshake processes when resuming a session.  This is used to
     implement a zero-roundtrip (0-RTT) mode.  It has the same semantics
     as ‘gnutls_record_send()’ .

There may be a limit to the amount of data sent as early data.  Use
     ‘gnutls_record_get_max_early_data_size()’ to check the limit.  If
     the limit exceeds, this function returns
     ‘GNUTLS_E_RECORD_LIMIT_REACHED’ .

*Since:* 3.6.5

gnutls_record_send_file
-----------------------

-- Function: ssize_t gnutls_record_send_file (gnutls_session_t SESSION,
          int FD, off_t * OFFSET, size_t COUNT)
     SESSION: is a ‘gnutls_session_t’ type.

FD: file descriptor from which to read data.

OFFSET: Is relative to file offset, denotes the starting location
     for reading.  after function returns, it point to position
     following last read byte.

COUNT: is the length of the data in bytes to be read from file and
     send.

This function sends data from ‘fd’ .  If KTLS (kernel TLS) is
     enabled, it will use the ‘sendfile()’ system call to avoid overhead
     of copying data between user space and the kernel.  Otherwise, this
     functionality is merely emulated by calling ‘read()’ and
     ‘gnutls_record_send()’ .  If this implementation is suboptimal,
     check whether KTLS is enabled using
     ‘gnutls_transport_is_ktls_enabled()’ .

If ‘offset’ is NULL then file offset is incremented by number of
     bytes send, otherwise file offset remains unchanged.

*Returns:* The number of bytes sent, or a negative error code.

gnutls_record_send_range
------------------------

-- Function: ssize_t gnutls_record_send_range (gnutls_session_t
          SESSION, const void * DATA, size_t DATA_SIZE, const
          gnutls_range_st * RANGE)
     SESSION: is a ‘gnutls_session_t’ type.

DATA: contains the data to send.

DATA_SIZE: is the length of the data.

RANGE: is the range of lengths in which the real data length must
     be hidden.

This function operates like ‘gnutls_record_send()’ but, while
     ‘gnutls_record_send()’ adds minimal padding to each TLS record,
     this function uses the TLS extra-padding feature to conceal the
     real data size within the range of lengths provided.  Some TLS
     sessions do not support extra padding (e.g.  stream ciphers in
     standard TLS or SSL3 sessions).  To know whether the current
     session supports extra padding, and hence length hiding, use the
     ‘gnutls_record_can_use_length_hiding()’ function.

*Note:* This function currently is limited to blocking sockets.

*Returns:* The number of bytes sent (that is data_size in a
     successful invocation), or a negative error code.

gnutls_record_set_max_early_data_size
-------------------------------------

-- Function: int gnutls_record_set_max_early_data_size
          (gnutls_session_t SESSION, size_t SIZE)
     SESSION: is a ‘gnutls_session_t’ type.

SIZE: is the new size

This function sets the maximum early data size in this connection.
     This property can only be set to servers.  The client may be
     provided with the maximum allowed size through the "early_data"
     extension of the NewSessionTicket handshake message.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

*Since:* 3.6.4

gnutls_record_set_max_recv_size
-------------------------------

-- Function: ssize_t gnutls_record_set_max_recv_size (gnutls_session_t
          SESSION, size_t SIZE)
     SESSION: is a ‘gnutls_session_t’ type.

SIZE: is the new size

This function sets the maximum amount of plaintext received in a
     record in this connection.

The limit is also negotiated through a TLS extension called 'record
     size limit'.  Note that while the 'record size limit' extension is
     preferred, not all TLS implementations use or even understand the
     extension.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

*Since:* 3.6.8

gnutls_record_set_max_size
--------------------------

-- Function: ssize_t gnutls_record_set_max_size (gnutls_session_t
          SESSION, size_t SIZE)
     SESSION: is a ‘gnutls_session_t’ type.

SIZE: is the new size

This function sets the maximum amount of plaintext sent and
     received in a record in this connection.

Prior to 3.6.4, this function was implemented using a TLS extension
     called 'max fragment length', which limits the acceptable values to
     512(=2^9), 1024(=2^10), 2048(=2^11) and 4096(=2^12).

Since 3.6.4, the limit is also negotiated through a new TLS
     extension called 'record size limit', which doesn't have the
     limitation, as long as the value ranges between 512 and 16384.
     Note that while the 'record size limit' extension is preferred, not
     all TLS implementations use or even understand the extension.

*Deprecated:* if the client can assume that the 'record size limit'
     extension is supported by the server, we recommend using
     ‘gnutls_record_set_max_recv_size()’ instead.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

gnutls_record_set_state
-----------------------

-- Function: int gnutls_record_set_state (gnutls_session_t SESSION,
          unsigned READ, const unsigned char [8] SEQ_NUMBER)
     SESSION: is a ‘gnutls_session_t’ type

READ: if non-zero the read parameters are returned, otherwise the
     write

SEQ_NUMBER: A 64-bit sequence number

This function will set the sequence number in the current record
     state.  This function is useful if sending and receiving are
     offloaded from gnutls.  That is, if ‘gnutls_record_get_state()’ was
     used.

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, or an error code.

Since 3.4.0

gnutls_record_set_timeout
-------------------------

-- Function: void gnutls_record_set_timeout (gnutls_session_t SESSION,
          unsigned int MS)
     SESSION: is a ‘gnutls_session_t’ type.

MS: is a timeout value in milliseconds

This function sets the receive timeout for the record layer to the
     provided value.  Use an ‘ms’ value of zero to disable timeout (the
     default), or ‘GNUTLS_INDEFINITE_TIMEOUT’ , to set an indefinite
     timeout.

This function requires to set a pull timeout callback.  See
     ‘gnutls_transport_set_pull_timeout_function()’ .

*Since:* 3.1.7

gnutls_record_uncork
--------------------

-- Function: int gnutls_record_uncork (gnutls_session_t SESSION,
          unsigned int FLAGS)
     SESSION: is a ‘gnutls_session_t’ type.

FLAGS: Could be zero or ‘GNUTLS_RECORD_WAIT’

*Returns:* On success the number of transmitted data is returned,
     or otherwise a negative error code.

*Since:* 3.1.9

gnutls_rehandshake
------------------

-- Function: int gnutls_rehandshake (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

This function can only be called in server side, and instructs a
     TLS 1.2 or earlier client to renegotiate parameters (perform a
     handshake), by sending a hello request message.

Once the ‘GNUTLS_E_REHANDSHAKE’ error code is seen, the calling
     application should proceed to calling ‘gnutls_handshake()’ to
     negotiate the new parameters.

This function always fails with ‘GNUTLS_E_INVALID_REQUEST’ when
     called in client side.

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, otherwise a negative
     error code.

gnutls_safe_renegotiation_status
--------------------------------

-- Function: unsigned gnutls_safe_renegotiation_status
          (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Can be used to check whether safe renegotiation is being used in
     the current session.

*Returns:* 0 when safe renegotiation is not used and non (0) when
     safe renegotiation is used.

*Since:* 2.10.0

gnutls_sec_param_get_name
-------------------------

-- Function: const char * gnutls_sec_param_get_name (gnutls_sec_param_t
          PARAM)
     PARAM: is a security parameter

Convert a ‘gnutls_sec_param_t’ value to a string.

*Returns:* a pointer to a string that contains the name of the
     specified security level, or ‘NULL’ .

*Since:* 2.12.0

gnutls_sec_param_to_pk_bits
---------------------------

-- Function: unsigned int gnutls_sec_param_to_pk_bits
          (gnutls_pk_algorithm_t ALGO, gnutls_sec_param_t PARAM)
     ALGO: is a public key algorithm

PARAM: is a security parameter

*Returns:* The number of bits, or (0).

*Since:* 2.12.0

gnutls_sec_param_to_symmetric_bits
----------------------------------

-- Function: unsigned int gnutls_sec_param_to_symmetric_bits
          (gnutls_sec_param_t PARAM)
     PARAM: is a security parameter

This function will return the number of bits that correspond to
     symmetric cipher strength for the given security parameter.

*Returns:* The number of bits, or (0).

*Since:* 3.3.0

gnutls_server_name_get
----------------------

-- Function: int gnutls_server_name_get (gnutls_session_t SESSION, void
          * DATA, size_t * DATA_LENGTH, unsigned int * TYPE, unsigned
          int INDX)
     SESSION: is a ‘gnutls_session_t’ type.

DATA: will hold the data

DATA_LENGTH: will hold the data length.  Must hold the maximum size
     of data.

TYPE: will hold the server name indicator type

INDX: is the index of the server_name

This function will allow you to get the name indication (if any), a
     client has sent.  The name indication may be any of the enumeration
     gnutls_server_name_type_t.

If ‘type’ is GNUTLS_NAME_DNS, then this function is to be used by
     servers that support virtual hosting, and the data will be a null
     terminated IDNA ACE string (prior to GnuTLS 3.4.0 it was a UTF-8
     string).

If ‘data’ has not enough size to hold the server name
     GNUTLS_E_SHORT_MEMORY_BUFFER is returned, and ‘data_length’ will
     hold the required size.

‘indx’ is used to retrieve more than one server names (if sent by
     the client).  The first server name has an index of 0, the second 1
     and so on.  If no name with the given index exists
     GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE is returned.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned, on UTF-8
     decoding error ‘GNUTLS_E_IDNA_ERROR’ is returned, otherwise a
     negative error code is returned.

gnutls_server_name_set
----------------------

-- Function: int gnutls_server_name_set (gnutls_session_t SESSION,
          gnutls_server_name_type_t TYPE, const void * NAME, size_t
          NAME_LENGTH)
     SESSION: is a ‘gnutls_session_t’ type.

TYPE: specifies the indicator type

NAME: is a string that contains the server name.

NAME_LENGTH: holds the length of name excluding the terminating
     null byte

This function is to be used by clients that want to inform (via a
     TLS extension mechanism) the server of the name they connected to.
     This should be used by clients that connect to servers that do
     virtual hosting.

The value of ‘name’ depends on the ‘type’ type.  In case of
     ‘GNUTLS_NAME_DNS’ , a UTF-8 null-terminated domain name string,
     without the trailing dot, is expected.

IPv4 or IPv6 addresses are not permitted to be set by this
     function.  If the function is called with a name of ‘name_length’
     zero it will clear all server names set.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

gnutls_session_channel_binding
------------------------------

-- Function: int gnutls_session_channel_binding (gnutls_session_t
          SESSION, gnutls_channel_binding_t CBTYPE, gnutls_datum_t * CB)
     SESSION: is a ‘gnutls_session_t’ type.

CBTYPE: an ‘gnutls_channel_binding_t’ enumeration type

CB: output buffer array with data

Extract given channel binding data of the ‘cbtype’ (e.g.,
     ‘GNUTLS_CB_TLS_UNIQUE’ ) type.

*Returns:* ‘GNUTLS_E_SUCCESS’ on success,
     ‘GNUTLS_E_UNIMPLEMENTED_FEATURE’ if the ‘cbtype’ is unsupported,
     ‘GNUTLS_E_CHANNEL_BINDING_NOT_AVAILABLE’ if the data is not
     currently available, or an error code.

*Since:* 2.12.0

gnutls_session_enable_compatibility_mode
----------------------------------------

-- Function: void gnutls_session_enable_compatibility_mode
          (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

This function can be used to disable certain (security) features in
     TLS in order to maintain maximum compatibility with buggy clients.
     Because several trade-offs with security are enabled, if required
     they will be reported through the audit subsystem.

Normally only servers that require maximum compatibility with
     everything out there, need to call this function.

Note that this function must be called after any call to
     gnutls_priority functions.

*Since:* 2.1.4

gnutls_session_etm_status
-------------------------

-- Function: unsigned gnutls_session_etm_status (gnutls_session_t
          SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Get the status of the encrypt-then-mac extension negotiation.  This
     is in accordance to rfc7366

*Returns:* Non-zero if the negotiation was successful or zero
     otherwise.

gnutls_session_ext_master_secret_status
---------------------------------------

-- Function: unsigned gnutls_session_ext_master_secret_status
          (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Get the status of the extended master secret extension negotiation.
     This is in accordance to RFC7627.  That information is also
     available to the more generic ‘gnutls_session_get_flags()’ .

*Returns:* Non-zero if the negotiation was successful or zero
     otherwise.

gnutls_session_ext_register
---------------------------

-- Function: int gnutls_session_ext_register (gnutls_session_t SESSION,
          const char * NAME, int ID, gnutls_ext_parse_type_t
          PARSE_POINT, gnutls_ext_recv_func RECV_FUNC,
          gnutls_ext_send_func SEND_FUNC, gnutls_ext_deinit_data_func
          DEINIT_FUNC, gnutls_ext_pack_func PACK_FUNC,
          gnutls_ext_unpack_func UNPACK_FUNC, unsigned FLAGS)
     SESSION: the session for which this extension will be set

NAME: the name of the extension to register

ID: the numeric id of the extension

PARSE_POINT: the parse type of the extension (see
     gnutls_ext_parse_type_t)

RECV_FUNC: a function to receive the data

SEND_FUNC: a function to send the data

DEINIT_FUNC: a function deinitialize any private data

PACK_FUNC: a function which serializes the extension's private data
     (used on session packing for resumption)

UNPACK_FUNC: a function which will deserialize the extension's
     private data

FLAGS: must be zero or flags from ‘gnutls_ext_flags_t’

This function will register a new extension type.  The extension
     will be only usable within the registered session.  If the
     extension type is already registered then
     ‘GNUTLS_E_ALREADY_REGISTERED’ will be returned, unless the flag
     ‘GNUTLS_EXT_FLAG_OVERRIDE_INTERNAL’ is specified.  The latter flag
     when specified can be used to override certain extensions
     introduced after 3.6.0.  It is expected to be used by applications
     which handle custom extensions that are not currently supported in
     GnuTLS, but direct support for them may be added in the future.

Each registered extension can store temporary data into the
     gnutls_session_t structure using ‘gnutls_ext_set_data()’ , and they
     can be retrieved using ‘gnutls_ext_get_data()’ .

The validity of the extension registered can be given by the
     appropriate flags of ‘gnutls_ext_flags_t’ .  If no validity is
     given, then the registered extension will be valid for client and
     TLS1.2 server hello (or encrypted extensions for TLS1.3).

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, otherwise a negative
     error code.

*Since:* 3.5.5

gnutls_session_force_valid
--------------------------

-- Function: void gnutls_session_force_valid (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Clears the invalid flag in a session.  That means that sessions
     were corrupt or invalid data were received can be re-used.  Use
     only when debugging or experimenting with the TLS protocol.  Should
     not be used in typical applications.

gnutls_session_get_data
-----------------------

-- Function: int gnutls_session_get_data (gnutls_session_t SESSION,
          void * SESSION_DATA, size_t * SESSION_DATA_SIZE)
     SESSION: is a ‘gnutls_session_t’ type.

SESSION_DATA: is a pointer to space to hold the session.

SESSION_DATA_SIZE: is the session_data's size, or it will be set by
     the function.

Returns all session parameters needed to be stored to support
     resumption, in a pre-allocated buffer.

See ‘gnutls_session_get_data2()’ for more information.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise an error code is returned.

gnutls_session_get_data2
------------------------

-- Function: int gnutls_session_get_data2 (gnutls_session_t SESSION,
          gnutls_datum_t * DATA)
     SESSION: is a ‘gnutls_session_t’ type.

DATA: is a pointer to a datum that will hold the session.

Returns necessary parameters to support resumption.  The client
     should call this function and store the returned session data.  A
     session can be resumed later by calling ‘gnutls_session_set_data()’
     with the returned data.  Note that under TLS 1.3, it is recommended
     for clients to use session parameters only once, to prevent
     passive-observers from correlating the different connections.

The returned ‘data’ are allocated and must be released using
     ‘gnutls_free()’ .

This function will fail if called prior to handshake completion.
     In case of false start TLS, the handshake completes only after data
     have been successfully received from the peer.

Under TLS1.3 session resumption is possible only after a session
     ticket is received by the client.  To ensure that such a ticket has
     been received use ‘gnutls_session_get_flags()’ and check for flag
     ‘GNUTLS_SFLAGS_SESSION_TICKET’ ; if this flag is not set, this
     function will wait for a new ticket within an estimated roundtrip,
     and if not received will return dummy data which cannot lead to
     resumption.

To get notified when new tickets are received by the server use
     ‘gnutls_handshake_set_hook_function()’ to wait for
     ‘GNUTLS_HANDSHAKE_NEW_SESSION_TICKET’ messages.  Each call of
     ‘gnutls_session_get_data2()’ after a ticket is received, will
     return session resumption data corresponding to the last received
     ticket.

Note that this function under TLS1.3 requires a callback to be set
     with ‘gnutls_transport_set_pull_timeout_function()’ for successful
     operation.  There was a bug before 3.6.10 which could make this
     function fail if that callback was not set.  On later versions if
     not set, the function will return a successful error code, but will
     return dummy data that cannot lead to a resumption.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise an error code is returned.

gnutls_session_get_desc
-----------------------

-- Function: char * gnutls_session_get_desc (gnutls_session_t SESSION)
     SESSION: is a gnutls session

This function returns a string describing the current session.  The
     string is null terminated and allocated using ‘gnutls_malloc()’ .

If initial negotiation is not complete when this function is
     called, ‘NULL’ will be returned.

*Returns:* a description of the protocols and algorithms in the
     current session.

*Since:* 3.1.10

gnutls_session_get_flags
------------------------

-- Function: unsigned gnutls_session_get_flags (gnutls_session_t
          SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

This function will return a series (ORed) of flags, applicable for
     the current session.

This replaces individual informational functions such as
     ‘gnutls_safe_renegotiation_status()’ ,
     ‘gnutls_session_ext_master_secret_status()’ , etc.

*Returns:* An ORed sequence of flags (see ‘gnutls_session_flags_t’
     )

*Since:* 3.5.0

gnutls_session_get_id
---------------------

-- Function: int gnutls_session_get_id (gnutls_session_t SESSION, void
          * SESSION_ID, size_t * SESSION_ID_SIZE)
     SESSION: is a ‘gnutls_session_t’ type.

SESSION_ID: is a pointer to space to hold the session id.

SESSION_ID_SIZE: initially should contain the maximum ‘session_id’
     size and will be updated.

Returns the TLS session identifier.  The session ID is selected by
     the server, and in older versions of TLS was a unique identifier
     shared between client and server which was persistent across
     resumption.  In the latest version of TLS (1.3) or TLS with session
     tickets, the notion of session identifiers is undefined and cannot
     be relied for uniquely identifying sessions across client and
     server.

The session identifier value returned is always less than
     ‘GNUTLS_MAX_SESSION_ID_SIZE’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise an error code is returned.

gnutls_session_get_id2
----------------------

-- Function: int gnutls_session_get_id2 (gnutls_session_t SESSION,
          gnutls_datum_t * SESSION_ID)
     SESSION: is a ‘gnutls_session_t’ type.

SESSION_ID: will point to the session ID.

The session identifier value returned is always less than
     ‘GNUTLS_MAX_SESSION_ID_SIZE’ and should be treated as constant.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise an error code is returned.

*Since:* 3.1.4

gnutls_session_get_keylog_function
----------------------------------

-- Function: gnutls_keylog_func gnutls_session_get_keylog_function
          (const gnutls_session_t SESSION)
     SESSION: is ‘gnutls_session_t’ type

This function will return the callback function set using
     ‘gnutls_session_set_keylog_function()’ .

*Returns:* The function set or ‘NULL’ otherwise.

*Since:* 3.6.13

gnutls_session_get_master_secret
--------------------------------

-- Function: void gnutls_session_get_master_secret (gnutls_session_t
          SESSION, gnutls_datum_t * SECRET)
     SESSION: is a ‘gnutls_session_t’ type.

SECRET: the session's master secret

This function returns pointers to the master secret used in the TLS
     session.  The pointers are not to be modified or deallocated.

This function is only applicable under TLS 1.2 or earlier versions.

*Since:* 3.5.0

gnutls_session_get_ptr
----------------------

-- Function: void * gnutls_session_get_ptr (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Get user pointer for session.  Useful in callbacks.  This is the
     pointer set with ‘gnutls_session_set_ptr()’ .

*Returns:* the user given pointer from the session structure, or
     ‘NULL’ if it was never set.

gnutls_session_get_random
-------------------------

-- Function: void gnutls_session_get_random (gnutls_session_t SESSION,
          gnutls_datum_t * CLIENT, gnutls_datum_t * SERVER)
     SESSION: is a ‘gnutls_session_t’ type.

CLIENT: the client part of the random

SERVER: the server part of the random

This function returns pointers to the client and server random
     fields used in the TLS handshake.  The pointers are not to be
     modified or deallocated.

If a client random value has not yet been established, the output
     will be garbage.

*Since:* 3.0

gnutls_session_get_verify_cert_status
-------------------------------------

-- Function: unsigned int gnutls_session_get_verify_cert_status
          (gnutls_session_t SESSION)
     SESSION: is a gnutls session

This function returns the status of the verification when initiated
     via auto-verification, i.e., by ‘gnutls_session_set_verify_cert2()’
     or ‘gnutls_session_set_verify_cert()’ .  If no certificate
     verification was occurred then the return value would be set to
     ((unsigned int)-1).

The certificate verification status is the same as in
     ‘gnutls_certificate_verify_peers()’ .

*Returns:* the certificate verification status.

*Since:* 3.4.6

gnutls_session_is_resumed
-------------------------

-- Function: int gnutls_session_is_resumed (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Checks whether session is resumed or not.  This is functional for
     both server and client side.

*Returns:* non zero if this session is resumed, or a zero if this
     is a new session.

gnutls_session_key_update
-------------------------

-- Function: int gnutls_session_key_update (gnutls_session_t SESSION,
          unsigned FLAGS)
     SESSION: is a ‘gnutls_session_t’ type.

FLAGS: zero of ‘GNUTLS_KU_PEER’

This function will update/refresh the session keys when the TLS
     protocol is 1.3 or better.  The peer is notified of the update by
     sending a message, so this function should be treated similarly to
     ‘gnutls_record_send()’ -i.e., it may return ‘GNUTLS_E_AGAIN’ or
     ‘GNUTLS_E_INTERRUPTED’ .

When this flag ‘GNUTLS_KU_PEER’ is specified, this function in
     addition to updating the local keys, will ask the peer to refresh
     its keys too.

If the negotiated version is not TLS 1.3 or better this function
     will return ‘GNUTLS_E_INVALID_REQUEST’ .

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, otherwise a negative
     error code.

*Since:* 3.6.3

gnutls_session_resumption_requested
-----------------------------------

-- Function: int gnutls_session_resumption_requested (gnutls_session_t
          SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Check whether the client has asked for session resumption.  This
     function is valid only on server side.

*Returns:* non zero if session resumption was asked, or a zero if
     not.

gnutls_session_set_data
-----------------------

-- Function: int gnutls_session_set_data (gnutls_session_t SESSION,
          const void * SESSION_DATA, size_t SESSION_DATA_SIZE)
     SESSION: is a ‘gnutls_session_t’ type.

SESSION_DATA: is a pointer to space to hold the session.

SESSION_DATA_SIZE: is the session's size

Sets all session parameters, in order to resume a previously
     established session.  The session data given must be the one
     returned by ‘gnutls_session_get_data()’ .  This function should be
     called before ‘gnutls_handshake()’ .

Keep in mind that session resuming is advisory.  The server may
     choose not to resume the session, thus a full handshake will be
     performed.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise an error code is returned.

gnutls_session_set_id
---------------------

-- Function: int gnutls_session_set_id (gnutls_session_t SESSION, const
          gnutls_datum_t * SID)
     SESSION: is a ‘gnutls_session_t’ type.

SID: the session identifier

This function sets the session ID to be used in a client hello.
     This is a function intended for exceptional uses.  Do not use this
     function unless you are implementing a custom protocol.

To set session resumption parameters use
     ‘gnutls_session_set_data()’ instead.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise an error code is returned.

*Since:* 3.2.1

gnutls_session_set_keylog_function
----------------------------------

-- Function: void gnutls_session_set_keylog_function (gnutls_session_t
          SESSION, gnutls_keylog_func FUNC)
     SESSION: is ‘gnutls_session_t’ type

FUNC: is the function to be called

This function will set a callback to be called when a new secret is
     derived and installed during handshake.

*Since:* 3.6.13

gnutls_session_set_premaster
----------------------------

-- Function: int gnutls_session_set_premaster (gnutls_session_t
          SESSION, unsigned int ENTITY, gnutls_protocol_t VERSION,
          gnutls_kx_algorithm_t KX, gnutls_cipher_algorithm_t CIPHER,
          gnutls_mac_algorithm_t MAC, gnutls_compression_method_t COMP,
          const gnutls_datum_t * MASTER, const gnutls_datum_t *
          SESSION_ID)
     SESSION: is a ‘gnutls_session_t’ type.

ENTITY: GNUTLS_SERVER or GNUTLS_CLIENT

VERSION: the TLS protocol version

KX: the key exchange method

CIPHER: the cipher

MAC: the MAC algorithm

COMP: the compression method (ignored)

MASTER: the master key to use

SESSION_ID: the session identifier

This function sets the premaster secret in a session.  This is a
     function intended for exceptional uses.  Do not use this function
     unless you are implementing a legacy protocol.  Use
     ‘gnutls_session_set_data()’ instead.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise an error code is returned.

gnutls_session_set_ptr
----------------------

-- Function: void gnutls_session_set_ptr (gnutls_session_t SESSION,
          void * PTR)
     SESSION: is a ‘gnutls_session_t’ type.

PTR: is the user pointer

This function will set (associate) the user given pointer ‘ptr’ to
     the session structure.  This pointer can be accessed with
     ‘gnutls_session_get_ptr()’ .

gnutls_session_set_verify_cert
------------------------------

-- Function: void gnutls_session_set_verify_cert (gnutls_session_t
          SESSION, const char * HOSTNAME, unsigned FLAGS)
     SESSION: is a gnutls session

HOSTNAME: is the expected name of the peer; may be ‘NULL’

FLAGS: flags for certificate verification -
     ‘gnutls_certificate_verify_flags’

If ‘flags’ is provided which contain a profile, this function
     should be called after any session priority setting functions.

The ‘gnutls_session_set_verify_cert()’ function is intended to be
     used by TLS clients to verify the server's certificate.

*Since:* 3.4.6

gnutls_session_set_verify_cert2
-------------------------------

-- Function: void gnutls_session_set_verify_cert2 (gnutls_session_t
          SESSION, gnutls_typed_vdata_st * DATA, unsigned ELEMENTS,
          unsigned FLAGS)
     SESSION: is a gnutls session

DATA: an array of typed data

ELEMENTS: the number of data elements

FLAGS: flags for certificate verification -
     ‘gnutls_certificate_verify_flags’

This function instructs GnuTLS to verify the peer's certificate
     using the provided typed data information.  If the verification
     fails the handshake will also fail with
     ‘GNUTLS_E_CERTIFICATE_VERIFICATION_ERROR’ .  In that case the
     verification result can be obtained using
     ‘gnutls_session_get_verify_cert_status()’ .

The acceptable typed data are the same as in
     ‘gnutls_certificate_verify_peers()’ , and once set must remain
     valid for the lifetime of the session.  More precisely they should
     be available during any subsequent handshakes.

If ‘flags’ is provided which contain a profile, this function
     should be called after any session priority setting functions.

*Since:* 3.4.6

gnutls_session_set_verify_function
----------------------------------

-- Function: void gnutls_session_set_verify_function (gnutls_session_t
          SESSION, gnutls_certificate_verify_function * FUNC)
     SESSION: is a ‘gnutls_session_t’ type.

FUNC: is the callback function

This function sets a callback to be called when peer's certificate
     has been received in order to verify it on receipt rather than
     doing after the handshake is completed.  This overrides any
     callback set using ‘gnutls_certificate_set_verify_function()’ .

The callback's function prototype is: int
     (*callback)(gnutls_session_t);

The callback function should return 0 for the handshake to continue
     or non-zero to terminate.

*Since:* 3.4.6

gnutls_session_supplemental_register
------------------------------------

-- Function: int gnutls_session_supplemental_register (gnutls_session_t
          SESSION, const char * NAME,
          gnutls_supplemental_data_format_type_t TYPE,
          gnutls_supp_recv_func RECV_FUNC, gnutls_supp_send_func
          SEND_FUNC, unsigned FLAGS)
     SESSION: the session for which this will be registered

NAME: the name of the supplemental data to register

TYPE: the type of the supplemental data format

RECV_FUNC: the function to receive the data

SEND_FUNC: the function to send the data

FLAGS: must be zero

This function will register a new supplemental data type (rfc4680).
     The registered supplemental functions will be used for that
     specific session.  The provided ‘type’ must be an unassigned type
     in ‘gnutls_supplemental_data_format_type_t’ .

If the type is already registered or handled by GnuTLS internally
     ‘GNUTLS_E_ALREADY_REGISTERED’ will be returned.

As supplemental data are not defined under TLS 1.3, this function
     will disable TLS 1.3 support for the given session.

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, otherwise a negative
     error code.

*Since:* 3.5.5

gnutls_session_ticket_enable_client
-----------------------------------

-- Function: int gnutls_session_ticket_enable_client (gnutls_session_t
          SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Request that the client should attempt session resumption using
     SessionTicket.  This call is typically unnecessary as session
     tickets are enabled by default.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned, or an
     error code.

*Since:* 2.10.0

gnutls_session_ticket_enable_server
-----------------------------------

-- Function: int gnutls_session_ticket_enable_server (gnutls_session_t
          SESSION, const gnutls_datum_t * KEY)
     SESSION: is a ‘gnutls_session_t’ type.

KEY: key to encrypt session parameters.

The default ticket expiration time can be overridden using
     ‘gnutls_db_set_cache_expiration()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned, or an
     error code.

*Since:* 2.10.0

gnutls_session_ticket_key_generate
----------------------------------

-- Function: int gnutls_session_ticket_key_generate (gnutls_datum_t *
          KEY)
     KEY: is a pointer to a ‘gnutls_datum_t’ which will contain a newly
     created key.

Generate a random key to encrypt security parameters within
     SessionTicket.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned, or an
     error code.

*Since:* 2.10.0

gnutls_session_ticket_send
--------------------------

-- Function: int gnutls_session_ticket_send (gnutls_session_t SESSION,
          unsigned NR, unsigned FLAGS)
     SESSION: is a ‘gnutls_session_t’ type.

NR: the number of tickets to send

FLAGS: must be zero

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, or a negative error code.

gnutls_set_default_priority
---------------------------

-- Function: int gnutls_set_default_priority (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Sets the default priority on the ciphers, key exchange methods, and
     macs.  This is the recommended method of setting the defaults, in
     order to promote consistency between applications using GnuTLS, and
     to allow GnuTLS using applications to update settings in par with
     the library.  For client applications which require maximum
     compatibility consider calling
     ‘gnutls_session_enable_compatibility_mode()’ after this function.

For an application to specify additional options to priority string
     consider using ‘gnutls_set_default_priority_append()’ .

To allow a user to override the defaults (e.g., when a user
     interface or configuration file is available), the functions
     ‘gnutls_priority_set_direct()’ or ‘gnutls_priority_set()’ can be
     used.

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, or an error code.

*Since:* 2.1.4

gnutls_set_default_priority_append
----------------------------------

-- Function: int gnutls_set_default_priority_append (gnutls_session_t
          SESSION, const char * ADD_PRIO, const char ** ERR_POS,
          unsigned FLAGS)
     SESSION: is a ‘gnutls_session_t’ type.

ADD_PRIO: is a string describing priorities to be appended to
     default

ERR_POS: In case of an error this will have the position in the
     string the error occurred

FLAGS: must be zero

Sets the default priority on the ciphers, key exchange methods, and
     macs with the additional options in ‘add_prio’ .  This is the
     recommended method of setting the defaults when only few additional
     options are to be added.  This promotes consistency between
     applications using GnuTLS, and allows GnuTLS using applications to
     update settings in par with the library.

The ‘add_prio’ string should start as a normal priority string,
     e.g., '-VERS-TLS-ALL:+VERS-TLS1.3:%COMPAT' or '%FORCE_ETM'. That
     is, it must not start with ':'.

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, or an error code.

*Since:* 3.6.3

gnutls_sign_algorithm_get
-------------------------

-- Function: int gnutls_sign_algorithm_get (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Returns the signature algorithm that is (or will be) used in this
     session by the server to sign data.  This function should be used
     only with TLS 1.2 or later.

*Returns:* The sign algorithm or ‘GNUTLS_SIGN_UNKNOWN’ .

*Since:* 3.1.1

gnutls_sign_algorithm_get_client
--------------------------------

-- Function: int gnutls_sign_algorithm_get_client (gnutls_session_t
          SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Returns the signature algorithm that is (or will be) used in this
     session by the client to sign data.  This function should be used
     only with TLS 1.2 or later.

*Returns:* The sign algorithm or ‘GNUTLS_SIGN_UNKNOWN’ .

*Since:* 3.1.11

gnutls_sign_algorithm_get_requested
-----------------------------------

-- Function: int gnutls_sign_algorithm_get_requested (gnutls_session_t
          SESSION, size_t INDX, gnutls_sign_algorithm_t * ALGO)
     SESSION: is a ‘gnutls_session_t’ type.

INDX: is an index of the signature algorithm to return

ALGO: the returned certificate type will be stored there

Returns the signature algorithm specified by index that was
     requested by the peer.  If the specified index has no data
     available this function returns
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ .  If the negotiated TLS
     version does not support signature algorithms then
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ will be returned even for
     the first index.  The first index is 0.

This function is useful in the certificate callback functions to
     assist in selecting the correct certificate.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise an error code is returned.

*Since:* 2.10.0

gnutls_sign_get_hash_algorithm
------------------------------

-- Function: gnutls_digest_algorithm_t gnutls_sign_get_hash_algorithm
          (gnutls_sign_algorithm_t SIGN)
     SIGN: is a signature algorithm

This function returns the digest algorithm corresponding to the
     given signature algorithms.

*Since:* 3.1.1

*Returns:* return a ‘gnutls_digest_algorithm_t’ value, or
     ‘GNUTLS_DIG_UNKNOWN’ on error.

gnutls_sign_get_id
------------------

-- Function: gnutls_sign_algorithm_t gnutls_sign_get_id (const char *
          NAME)
     NAME: is a sign algorithm name

The names are compared in a case insensitive way.

*Returns:* return a ‘gnutls_sign_algorithm_t’ value corresponding
     to the specified algorithm, or ‘GNUTLS_SIGN_UNKNOWN’ on error.

gnutls_sign_get_name
--------------------

-- Function: const char * gnutls_sign_get_name (gnutls_sign_algorithm_t
          ALGORITHM)
     ALGORITHM: is a sign algorithm

Convert a ‘gnutls_sign_algorithm_t’ value to a string.

*Returns:* a string that contains the name of the specified sign
     algorithm, or ‘NULL’ .

gnutls_sign_get_oid
-------------------

-- Function: const char * gnutls_sign_get_oid (gnutls_sign_algorithm_t
          SIGN)
     SIGN: is a sign algorithm

Convert a ‘gnutls_sign_algorithm_t’ value to its object identifier.

*Returns:* a string that contains the object identifier of the
     specified sign algorithm, or ‘NULL’ .

*Since:* 3.4.3

gnutls_sign_get_pk_algorithm
----------------------------

-- Function: gnutls_pk_algorithm_t gnutls_sign_get_pk_algorithm
          (gnutls_sign_algorithm_t SIGN)
     SIGN: is a signature algorithm

This function returns the public key algorithm corresponding to the
     given signature algorithms.  Note that there may be multiple public
     key algorithms supporting a particular signature type; when dealing
     with such algorithms use instead
     ‘gnutls_sign_supports_pk_algorithm()’ .

*Since:* 3.1.1

*Returns:* return a ‘gnutls_pk_algorithm_t’ value, or
     ‘GNUTLS_PK_UNKNOWN’ on error.

gnutls_sign_is_secure
---------------------

-- Function: unsigned gnutls_sign_is_secure (gnutls_sign_algorithm_t
          ALGORITHM)
     ALGORITHM: is a sign algorithm

*Returns:* Non-zero if the provided signature algorithm is
     considered to be secure.

gnutls_sign_is_secure2
----------------------

-- Function: unsigned gnutls_sign_is_secure2 (gnutls_sign_algorithm_t
          ALGORITHM, unsigned int FLAGS)
     ALGORITHM: is a sign algorithm

FLAGS: zero or ‘GNUTLS_SIGN_FLAG_SECURE_FOR_CERTS’

*Returns:* Non-zero if the provided signature algorithm is
     considered to be secure.

gnutls_sign_list
----------------

-- Function: const gnutls_sign_algorithm_t * gnutls_sign_list ( VOID)

Get a list of supported public key signature algorithms.  This
     function is not thread safe.

*Returns:* a (0)-terminated list of ‘gnutls_sign_algorithm_t’
     integers indicating the available ciphers.

gnutls_sign_set_secure
----------------------

-- Function: int gnutls_sign_set_secure (gnutls_sign_algorithm_t SIGN,
          unsigned int SECURE)
     SIGN: the sign algorithm

SECURE: whether to mark the sign algorithm secure

Modify the previous system wide setting that marked ‘sign’ as
     secure or insecure.  Calling this function is allowed only if
     allowlisting mode is set in the configuration file, and only if the
     system-wide TLS priority string has not been initialized yet.  The
     intended usage is to provide applications with a way to expressly
     deviate from the distribution or site defaults inherited from the
     configuration file.  The modification is composable with further
     modifications performed through the priority string mechanism.

This function is not thread-safe and is intended to be called in
     the main thread at the beginning of the process execution.

Even when ‘secure’ is true, ‘sign’ is not marked as secure for the
     use in certificates.  Use ‘gnutls_sign_set_secure_for_certs()’ to
     mark it secure as well for certificates.

*Returns:* 0 on success or negative error code otherwise.

*Since:* 3.7.3

gnutls_sign_set_secure_for_certs
--------------------------------

-- Function: int gnutls_sign_set_secure_for_certs
          (gnutls_sign_algorithm_t SIGN, unsigned int SECURE)
     SIGN: the sign algorithm

SECURE: whether to mark the sign algorithm secure for certificates

Modify the previous system wide setting that marked ‘sign’ as
     secure or insecure for the use in certificates.  Calling this
     function is allowed only if allowlisting mode is set in the
     configuration file, and only if the system-wide TLS priority string
     has not been initialized yet.  The intended usage is to provide
     applications with a way to expressly deviate from the distribution
     or site defaults inherited from the configuration file.  The
     modification is composable with further modifications performed
     through the priority string mechanism.

This function is not thread-safe and is intended to be called in
     the main thread at the beginning of the process execution.  When
     ‘secure’ is true, ‘sign’ is marked as secure for any use unlike
     ‘gnutls_sign_set_secure()’ .  Otherwise, it is marked as insecure
     only for the use in certificates.  Use ‘gnutls_sign_set_secure()’
     to mark it insecure for any uses.

*Returns:* 0 on success or negative error code otherwise.

*Since:* 3.7.3

gnutls_sign_supports_pk_algorithm
---------------------------------

-- Function: unsigned gnutls_sign_supports_pk_algorithm
          (gnutls_sign_algorithm_t SIGN, gnutls_pk_algorithm_t PK)
     SIGN: is a signature algorithm

PK: is a public key algorithm

This function returns non-zero if the public key algorithm
     corresponds to the given signature algorithm.  That is, if that
     signature can be generated from the given private key algorithm.

*Since:* 3.6.0

*Returns:* return non-zero when the provided algorithms are
     compatible.

gnutls_srp_allocate_client_credentials
--------------------------------------

-- Function: int gnutls_srp_allocate_client_credentials
          (gnutls_srp_client_credentials_t * SC)
     SC: is a pointer to a ‘gnutls_srp_server_credentials_t’ type.

Allocate a gnutls_srp_client_credentials_t structure.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned, or an
     error code.

gnutls_srp_allocate_server_credentials
--------------------------------------

-- Function: int gnutls_srp_allocate_server_credentials
          (gnutls_srp_server_credentials_t * SC)
     SC: is a pointer to a ‘gnutls_srp_server_credentials_t’ type.

Allocate a gnutls_srp_server_credentials_t structure.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned, or an
     error code.

gnutls_srp_base64_decode
------------------------

-- Function: int gnutls_srp_base64_decode (const gnutls_datum_t *
          B64_DATA, char * RESULT, size_t * RESULT_SIZE)
     B64_DATA: contain the encoded data

RESULT: the place where decoded data will be copied

RESULT_SIZE: holds the size of the result

This function will decode the given encoded data, using the base64
     encoding found in libsrp.

Note that ‘b64_data’ should be null terminated.

Warning!  This base64 encoding is not the "standard" encoding, so
     do not use it for non-SRP purposes.

*Returns:* ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ if the buffer given is
     not long enough, or 0 on success.

gnutls_srp_base64_decode2
-------------------------

-- Function: int gnutls_srp_base64_decode2 (const gnutls_datum_t *
          B64_DATA, gnutls_datum_t * RESULT)
     B64_DATA: contains the encoded data

RESULT: the place where decoded data lie

This function will decode the given encoded data.  The decoded data
     will be allocated, and stored into result.  It will decode using
     the base64 algorithm as used in libsrp.

You should use ‘gnutls_free()’ to free the returned data.

Warning!  This base64 encoding is not the "standard" encoding, so
     do not use it for non-SRP purposes.

*Returns:* 0 on success, or an error code.

gnutls_srp_base64_encode
------------------------

-- Function: int gnutls_srp_base64_encode (const gnutls_datum_t * DATA,
          char * RESULT, size_t * RESULT_SIZE)
     DATA: contain the raw data

RESULT: the place where base64 data will be copied

RESULT_SIZE: holds the size of the result

This function will convert the given data to printable data, using
     the base64 encoding, as used in the libsrp.  This is the encoding
     used in SRP password files.  If the provided buffer is not long
     enough GNUTLS_E_SHORT_MEMORY_BUFFER is returned.

Warning!  This base64 encoding is not the "standard" encoding, so
     do not use it for non-SRP purposes.

*Returns:* ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ if the buffer given is
     not long enough, or 0 on success.

gnutls_srp_base64_encode2
-------------------------

-- Function: int gnutls_srp_base64_encode2 (const gnutls_datum_t *
          DATA, gnutls_datum_t * RESULT)
     DATA: contains the raw data

RESULT: will hold the newly allocated encoded data

This function will convert the given data to printable data, using
     the base64 encoding.  This is the encoding used in SRP password
     files.  This function will allocate the required memory to hold the
     encoded data.

You should use ‘gnutls_free()’ to free the returned data.

Warning!  This base64 encoding is not the "standard" encoding, so
     do not use it for non-SRP purposes.

*Returns:* 0 on success, or an error code.

gnutls_srp_free_client_credentials
----------------------------------

-- Function: void gnutls_srp_free_client_credentials
          (gnutls_srp_client_credentials_t SC)
     SC: is a ‘gnutls_srp_client_credentials_t’ type.

Free a gnutls_srp_client_credentials_t structure.

gnutls_srp_free_server_credentials
----------------------------------

-- Function: void gnutls_srp_free_server_credentials
          (gnutls_srp_server_credentials_t SC)
     SC: is a ‘gnutls_srp_server_credentials_t’ type.

Free a gnutls_srp_server_credentials_t structure.

gnutls_srp_server_get_username
------------------------------

-- Function: const char * gnutls_srp_server_get_username
          (gnutls_session_t SESSION)
     SESSION: is a gnutls session

This function will return the username of the peer.  This should
     only be called in case of SRP authentication and in case of a
     server.  Returns NULL in case of an error.

*Returns:* SRP username of the peer, or NULL in case of error.

gnutls_srp_set_client_credentials
---------------------------------

-- Function: int gnutls_srp_set_client_credentials
          (gnutls_srp_client_credentials_t RES, const char * USERNAME,
          const char * PASSWORD)
     RES: is a ‘gnutls_srp_client_credentials_t’ type.

USERNAME: is the user's userid

PASSWORD: is the user's password

This function sets the username and password, in a
     ‘gnutls_srp_client_credentials_t’ type.  Those will be used in SRP
     authentication.  ‘username’ should be an ASCII string or UTF-8
     string.  In case of a UTF-8 string it is recommended to be
     following the PRECIS framework for usernames (rfc8265).  The
     password can be in ASCII format, or normalized using
     ‘gnutls_utf8_password_normalize()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned, or an
     error code.

gnutls_srp_set_client_credentials_function
------------------------------------------

FUNC: is the callback function

This function can be used to set a callback to retrieve the
     username and password for client SRP authentication.  The
     callback's function form is:

int (*callback)(gnutls_session_t, char** username, char**password);

The ‘username’ and ‘password’ must be allocated using
     ‘gnutls_malloc()’ .

The callback function will be called once per handshake before the
     initial hello message is sent.

The callback should not return a negative error code the second
     time called, since the handshake procedure will be aborted.

The callback function should return 0 on success.  -1 indicates an
     error.

gnutls_srp_set_prime_bits
-------------------------

-- Function: void gnutls_srp_set_prime_bits (gnutls_session_t SESSION,
          unsigned int BITS)
     SESSION: is a ‘gnutls_session_t’ type.

BITS: is the number of bits

This function sets the minimum accepted number of bits, for use in
     an SRP key exchange.  If zero, the default 2048 bits will be used.

In the client side it sets the minimum accepted number of bits.  If
     a server sends a prime with less bits than that
     ‘GNUTLS_E_RECEIVED_ILLEGAL_PARAMETER’ will be returned by the
     handshake.

This function has no effect in server side.

*Since:* 2.6.0

gnutls_srp_set_server_credentials_file
--------------------------------------

PASSWORD_FILE: is the SRP password file (tpasswd)

PASSWORD_CONF_FILE: is the SRP password conf file (tpasswd.conf)

This function sets the password files, in a
     ‘gnutls_srp_server_credentials_t’ type.  Those password files hold
     usernames and verifiers and will be used for SRP authentication.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned, or an
     error code.

gnutls_srp_set_server_credentials_function
------------------------------------------

FUNC: is the callback function

This function can be used to set a callback to retrieve the user's
     SRP credentials.  The callback's function form is:

int (*callback)(gnutls_session_t, const char* username,
     gnutls_datum_t *salt, gnutls_datum_t *verifier, gnutls_datum_t
     *generator, gnutls_datum_t *prime);

The callback function will only be called once per handshake.  The
     callback function should return 0 on success, while -1 indicates an
     error.

gnutls_srp_set_server_fake_salt_seed
------------------------------------

-- Function: void gnutls_srp_set_server_fake_salt_seed
          (gnutls_srp_server_credentials_t CRED, const gnutls_datum_t *
          SEED, unsigned int SALT_LENGTH)
     CRED: is a ‘gnutls_srp_server_credentials_t’ type

SEED: is the seed data, only needs to be valid until the function
     returns; size of the seed must be greater than zero

SALT_LENGTH: is the length of the generated fake salts

This function sets the seed that is used to generate salts for
     invalid (non-existent) usernames.

In order to prevent attackers from guessing valid usernames, when a
     user does not exist gnutls generates a salt and a verifier and
     proceeds with the protocol as usual.  The authentication will
     ultimately fail, but the client cannot tell whether the username is
     valid (exists) or invalid.

If an attacker learns the seed, given a salt (which is part of the
     handshake) which was generated when the seed was in use, it can
     tell whether or not the authentication failed because of an unknown
     username.  This seed cannot be used to reveal application data or
     passwords.

‘salt_length’ should represent the salt length your application
     uses.  Generating fake salts longer than 20 bytes is not supported.

By default the seed is a random value, different each time a
     ‘gnutls_srp_server_credentials_t’ is allocated and fake salts are
     16 bytes long.

*Since:* 3.3.0

gnutls_srp_verifier
-------------------

PASSWORD: is the user's password

SALT: should be some randomly generated bytes

GENERATOR: is the generator of the group

PRIME: is the group's prime

RES: where the verifier will be stored.

The verifier will be allocated with ‘gnutls_malloc’ () and will be
     stored in ‘res’ using binary format.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned, or an
     error code.

gnutls_srtp_get_keys
--------------------

KEY_MATERIAL: Space to hold the generated key material

KEY_MATERIAL_SIZE: The maximum size of the key material

CLIENT_KEY: The master client write key, pointing inside the key
     material

CLIENT_SALT: The master client write salt, pointing inside the key
     material

SERVER_KEY: The master server write key, pointing inside the key
     material

SERVER_SALT: The master server write salt, pointing inside the key
     material

*Returns:* On success the size of the key material is returned,
     otherwise, ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ if the buffer given is
     not sufficient, or a negative error code.

Since 3.1.4

gnutls_srtp_get_mki
-------------------

-- Function: int gnutls_srtp_get_mki (gnutls_session_t SESSION,
          gnutls_datum_t * MKI)
     SESSION: is a ‘gnutls_session_t’ type.

MKI: will hold the MKI

This function exports the negotiated Master Key Identifier,
     received by the peer if any.  The returned value in ‘mki’ should be
     treated as constant and valid only during the session's lifetime.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

Since 3.1.4

gnutls_srtp_get_profile_id
--------------------------

-- Function: int gnutls_srtp_get_profile_id (const char * NAME,
          gnutls_srtp_profile_t * PROFILE)
     NAME: The name of the profile to look up

PROFILE: Will hold the profile id

This function allows you to look up a profile based on a string.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

Since 3.1.4

gnutls_srtp_get_profile_name
----------------------------

-- Function: const char * gnutls_srtp_get_profile_name
          (gnutls_srtp_profile_t PROFILE)
     PROFILE: The profile to look up a string for

This function allows you to get the corresponding name for a SRTP
     protection profile.

*Returns:* On success, the name of a SRTP profile as a string,
     otherwise NULL.

Since 3.1.4

gnutls_srtp_get_selected_profile
--------------------------------

-- Function: int gnutls_srtp_get_selected_profile (gnutls_session_t
          SESSION, gnutls_srtp_profile_t * PROFILE)
     SESSION: is a ‘gnutls_session_t’ type.

PROFILE: will hold the profile

This function allows you to get the negotiated SRTP profile.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

Since 3.1.4

gnutls_srtp_set_mki
-------------------

-- Function: int gnutls_srtp_set_mki (gnutls_session_t SESSION, const
          gnutls_datum_t * MKI)
     SESSION: is a ‘gnutls_session_t’ type.

MKI: holds the MKI

This function sets the Master Key Identifier, to be used by this
     session (if any).

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

Since 3.1.4

gnutls_srtp_set_profile
-----------------------

-- Function: int gnutls_srtp_set_profile (gnutls_session_t SESSION,
          gnutls_srtp_profile_t PROFILE)
     SESSION: is a ‘gnutls_session_t’ type.

PROFILE: is the profile id to add.

This function is to be used by both clients and servers, to declare
     what SRTP profiles they support, to negotiate with the peer.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

Since 3.1.4

gnutls_srtp_set_profile_direct
------------------------------

-- Function: int gnutls_srtp_set_profile_direct (gnutls_session_t
          SESSION, const char * PROFILES, const char ** ERR_POS)
     SESSION: is a ‘gnutls_session_t’ type.

PROFILES: is a string that contains the supported SRTP profiles,
     separated by colons.

ERR_POS: In case of an error this will have the position in the
     string the error occurred, may be NULL.

This function is to be used by both clients and servers, to declare
     what SRTP profiles they support, to negotiate with the peer.

*Returns:* On syntax error ‘GNUTLS_E_INVALID_REQUEST’ is returned,
     ‘GNUTLS_E_SUCCESS’ on success, or an error code.

Since 3.1.4

gnutls_store_commitment
-----------------------

TDB: A storage structure or NULL to use the default

HOST: The peer's name

SERVICE: non-NULL if this key is specific to a service (e.g.  http)

HASH_ALGO: The hash algorithm type

HASH: The raw hash

EXPIRATION: The expiration time (use 0 to disable expiration)

FLAGS: should be 0 or ‘GNUTLS_SCOMMIT_FLAG_ALLOW_BROKEN’ .

This function will store the provided hash commitment to the list
     of stored public keys.  The key with the given hash will be
     considered valid until the provided expiration time.

The ‘tdb’ variable if non-null specifies a custom backend for the
     storage of entries.  If it is NULL then the default file backend
     will be used.

Note that this function is not thread safe with the default
     backend.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.0

gnutls_store_pubkey
-------------------

TDB: A storage structure or NULL to use the default

HOST: The peer's name

SERVICE: non-NULL if this key is specific to a service (e.g.  http)

CERT_TYPE: The type of the certificate

CERT: The data of the certificate

EXPIRATION: The expiration time (use 0 to disable expiration)

FLAGS: should be 0.

The ‘tdb’ variable if non-null specifies a custom backend for the
     storage of entries.  If it is NULL then the default file backend
     will be used.

As of GnuTLS 3.6.6 this function also accepts raw public keys.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.0.13

gnutls_strerror
---------------

-- Function: const char * gnutls_strerror (int ERROR)
     ERROR: is a GnuTLS error code, a negative error code

This function is similar to strerror.  The difference is that it
     accepts an error number returned by a gnutls function; In case of
     an unknown error a descriptive string is sent instead of ‘NULL’ .

Error codes are always a negative error code.

*Returns:* A string explaining the GnuTLS error message.

gnutls_strerror_name
--------------------

-- Function: const char * gnutls_strerror_name (int ERROR)
     ERROR: is an error returned by a gnutls function.

Return the GnuTLS error code define as a string.  For example,
     gnutls_strerror_name (GNUTLS_E_DH_PRIME_UNACCEPTABLE) will return
     the string "GNUTLS_E_DH_PRIME_UNACCEPTABLE".

*Returns:* A string corresponding to the symbol name of the error
     code.

*Since:* 2.6.0

gnutls_supplemental_get_name
----------------------------

-- Function: const char * gnutls_supplemental_get_name
          (gnutls_supplemental_data_format_type_t TYPE)
     TYPE: is a supplemental data format type

Convert a ‘gnutls_supplemental_data_format_type_t’ value to a
     string.

*Returns:* a string that contains the name of the specified
     supplemental data format type, or ‘NULL’ for unknown types.

gnutls_supplemental_recv
------------------------

-- Function: void gnutls_supplemental_recv (gnutls_session_t SESSION,
          unsigned DO_RECV_SUPPLEMENTAL)
     SESSION: is a ‘gnutls_session_t’ type.

DO_RECV_SUPPLEMENTAL: non-zero in order to expect supplemental data

This function is to be called by an extension handler to instruct
     gnutls to attempt to receive supplemental data during the handshake
     process.

*Since:* 3.4.0

gnutls_supplemental_register
----------------------------

-- Function: int gnutls_supplemental_register (const char * NAME,
          gnutls_supplemental_data_format_type_t TYPE,
          gnutls_supp_recv_func RECV_FUNC, gnutls_supp_send_func
          SEND_FUNC)
     NAME: the name of the supplemental data to register

TYPE: the type of the supplemental data format

RECV_FUNC: the function to receive the data

SEND_FUNC: the function to send the data

This function will register a new supplemental data type (rfc4680).
     The registered data will remain until ‘gnutls_global_deinit()’ is
     called.  The provided ‘type’ must be an unassigned type in
     ‘gnutls_supplemental_data_format_type_t’ .  If the type is already
     registered or handled by GnuTLS internally
     ‘GNUTLS_E_ALREADY_REGISTERED’ will be returned.

This function is not thread safe.  As supplemental data are not
     defined under TLS 1.3, this function will disable TLS 1.3 support
     globally.

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, otherwise a negative
     error code.

*Since:* 3.4.0

gnutls_supplemental_send
------------------------

-- Function: void gnutls_supplemental_send (gnutls_session_t SESSION,
          unsigned DO_SEND_SUPPLEMENTAL)
     SESSION: is a ‘gnutls_session_t’ type.

DO_SEND_SUPPLEMENTAL: non-zero in order to send supplemental data

This function is to be called by an extension handler to instruct
     gnutls to send supplemental data during the handshake process.

*Since:* 3.4.0

gnutls_system_recv_timeout
--------------------------

-- Function: int gnutls_system_recv_timeout (gnutls_transport_ptr_t
          PTR, unsigned int MS)
     PTR: A file descriptor (wrapped in a gnutls_transport_ptr_t
     pointer)

MS: The number of milliseconds to wait.

Wait for data to be received from the provided socket ( ‘ptr’ )
     within a timeout period in milliseconds, using ‘select()’ on the
     provided ‘ptr’ .

This function is provided as a helper for constructing custom
     callbacks for ‘gnutls_transport_set_pull_timeout_function()’ ,
     which can be used if you rely on socket file descriptors.

Returns -1 on error, 0 on timeout, positive value if data are
     available for reading.

*Since:* 3.4.0

gnutls_tdb_deinit
-----------------

-- Function: void gnutls_tdb_deinit (gnutls_tdb_t TDB)
     TDB: The structure to be deinitialized

This function will deinitialize a public key trust storage
     structure.

gnutls_tdb_init
---------------

-- Function: int gnutls_tdb_init (gnutls_tdb_t * TDB)
     TDB: A pointer to the type to be initialized

This function will initialize a public key trust storage structure.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_tdb_set_store_commitment_func
------------------------------------

-- Function: void gnutls_tdb_set_store_commitment_func (gnutls_tdb_t
          TDB, gnutls_tdb_store_commitment_func CSTORE)
     TDB: The trust storage

CSTORE: The commitment storage function

This function will associate a commitment (hash) storage function
     with the trust storage structure.  The function is of the following
     form.

int gnutls_tdb_store_commitment_func(const char* db_name, const
     char* host, const char* service, time_t expiration,
     gnutls_digest_algorithm_t, const gnutls_datum_t* hash);

The ‘db_name’ should be used to pass any private data to this
     function.

gnutls_tdb_set_store_func
-------------------------

-- Function: void gnutls_tdb_set_store_func (gnutls_tdb_t TDB,
          gnutls_tdb_store_func STORE)
     TDB: The trust storage

STORE: The storage function

This function will associate a storage function with the trust
     storage structure.  The function is of the following form.

int gnutls_tdb_store_func(const char* db_name, const char* host,
     const char* service, time_t expiration, const gnutls_datum_t*
     pubkey);

The ‘db_name’ should be used to pass any private data to this
     function.

gnutls_tdb_set_verify_func
--------------------------

-- Function: void gnutls_tdb_set_verify_func (gnutls_tdb_t TDB,
          gnutls_tdb_verify_func VERIFY)
     TDB: The trust storage

VERIFY: The verification function

This function will associate a retrieval function with the trust
     storage structure.  The function is of the following form.

int gnutls_tdb_verify_func(const char* db_name, const char* host,
     const char* service, const gnutls_datum_t* pubkey);

The verify function should return zero on a match,
     ‘GNUTLS_E_CERTIFICATE_KEY_MISMATCH’ if there is a mismatch and any
     other negative error code otherwise.

The ‘db_name’ should be used to pass any private data to this
     function.

gnutls_transport_get_int
------------------------

-- Function: int gnutls_transport_get_int (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Used to get the first argument of the transport function (like PUSH
     and PULL). This must have been set using
     ‘gnutls_transport_set_int()’ .

*Returns:* The first argument of the transport function.

*Since:* 3.1.9

gnutls_transport_get_int2
-------------------------

-- Function: void gnutls_transport_get_int2 (gnutls_session_t SESSION,
          int * RECV_INT, int * SEND_INT)
     SESSION: is a ‘gnutls_session_t’ type.

RECV_INT: will hold the value for the pull function

SEND_INT: will hold the value for the push function

Used to get the arguments of the transport functions (like PUSH and
     PULL). These should have been set using
     ‘gnutls_transport_set_int2()’ .

*Since:* 3.1.9

gnutls_transport_get_ptr
------------------------

-- Function: gnutls_transport_ptr_t gnutls_transport_get_ptr
          (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Used to get the first argument of the transport function (like PUSH
     and PULL). This must have been set using
     ‘gnutls_transport_set_ptr()’ .

*Returns:* The first argument of the transport function.

gnutls_transport_get_ptr2
-------------------------

-- Function: void gnutls_transport_get_ptr2 (gnutls_session_t SESSION,
          gnutls_transport_ptr_t * RECV_PTR, gnutls_transport_ptr_t *
          SEND_PTR)
     SESSION: is a ‘gnutls_session_t’ type.

RECV_PTR: will hold the value for the pull function

SEND_PTR: will hold the value for the push function

Used to get the arguments of the transport functions (like PUSH and
     PULL). These should have been set using
     ‘gnutls_transport_set_ptr2()’ .

gnutls_transport_is_ktls_enabled
--------------------------------

-- Function: gnutls_transport_ktls_enable_flags_t
          gnutls_transport_is_ktls_enabled (gnutls_session_t SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Checks if KTLS is now enabled and was properly inicialized.

*Returns:* ‘GNUTLS_KTLS_RECV’ , ‘GNUTLS_KTLS_SEND’ ,
     ‘GNUTLS_KTLS_DUPLEX’ , otherwise 0

*Since:* 3.7.3

gnutls_transport_set_errno
--------------------------

-- Function: void gnutls_transport_set_errno (gnutls_session_t SESSION,
          int ERR)
     SESSION: is a ‘gnutls_session_t’ type.

ERR: error value to store in session-specific errno variable.

This function is unreliable if you are using the same ‘session’ in
     different threads for sending and receiving.

gnutls_transport_set_errno_function
-----------------------------------

-- Function: void gnutls_transport_set_errno_function (gnutls_session_t
          SESSION, gnutls_errno_func ERRNO_FUNC)
     SESSION: is a ‘gnutls_session_t’ type.

ERRNO_FUNC: a callback function similar to ‘write()’

This is the function where you set a function to retrieve errno
     after a failed push or pull operation.

‘errno_func’ is of the form, int
     (*gnutls_errno_func)(gnutls_transport_ptr_t); and should return the
     errno.

*Since:* 2.12.0

gnutls_transport_set_int
------------------------

-- Function: void gnutls_transport_set_int (gnutls_session_t SESSION,
          int FD)
     SESSION: is a ‘gnutls_session_t’ type.

FD: is the socket descriptor for the connection.

This function sets the first argument of the transport function,
     such as ‘send()’ and ‘recv()’ for the default callbacks using the
     system's socket API.

This function is equivalent to calling ‘gnutls_transport_set_ptr()’
     with the descriptor, but requires no casts.

*Since:* 3.1.9

gnutls_transport_set_int2
-------------------------

-- Function: void gnutls_transport_set_int2 (gnutls_session_t SESSION,
          int RECV_FD, int SEND_FD)
     SESSION: is a ‘gnutls_session_t’ type.

RECV_FD: is socket descriptor for the pull function

SEND_FD: is socket descriptor for the push function

This function sets the first argument of the transport functions,
     such as ‘send()’ and ‘recv()’ for the default callbacks using the
     system's socket API. With this function you can set two different
     descriptors for receiving and sending.

This function is equivalent to calling
     ‘gnutls_transport_set_ptr2()’ with the descriptors, but requires no
     casts.

*Since:* 3.1.9

gnutls_transport_set_ptr
------------------------

-- Function: void gnutls_transport_set_ptr (gnutls_session_t SESSION,
          gnutls_transport_ptr_t PTR)
     SESSION: is a ‘gnutls_session_t’ type.

PTR: is the value.

Used to set the first argument of the transport function (for push
     and pull callbacks).  In berkeley style sockets this function will
     set the connection descriptor.

gnutls_transport_set_ptr2
-------------------------

-- Function: void gnutls_transport_set_ptr2 (gnutls_session_t SESSION,
          gnutls_transport_ptr_t RECV_PTR, gnutls_transport_ptr_t
          SEND_PTR)
     SESSION: is a ‘gnutls_session_t’ type.

RECV_PTR: is the value for the pull function

SEND_PTR: is the value for the push function

Used to set the first argument of the transport function (for push
     and pull callbacks).  In berkeley style sockets this function will
     set the connection descriptor.  With this function you can use two
     different pointers for receiving and sending.

gnutls_transport_set_pull_function
----------------------------------

-- Function: void gnutls_transport_set_pull_function (gnutls_session_t
          SESSION, gnutls_pull_func PULL_FUNC)
     SESSION: is a ‘gnutls_session_t’ type.

PULL_FUNC: a callback function similar to ‘read()’

‘gnutls_pull_func’ is of the form, ssize_t
     (*gnutls_pull_func)(gnutls_transport_ptr_t, void*, size_t);

gnutls_transport_set_pull_timeout_function
------------------------------------------

-- Function: void gnutls_transport_set_pull_timeout_function
          (gnutls_session_t SESSION, gnutls_pull_timeout_func FUNC)
     SESSION: is a ‘gnutls_session_t’ type.

FUNC: a callback function

‘gnutls_pull_timeout_func’ is of the form, int
     (*gnutls_pull_timeout_func)(gnutls_transport_ptr_t, unsigned int
     ms);

The helper function ‘gnutls_system_recv_timeout()’ is provided to
     simplify writing callbacks.

*Since:* 3.0

gnutls_transport_set_push_function
----------------------------------

-- Function: void gnutls_transport_set_push_function (gnutls_session_t
          SESSION, gnutls_push_func PUSH_FUNC)
     SESSION: is a ‘gnutls_session_t’ type.

PUSH_FUNC: a callback function similar to ‘write()’

‘push_func’ is of the form, ssize_t
     (*gnutls_push_func)(gnutls_transport_ptr_t, const void*, size_t);

gnutls_transport_set_vec_push_function
--------------------------------------

-- Function: void gnutls_transport_set_vec_push_function
          (gnutls_session_t SESSION, gnutls_vec_push_func VEC_FUNC)
     SESSION: is a ‘gnutls_session_t’ type.

VEC_FUNC: a callback function similar to ‘writev()’

‘vec_func’ is of the form, ssize_t (*gnutls_vec_push_func)
     (gnutls_transport_ptr_t, const giovec_t * iov, int iovcnt);

*Since:* 2.12.0

gnutls_url_is_supported
-----------------------

-- Function: unsigned gnutls_url_is_supported (const char * URL)
     URL: A URI to be tested

Check whether the provided ‘url’ is supported.  Depending on the
     system libraries GnuTLS may support pkcs11, tpmkey or other URLs.

*Returns:* return non-zero if the given URL is supported, and zero
     if it is not known.

*Since:* 3.1.0

gnutls_utf8_password_normalize
------------------------------

-- Function: int gnutls_utf8_password_normalize (const unsigned char *
          PASSWORD, unsigned PLEN, gnutls_datum_t * OUT, unsigned FLAGS)
     PASSWORD: contain the UTF-8 formatted password

PLEN: the length of the provided password

OUT: the result in an null-terminated allocated string

FLAGS: should be zero

This function will convert the provided UTF-8 password according to
     the normalization rules in RFC7613.

If the flag ‘GNUTLS_UTF8_IGNORE_ERRS’ is specified, any UTF-8
     encoding errors will be ignored, and in that case the output will
     be a copy of the input.

*Returns:* ‘GNUTLS_E_INVALID_UTF8_STRING’ on invalid UTF-8 data, or
     0 on success.

*Since:* 3.5.7

gnutls_verify_stored_pubkey
---------------------------

TDB: A storage structure or NULL to use the default

HOST: The peer's name

SERVICE: non-NULL if this key is specific to a service (e.g.  http)

CERT_TYPE: The type of the certificate

CERT: The raw (der) data of the certificate

FLAGS: should be 0.

As of GnuTLS 3.6.6 this function also verifies raw public keys.

*Since:* 3.0.13

File: gnutls.info,  Node: Datagram TLS API,  Next: X509 certificate API,  Prev: Core TLS API,  Up: API reference

E.2 Datagram TLS API
====================

The prototypes for the following functions lie in ‘gnutls/dtls.h’.

gnutls_dtls_cookie_send
-----------------------

-- Function: int gnutls_dtls_cookie_send (gnutls_datum_t * KEY, void *
          CLIENT_DATA, size_t CLIENT_DATA_SIZE, gnutls_dtls_prestate_st
          * PRESTATE, gnutls_transport_ptr_t PTR, gnutls_push_func
          PUSH_FUNC)
     KEY: is a random key to be used at cookie generation

CLIENT_DATA: contains data identifying the client (i.e.  address)

CLIENT_DATA_SIZE: The size of client's data

PRESTATE: The previous cookie returned by
     ‘gnutls_dtls_cookie_verify()’

PTR: A transport pointer to be used by ‘push_func’

PUSH_FUNC: A function that will be used to reply

This function can be used to prevent denial of service attacks to a
     DTLS server by requiring the client to reply using a cookie sent by
     this function.  That way it can be ensured that a client we
     allocated resources for (i.e.  ‘gnutls_session_t’ ) is the one that
     the original incoming packet was originated from.

This function must be called at the first incoming packet, prior to
     allocating any resources and must be succeeded by
     ‘gnutls_dtls_cookie_verify()’ .

*Returns:* the number of bytes sent, or a negative error code.

*Since:* 3.0

gnutls_dtls_cookie_verify
-------------------------

-- Function: int gnutls_dtls_cookie_verify (gnutls_datum_t * KEY, void
          * CLIENT_DATA, size_t CLIENT_DATA_SIZE, void * _MSG, size_t
          MSG_SIZE, gnutls_dtls_prestate_st * PRESTATE)
     KEY: is a random key to be used at cookie generation

CLIENT_DATA: contains data identifying the client (i.e.  address)

CLIENT_DATA_SIZE: The size of client's data

_MSG: An incoming message that initiates a connection.

MSG_SIZE: The size of the message.

PRESTATE: The cookie of this client.

This function will verify the received message for a valid cookie.
     If a valid cookie is returned then it should be associated with the
     session using ‘gnutls_dtls_prestate_set()’ ;

This function must be called after ‘gnutls_dtls_cookie_send()’ .

*Returns:* ‘GNUTLS_E_SUCCESS’ (0) on success, or a negative error
     code.

*Since:* 3.0

gnutls_dtls_get_data_mtu
------------------------

-- Function: unsigned int gnutls_dtls_get_data_mtu (gnutls_session_t
          SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

This function will return the actual maximum transfer unit for
     application data.  I.e.  DTLS headers are subtracted from the
     actual MTU which is set using ‘gnutls_dtls_set_mtu()’ .

*Returns:* the maximum allowed transfer unit.

*Since:* 3.0

gnutls_dtls_get_mtu
-------------------

-- Function: unsigned int gnutls_dtls_get_mtu (gnutls_session_t
          SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

This function will return the MTU size as set with
     ‘gnutls_dtls_set_mtu()’ .  This is not the actual MTU of data you
     can transmit.  Use ‘gnutls_dtls_get_data_mtu()’ for that reason.

*Returns:* the set maximum transfer unit.

*Since:* 3.0

gnutls_dtls_get_timeout
-----------------------

-- Function: unsigned int gnutls_dtls_get_timeout (gnutls_session_t
          SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

*Returns:* the remaining time in milliseconds.

*Since:* 3.0

gnutls_dtls_prestate_set
------------------------

-- Function: void gnutls_dtls_prestate_set (gnutls_session_t SESSION,
          gnutls_dtls_prestate_st * PRESTATE)
     SESSION: a new session

PRESTATE: contains the client's prestate

This function will associate the prestate acquired by the cookie
     authentication with the client, with the newly established session.

This functions must be called after a successful
     ‘gnutls_dtls_cookie_verify()’ and should be succeeded by the actual
     DTLS handshake using ‘gnutls_handshake()’ .

*Since:* 3.0

gnutls_dtls_set_data_mtu
------------------------

-- Function: int gnutls_dtls_set_data_mtu (gnutls_session_t SESSION,
          unsigned int MTU)
     SESSION: is a ‘gnutls_session_t’ type.

MTU: The maximum unencrypted transfer unit of the session

This function will set the maximum size of the *unencrypted*
     records which will be sent over a DTLS session.  It is equivalent
     to calculating the DTLS packet overhead with the current encryption
     parameters, and calling ‘gnutls_dtls_set_mtu()’ with that value.
     In particular, this means that you may need to call this function
     again after any negotiation or renegotiation, in order to ensure
     that the MTU is still sufficient to account for the new protocol
     overhead.

In most cases you only need to call ‘gnutls_dtls_set_mtu()’ with
     the maximum MTU of your transport layer.

*Returns:* ‘GNUTLS_E_SUCCESS’ (0) on success, or a negative error
     code.

*Since:* 3.1

gnutls_dtls_set_mtu
-------------------

-- Function: void gnutls_dtls_set_mtu (gnutls_session_t SESSION,
          unsigned int MTU)
     SESSION: is a ‘gnutls_session_t’ type.

MTU: The maximum transfer unit of the transport

This function will set the maximum transfer unit of the transport
     that DTLS packets are sent over.  Note that this should exclude the
     IP (or IPv6) and UDP headers.  So for DTLS over IPv6 on an Ethernet
     device with MTU 1500, the DTLS MTU set with this function would be
     1500 - 40 (IPV6 header) - 8 (UDP header) = 1452.

*Since:* 3.0

gnutls_dtls_set_timeouts
------------------------

-- Function: void gnutls_dtls_set_timeouts (gnutls_session_t SESSION,
          unsigned int RETRANS_TIMEOUT, unsigned int TOTAL_TIMEOUT)
     SESSION: is a ‘gnutls_session_t’ type.

RETRANS_TIMEOUT: The time at which a retransmission will occur in
     milliseconds

TOTAL_TIMEOUT: The time at which the connection will be aborted, in
     milliseconds.

This function will set the timeouts required for the DTLS handshake
     protocol.  The retransmission timeout is the time after which a
     message from the peer is not received, the previous messages will
     be retransmitted.  The total timeout is the time after which the
     handshake will be aborted with ‘GNUTLS_E_TIMEDOUT’ .

The DTLS protocol recommends the values of 1 sec and 60 seconds
     respectively, and these are the default values.

To disable retransmissions set a ‘retrans_timeout’ larger than the
     ‘total_timeout’ .

*Since:* 3.0

gnutls_record_get_discarded
---------------------------

-- Function: unsigned int gnutls_record_get_discarded (gnutls_session_t
          SESSION)
     SESSION: is a ‘gnutls_session_t’ type.

Returns the number of discarded packets in a DTLS connection.

*Returns:* The number of discarded packets.

*Since:* 3.0

File: gnutls.info,  Node: X509 certificate API,  Next: PKCS 7 API,  Prev: Datagram TLS API,  Up: API reference

E.3 X.509 certificate API
=========================

The following functions are to be used for X.509 certificate handling.
Their prototypes lie in ‘gnutls/x509.h’.

gnutls_certificate_get_trust_list
---------------------------------

-- Function: void gnutls_certificate_get_trust_list
          (gnutls_certificate_credentials_t RES,
          gnutls_x509_trust_list_t * TLIST)
     RES: is a ‘gnutls_certificate_credentials_t’ type.

TLIST: Location where to store the trust list.

Obtains the list of trusted certificates stored in ‘res’ and writes
     a pointer to it to the location ‘tlist’ .  The pointer will point
     to memory internal to ‘res’ , and must not be deinitialized.  It
     will be automatically deallocated when the ‘res’ structure is
     deinitialized.

*Since:* 3.4.0

gnutls_certificate_set_trust_list
---------------------------------

-- Function: void gnutls_certificate_set_trust_list
          (gnutls_certificate_credentials_t RES,
          gnutls_x509_trust_list_t TLIST, unsigned FLAGS)
     RES: is a ‘gnutls_certificate_credentials_t’ type.

TLIST: is a ‘gnutls_x509_trust_list_t’ type

FLAGS: must be zero

This function sets a trust list in the
     gnutls_certificate_credentials_t type.

Note that the ‘tlist’ will become part of the credentials structure
     and must not be deallocated.  It will be automatically deallocated
     when the ‘res’ structure is deinitialized.

*Since:* 3.2.2

gnutls_certificate_verification_profile_get_id
----------------------------------------------

-- Function: gnutls_certificate_verification_profiles_t
          gnutls_certificate_verification_profile_get_id (const char *
          NAME)
     NAME: is a profile name

Convert a string to a ‘gnutls_certificate_verification_profiles_t’
     value.  The names are compared in a case insensitive way.

*Returns:* a ‘gnutls_certificate_verification_profiles_t’ id of the
     specified profile, or ‘GNUTLS_PROFILE_UNKNOWN’ on failure.

gnutls_certificate_verification_profile_get_name
------------------------------------------------

-- Function: const char *
          gnutls_certificate_verification_profile_get_name
          (gnutls_certificate_verification_profiles_t ID)
     ID: is a profile ID

Convert a ‘gnutls_certificate_verification_profiles_t’ value to a
     string.

*Returns:* a string that contains the name of the specified profile
     or ‘NULL’ .

gnutls_pkcs8_info
-----------------

-- Function: int gnutls_pkcs8_info (const gnutls_datum_t * DATA,
          gnutls_x509_crt_fmt_t FORMAT, unsigned int * SCHEMA, unsigned
          int * CIPHER, void * SALT, unsigned int * SALT_SIZE, unsigned
          int * ITER_COUNT, char ** OID)
     DATA: Holds the PKCS ‘8’ data

FORMAT: the format of the PKCS ‘8’ data

SCHEMA: indicate the schema as one of ‘gnutls_pkcs_encrypt_flags_t’

CIPHER: the cipher used as ‘gnutls_cipher_algorithm_t’

SALT: PBKDF2 salt (if non-NULL then ‘salt_size’ initially holds its
     size)

SALT_SIZE: PBKDF2 salt size

ITER_COUNT: PBKDF2 iteration count

OID: if non-NULL it will contain an allocated null-terminated
     variable with the OID

This function will provide information on the algorithms used in a
     particular PKCS ‘8’ structure.  If the structure algorithms are
     unknown the code ‘GNUTLS_E_UNKNOWN_CIPHER_TYPE’ will be returned,
     and only ‘oid’ , will be set.  That is, ‘oid’ will be set on
     encrypted PKCS ‘8’ structures whether supported or not.  It must be
     deinitialized using ‘gnutls_free()’ .  The other variables are only
     set on supported structures.

*Returns:* ‘GNUTLS_E_INVALID_REQUEST’ if the provided structure
     isn't an encrypted key, ‘GNUTLS_E_UNKNOWN_CIPHER_TYPE’ if the
     structure's encryption isn't supported, or another negative error
     code in case of a failure.  Zero on success.

*Since:* 3.4.0

gnutls_pkcs_schema_get_name
---------------------------

-- Function: const char * gnutls_pkcs_schema_get_name (unsigned int
          SCHEMA)
     SCHEMA: Holds the PKCS ‘12’ or PBES2 schema
     (‘gnutls_pkcs_encrypt_flags_t’ )

This function will return a human readable description of the
     PKCS12 or PBES2 schema.

*Returns:* a constraint string or ‘NULL’ on error.

*Since:* 3.4.0

gnutls_pkcs_schema_get_oid
--------------------------

-- Function: const char * gnutls_pkcs_schema_get_oid (unsigned int
          SCHEMA)
     SCHEMA: Holds the PKCS ‘12’ or PBES2 schema
     (‘gnutls_pkcs_encrypt_flags_t’ )

This function will return the object identifier of the PKCS12 or
     PBES2 schema.

*Returns:* a constraint string or ‘NULL’ on error.

*Since:* 3.4.0

gnutls_session_set_verify_output_function
-----------------------------------------

-- Function: void gnutls_session_set_verify_output_function
          (gnutls_session_t SESSION, gnutls_verify_output_function *
          FUNC)
     SESSION: is a ‘gnutls_x509_trust_list_t’ type.

FUNC: is the callback function

This function sets a callback to be called when the peer's
     certificate chain has to be verified and full path to the trusted
     root has to be printed.

The callback's function prototype is defined in 'x509.h': int
     (*callback)( gnutls_x509_crt_t cert, gnutls_x509_crt_t issuer,
     gnutls_x509_crl_t crl, unsigned int verification_output);

If the callback function is provided then gnutls will call it, in
     the certificate verification procedure.  To verify the certificate
     chain and print its path uptp the trusted root, functions such as
     ‘gnutls_certificate_verify_peers()’ ,
     ‘gnutls_x509_trust_list_verify_crt()’ , and
     ‘gnutls_x509_trust_list_verify_crt2()’ can be used.  The callback
     is set in ‘_gnutls_verify_crt_status()’ and
     ‘_gnutls_pkcs11_verify_crt_status()’ .

*Since:* 3.7.0

gnutls_subject_alt_names_deinit
-------------------------------

-- Function: void gnutls_subject_alt_names_deinit
          (gnutls_subject_alt_names_t SANS)
     SANS: The alternative names

This function will deinitialize an alternative names structure.

*Since:* 3.3.0

gnutls_subject_alt_names_get
----------------------------

-- Function: int gnutls_subject_alt_names_get
          (gnutls_subject_alt_names_t SANS, unsigned int SEQ, unsigned
          int * SAN_TYPE, gnutls_datum_t * SAN, gnutls_datum_t *
          OTHERNAME_OID)
     SANS: The alternative names

SEQ: The index of the name to get

SAN_TYPE: Will hold the type of the name (of
     ‘gnutls_subject_alt_names_t’ )

SAN: The alternative name data (should be treated as constant)

OTHERNAME_OID: The object identifier if ‘san_type’ is
     ‘GNUTLS_SAN_OTHERNAME’ (should be treated as constant)

This function will return a specific alternative name as stored in
     the ‘sans’ type.  The returned values should be treated as constant
     and valid for the lifetime of ‘sans’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ if the index is out of
     bounds, otherwise a negative error value.

*Since:* 3.3.0

gnutls_subject_alt_names_init
-----------------------------

-- Function: int gnutls_subject_alt_names_init
          (gnutls_subject_alt_names_t * SANS)
     SANS: The alternative names

This function will initialize an alternative names structure.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_subject_alt_names_set
----------------------------

-- Function: int gnutls_subject_alt_names_set
          (gnutls_subject_alt_names_t SANS, unsigned int SAN_TYPE, const
          gnutls_datum_t * SAN, const char * OTHERNAME_OID)
     SANS: The alternative names

SAN_TYPE: The type of the name (of ‘gnutls_subject_alt_names_t’ )

SAN: The alternative name data

OTHERNAME_OID: The object identifier if ‘san_type’ is
     ‘GNUTLS_SAN_OTHERNAME’

This function will store the specified alternative name in the
     ‘sans’ .

Since version 3.5.7 the ‘GNUTLS_SAN_RFC822NAME’ ,
     ‘GNUTLS_SAN_DNSNAME’ , and ‘GNUTLS_SAN_OTHERNAME_XMPP’ are
     converted to ACE format when necessary.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0), otherwise a negative
     error value.

*Since:* 3.3.0

gnutls_x509_aia_deinit
----------------------

-- Function: void gnutls_x509_aia_deinit (gnutls_x509_aia_t AIA)
     AIA: The authority info access

This function will deinitialize an authority info access type.

*Since:* 3.3.0

gnutls_x509_aia_get
-------------------

-- Function: int gnutls_x509_aia_get (gnutls_x509_aia_t AIA, unsigned
          int SEQ, gnutls_datum_t * OID, unsigned * SAN_TYPE,
          gnutls_datum_t * SAN)
     AIA: The authority info access

SEQ: specifies the sequence number of the access descriptor (0 for
     the first one, 1 for the second etc.)

OID: the type of available data; to be treated as constant.

SAN_TYPE: Will hold the type of the name of
     ‘gnutls_subject_alt_names_t’ (may be null).

SAN: the access location name; to be treated as constant (may be
     null).

This function reads from the Authority Information Access type.

The ‘seq’ input parameter is used to indicate which member of the
     sequence the caller is interested in.  The first member is 0, the
     second member 1 and so on.  When the ‘seq’ value is out of bounds,
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ is returned.

Typically ‘oid’ is ‘GNUTLS_OID_AD_CAISSUERS’ or
     ‘GNUTLS_OID_AD_OCSP’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_aia_init
--------------------

-- Function: int gnutls_x509_aia_init (gnutls_x509_aia_t * AIA)
     AIA: The authority info access

This function will initialize an authority info access type.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_aia_set
-------------------

-- Function: int gnutls_x509_aia_set (gnutls_x509_aia_t AIA, const char
          * OID, unsigned SAN_TYPE, const gnutls_datum_t * SAN)
     AIA: The authority info access

OID: the type of data.

SAN_TYPE: The type of the name (of ‘gnutls_subject_alt_names_t’ )

SAN: The alternative name data

This function will store the specified alternative name in the
     ‘aia’ type.

Typically the value for ‘oid’ should be ‘GNUTLS_OID_AD_OCSP’ , or
     ‘GNUTLS_OID_AD_CAISSUERS’ .

Since version 3.5.7 the ‘GNUTLS_SAN_RFC822NAME’ , and
     ‘GNUTLS_SAN_DNSNAME’ , are converted to ACE format when necessary.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0), otherwise a negative
     error value.

*Since:* 3.3.0

gnutls_x509_aki_deinit
----------------------

-- Function: void gnutls_x509_aki_deinit (gnutls_x509_aki_t AKI)
     AKI: The authority key identifier type

This function will deinitialize an authority key identifier.

*Since:* 3.3.0

gnutls_x509_aki_get_cert_issuer
-------------------------------

-- Function: int gnutls_x509_aki_get_cert_issuer (gnutls_x509_aki_t
          AKI, unsigned int SEQ, unsigned int * SAN_TYPE, gnutls_datum_t
          * SAN, gnutls_datum_t * OTHERNAME_OID, gnutls_datum_t *
          SERIAL)
     AKI: The authority key ID

SEQ: The index of the name to get

SAN_TYPE: Will hold the type of the name (of
     ‘gnutls_subject_alt_names_t’ )

SAN: The alternative name data

OTHERNAME_OID: The object identifier if ‘san_type’ is
     ‘GNUTLS_SAN_OTHERNAME’

SERIAL: The authorityCertSerialNumber number

This function will return a specific authorityCertIssuer name as
     stored in the ‘aki’ type, as well as the authorityCertSerialNumber.
     All the returned values should be treated as constant, and may be
     set to ‘NULL’ when are not required.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ if the index is out of
     bounds, otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_aki_get_id
----------------------

-- Function: int gnutls_x509_aki_get_id (gnutls_x509_aki_t AKI,
          gnutls_datum_t * ID)
     AKI: The authority key ID

ID: Will hold the identifier

This function will return the key identifier as stored in the ‘aki’
     type.  The identifier should be treated as constant.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ if the index is out of
     bounds, otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_aki_init
--------------------

-- Function: int gnutls_x509_aki_init (gnutls_x509_aki_t * AKI)
     AKI: The authority key ID type

This function will initialize an authority key ID.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_aki_set_cert_issuer
-------------------------------

-- Function: int gnutls_x509_aki_set_cert_issuer (gnutls_x509_aki_t
          AKI, unsigned int SAN_TYPE, const gnutls_datum_t * SAN, const
          char * OTHERNAME_OID, const gnutls_datum_t * SERIAL)
     AKI: The authority key ID

SAN_TYPE: the type of the name (of ‘gnutls_subject_alt_names_t’ ),
     may be null

SAN: The alternative name data

OTHERNAME_OID: The object identifier if ‘san_type’ is
     ‘GNUTLS_SAN_OTHERNAME’

SERIAL: The authorityCertSerialNumber number (may be null)

This function will set the authorityCertIssuer name and the
     authorityCertSerialNumber to be stored in the ‘aki’ type.  When
     storing multiple names, the serial should be set on the first call,
     and subsequent calls should use a ‘NULL’ serial.

Since version 3.5.7 the ‘GNUTLS_SAN_RFC822NAME’ ,
     ‘GNUTLS_SAN_DNSNAME’ , and ‘GNUTLS_SAN_OTHERNAME_XMPP’ are
     converted to ACE format when necessary.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_aki_set_id
----------------------

-- Function: int gnutls_x509_aki_set_id (gnutls_x509_aki_t AKI, const
          gnutls_datum_t * ID)
     AKI: The authority key ID

ID: the key identifier

This function will set the keyIdentifier to be stored in the ‘aki’
     type.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_cidr_to_rfc5280
---------------------------

-- Function: int gnutls_x509_cidr_to_rfc5280 (const char * CIDR,
          gnutls_datum_t * CIDR_RFC5280)
     CIDR: CIDR in RFC4632 format (IP/prefix), null-terminated

CIDR_RFC5280: CIDR range converted to RFC5280 format

This function will convert text CIDR range with prefix (such as
     '10.0.0.0/8') to RFC5280 (IP address in network byte order followed
     by its network mask).  Works for both IPv4 and IPv6.

The resulting object is directly usable for IP name constraints
     usage, for example in functions
     ‘gnutls_x509_name_constraints_add_permitted’ or
     ‘gnutls_x509_name_constraints_add_excluded’ .

The data in datum needs to be deallocated using ‘gnutls_free()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.5.4

gnutls_x509_crl_check_issuer
----------------------------

-- Function: unsigned gnutls_x509_crl_check_issuer (gnutls_x509_crl_t
          CRL, gnutls_x509_crt_t ISSUER)
     CRL: is the CRL to be checked

ISSUER: is the certificate of a possible issuer

This function will check if the given CRL was issued by the given
     issuer certificate.

*Returns:* true (1) if the given CRL was issued by the given
     issuer, and false (0) if not.

gnutls_x509_crl_deinit
----------------------

-- Function: void gnutls_x509_crl_deinit (gnutls_x509_crl_t CRL)
     CRL: The data to be deinitialized

This function will deinitialize a CRL structure.

gnutls_x509_crl_dist_points_deinit
----------------------------------

-- Function: void gnutls_x509_crl_dist_points_deinit
          (gnutls_x509_crl_dist_points_t CDP)
     CDP: The CRL distribution points

This function will deinitialize a CRL distribution points type.

*Since:* 3.3.0

gnutls_x509_crl_dist_points_get
-------------------------------

-- Function: int gnutls_x509_crl_dist_points_get
          (gnutls_x509_crl_dist_points_t CDP, unsigned int SEQ, unsigned
          int * TYPE, gnutls_datum_t * SAN, unsigned int * REASONS)
     CDP: The CRL distribution points

SEQ: specifies the sequence number of the distribution point (0 for
     the first one, 1 for the second etc.)

TYPE: The name type of the corresponding name
     (gnutls_x509_subject_alt_name_t)

SAN: The distribution point names (to be treated as constant)

REASONS: Revocation reasons.  An ORed sequence of flags from
     ‘gnutls_x509_crl_reason_flags_t’ .

This function retrieves the individual CRL distribution points
     (2.5.29.31), contained in provided type.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ if the index is out of
     bounds, otherwise a negative error value.

gnutls_x509_crl_dist_points_init
--------------------------------

-- Function: int gnutls_x509_crl_dist_points_init
          (gnutls_x509_crl_dist_points_t * CDP)
     CDP: The CRL distribution points

This function will initialize a CRL distribution points type.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_crl_dist_points_set
-------------------------------

-- Function: int gnutls_x509_crl_dist_points_set
          (gnutls_x509_crl_dist_points_t CDP,
          gnutls_x509_subject_alt_name_t TYPE, const gnutls_datum_t *
          SAN, unsigned int REASONS)
     CDP: The CRL distribution points

TYPE: The type of the name (of ‘gnutls_subject_alt_names_t’ )

SAN: The point name data

REASONS: Revocation reasons.  An ORed sequence of flags from
     ‘gnutls_x509_crl_reason_flags_t’ .

This function will store the specified CRL distribution point value
     the ‘cdp’ type.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0), otherwise a negative
     error value.

*Since:* 3.3.0

gnutls_x509_crl_export
----------------------

-- Function: int gnutls_x509_crl_export (gnutls_x509_crl_t CRL,
          gnutls_x509_crt_fmt_t FORMAT, void * OUTPUT_DATA, size_t *
          OUTPUT_DATA_SIZE)
     CRL: Holds the revocation list

FORMAT: the format of output params.  One of PEM or DER.

OUTPUT_DATA: will contain a private key PEM or DER encoded

OUTPUT_DATA_SIZE: holds the size of output_data (and will be
     replaced by the actual size of parameters)

This function will export the revocation list to DER or PEM format.

If the buffer provided is not long enough to hold the output, then
     ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ will be returned.

If the structure is PEM encoded, it will have a header of "BEGIN
     X509 CRL".

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crl_export2
-----------------------

-- Function: int gnutls_x509_crl_export2 (gnutls_x509_crl_t CRL,
          gnutls_x509_crt_fmt_t FORMAT, gnutls_datum_t * OUT)
     CRL: Holds the revocation list

FORMAT: the format of output params.  One of PEM or DER.

OUT: will contain a private key PEM or DER encoded

This function will export the revocation list to DER or PEM format.

The output buffer is allocated using ‘gnutls_malloc()’ .

If the structure is PEM encoded, it will have a header of "BEGIN
     X509 CRL".

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

Since 3.1.3

gnutls_x509_crl_get_authority_key_gn_serial
-------------------------------------------

-- Function: int gnutls_x509_crl_get_authority_key_gn_serial
          (gnutls_x509_crl_t CRL, unsigned int SEQ, void * ALT, size_t *
          ALT_SIZE, unsigned int * ALT_TYPE, void * SERIAL, size_t *
          SERIAL_SIZE, unsigned int * CRITICAL)
     CRL: should contain a ‘gnutls_x509_crl_t’ type

SEQ: specifies the sequence number of the alt name (0 for the first
     one, 1 for the second etc.)

ALT: is the place where the alternative name will be copied to

ALT_SIZE: holds the size of alt.

ALT_TYPE: holds the type of the alternative name (one of
     gnutls_x509_subject_alt_name_t).

SERIAL: buffer to store the serial number (may be null)

SERIAL_SIZE: Holds the size of the serial field (may be null)

CRITICAL: will be non-zero if the extension is marked as critical
     (may be null)

This function will return the X.509 authority key identifier when
     stored as a general name (authorityCertIssuer) and serial number.

Because more than one general names might be stored ‘seq’ can be
     used as a counter to request them all until
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ is returned.

*Returns:* Returns 0 on success, or an error code.

*Since:* 3.0

gnutls_x509_crl_get_authority_key_id
------------------------------------

-- Function: int gnutls_x509_crl_get_authority_key_id
          (gnutls_x509_crl_t CRL, void * ID, size_t * ID_SIZE, unsigned
          int * CRITICAL)
     CRL: should contain a ‘gnutls_x509_crl_t’ type

ID: The place where the identifier will be copied

ID_SIZE: Holds the size of the result field.

CRITICAL: will be non-zero if the extension is marked as critical
     (may be null)

This function will return the CRL authority's key identifier.  This
     is obtained by the X.509 Authority Key identifier extension field
     (2.5.29.35).  Note that this function only returns the
     keyIdentifier field of the extension and
     ‘GNUTLS_E_X509_UNSUPPORTED_EXTENSION’ , if the extension contains
     the name and serial number of the certificate.  In that case
     ‘gnutls_x509_crl_get_authority_key_gn_serial()’ may be used.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code in case of an error.

*Since:* 2.8.0

gnutls_x509_crl_get_crt_count
-----------------------------

-- Function: int gnutls_x509_crl_get_crt_count (gnutls_x509_crl_t CRL)
     CRL: should contain a ‘gnutls_x509_crl_t’ type

This function will return the number of revoked certificates in the
     given CRL.

*Returns:* number of certificates, a negative error code on
     failure.

gnutls_x509_crl_get_crt_serial
------------------------------

INDX: the index of the certificate to extract (starting from 0)

SERIAL: where the serial number will be copied

SERIAL_SIZE: initially holds the size of serial

T: if non null, will hold the time this certificate was revoked

This function will retrieve the serial number of the specified, by
     the index, revoked certificate.

Note that this function will have performance issues in large
     sequences of revoked certificates.  In that case use
     ‘gnutls_x509_crl_iter_crt_serial()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crl_get_dn_oid
--------------------------

-- Function: int gnutls_x509_crl_get_dn_oid (gnutls_x509_crl_t CRL,
          unsigned INDX, void * OID, size_t * SIZEOF_OID)
     CRL: should contain a gnutls_x509_crl_t type

INDX: Specifies which DN OID to send.  Use (0) to get the first
     one.

OID: a pointer to store the OID (may be null)

SIZEOF_OID: initially holds the size of 'oid'

This function will extract the requested OID of the name of the CRL
     issuer, specified by the given index.

If oid is null then only the size will be filled.

*Returns:* ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ if the provided buffer is
     not long enough, and in that case the sizeof_oid will be updated
     with the required size.  On success 0 is returned.

gnutls_x509_crl_get_extension_data
----------------------------------

-- Function: int gnutls_x509_crl_get_extension_data (gnutls_x509_crl_t
          CRL, unsigned INDX, void * DATA, size_t * SIZEOF_DATA)
     CRL: should contain a ‘gnutls_x509_crl_t’ type

INDX: Specifies which extension OID to send.  Use (0) to get the
     first one.

DATA: a pointer to a structure to hold the data (may be null)

SIZEOF_DATA: initially holds the size of ‘oid’

This function will return the requested extension data in the CRL.
     The extension data will be stored as a string in the provided
     buffer.

Use ‘gnutls_x509_crl_get_extension_info()’ to extract the OID and
     critical flag.  Use ‘gnutls_x509_crl_get_extension_info()’ instead,
     if you want to get data indexed by the extension OID rather than
     sequence.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code in case of an error.  If your have
     reached the last extension available
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ will be returned.

*Since:* 2.8.0

gnutls_x509_crl_get_extension_data2
-----------------------------------

-- Function: int gnutls_x509_crl_get_extension_data2 (gnutls_x509_crl_t
          CRL, unsigned INDX, gnutls_datum_t * DATA)
     CRL: should contain a ‘gnutls_x509_crl_t’ type

INDX: Specifies which extension OID to read.  Use (0) to get the
     first one.

DATA: will contain the extension DER-encoded data

This function will return the requested by the index extension data
     in the certificate revocation list.  The extension data will be
     allocated using ‘gnutls_malloc()’ .

Use ‘gnutls_x509_crt_get_extension_info()’ to extract the OID.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.  If you have reached
     the last extension available
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ will be returned.

gnutls_x509_crl_get_extension_info
----------------------------------

-- Function: int gnutls_x509_crl_get_extension_info (gnutls_x509_crl_t
          CRL, unsigned INDX, void * OID, size_t * SIZEOF_OID, unsigned
          int * CRITICAL)
     CRL: should contain a ‘gnutls_x509_crl_t’ type

INDX: Specifies which extension OID to send, use (0) to get the
     first one.

OID: a pointer to store the OID

SIZEOF_OID: initially holds the maximum size of ‘oid’ , on return
     holds actual size of ‘oid’ .

CRITICAL: output variable with critical flag, may be NULL.

This function will return the requested extension OID in the CRL,
     and the critical flag for it.  The extension OID will be stored as
     a string in the provided buffer.  Use
     ‘gnutls_x509_crl_get_extension_data()’ to extract the data.

If the buffer provided is not long enough to hold the output, then
     * ‘sizeof_oid’ is updated and ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ will
     be returned.

*Since:* 2.8.0

gnutls_x509_crl_get_extension_oid
---------------------------------

-- Function: int gnutls_x509_crl_get_extension_oid (gnutls_x509_crl_t
          CRL, unsigned INDX, void * OID, size_t * SIZEOF_OID)
     CRL: should contain a ‘gnutls_x509_crl_t’ type

INDX: Specifies which extension OID to send, use (0) to get the
     first one.

OID: a pointer to store the OID (may be null)

SIZEOF_OID: initially holds the size of ‘oid’

This function will return the requested extension OID in the CRL.
     The extension OID will be stored as a string in the provided
     buffer.

*Since:* 2.8.0

gnutls_x509_crl_get_issuer_dn
-----------------------------

-- Function: int gnutls_x509_crl_get_issuer_dn (gnutls_x509_crl_t CRL,
          char * BUF, size_t * SIZEOF_BUF)
     CRL: should contain a gnutls_x509_crl_t type

BUF: a pointer to a structure to hold the peer's name (may be null)

SIZEOF_BUF: initially holds the size of ‘buf’

This function will copy the name of the CRL issuer in the provided
     buffer.  The name will be in the form "C=xxxx,O=yyyy,CN=zzzz" as
     described in RFC4514.  The output string will be ASCII or UTF-8
     encoded, depending on the certificate data.

If buf is ‘NULL’ then only the size will be filled.

This function does not output a fully RFC4514 compliant string, if
     that is required see ‘gnutls_x509_crl_get_issuer_dn3()’ .

*Returns:* ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ if the provided buffer is
     not long enough, and in that case the sizeof_buf will be updated
     with the required size, and 0 on success.

gnutls_x509_crl_get_issuer_dn2
------------------------------

-- Function: int gnutls_x509_crl_get_issuer_dn2 (gnutls_x509_crl_t CRL,
          gnutls_datum_t * DN)
     CRL: should contain a ‘gnutls_x509_crl_t’ type

DN: a pointer to a structure to hold the name; must be freed using
     ‘gnutls_free()’

This function will allocate buffer and copy the name of the CRL
     issuer.  The name will be in the form "C=xxxx,O=yyyy,CN=zzzz" as
     described in RFC4514.  The output string will be ASCII or UTF-8
     encoded, depending on the certificate data.

This function does not output a fully RFC4514 compliant string, if
     that is required see ‘gnutls_x509_crl_get_issuer_dn3()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.1.10

gnutls_x509_crl_get_issuer_dn3
------------------------------

-- Function: int gnutls_x509_crl_get_issuer_dn3 (gnutls_x509_crl_t CRL,
          gnutls_datum_t * DN, unsigned FLAGS)
     CRL: should contain a ‘gnutls_x509_crl_t’ type

DN: a pointer to a structure to hold the name; must be freed using
     ‘gnutls_free()’

FLAGS: zero or ‘GNUTLS_X509_DN_FLAG_COMPAT’

When the flag ‘GNUTLS_X509_DN_FLAG_COMPAT’ is specified, the output
     format will match the format output by previous to 3.5.6 versions
     of GnuTLS which was not not fully RFC4514-compliant.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.5.7

gnutls_x509_crl_get_issuer_dn_by_oid
------------------------------------

-- Function: int gnutls_x509_crl_get_issuer_dn_by_oid
          (gnutls_x509_crl_t CRL, const char * OID, unsigned INDX,
          unsigned int RAW_FLAG, void * BUF, size_t * SIZEOF_BUF)
     CRL: should contain a gnutls_x509_crl_t type

OID: holds an Object Identified in null terminated string

INDX: In case multiple same OIDs exist in the RDN, this specifies
     which to send.  Use (0) to get the first one.

RAW_FLAG: If non-zero returns the raw DER data of the DN part.

BUF: a pointer to a structure to hold the peer's name (may be null)

SIZEOF_BUF: initially holds the size of ‘buf’

This function will extract the part of the name of the CRL issuer
     specified by the given OID. The output will be encoded as described
     in RFC4514.  The output string will be ASCII or UTF-8 encoded,
     depending on the certificate data.

Some helper macros with popular OIDs can be found in gnutls/x509.h
     If raw flag is (0), this function will only return known OIDs as
     text.  Other OIDs will be DER encoded, as described in RFC4514 - in
     hex format with a '#' prefix.  You can check about known OIDs using
     ‘gnutls_x509_dn_oid_known()’ .

If buf is null then only the size will be filled.

*Returns:* ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ if the provided buffer is
     not long enough, and in that case the sizeof_buf will be updated
     with the required size, and 0 on success.

gnutls_x509_crl_get_next_update
-------------------------------

-- Function: time_t gnutls_x509_crl_get_next_update (gnutls_x509_crl_t
          CRL)
     CRL: should contain a ‘gnutls_x509_crl_t’ type

This function will return the time the next CRL will be issued.
     This field is optional in a CRL so it might be normal to get an
     error instead.

*Returns:* when the next CRL will be issued, or (time_t)-1 on
     error.

gnutls_x509_crl_get_number
--------------------------

-- Function: int gnutls_x509_crl_get_number (gnutls_x509_crl_t CRL,
          void * RET, size_t * RET_SIZE, unsigned int * CRITICAL)
     CRL: should contain a ‘gnutls_x509_crl_t’ type

RET: The place where the number will be copied

RET_SIZE: Holds the size of the result field.

CRITICAL: will be non-zero if the extension is marked as critical
     (may be null)

This function will return the CRL number extension.  This is
     obtained by the CRL Number extension field (2.5.29.20).

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code in case of an error.

*Since:* 2.8.0

gnutls_x509_crl_get_raw_issuer_dn
---------------------------------

-- Function: int gnutls_x509_crl_get_raw_issuer_dn (gnutls_x509_crl_t
          CRL, gnutls_datum_t * DN)
     CRL: should contain a gnutls_x509_crl_t type

DN: will hold the starting point of the DN

This function will return a pointer to the DER encoded DN structure
     and the length.

*Returns:* a negative error code on error, and (0) on success.

*Since:* 2.12.0

gnutls_x509_crl_get_signature
-----------------------------

-- Function: int gnutls_x509_crl_get_signature (gnutls_x509_crl_t CRL,
          char * SIG, size_t * SIZEOF_SIG)
     CRL: should contain a gnutls_x509_crl_t type

SIG: a pointer where the signature part will be copied (may be
     null).

SIZEOF_SIG: initially holds the size of ‘sig’

This function will extract the signature field of a CRL.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crl_get_signature_algorithm
---------------------------------------

-- Function: int gnutls_x509_crl_get_signature_algorithm
          (gnutls_x509_crl_t CRL)
     CRL: should contain a ‘gnutls_x509_crl_t’ type

This function will return a value of the ‘gnutls_sign_algorithm_t’
     enumeration that is the signature algorithm.

Since 3.6.0 this function never returns a negative error code.
     Error cases and unknown/unsupported signature algorithms are mapped
     to ‘GNUTLS_SIGN_UNKNOWN’ .

*Returns:* a ‘gnutls_sign_algorithm_t’ value

gnutls_x509_crl_get_signature_oid
---------------------------------

-- Function: int gnutls_x509_crl_get_signature_oid (gnutls_x509_crl_t
          CRL, char * OID, size_t * OID_SIZE)
     CRL: should contain a ‘gnutls_x509_crl_t’ type

OID: a pointer to a buffer to hold the OID (may be null)

OID_SIZE: initially holds the size of ‘oid’

This function will return the OID of the signature algorithm that
     has been used to sign this CRL. This is function is useful in the
     case ‘gnutls_x509_crl_get_signature_algorithm()’ returned
     ‘GNUTLS_SIGN_UNKNOWN’ .

*Returns:* zero or a negative error code on error.

*Since:* 3.5.0

gnutls_x509_crl_get_this_update
-------------------------------

-- Function: time_t gnutls_x509_crl_get_this_update (gnutls_x509_crl_t
          CRL)
     CRL: should contain a ‘gnutls_x509_crl_t’ type

This function will return the time this CRL was issued.

*Returns:* when the CRL was issued, or (time_t)-1 on error.

gnutls_x509_crl_get_version
---------------------------

-- Function: int gnutls_x509_crl_get_version (gnutls_x509_crl_t CRL)
     CRL: should contain a ‘gnutls_x509_crl_t’ type

This function will return the version of the specified CRL.

*Returns:* The version number, or a negative error code on error.

gnutls_x509_crl_import
----------------------

-- Function: int gnutls_x509_crl_import (gnutls_x509_crl_t CRL, const
          gnutls_datum_t * DATA, gnutls_x509_crt_fmt_t FORMAT)
     CRL: The data to store the parsed CRL.

DATA: The DER or PEM encoded CRL.

FORMAT: One of DER or PEM

This function will convert the given DER or PEM encoded CRL to the
     native ‘gnutls_x509_crl_t’ format.  The output will be stored in
     'crl'.

If the CRL is PEM encoded it should have a header of "X509 CRL".

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crl_init
--------------------

-- Function: int gnutls_x509_crl_init (gnutls_x509_crl_t * CRL)
     CRL: A pointer to the type to be initialized

This function will initialize a CRL structure.  CRL stands for
     Certificate Revocation List.  A revocation list usually contains
     lists of certificate serial numbers that have been revoked by an
     Authority.  The revocation lists are always signed with the
     authority's private key.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crl_iter_crt_serial
-------------------------------

-- Function: int gnutls_x509_crl_iter_crt_serial (gnutls_x509_crl_t
          CRL, gnutls_x509_crl_iter_t * ITER, unsigned char * SERIAL,
          size_t * SERIAL_SIZE, time_t * T)
     CRL: should contain a ‘gnutls_x509_crl_t’ type

ITER: A pointer to an iterator (initially the iterator should be
     ‘NULL’ )

SERIAL: where the serial number will be copied

SERIAL_SIZE: initially holds the size of serial

T: if non null, will hold the time this certificate was revoked

This function performs the same as
     ‘gnutls_x509_crl_get_crt_serial()’ , but reads sequentially and
     keeps state in the iterator between calls.  That allows it to
     provide better performance in sequences with many elements
     (50000+).

When past the last element is accessed
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ is returned and the
     iterator is reset.

After use, the iterator must be deinitialized using
     ‘gnutls_x509_crl_iter_deinit()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crl_iter_deinit
---------------------------

-- Function: void gnutls_x509_crl_iter_deinit (gnutls_x509_crl_iter_t
          ITER)
     ITER: The iterator to be deinitialized

This function will deinitialize an iterator type.

gnutls_x509_crl_list_import
---------------------------

-- Function: int gnutls_x509_crl_list_import (gnutls_x509_crl_t * CRLS,
          unsigned int * CRL_MAX, const gnutls_datum_t * DATA,
          gnutls_x509_crt_fmt_t FORMAT, unsigned int FLAGS)
     CRLS: Indicates where the parsed CRLs will be copied to.  Must not
     be initialized.

CRL_MAX: Initially must hold the maximum number of crls.  It will
     be updated with the number of crls available.

DATA: The CRL data

FORMAT: One of DER or PEM.

FLAGS: must be (0) or an OR'd sequence of
     gnutls_certificate_import_flags.

This function will convert the given CRL list to the native
     gnutls_x509_crl_t format.  The output will be stored in ‘crls’ .
     They will be automatically initialized.

If the Certificate is PEM encoded it should have a header of "X509
     CRL".

*Returns:* the number of certificates read or a negative error
     value.

*Since:* 3.0

gnutls_x509_crl_list_import2
----------------------------

-- Function: int gnutls_x509_crl_list_import2 (gnutls_x509_crl_t **
          CRLS, unsigned int * SIZE, const gnutls_datum_t * DATA,
          gnutls_x509_crt_fmt_t FORMAT, unsigned int FLAGS)
     CRLS: Will contain the parsed crl list.

SIZE: It will contain the size of the list.

DATA: The CRL data.

FORMAT: One of DER or PEM.

FLAGS: must be (0) or an OR'd sequence of
     gnutls_certificate_import_flags.

This function will convert the given CRL list to the native
     gnutls_x509_crl_t format.  The output will be stored in ‘crls’ .
     They will be automatically initialized.

If the Certificate is PEM encoded it should have a header of "X509
     CRL".

*Returns:* the number of certificates read or a negative error
     value.

*Since:* 3.0

gnutls_x509_crl_print
---------------------

-- Function: int gnutls_x509_crl_print (gnutls_x509_crl_t CRL,
          gnutls_certificate_print_formats_t FORMAT, gnutls_datum_t *
          OUT)
     CRL: The data to be printed

FORMAT: Indicate the format to use

OUT: Newly allocated datum with null terminated string.

This function will pretty print a X.509 certificate revocation
     list, suitable for display to a human.

The output ‘out’ needs to be deallocated using ‘gnutls_free()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crl_set_authority_key_id
------------------------------------

-- Function: int gnutls_x509_crl_set_authority_key_id
          (gnutls_x509_crl_t CRL, const void * ID, size_t ID_SIZE)
     CRL: a CRL of type ‘gnutls_x509_crl_t’

ID: The key ID

ID_SIZE: Holds the size of the serial field.

This function will set the CRL's authority key ID extension.  Only
     the keyIdentifier field can be set with this function.  This may be
     used by an authority that holds multiple private keys, to
     distinguish the used key.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 2.8.0

gnutls_x509_crl_set_crt
-----------------------

-- Function: int gnutls_x509_crl_set_crt (gnutls_x509_crl_t CRL,
          gnutls_x509_crt_t CRT, time_t REVOCATION_TIME)
     CRL: should contain a gnutls_x509_crl_t type

CRT: a certificate of type ‘gnutls_x509_crt_t’ with the revoked
     certificate

REVOCATION_TIME: The time this certificate was revoked

This function will set a revoked certificate's serial number to the
     CRL.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crl_set_crt_serial
------------------------------

-- Function: int gnutls_x509_crl_set_crt_serial (gnutls_x509_crl_t CRL,
          const void * SERIAL, size_t SERIAL_SIZE, time_t
          REVOCATION_TIME)
     CRL: should contain a gnutls_x509_crl_t type

SERIAL: The revoked certificate's serial number

SERIAL_SIZE: Holds the size of the serial field.

REVOCATION_TIME: The time this certificate was revoked

This function will set a revoked certificate's serial number to the
     CRL.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crl_set_next_update
-------------------------------

-- Function: int gnutls_x509_crl_set_next_update (gnutls_x509_crl_t
          CRL, time_t EXP_TIME)
     CRL: should contain a gnutls_x509_crl_t type

EXP_TIME: The actual time

This function will set the time this CRL will be updated.  This is
     an optional value to be set on a CRL and this call can be omitted
     when generating a CRL.

Prior to GnuTLS 3.5.7, setting a nextUpdate field was required in
     order to generate a CRL.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crl_set_number
--------------------------

-- Function: int gnutls_x509_crl_set_number (gnutls_x509_crl_t CRL,
          const void * NR, size_t NR_SIZE)
     CRL: a CRL of type ‘gnutls_x509_crl_t’

NR: The CRL number

NR_SIZE: Holds the size of the nr field.

This function will set the CRL's number extension.  This is to be
     used as a unique and monotonic number assigned to the CRL by the
     authority.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 2.8.0

gnutls_x509_crl_set_this_update
-------------------------------

-- Function: int gnutls_x509_crl_set_this_update (gnutls_x509_crl_t
          CRL, time_t ACT_TIME)
     CRL: should contain a gnutls_x509_crl_t type

ACT_TIME: The actual time

This function will set the time this CRL was issued.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crl_set_version
---------------------------

-- Function: int gnutls_x509_crl_set_version (gnutls_x509_crl_t CRL,
          unsigned int VERSION)
     CRL: should contain a gnutls_x509_crl_t type

VERSION: holds the version number.  For CRLv1 crls must be 1.

This function will set the version of the CRL. This must be one for
     CRL version 1, and so on.  The CRLs generated by gnutls should have
     a version number of 2.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crl_sign
--------------------

-- Function: int gnutls_x509_crl_sign (gnutls_x509_crl_t CRL,
          gnutls_x509_crt_t ISSUER, gnutls_x509_privkey_t ISSUER_KEY)
     CRL: should contain a gnutls_x509_crl_t type

ISSUER: is the certificate of the certificate issuer

ISSUER_KEY: holds the issuer's private key

This function is the same a ‘gnutls_x509_crl_sign2()’ with no
     flags, and an appropriate hash algorithm.  The hash algorithm used
     may vary between versions of GnuTLS, and it is tied to the security
     level of the issuer's public key.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crl_sign2
---------------------

ISSUER: is the certificate of the certificate issuer

ISSUER_KEY: holds the issuer's private key

DIG: The message digest to use.  GNUTLS_DIG_SHA256 is the safe
     choice unless you know what you're doing.

FLAGS: must be 0

This function will sign the CRL with the issuer's private key, and
     will copy the issuer's information into the CRL.

This must be the last step in a certificate CRL since all the
     previously set parameters are now signed.

A known limitation of this function is, that a newly-signed CRL
     will not be fully functional (e.g., for signature verification),
     until it is exported an re-imported.

After GnuTLS 3.6.1 the value of ‘dig’ may be ‘GNUTLS_DIG_UNKNOWN’ ,
     and in that case, a suitable but reasonable for the key algorithm
     will be selected.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crl_verify
----------------------

-- Function: int gnutls_x509_crl_verify (gnutls_x509_crl_t CRL, const
          gnutls_x509_crt_t * TRUSTED_CAS, unsigned TCAS_SIZE, unsigned
          int FLAGS, unsigned int * VERIFY)
     CRL: is the crl to be verified

TRUSTED_CAS: is a certificate list that is considered to be trusted
     one

TCAS_SIZE: holds the number of CA certificates in CA_list

FLAGS: Flags that may be used to change the verification algorithm.
     Use OR of the gnutls_certificate_verify_flags enumerations.

VERIFY: will hold the crl verification output.

This function will try to verify the given crl and return its
     verification status.  See ‘gnutls_x509_crt_list_verify()’ for a
     detailed description of return values.  Note that since GnuTLS
     3.1.4 this function includes the time checks.

Note that value in ‘verify’ is set only when the return value of
     this function is success (i.e, failure to trust a CRL a certificate
     does not imply a negative return value).

Before GnuTLS 3.5.7 this function would return zero or a positive
     number on success.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0), otherwise a negative
     error value.

gnutls_x509_crq_deinit
----------------------

-- Function: void gnutls_x509_crq_deinit (gnutls_x509_crq_t CRQ)
     CRQ: the type to be deinitialized

This function will deinitialize a PKCS‘10’ certificate request
     structure.

gnutls_x509_crq_export
----------------------

-- Function: int gnutls_x509_crq_export (gnutls_x509_crq_t CRQ,
          gnutls_x509_crt_fmt_t FORMAT, void * OUTPUT_DATA, size_t *
          OUTPUT_DATA_SIZE)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

FORMAT: the format of output params.  One of PEM or DER.

OUTPUT_DATA: will contain a certificate request PEM or DER encoded

OUTPUT_DATA_SIZE: holds the size of output_data (and will be
     replaced by the actual size of parameters)

This function will export the certificate request to a PEM or DER
     encoded PKCS10 structure.

If the buffer provided is not long enough to hold the output, then
     ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ will be returned and *
     ‘output_data_size’ will be updated.

If the structure is PEM encoded, it will have a header of "BEGIN
     NEW CERTIFICATE REQUEST".

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crq_export2
-----------------------

-- Function: int gnutls_x509_crq_export2 (gnutls_x509_crq_t CRQ,
          gnutls_x509_crt_fmt_t FORMAT, gnutls_datum_t * OUT)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

FORMAT: the format of output params.  One of PEM or DER.

OUT: will contain a certificate request PEM or DER encoded

This function will export the certificate request to a PEM or DER
     encoded PKCS10 structure.

The output buffer is allocated using ‘gnutls_malloc()’ .

If the structure is PEM encoded, it will have a header of "BEGIN
     NEW CERTIFICATE REQUEST".

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

Since 3.1.3

gnutls_x509_crq_get_attribute_by_oid
------------------------------------

-- Function: int gnutls_x509_crq_get_attribute_by_oid
          (gnutls_x509_crq_t CRQ, const char * OID, unsigned INDX, void
          * BUF, size_t * BUF_SIZE)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

OID: holds an Object Identifier in null-terminated string

INDX: In case multiple same OIDs exist in the attribute list, this
     specifies which to get, use (0) to get the first one

BUF: a pointer to a structure to hold the attribute data (may be
     ‘NULL’ )

BUF_SIZE: initially holds the size of ‘buf’

This function will return the attribute in the certificate request
     specified by the given Object ID. The attribute will be DER
     encoded.

Attributes in a certificate request is an optional set of data
     appended to the request.  Their interpretation depends on the CA
     policy.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crq_get_attribute_data
----------------------------------

-- Function: int gnutls_x509_crq_get_attribute_data (gnutls_x509_crq_t
          CRQ, unsigned INDX, void * DATA, size_t * SIZEOF_DATA)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

INDX: Specifies which attribute number to get.  Use (0) to get the
     first one.

DATA: a pointer to a structure to hold the data (may be null)

SIZEOF_DATA: initially holds the size of ‘oid’

This function will return the requested attribute data in the
     certificate request.  The attribute data will be stored as a string
     in the provided buffer.

Use ‘gnutls_x509_crq_get_attribute_info()’ to extract the OID. Use
     ‘gnutls_x509_crq_get_attribute_by_oid()’ instead, if you want to
     get data indexed by the attribute OID rather than sequence.

*Since:* 2.8.0

gnutls_x509_crq_get_attribute_info
----------------------------------

-- Function: int gnutls_x509_crq_get_attribute_info (gnutls_x509_crq_t
          CRQ, unsigned INDX, void * OID, size_t * SIZEOF_OID)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

INDX: Specifies which attribute number to get.  Use (0) to get the
     first one.

OID: a pointer to a structure to hold the OID

SIZEOF_OID: initially holds the maximum size of ‘oid’ , on return
     holds actual size of ‘oid’ .

This function will return the requested attribute OID in the
     certificate, and the critical flag for it.  The attribute OID will
     be stored as a string in the provided buffer.  Use
     ‘gnutls_x509_crq_get_attribute_data()’ to extract the data.

If the buffer provided is not long enough to hold the output, then
     * ‘sizeof_oid’ is updated and ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ will
     be returned.

*Since:* 2.8.0

gnutls_x509_crq_get_basic_constraints
-------------------------------------

-- Function: int gnutls_x509_crq_get_basic_constraints
          (gnutls_x509_crq_t CRQ, unsigned int * CRITICAL, unsigned int
          * CA, int * PATHLEN)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

CRITICAL: will be non-zero if the extension is marked as critical

CA: pointer to output integer indicating CA status, may be NULL,
     value is 1 if the certificate CA flag is set, 0 otherwise.

PATHLEN: pointer to output integer indicating path length (may be
     NULL), non-negative error codes indicate a present
     pathLenConstraint field and the actual value, -1 indicate that the
     field is absent.

This function will read the certificate's basic constraints, and
     return the certificates CA status.  It reads the basicConstraints
     X.509 extension (2.5.29.19).

*Returns:* If the certificate is a CA a positive value will be
     returned, or (0) if the certificate does not have CA flag set.  A
     negative error code may be returned in case of errors.  If the
     certificate does not contain the basicConstraints extension
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ will be returned.

*Since:* 2.8.0

gnutls_x509_crq_get_challenge_password
--------------------------------------

-- Function: int gnutls_x509_crq_get_challenge_password
          (gnutls_x509_crq_t CRQ, char * PASS, size_t * PASS_SIZE)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

PASS: will hold a (0)-terminated password string

PASS_SIZE: Initially holds the size of ‘pass’ .

This function will return the challenge password in the request.
     The challenge password is intended to be used for requesting a
     revocation of the certificate.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crq_get_dn
----------------------

-- Function: int gnutls_x509_crq_get_dn (gnutls_x509_crq_t CRQ, char *
          BUF, size_t * BUF_SIZE)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

BUF: a pointer to a structure to hold the name (may be ‘NULL’ )

BUF_SIZE: initially holds the size of ‘buf’

This function will copy the name of the Certificate request subject
     to the provided buffer.  The name will be in the form
     "C=xxxx,O=yyyy,CN=zzzz" as described in RFC 2253.  The output
     string ‘buf’ will be ASCII or UTF-8 encoded, depending on the
     certificate data.

This function does not output a fully RFC4514 compliant string, if
     that is required see ‘gnutls_x509_crq_get_dn3()’ .

*Returns:* ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ if the provided buffer is
     not long enough, and in that case the * ‘buf_size’ will be updated
     with the required size.  On success 0 is returned.

gnutls_x509_crq_get_dn2
-----------------------

-- Function: int gnutls_x509_crq_get_dn2 (gnutls_x509_crq_t CRQ,
          gnutls_datum_t * DN)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

DN: a pointer to a structure to hold the name; must be freed using
     ‘gnutls_free()’

This function will allocate buffer and copy the name of the
     Certificate request.  The name will be in the form
     "C=xxxx,O=yyyy,CN=zzzz" as described in RFC4514.  The output string
     will be ASCII or UTF-8 encoded, depending on the certificate data.

This function does not output a fully RFC4514 compliant string, if
     that is required see ‘gnutls_x509_crq_get_dn3()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.  and a negative error code on
     error.

*Since:* 3.1.10

gnutls_x509_crq_get_dn3
-----------------------

-- Function: int gnutls_x509_crq_get_dn3 (gnutls_x509_crq_t CRQ,
          gnutls_datum_t * DN, unsigned FLAGS)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

DN: a pointer to a structure to hold the name; must be freed using
     ‘gnutls_free()’

FLAGS: zero or ‘GNUTLS_X509_DN_FLAG_COMPAT’

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.  and a negative error code on
     error.

*Since:* 3.5.7

gnutls_x509_crq_get_dn_by_oid
-----------------------------

-- Function: int gnutls_x509_crq_get_dn_by_oid (gnutls_x509_crq_t CRQ,
          const char * OID, unsigned INDX, unsigned int RAW_FLAG, void *
          BUF, size_t * BUF_SIZE)
     CRQ: should contain a gnutls_x509_crq_t type

OID: holds an Object Identifier in a null terminated string

INDX: In case multiple same OIDs exist in the RDN, this specifies
     which to get.  Use (0) to get the first one.

RAW_FLAG: If non-zero returns the raw DER data of the DN part.

BUF: a pointer to a structure to hold the name (may be ‘NULL’ )

BUF_SIZE: initially holds the size of ‘buf’

This function will extract the part of the name of the Certificate
     request subject, specified by the given OID. The output will be
     encoded as described in RFC2253.  The output string will be ASCII
     or UTF-8 encoded, depending on the certificate data.

Some helper macros with popular OIDs can be found in gnutls/x509.h
     If raw flag is (0), this function will only return known OIDs as
     text.  Other OIDs will be DER encoded, as described in RFC2253 - in
     hex format with a '\#' prefix.  You can check about known OIDs
     using ‘gnutls_x509_dn_oid_known()’ .

gnutls_x509_crq_get_dn_oid
--------------------------

-- Function: int gnutls_x509_crq_get_dn_oid (gnutls_x509_crq_t CRQ,
          unsigned INDX, void * OID, size_t * SIZEOF_OID)
     CRQ: should contain a gnutls_x509_crq_t type

INDX: Specifies which DN OID to get.  Use (0) to get the first one.

OID: a pointer to a structure to hold the name (may be ‘NULL’ )

SIZEOF_OID: initially holds the size of ‘oid’

This function will extract the requested OID of the name of the
     certificate request subject, specified by the given index.

*Returns:* ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ if the provided buffer is
     not long enough, and in that case the * ‘sizeof_oid’ will be
     updated with the required size.  On success 0 is returned.

gnutls_x509_crq_get_extension_by_oid
------------------------------------

-- Function: int gnutls_x509_crq_get_extension_by_oid
          (gnutls_x509_crq_t CRQ, const char * OID, unsigned INDX, void
          * BUF, size_t * BUF_SIZE, unsigned int * CRITICAL)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

OID: holds an Object Identifier in a null terminated string

INDX: In case multiple same OIDs exist in the extensions, this
     specifies which to get.  Use (0) to get the first one.

BUF: a pointer to a structure to hold the name (may be null)

BUF_SIZE: initially holds the size of ‘buf’

CRITICAL: will be non-zero if the extension is marked as critical

This function will return the extension specified by the OID in the
     certificate.  The extensions will be returned as binary data DER
     encoded, in the provided buffer.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code in case of an error.  If the
     certificate does not contain the specified extension
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ will be returned.

*Since:* 2.8.0

gnutls_x509_crq_get_extension_by_oid2
-------------------------------------

-- Function: int gnutls_x509_crq_get_extension_by_oid2
          (gnutls_x509_crq_t CRQ, const char * OID, unsigned INDX,
          gnutls_datum_t * OUTPUT, unsigned int * CRITICAL)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

OID: holds an Object Identifier in a null terminated string

INDX: In case multiple same OIDs exist in the extensions, this
     specifies which to get.  Use (0) to get the first one.

OUTPUT: will hold the allocated extension data

CRITICAL: will be non-zero if the extension is marked as critical

This function will return the extension specified by the OID in the
     certificate.  The extensions will be returned as binary data DER
     encoded, in the provided buffer.

*Since:* 3.3.8

gnutls_x509_crq_get_extension_data
----------------------------------

-- Function: int gnutls_x509_crq_get_extension_data (gnutls_x509_crq_t
          CRQ, unsigned INDX, void * DATA, size_t * SIZEOF_DATA)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

INDX: Specifies which extension number to get.  Use (0) to get the
     first one.

DATA: a pointer to a structure to hold the data (may be null)

SIZEOF_DATA: initially holds the size of ‘oid’

This function will return the requested extension data in the
     certificate.  The extension data will be stored as a string in the
     provided buffer.

Use ‘gnutls_x509_crq_get_extension_info()’ to extract the OID and
     critical flag.  Use ‘gnutls_x509_crq_get_extension_by_oid()’
     instead, if you want to get data indexed by the extension OID
     rather than sequence.

*Since:* 2.8.0

gnutls_x509_crq_get_extension_data2
-----------------------------------

-- Function: int gnutls_x509_crq_get_extension_data2 (gnutls_x509_crq_t
          CRQ, unsigned INDX, gnutls_datum_t * DATA)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

INDX: Specifies which extension OID to read.  Use (0) to get the
     first one.

DATA: will contain the extension DER-encoded data

This function will return the requested extension data in the
     certificate request.  The extension data will be allocated using
     ‘gnutls_malloc()’ .

Use ‘gnutls_x509_crq_get_extension_info()’ to extract the OID.

*Since:* 3.3.0

gnutls_x509_crq_get_extension_info
----------------------------------

-- Function: int gnutls_x509_crq_get_extension_info (gnutls_x509_crq_t
          CRQ, unsigned INDX, void * OID, size_t * SIZEOF_OID, unsigned
          int * CRITICAL)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

INDX: Specifies which extension number to get.  Use (0) to get the
     first one.

OID: a pointer to store the OID

SIZEOF_OID: initially holds the maximum size of ‘oid’ , on return
     holds actual size of ‘oid’ .

CRITICAL: output variable with critical flag, may be NULL.

This function will return the requested extension OID in the
     certificate, and the critical flag for it.  The extension OID will
     be stored as a string in the provided buffer.  Use
     ‘gnutls_x509_crq_get_extension_data()’ to extract the data.

If the buffer provided is not long enough to hold the output, then
     * ‘sizeof_oid’ is updated and ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ will
     be returned.

*Since:* 2.8.0

gnutls_x509_crq_get_key_id
--------------------------

-- Function: int gnutls_x509_crq_get_key_id (gnutls_x509_crq_t CRQ,
          unsigned int FLAGS, unsigned char * OUTPUT_DATA, size_t *
          OUTPUT_DATA_SIZE)
     CRQ: a certificate of type ‘gnutls_x509_crq_t’

FLAGS: should be one of the flags from ‘gnutls_keyid_flags_t’

OUTPUT_DATA: will contain the key ID

OUTPUT_DATA_SIZE: holds the size of output_data (and will be
     replaced by the actual size of parameters)

This function will return a unique ID that depends on the public
     key parameters.  This ID can be used in checking whether a
     certificate corresponds to the given private key.

If the buffer provided is not long enough to hold the output, then
     * ‘output_data_size’ is updated and GNUTLS_E_SHORT_MEMORY_BUFFER
     will be returned.  The output will normally be a SHA-1 hash output,
     which is 20 bytes.

*Returns:* In case of failure a negative error code will be
     returned, and 0 on success.

*Since:* 2.8.0

gnutls_x509_crq_get_key_purpose_oid
-----------------------------------

-- Function: int gnutls_x509_crq_get_key_purpose_oid (gnutls_x509_crq_t
          CRQ, unsigned INDX, void * OID, size_t * SIZEOF_OID, unsigned
          int * CRITICAL)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

INDX: This specifies which OID to return, use (0) to get the first
     one

OID: a pointer to store the OID (may be ‘NULL’ )

SIZEOF_OID: initially holds the size of ‘oid’

CRITICAL: output variable with critical flag, may be ‘NULL’ .

This function will extract the key purpose OIDs of the Certificate
     specified by the given index.  These are stored in the Extended Key
     Usage extension (2.5.29.37).  See the GNUTLS_KP_* definitions for
     human readable names.

*Since:* 2.8.0

gnutls_x509_crq_get_key_rsa_raw
-------------------------------

-- Function: int gnutls_x509_crq_get_key_rsa_raw (gnutls_x509_crq_t
          CRQ, gnutls_datum_t * M, gnutls_datum_t * E)
     CRQ: Holds the certificate

M: will hold the modulus

E: will hold the public exponent

This function will export the RSA public key's parameters found in
     the given structure.  The new parameters will be allocated using
     ‘gnutls_malloc()’ and will be stored in the appropriate datum.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 2.8.0

gnutls_x509_crq_get_key_usage
-----------------------------

-- Function: int gnutls_x509_crq_get_key_usage (gnutls_x509_crq_t CRQ,
          unsigned int * KEY_USAGE, unsigned int * CRITICAL)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

KEY_USAGE: where the key usage bits will be stored

CRITICAL: will be non-zero if the extension is marked as critical

This function will return certificate's key usage, by reading the
     keyUsage X.509 extension (2.5.29.15).  The key usage value will
     ORed values of the: ‘GNUTLS_KEY_DIGITAL_SIGNATURE’ ,
     ‘GNUTLS_KEY_NON_REPUDIATION’ , ‘GNUTLS_KEY_KEY_ENCIPHERMENT’ ,
     ‘GNUTLS_KEY_DATA_ENCIPHERMENT’ , ‘GNUTLS_KEY_KEY_AGREEMENT’ ,
     ‘GNUTLS_KEY_KEY_CERT_SIGN’ , ‘GNUTLS_KEY_CRL_SIGN’ ,
     ‘GNUTLS_KEY_ENCIPHER_ONLY’ , ‘GNUTLS_KEY_DECIPHER_ONLY’ .

*Returns:* the certificate key usage, or a negative error code in
     case of parsing error.  If the certificate does not contain the
     keyUsage extension ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ will be
     returned.

*Since:* 2.8.0

gnutls_x509_crq_get_pk_algorithm
--------------------------------

-- Function: int gnutls_x509_crq_get_pk_algorithm (gnutls_x509_crq_t
          CRQ, unsigned int * BITS)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

BITS: if bits is non-‘NULL’ it will hold the size of the
     parameters' in bits

This function will return the public key algorithm of a PKCS‘10’
     certificate request.

If bits is non-‘NULL’ , it should have enough size to hold the
     parameters size in bits.  For RSA the bits returned is the modulus.
     For DSA the bits returned are of the public exponent.

*Returns:* a member of the ‘gnutls_pk_algorithm_t’ enumeration on
     success, or a negative error code on error.

gnutls_x509_crq_get_pk_oid
--------------------------

-- Function: int gnutls_x509_crq_get_pk_oid (gnutls_x509_crq_t CRQ,
          char * OID, size_t * OID_SIZE)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

OID: a pointer to a buffer to hold the OID (may be null)

OID_SIZE: initially holds the size of ‘oid’

This function will return the OID of the public key algorithm on
     that certificate request.  This function is useful in the case
     ‘gnutls_x509_crq_get_pk_algorithm()’ returned ‘GNUTLS_PK_UNKNOWN’ .

*Returns:* zero or a negative error code on error.

*Since:* 3.5.0

gnutls_x509_crq_get_private_key_usage_period
--------------------------------------------

-- Function: int gnutls_x509_crq_get_private_key_usage_period
          (gnutls_x509_crq_t CRQ, time_t * ACTIVATION, time_t *
          EXPIRATION, unsigned int * CRITICAL)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

ACTIVATION: The activation time

EXPIRATION: The expiration time

CRITICAL: the extension status

This function will return the expiration and activation times of
     the private key of the certificate.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ if the extension is not
     present, otherwise a negative error value.

gnutls_x509_crq_get_signature_algorithm
---------------------------------------

-- Function: int gnutls_x509_crq_get_signature_algorithm
          (gnutls_x509_crq_t CRQ)
     CRQ: should contain a ‘gnutls_x509_cr_t’ type

This function will return a value of the ‘gnutls_sign_algorithm_t’
     enumeration that is the signature algorithm that has been used to
     sign this certificate request.

Since 3.6.0 this function never returns a negative error code.
     Error cases and unknown/unsupported signature algorithms are mapped
     to ‘GNUTLS_SIGN_UNKNOWN’ .

*Returns:* a ‘gnutls_sign_algorithm_t’ value

*Since:* 3.4.0

gnutls_x509_crq_get_signature_oid
---------------------------------

-- Function: int gnutls_x509_crq_get_signature_oid (gnutls_x509_crq_t
          CRQ, char * OID, size_t * OID_SIZE)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

OID: a pointer to a buffer to hold the OID (may be null)

OID_SIZE: initially holds the size of ‘oid’

This function will return the OID of the signature algorithm that
     has been used to sign this certificate request.  This function is
     useful in the case ‘gnutls_x509_crq_get_signature_algorithm()’
     returned ‘GNUTLS_SIGN_UNKNOWN’ .

*Returns:* zero or a negative error code on error.

*Since:* 3.5.0

gnutls_x509_crq_get_spki
------------------------

-- Function: int gnutls_x509_crq_get_spki (gnutls_x509_crq_t CRQ,
          gnutls_x509_spki_t SPKI, unsigned int FLAGS)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

SPKI: a SubjectPublicKeyInfo structure of type ‘gnutls_x509_spki_t’

FLAGS: must be zero

This function will return the public key information of a PKCS‘10’
     certificate request.  The provided ‘spki’ must be initialized.

*Returns:* Zero on success, or a negative error code on error.

gnutls_x509_crq_get_subject_alt_name
------------------------------------

-- Function: int gnutls_x509_crq_get_subject_alt_name
          (gnutls_x509_crq_t CRQ, unsigned int SEQ, void * RET, size_t *
          RET_SIZE, unsigned int * RET_TYPE, unsigned int * CRITICAL)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

SEQ: specifies the sequence number of the alt name, 0 for the first
     one, 1 for the second etc.

RET: is the place where the alternative name will be copied to

RET_SIZE: holds the size of ret.

RET_TYPE: holds the ‘gnutls_x509_subject_alt_name_t’ name type

CRITICAL: will be non-zero if the extension is marked as critical
     (may be null)

This function will return the alternative names, contained in the
     given certificate.  It is the same as
     ‘gnutls_x509_crq_get_subject_alt_name()’ except for the fact that
     it will return the type of the alternative name in ‘ret_type’ even
     if the function fails for some reason (i.e.  the buffer provided is
     not enough).

*Returns:* the alternative subject name type on success, one of the
     enumerated ‘gnutls_x509_subject_alt_name_t’ .  It will return
     ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ if ‘ret_size’ is not large enough to
     hold the value.  In that case ‘ret_size’ will be updated with the
     required size.  If the certificate request does not have an
     Alternative name with the specified sequence number then
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ is returned.

*Since:* 2.8.0

gnutls_x509_crq_get_subject_alt_othername_oid
---------------------------------------------

-- Function: int gnutls_x509_crq_get_subject_alt_othername_oid
          (gnutls_x509_crq_t CRQ, unsigned int SEQ, void * RET, size_t *
          RET_SIZE)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

SEQ: specifies the sequence number of the alt name (0 for the first
     one, 1 for the second etc.)

RET: is the place where the otherName OID will be copied to

RET_SIZE: holds the size of ret.

This function will extract the type OID of an otherName Subject
     Alternative Name, contained in the given certificate, and return
     the type as an enumerated element.

This function is only useful if
     ‘gnutls_x509_crq_get_subject_alt_name()’ returned
     ‘GNUTLS_SAN_OTHERNAME’ .

*Returns:* the alternative subject name type on success, one of the
     enumerated gnutls_x509_subject_alt_name_t.  For supported OIDs, it
     will return one of the virtual (GNUTLS_SAN_OTHERNAME_*) types, e.g.
     ‘GNUTLS_SAN_OTHERNAME_XMPP’ , and ‘GNUTLS_SAN_OTHERNAME’ for
     unknown OIDs.  It will return ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ if
     ‘ret_size’ is not large enough to hold the value.  In that case
     ‘ret_size’ will be updated with the required size.  If the
     certificate does not have an Alternative name with the specified
     sequence number and with the otherName type then
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ is returned.

*Since:* 2.8.0

gnutls_x509_crq_get_tlsfeatures
-------------------------------

-- Function: int gnutls_x509_crq_get_tlsfeatures (gnutls_x509_crq_t
          CRQ, gnutls_x509_tlsfeatures_t FEATURES, unsigned int FLAGS,
          unsigned int * CRITICAL)
     CRQ: An X.509 certificate request

FEATURES: If the function succeeds, the features will be stored in
     this variable.

FLAGS: zero or ‘GNUTLS_EXT_FLAG_APPEND’

CRITICAL: the extension status

This function will get the X.509 TLS features extension structure
     from the certificate request.  The returned structure needs to be
     freed using ‘gnutls_x509_tlsfeatures_deinit()’ .

When the ‘flags’ is set to ‘GNUTLS_EXT_FLAG_APPEND’ , then if the
     ‘features’ structure is empty this function will behave identically
     as if the flag was not set.  Otherwise if there are elements in the
     ‘features’ structure then they will be merged with.

Note that ‘features’ must be initialized prior to calling this
     function.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.5.1

gnutls_x509_crq_get_version
---------------------------

-- Function: int gnutls_x509_crq_get_version (gnutls_x509_crq_t CRQ)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

This function will return the version of the specified Certificate
     request.

*Returns:* version of certificate request, or a negative error code
     on error.

gnutls_x509_crq_import
----------------------

-- Function: int gnutls_x509_crq_import (gnutls_x509_crq_t CRQ, const
          gnutls_datum_t * DATA, gnutls_x509_crt_fmt_t FORMAT)
     CRQ: The data to store the parsed certificate request.

DATA: The DER or PEM encoded certificate.

FORMAT: One of DER or PEM

This function will convert the given DER or PEM encoded certificate
     request to a ‘gnutls_x509_crq_t’ type.  The output will be stored
     in ‘crq’ .

If the Certificate is PEM encoded it should have a header of "NEW
     CERTIFICATE REQUEST".

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crq_init
--------------------

-- Function: int gnutls_x509_crq_init (gnutls_x509_crq_t * CRQ)
     CRQ: A pointer to the type to be initialized

This function will initialize a PKCS‘10’ certificate request
     structure.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crq_print
---------------------

-- Function: int gnutls_x509_crq_print (gnutls_x509_crq_t CRQ,
          gnutls_certificate_print_formats_t FORMAT, gnutls_datum_t *
          OUT)
     CRQ: The data to be printed

FORMAT: Indicate the format to use

OUT: Newly allocated datum with null terminated string.

This function will pretty print a certificate request, suitable for
     display to a human.

The output ‘out’ needs to be deallocated using ‘gnutls_free()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 2.8.0

gnutls_x509_crq_set_attribute_by_oid
------------------------------------

-- Function: int gnutls_x509_crq_set_attribute_by_oid
          (gnutls_x509_crq_t CRQ, const char * OID, void * BUF, size_t
          BUF_SIZE)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

OID: holds an Object Identifier in a null-terminated string

BUF: a pointer to a structure that holds the attribute data

BUF_SIZE: holds the size of ‘buf’

This function will set the attribute in the certificate request
     specified by the given Object ID. The provided attribute must be be
     DER encoded.

Attributes in a certificate request is an optional set of data
     appended to the request.  Their interpretation depends on the CA
     policy.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crq_set_basic_constraints
-------------------------------------

-- Function: int gnutls_x509_crq_set_basic_constraints
          (gnutls_x509_crq_t CRQ, unsigned int CA, int
          PATHLENCONSTRAINT)
     CRQ: a certificate request of type ‘gnutls_x509_crq_t’

CA: true(1) or false(0) depending on the Certificate authority
     status.

PATHLENCONSTRAINT: non-negative error codes indicate maximum length
     of path, and negative error codes indicate that the
     pathLenConstraints field should not be present.

This function will set the basicConstraints certificate extension.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 2.8.0

gnutls_x509_crq_set_challenge_password
--------------------------------------

-- Function: int gnutls_x509_crq_set_challenge_password
          (gnutls_x509_crq_t CRQ, const char * PASS)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

PASS: holds a (0)-terminated password

This function will set a challenge password to be used when
     revoking the request.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crq_set_dn
----------------------

-- Function: int gnutls_x509_crq_set_dn (gnutls_x509_crq_t CRQ, const
          char * DN, const char ** ERR)
     CRQ: a certificate of type ‘gnutls_x509_crq_t’

DN: a comma separated DN string (RFC4514)

ERR: indicates the error position (if any)

This function will set the DN on the provided certificate.  The
     input string should be plain ASCII or UTF-8 encoded.  On DN parsing
     error ‘GNUTLS_E_PARSING_ERROR’ is returned.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crq_set_dn_by_oid
-----------------------------

-- Function: int gnutls_x509_crq_set_dn_by_oid (gnutls_x509_crq_t CRQ,
          const char * OID, unsigned int RAW_FLAG, const void * DATA,
          unsigned int SIZEOF_DATA)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

OID: holds an Object Identifier in a (0)-terminated string

RAW_FLAG: must be 0, or 1 if the data are DER encoded

DATA: a pointer to the input data

SIZEOF_DATA: holds the size of ‘data’

This function will set the part of the name of the Certificate
     request subject, specified by the given OID. The input string
     should be ASCII or UTF-8 encoded.

Some helper macros with popular OIDs can be found in gnutls/x509.h
     With this function you can only set the known OIDs.  You can test
     for known OIDs using ‘gnutls_x509_dn_oid_known()’ .  For OIDs that
     are not known (by gnutls) you should properly DER encode your data,
     and call this function with raw_flag set.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crq_set_extension_by_oid
------------------------------------

-- Function: int gnutls_x509_crq_set_extension_by_oid
          (gnutls_x509_crq_t CRQ, const char * OID, const void * BUF,
          size_t SIZEOF_BUF, unsigned int CRITICAL)
     CRQ: a certificate of type ‘gnutls_x509_crq_t’

OID: holds an Object Identifier in null terminated string

BUF: a pointer to a DER encoded data

SIZEOF_BUF: holds the size of ‘buf’

CRITICAL: should be non-zero if the extension is to be marked as
     critical

This function will set an the extension, by the specified OID, in
     the certificate request.  The extension data should be binary data
     DER encoded.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crq_set_key
-----------------------

-- Function: int gnutls_x509_crq_set_key (gnutls_x509_crq_t CRQ,
          gnutls_x509_privkey_t KEY)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

KEY: holds a private key

This function will set the public parameters from the given private
     key to the request.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crq_set_key_purpose_oid
-----------------------------------

-- Function: int gnutls_x509_crq_set_key_purpose_oid (gnutls_x509_crq_t
          CRQ, const void * OID, unsigned int CRITICAL)
     CRQ: a certificate of type ‘gnutls_x509_crq_t’

OID: a pointer to a null-terminated string that holds the OID

CRITICAL: Whether this extension will be critical or not

This function will set the key purpose OIDs of the Certificate.
     These are stored in the Extended Key Usage extension (2.5.29.37)
     See the GNUTLS_KP_* definitions for human readable names.

Subsequent calls to this function will append OIDs to the OID list.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 2.8.0

gnutls_x509_crq_set_key_rsa_raw
-------------------------------

-- Function: int gnutls_x509_crq_set_key_rsa_raw (gnutls_x509_crq_t
          CRQ, const gnutls_datum_t * M, const gnutls_datum_t * E)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

M: holds the modulus

E: holds the public exponent

This function will set the public parameters from the given private
     key to the request.  Only RSA keys are currently supported.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 2.6.0

gnutls_x509_crq_set_key_usage
-----------------------------

-- Function: int gnutls_x509_crq_set_key_usage (gnutls_x509_crq_t CRQ,
          unsigned int USAGE)
     CRQ: a certificate request of type ‘gnutls_x509_crq_t’

USAGE: an ORed sequence of the GNUTLS_KEY_* elements.

This function will set the keyUsage certificate extension.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 2.8.0

gnutls_x509_crq_set_private_key_usage_period
--------------------------------------------

-- Function: int gnutls_x509_crq_set_private_key_usage_period
          (gnutls_x509_crq_t CRQ, time_t ACTIVATION, time_t EXPIRATION)
     CRQ: a certificate of type ‘gnutls_x509_crq_t’

ACTIVATION: The activation time

EXPIRATION: The expiration time

This function will set the private key usage period extension
     (2.5.29.16).

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crq_set_spki
------------------------

-- Function: int gnutls_x509_crq_set_spki (gnutls_x509_crq_t CRQ, const
          gnutls_x509_spki_t SPKI, unsigned int FLAGS)
     CRQ: a certificate request of type ‘gnutls_x509_crq_t’

SPKI: a SubjectPublicKeyInfo structure of type ‘gnutls_x509_spki_t’

FLAGS: must be zero

This function will set the certificate request's subject public key
     information explicitly.  This is intended to be used in the cases
     where a single public key (e.g., RSA) can be used for multiple
     signature algorithms (RSA PKCS1-1.5, and RSA-PSS).

To export the public key (i.e., the SubjectPublicKeyInfo part),
     check ‘gnutls_pubkey_import_x509()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.6.0

gnutls_x509_crq_set_subject_alt_name
------------------------------------

-- Function: int gnutls_x509_crq_set_subject_alt_name
          (gnutls_x509_crq_t CRQ, gnutls_x509_subject_alt_name_t NT,
          const void * DATA, unsigned int DATA_SIZE, unsigned int FLAGS)
     CRQ: a certificate request of type ‘gnutls_x509_crq_t’

NT: is one of the ‘gnutls_x509_subject_alt_name_t’ enumerations

DATA: The data to be set

DATA_SIZE: The size of data to be set

FLAGS: ‘GNUTLS_FSAN_SET’ to clear previous data or
     ‘GNUTLS_FSAN_APPEND’ to append.

This function will set the subject alternative name certificate
     extension.  It can set the following types:

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 2.8.0

gnutls_x509_crq_set_subject_alt_othername
-----------------------------------------

-- Function: int gnutls_x509_crq_set_subject_alt_othername
          (gnutls_x509_crq_t CRQ, const char * OID, const void * DATA,
          unsigned int DATA_SIZE, unsigned int FLAGS)
     CRQ: a certificate request of type ‘gnutls_x509_crq_t’

OID: is the othername OID

DATA: The data to be set

DATA_SIZE: The size of data to be set

FLAGS: ‘GNUTLS_FSAN_SET’ to clear previous data or
     ‘GNUTLS_FSAN_APPEND’ to append.

This function will set the subject alternative name certificate
     extension.  It can set the following types:

The values set must be binary values and must be properly DER
     encoded.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.5.0

gnutls_x509_crq_set_tlsfeatures
-------------------------------

-- Function: int gnutls_x509_crq_set_tlsfeatures (gnutls_x509_crq_t
          CRQ, gnutls_x509_tlsfeatures_t FEATURES)
     CRQ: An X.509 certificate request

FEATURES: If the function succeeds, the features will be added to
     the certificate request.

This function will set the certificate request's X.509 TLS
     extension from the given structure.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.5.1

gnutls_x509_crq_set_version
---------------------------

-- Function: int gnutls_x509_crq_set_version (gnutls_x509_crq_t CRQ,
          unsigned int VERSION)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

VERSION: holds the version number, for v1 Requests must be 1

This function will set the version of the certificate request.  For
     version 1 requests this must be one.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crq_sign
--------------------

-- Function: int gnutls_x509_crq_sign (gnutls_x509_crq_t CRQ,
          gnutls_x509_privkey_t KEY)
     CRQ: should contain a ‘gnutls_x509_crq_t’ type

KEY: holds a private key

This function is the same a ‘gnutls_x509_crq_sign2()’ with no
     flags, and an appropriate hash algorithm.  The hash algorithm used
     may vary between versions of GnuTLS, and it is tied to the security
     level of the issuer's public key.

A known limitation of this function is, that a newly-signed request
     will not be fully functional (e.g., for signature verification),
     until it is exported an re-imported.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crq_sign2
---------------------

KEY: holds a private key

DIG: The message digest to use, i.e., ‘GNUTLS_DIG_SHA256’

FLAGS: must be 0

This must be the last step in a certificate request generation
     since all the previously set parameters are now signed.

A known limitation of this function is, that a newly-signed request
     will not be fully functional (e.g., for signature verification),
     until it is exported an re-imported.

After GnuTLS 3.6.1 the value of ‘dig’ may be ‘GNUTLS_DIG_UNKNOWN’ ,
     and in that case, a suitable but reasonable for the key algorithm
     will be selected.

gnutls_x509_crq_verify
----------------------

-- Function: int gnutls_x509_crq_verify (gnutls_x509_crq_t CRQ,
          unsigned int FLAGS)
     CRQ: is the crq to be verified

FLAGS: Flags that may be used to change the verification algorithm.
     Use OR of the gnutls_certificate_verify_flags enumerations.

This function will verify self signature in the certificate request
     and return its status.

*Returns:* In case of a verification failure
     ‘GNUTLS_E_PK_SIG_VERIFY_FAILED’ is returned, and zero or positive
     code on success.

Since 2.12.0

gnutls_x509_crt_check_email
---------------------------

-- Function: unsigned gnutls_x509_crt_check_email (gnutls_x509_crt_t
          CERT, const char * EMAIL, unsigned int FLAGS)
     CERT: should contain an gnutls_x509_crt_t type

EMAIL: A null terminated string that contains an email address
     (RFC822)

FLAGS: should be zero

This function will check if the given certificate's subject matches
     the given email address.

*Returns:* non-zero for a successful match, and zero on failure.

gnutls_x509_crt_check_hostname
------------------------------

-- Function: unsigned gnutls_x509_crt_check_hostname (gnutls_x509_crt_t
          CERT, const char * HOSTNAME)
     CERT: should contain an gnutls_x509_crt_t type

HOSTNAME: A null terminated string that contains a DNS name

This function will check if the given certificate's subject matches
     the given hostname.  This is a basic implementation of the matching
     described in RFC6125, and takes into account wildcards, and the
     DNSName/IPAddress subject alternative name PKIX extension.

For details see also ‘gnutls_x509_crt_check_hostname2()’ .

*Returns:* non-zero for a successful match, and zero on failure.

gnutls_x509_crt_check_hostname2
-------------------------------

-- Function: unsigned gnutls_x509_crt_check_hostname2
          (gnutls_x509_crt_t CERT, const char * HOSTNAME, unsigned int
          FLAGS)
     CERT: should contain an gnutls_x509_crt_t type

HOSTNAME: A null terminated string that contains a DNS name

FLAGS: gnutls_certificate_verify_flags

IPv4 addresses are accepted by this function in the dotted-decimal
     format (e.g, ddd.ddd.ddd.ddd), and IPv6 addresses in the
     hexadecimal x:x:x:x:x:x:x:x format.  For them the IPAddress subject
     alternative name extension is consulted.  Previous versions to
     3.6.0 of GnuTLS in case of a non-match would consult (in a
     non-standard extension) the DNSname and CN fields.  This is no
     longer the case.

When the flag ‘GNUTLS_VERIFY_DO_NOT_ALLOW_WILDCARDS’ is specified
     no wildcards are considered.  Otherwise they are only considered if
     the domain name consists of three components or more, and the
     wildcard starts at the leftmost position.  When the flag
     ‘GNUTLS_VERIFY_DO_NOT_ALLOW_IP_MATCHES’ is specified, the input
     will be treated as a DNS name, and matching of textual IP addresses
     against the IPAddress part of the alternative name will not be
     allowed.

The function ‘gnutls_x509_crt_check_ip()’ is available for matching
     IP addresses.

*Returns:* non-zero for a successful match, and zero on failure.

*Since:* 3.3.0

gnutls_x509_crt_check_ip
------------------------

-- Function: unsigned gnutls_x509_crt_check_ip (gnutls_x509_crt_t CERT,
          const unsigned char * IP, unsigned int IP_SIZE, unsigned int
          FLAGS)
     CERT: should contain an gnutls_x509_crt_t type

IP: A pointer to the raw IP address

IP_SIZE: the number of bytes in ip (4 or 16)

FLAGS: should be zero

This function will check if the IP allowed IP addresses in the
     certificate's subject alternative name match the provided IP
     address.

*Returns:* non-zero for a successful match, and zero on failure.

gnutls_x509_crt_check_issuer
----------------------------

-- Function: unsigned gnutls_x509_crt_check_issuer (gnutls_x509_crt_t
          CERT, gnutls_x509_crt_t ISSUER)
     CERT: is the certificate to be checked

ISSUER: is the certificate of a possible issuer

This function will check if the given certificate was issued by the
     given issuer.  It checks the DN fields and the authority key
     identifier and subject key identifier fields match.

If the same certificate is provided at the ‘cert’ and ‘issuer’
     fields, it will check whether the certificate is self-signed.

*Returns:* It will return true (1) if the given certificate is
     issued by the given issuer, and false (0) if not.

gnutls_x509_crt_check_key_purpose
---------------------------------

-- Function: unsigned gnutls_x509_crt_check_key_purpose
          (gnutls_x509_crt_t CERT, const char * PURPOSE, unsigned FLAGS)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

PURPOSE: a key purpose OID (e.g., ‘GNUTLS_KP_CODE_SIGNING’ )

FLAGS: zero or ‘GNUTLS_KP_FLAG_DISALLOW_ANY’

This function will check whether the given certificate matches the
     provided key purpose.  If ‘flags’ contains
     ‘GNUTLS_KP_FLAG_ALLOW_ANY’ then it a certificate marked for any
     purpose will not match.

*Returns:* zero if the key purpose doesn't match, and non-zero
     otherwise.

*Since:* 3.5.6

gnutls_x509_crt_check_revocation
--------------------------------

-- Function: int gnutls_x509_crt_check_revocation (gnutls_x509_crt_t
          CERT, const gnutls_x509_crl_t * CRL_LIST, unsigned
          CRL_LIST_LENGTH)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

CRL_LIST: should contain a list of gnutls_x509_crl_t types

CRL_LIST_LENGTH: the length of the crl_list

This function will check if the given certificate is revoked.  It
     is assumed that the CRLs have been verified before.

*Returns:* 0 if the certificate is NOT revoked, and 1 if it is.  A
     negative error code is returned on error.

gnutls_x509_crt_cpy_crl_dist_points
-----------------------------------

-- Function: int gnutls_x509_crt_cpy_crl_dist_points (gnutls_x509_crt_t
          DST, gnutls_x509_crt_t SRC)
     DST: a certificate of type ‘gnutls_x509_crt_t’

SRC: the certificate where the dist points will be copied from

This function will copy the CRL distribution points certificate
     extension, from the source to the destination certificate.  This
     may be useful to copy from a CA certificate to issued ones.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crt_deinit
----------------------

-- Function: void gnutls_x509_crt_deinit (gnutls_x509_crt_t CERT)
     CERT: The data to be deinitialized

This function will deinitialize a certificate structure.

gnutls_x509_crt_equals
----------------------

-- Function: unsigned gnutls_x509_crt_equals (gnutls_x509_crt_t CERT1,
          gnutls_x509_crt_t CERT2)
     CERT1: The first certificate

CERT2: The second certificate

This function will compare two X.509 certificate structures.

*Returns:* On equality non-zero is returned, otherwise zero.

*Since:* 3.5.0

gnutls_x509_crt_equals2
-----------------------

-- Function: unsigned gnutls_x509_crt_equals2 (gnutls_x509_crt_t CERT1,
          const gnutls_datum_t * DER)
     CERT1: The first certificate

DER: A DER encoded certificate

This function will compare an X.509 certificate structures, with
     DER encoded certificate data.

*Returns:* On equality non-zero is returned, otherwise zero.

*Since:* 3.5.0

gnutls_x509_crt_export
----------------------

-- Function: int gnutls_x509_crt_export (gnutls_x509_crt_t CERT,
          gnutls_x509_crt_fmt_t FORMAT, void * OUTPUT_DATA, size_t *
          OUTPUT_DATA_SIZE)
     CERT: Holds the certificate

FORMAT: the format of output params.  One of PEM or DER.

OUTPUT_DATA: will contain a certificate PEM or DER encoded

OUTPUT_DATA_SIZE: holds the size of output_data (and will be
     replaced by the actual size of parameters)

This function will export the certificate to DER or PEM format.

If the buffer provided is not long enough to hold the output, then
     *output_data_size is updated and GNUTLS_E_SHORT_MEMORY_BUFFER will
     be returned.

If the structure is PEM encoded, it will have a header of "BEGIN
     CERTIFICATE".

*Returns:* In case of failure a negative error code will be
     returned, and 0 on success.

gnutls_x509_crt_export2
-----------------------

-- Function: int gnutls_x509_crt_export2 (gnutls_x509_crt_t CERT,
          gnutls_x509_crt_fmt_t FORMAT, gnutls_datum_t * OUT)
     CERT: Holds the certificate

FORMAT: the format of output params.  One of PEM or DER.

OUT: will contain a certificate PEM or DER encoded

This function will export the certificate to DER or PEM format.
     The output buffer is allocated using ‘gnutls_malloc()’ .

If the structure is PEM encoded, it will have a header of "BEGIN
     CERTIFICATE".

*Returns:* In case of failure a negative error code will be
     returned, and 0 on success.

*Since:* 3.1.3

gnutls_x509_crt_get_activation_time
-----------------------------------

-- Function: time_t gnutls_x509_crt_get_activation_time
          (gnutls_x509_crt_t CERT)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

This function will return the time this Certificate was or will be
     activated.

*Returns:* activation time, or (time_t)-1 on error.

gnutls_x509_crt_get_authority_info_access
-----------------------------------------

-- Function: int gnutls_x509_crt_get_authority_info_access
          (gnutls_x509_crt_t CRT, unsigned int SEQ, int WHAT,
          gnutls_datum_t * DATA, unsigned int * CRITICAL)
     CRT: Holds the certificate

SEQ: specifies the sequence number of the access descriptor (0 for
     the first one, 1 for the second etc.)

WHAT: what data to get, a ‘gnutls_info_access_what_t’ type.

DATA: output data to be freed with ‘gnutls_free()’ .

CRITICAL: pointer to output integer that is set to non-zero if the
     extension is marked as critical (may be ‘NULL’ )

Note that a simpler API to access the authority info data is
     provided by ‘gnutls_x509_aia_get()’ and
     ‘gnutls_x509_ext_import_aia()’ .

This function extracts the Authority Information Access (AIA)
     extension, see RFC 5280 section 4.2.2.1 for more information.  The
     AIA extension holds a sequence of AccessDescription (AD) data.

The type of data returned in ‘data’ is specified via ‘what’ which
     should be ‘gnutls_info_access_what_t’ values.

If ‘what’ is ‘GNUTLS_IA_ACCESSMETHOD_OID’ then ‘data’ will hold the
     accessMethod OID (e.g., "1.3.6.1.5.5.7.48.1").

If ‘what’ is ‘GNUTLS_IA_ACCESSLOCATION_GENERALNAME_TYPE’ , ‘data’
     will hold the accessLocation GeneralName type (e.g.,
     "uniformResourceIdentifier").

If ‘what’ is ‘GNUTLS_IA_URI’ , ‘data’ will hold the accessLocation
     URI data.  Requesting this ‘what’ value leads to an error if the
     accessLocation is not of the "uniformResourceIdentifier" type.

If ‘what’ is ‘GNUTLS_IA_OCSP_URI’ , ‘data’ will hold the OCSP URI.
     Requesting this ‘what’ value leads to an error if the accessMethod
     is not 1.3.6.1.5.5.7.48.1 aka OCSP, or if accessLocation is not of
     the "uniformResourceIdentifier" type.  In that case
     ‘GNUTLS_E_UNKNOWN_ALGORITHM’ will be returned, and ‘seq’ should be
     increased and this function called again.

If ‘what’ is ‘GNUTLS_IA_CAISSUERS_URI’ , ‘data’ will hold the
     caIssuers URI. Requesting this ‘what’ value leads to an error if
     the accessMethod is not 1.3.6.1.5.5.7.48.2 aka caIssuers, or if
     accessLocation is not of the "uniformResourceIdentifier" type.  In
     that case handle as in ‘GNUTLS_IA_OCSP_URI’ .

More ‘what’ values may be allocated in the future as needed.

If ‘data’ is NULL, the function does the same without storing the
     output data, that is, it will set ‘critical’ and do error checking
     as usual.

The value of the critical flag is returned in * ‘critical’ .
     Supply a NULL ‘critical’ if you want the function to make sure the
     extension is non-critical, as required by RFC 5280.

*Returns:* ‘GNUTLS_E_SUCCESS’ on success,
     ‘GNUTLS_E_INVALID_REQUEST’ on invalid ‘crt’ ,
     ‘GNUTLS_E_CONSTRAINT_ERROR’ if the extension is incorrectly marked
     as critical (use a non-NULL ‘critical’ to override),
     ‘GNUTLS_E_UNKNOWN_ALGORITHM’ if the requested OID does not match
     (e.g., when using ‘GNUTLS_IA_OCSP_URI’ ), otherwise a negative
     error code.

*Since:* 3.0

gnutls_x509_crt_get_authority_key_gn_serial
-------------------------------------------

-- Function: int gnutls_x509_crt_get_authority_key_gn_serial
          (gnutls_x509_crt_t CERT, unsigned int SEQ, void * ALT, size_t
          * ALT_SIZE, unsigned int * ALT_TYPE, void * SERIAL, size_t *
          SERIAL_SIZE, unsigned int * CRITICAL)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

SEQ: specifies the sequence number of the alt name (0 for the first
     one, 1 for the second etc.)

ALT: is the place where the alternative name will be copied to

ALT_SIZE: holds the size of alt.

ALT_TYPE: holds the type of the alternative name (one of
     gnutls_x509_subject_alt_name_t).

SERIAL: buffer to store the serial number (may be null)

SERIAL_SIZE: Holds the size of the serial field (may be null)

CRITICAL: will be non-zero if the extension is marked as critical
     (may be null)

This function will return the X.509 authority key identifier when
     stored as a general name (authorityCertIssuer) and serial number.

Because more than one general names might be stored ‘seq’ can be
     used as a counter to request them all until
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ is returned.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ if the extension is not
     present, otherwise a negative error value.

*Since:* 3.0

gnutls_x509_crt_get_authority_key_id
------------------------------------

-- Function: int gnutls_x509_crt_get_authority_key_id
          (gnutls_x509_crt_t CERT, void * ID, size_t * ID_SIZE, unsigned
          int * CRITICAL)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

ID: The place where the identifier will be copied

ID_SIZE: Holds the size of the id field.

CRITICAL: will be non-zero if the extension is marked as critical
     (may be null)

This function will return the X.509v3 certificate authority's key
     identifier.  This is obtained by the X.509 Authority Key identifier
     extension field (2.5.29.35).  Note that this function only returns
     the keyIdentifier field of the extension and
     ‘GNUTLS_E_X509_UNSUPPORTED_EXTENSION’ , if the extension contains
     the name and serial number of the certificate.  In that case
     ‘gnutls_x509_crt_get_authority_key_gn_serial()’ may be used.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ if the extension is not
     present, otherwise a negative error value.

gnutls_x509_crt_get_basic_constraints
-------------------------------------

-- Function: int gnutls_x509_crt_get_basic_constraints
          (gnutls_x509_crt_t CERT, unsigned int * CRITICAL, unsigned int
          * CA, int * PATHLEN)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

CRITICAL: will be non-zero if the extension is marked as critical

CA: pointer to output integer indicating CA status, may be NULL,
     value is 1 if the certificate CA flag is set, 0 otherwise.

This function will read the certificate's basic constraints, and
     return the certificates CA status.  It reads the basicConstraints
     X.509 extension (2.5.29.19).

*Returns:* If the certificate is a CA a positive value will be
     returned, or (0) if the certificate does not have CA flag set.  A
     negative error code may be returned in case of errors.  If the
     certificate does not contain the basicConstraints extension
     GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE will be returned.

gnutls_x509_crt_get_ca_status
-----------------------------

-- Function: int gnutls_x509_crt_get_ca_status (gnutls_x509_crt_t CERT,
          unsigned int * CRITICAL)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

CRITICAL: will be non-zero if the extension is marked as critical

This function will return certificates CA status, by reading the
     basicConstraints X.509 extension (2.5.29.19).  If the certificate
     is a CA a positive value will be returned, or (0) if the
     certificate does not have CA flag set.

Use ‘gnutls_x509_crt_get_basic_constraints()’ if you want to read
     the pathLenConstraint field too.

*Returns:* If the certificate is a CA a positive value will be
     returned, or (0) if the certificate does not have CA flag set.  A
     negative error code may be returned in case of errors.  If the
     certificate does not contain the basicConstraints extension
     GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE will be returned.

gnutls_x509_crt_get_crl_dist_points
-----------------------------------

-- Function: int gnutls_x509_crt_get_crl_dist_points (gnutls_x509_crt_t
          CERT, unsigned int SEQ, void * SAN, size_t * SAN_SIZE,
          unsigned int * REASON_FLAGS, unsigned int * CRITICAL)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

SEQ: specifies the sequence number of the distribution point (0 for
     the first one, 1 for the second etc.)

SAN: is the place where the distribution point will be copied to

SAN_SIZE: holds the size of ret.

REASON_FLAGS: Revocation reasons.  An ORed sequence of flags from
     ‘gnutls_x509_crl_reason_flags_t’ .

CRITICAL: will be non-zero if the extension is marked as critical
     (may be null)

This function retrieves the CRL distribution points (2.5.29.31),
     contained in the given certificate in the X509v3 Certificate
     Extensions.

*Returns:* ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ and updates ‘ret_size’ if
     ‘ret_size’ is not enough to hold the distribution point, or the
     type of the distribution point if everything was ok.  The type is
     one of the enumerated ‘gnutls_x509_subject_alt_name_t’ .  If the
     certificate does not have an Alternative name with the specified
     sequence number then ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ is
     returned.

gnutls_x509_crt_get_dn
----------------------

-- Function: int gnutls_x509_crt_get_dn (gnutls_x509_crt_t CERT, char *
          BUF, size_t * BUF_SIZE)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

BUF: a pointer to a structure to hold the name (may be null)

BUF_SIZE: initially holds the size of ‘buf’

This function will copy the name of the Certificate in the provided
     buffer.  The name will be in the form "C=xxxx,O=yyyy,CN=zzzz" as
     described in RFC4514.  The output string will be ASCII or UTF-8
     encoded, depending on the certificate data.

The ‘buf’ returned will be null terminated and the ‘buf_size’ will
     account for the trailing null.  If ‘buf’ is null then only the size
     will be filled.

This function does not output a fully RFC4514 compliant string, if
     that is required see ‘gnutls_x509_crt_get_dn3()’ .

*Returns:* ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ if the provided buffer is
     not long enough, and in that case the ‘buf_size’ will be updated
     with the required size.  ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ if
     the DN does not exist, or another error value on error.  On success
     0 is returned.

gnutls_x509_crt_get_dn2
-----------------------

-- Function: int gnutls_x509_crt_get_dn2 (gnutls_x509_crt_t CERT,
          gnutls_datum_t * DN)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

DN: a pointer to a structure to hold the name; must be freed using
     ‘gnutls_free()’

This function does not output a fully RFC4514 compliant string, if
     that is required see ‘gnutls_x509_crt_get_dn3()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.1.10

gnutls_x509_crt_get_dn3
-----------------------

-- Function: int gnutls_x509_crt_get_dn3 (gnutls_x509_crt_t CERT,
          gnutls_datum_t * DN, unsigned FLAGS)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

DN: a pointer to a structure to hold the name; must be freed using
     ‘gnutls_free()’

FLAGS: zero or ‘GNUTLS_X509_DN_FLAG_COMPAT’

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.5.7

gnutls_x509_crt_get_dn_by_oid
-----------------------------

-- Function: int gnutls_x509_crt_get_dn_by_oid (gnutls_x509_crt_t CERT,
          const char * OID, unsigned INDX, unsigned int RAW_FLAG, void *
          BUF, size_t * BUF_SIZE)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

OID: holds an Object Identified in null terminated string

INDX: In case multiple same OIDs exist in the RDN, this specifies
     which to send.  Use (0) to get the first one.

RAW_FLAG: If non-zero returns the raw DER data of the DN part.

BUF: a pointer where the DN part will be copied (may be null).

BUF_SIZE: initially holds the size of ‘buf’

This function will extract the part of the name of the Certificate
     subject specified by the given OID. The output, if the raw flag is
     not used, will be encoded as described in RFC4514.  Thus a string
     that is ASCII or UTF-8 encoded, depending on the certificate data.

If ‘buf’ is null then only the size will be filled.  If the
     ‘raw_flag’ is not specified the output is always null terminated,
     although the ‘buf_size’ will not include the null character.

*Returns:* ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ if the provided buffer is
     not long enough, and in that case the ‘buf_size’ will be updated
     with the required size.  ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ if
     there are no data in the current index.  On success 0 is returned.

gnutls_x509_crt_get_dn_oid
--------------------------

-- Function: int gnutls_x509_crt_get_dn_oid (gnutls_x509_crt_t CERT,
          unsigned INDX, void * OID, size_t * OID_SIZE)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

INDX: This specifies which OID to return.  Use (0) to get the first
     one.

OID: a pointer to a buffer to hold the OID (may be null)

OID_SIZE: initially holds the size of ‘oid’

This function will extract the OIDs of the name of the Certificate
     subject specified by the given index.

If ‘oid’ is null then only the size will be filled.  The ‘oid’
     returned will be null terminated, although ‘oid_size’ will not
     account for the trailing null.

*Returns:* ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ if the provided buffer is
     not long enough, and in that case the ‘buf_size’ will be updated
     with the required size.  ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ if
     there are no data in the current index.  On success 0 is returned.

gnutls_x509_crt_get_expiration_time
-----------------------------------

-- Function: time_t gnutls_x509_crt_get_expiration_time
          (gnutls_x509_crt_t CERT)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

This function will return the time this certificate was or will be
     expired.

*Returns:* expiration time, or (time_t)-1 on error.

gnutls_x509_crt_get_extension_by_oid
------------------------------------

-- Function: int gnutls_x509_crt_get_extension_by_oid
          (gnutls_x509_crt_t CERT, const char * OID, unsigned INDX, void
          * BUF, size_t * BUF_SIZE, unsigned int * CRITICAL)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

OID: holds an Object Identified in null terminated string

INDX: In case multiple same OIDs exist in the extensions, this
     specifies which to send.  Use (0) to get the first one.

BUF: a pointer to a structure to hold the name (may be null)

BUF_SIZE: initially holds the size of ‘buf’

CRITICAL: will be non-zero if the extension is marked as critical

This function will return the extension specified by the OID in the
     certificate.  The extensions will be returned as binary data DER
     encoded, in the provided buffer.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.  If the certificate
     does not contain the specified extension
     GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE will be returned.

gnutls_x509_crt_get_extension_by_oid2
-------------------------------------

-- Function: int gnutls_x509_crt_get_extension_by_oid2
          (gnutls_x509_crt_t CERT, const char * OID, unsigned INDX,
          gnutls_datum_t * OUTPUT, unsigned int * CRITICAL)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

OID: holds an Object Identified in null terminated string

INDX: In case multiple same OIDs exist in the extensions, this
     specifies which to send.  Use (0) to get the first one.

OUTPUT: will hold the allocated extension data

CRITICAL: will be non-zero if the extension is marked as critical

This function will return the extension specified by the OID in the
     certificate.  The extensions will be returned as binary data DER
     encoded, in the provided buffer.

*Since:* 3.3.8

gnutls_x509_crt_get_extension_data
----------------------------------

-- Function: int gnutls_x509_crt_get_extension_data (gnutls_x509_crt_t
          CERT, unsigned INDX, void * DATA, size_t * SIZEOF_DATA)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

INDX: Specifies which extension OID to send.  Use (0) to get the
     first one.

DATA: a pointer to a structure to hold the data (may be null)

SIZEOF_DATA: initially holds the size of ‘data’

This function will return the requested extension data in the
     certificate.  The extension data will be stored in the provided
     buffer.

Use ‘gnutls_x509_crt_get_extension_info()’ to extract the OID and
     critical flag.  Use ‘gnutls_x509_crt_get_extension_by_oid()’
     instead, if you want to get data indexed by the extension OID
     rather than sequence.

gnutls_x509_crt_get_extension_data2
-----------------------------------

-- Function: int gnutls_x509_crt_get_extension_data2 (gnutls_x509_crt_t
          CERT, unsigned INDX, gnutls_datum_t * DATA)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

INDX: Specifies which extension OID to read.  Use (0) to get the
     first one.

DATA: will contain the extension DER-encoded data

This function will return the requested by the index extension data
     in the certificate.  The extension data will be allocated using
     ‘gnutls_malloc()’ .

Use ‘gnutls_x509_crt_get_extension_info()’ to extract the OID.

gnutls_x509_crt_get_extension_info
----------------------------------

-- Function: int gnutls_x509_crt_get_extension_info (gnutls_x509_crt_t
          CERT, unsigned INDX, void * OID, size_t * OID_SIZE, unsigned
          int * CRITICAL)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

INDX: Specifies which extension OID to send.  Use (0) to get the
     first one.

OID: a pointer to a structure to hold the OID

OID_SIZE: initially holds the maximum size of ‘oid’ , on return
     holds actual size of ‘oid’ .

CRITICAL: output variable with critical flag, may be NULL.

If the buffer provided is not long enough to hold the output, then
     ‘oid_size’ is updated and ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ will be
     returned.  The ‘oid’ returned will be null terminated, although
     ‘oid_size’ will not account for the trailing null (the latter is
     not true for GnuTLS prior to 3.6.0).

gnutls_x509_crt_get_extension_oid
---------------------------------

-- Function: int gnutls_x509_crt_get_extension_oid (gnutls_x509_crt_t
          CERT, unsigned INDX, void * OID, size_t * OID_SIZE)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

INDX: Specifies which extension OID to send.  Use (0) to get the
     first one.

OID: a pointer to a structure to hold the OID (may be null)

OID_SIZE: initially holds the size of ‘oid’

This function will return the requested extension OID in the
     certificate.  The extension OID will be stored as a string in the
     provided buffer.

The ‘oid’ returned will be null terminated, although ‘oid_size’
     will not account for the trailing null.

gnutls_x509_crt_get_fingerprint
-------------------------------

-- Function: int gnutls_x509_crt_get_fingerprint (gnutls_x509_crt_t
          CERT, gnutls_digest_algorithm_t ALGO, void * BUF, size_t *
          BUF_SIZE)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

ALGO: is a digest algorithm

BUF: a pointer to a structure to hold the fingerprint (may be null)

BUF_SIZE: initially holds the size of ‘buf’

This function will calculate and copy the certificate's fingerprint
     in the provided buffer.  The fingerprint is a hash of the
     DER-encoded data of the certificate.

If the buffer is null then only the size will be filled.

*Returns:* ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ if the provided buffer is
     not long enough, and in that case the *buf_size will be updated
     with the required size.  On success 0 is returned.

gnutls_x509_crt_get_inhibit_anypolicy
-------------------------------------

-- Function: int gnutls_x509_crt_get_inhibit_anypolicy
          (gnutls_x509_crt_t CERT, unsigned int * SKIPCERTS, unsigned
          int * CRITICAL)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

SKIPCERTS: will hold the number of certificates after which
     anypolicy is no longer acceptable.

CRITICAL: will be non-zero if the extension is marked as critical

This function will return certificate's value of the SkipCerts,
     i.e., the Inhibit anyPolicy X.509 extension (2.5.29.54).

The returned value is the number of additional certificates that
     may appear in the path before the anyPolicy is no longer
     acceptable.

*Returns:* zero on success, or a negative error code in case of
     parsing error.  If the certificate does not contain the Inhibit
     anyPolicy extension ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ will be
     returned.

*Since:* 3.6.0

gnutls_x509_crt_get_issuer
--------------------------

-- Function: int gnutls_x509_crt_get_issuer (gnutls_x509_crt_t CERT,
          gnutls_x509_dn_t * DN)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

DN: output variable with pointer to uint8_t DN

Return the Certificate's Issuer DN as a ‘gnutls_x509_dn_t’ data
     type, that can be decoded using ‘gnutls_x509_dn_get_rdn_ava()’ .

Note that ‘dn’ should be treated as constant.  Because it points
     into the ‘cert’ object, you should not use ‘dn’ after ‘cert’ is
     deallocated.

*Returns:* Returns 0 on success, or an error code.

gnutls_x509_crt_get_issuer_alt_name
-----------------------------------

-- Function: int gnutls_x509_crt_get_issuer_alt_name (gnutls_x509_crt_t
          CERT, unsigned int SEQ, void * IAN, size_t * IAN_SIZE,
          unsigned int * CRITICAL)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

SEQ: specifies the sequence number of the alt name (0 for the first
     one, 1 for the second etc.)

IAN: is the place where the alternative name will be copied to

IAN_SIZE: holds the size of ian.

CRITICAL: will be non-zero if the extension is marked as critical
     (may be null)

This function retrieves the Issuer Alternative Name (2.5.29.18),
     contained in the given certificate in the X509v3 Certificate
     Extensions.

When the SAN type is otherName, it will extract the data in the
     otherName's value field, and ‘GNUTLS_SAN_OTHERNAME’ is returned.
     You may use ‘gnutls_x509_crt_get_subject_alt_othername_oid()’ to
     get the corresponding OID and the "virtual" SAN types (e.g.,
     ‘GNUTLS_SAN_OTHERNAME_XMPP’ ).

If an otherName OID is known, the data will be decoded.  Otherwise
     the returned data will be DER encoded, and you will have to decode
     it yourself.  Currently, only the RFC 3920 id-on-xmppAddr Issuer
     AltName is recognized.

*Returns:* the alternative issuer name type on success, one of the
     enumerated ‘gnutls_x509_subject_alt_name_t’ .  It will return
     ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ if ‘ian_size’ is not large enough to
     hold the value.  In that case ‘ian_size’ will be updated with the
     required size.  If the certificate does not have an Alternative
     name with the specified sequence number then
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ is returned.

*Since:* 2.10.0

gnutls_x509_crt_get_issuer_alt_name2
------------------------------------

-- Function: int gnutls_x509_crt_get_issuer_alt_name2
          (gnutls_x509_crt_t CERT, unsigned int SEQ, void * IAN, size_t
          * IAN_SIZE, unsigned int * IAN_TYPE, unsigned int * CRITICAL)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

SEQ: specifies the sequence number of the alt name (0 for the first
     one, 1 for the second etc.)

IAN: is the place where the alternative name will be copied to

IAN_SIZE: holds the size of ret.

IAN_TYPE: holds the type of the alternative name (one of
     gnutls_x509_subject_alt_name_t).

CRITICAL: will be non-zero if the extension is marked as critical
     (may be null)

This function will return the alternative names, contained in the
     given certificate.  It is the same as
     ‘gnutls_x509_crt_get_issuer_alt_name()’ except for the fact that it
     will return the type of the alternative name in ‘ian_type’ even if
     the function fails for some reason (i.e.  the buffer provided is
     not enough).

*Since:* 2.10.0

gnutls_x509_crt_get_issuer_alt_othername_oid
--------------------------------------------

-- Function: int gnutls_x509_crt_get_issuer_alt_othername_oid
          (gnutls_x509_crt_t CERT, unsigned int SEQ, void * RET, size_t
          * RET_SIZE)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

SEQ: specifies the sequence number of the alt name (0 for the first
     one, 1 for the second etc.)

RET: is the place where the otherName OID will be copied to

RET_SIZE: holds the size of ret.

This function will extract the type OID of an otherName Subject
     Alternative Name, contained in the given certificate, and return
     the type as an enumerated element.

If ‘oid’ is null then only the size will be filled.  The ‘oid’
     returned will be null terminated, although ‘oid_size’ will not
     account for the trailing null.

This function is only useful if
     ‘gnutls_x509_crt_get_issuer_alt_name()’ returned
     ‘GNUTLS_SAN_OTHERNAME’ .

*Returns:* the alternative issuer name type on success, one of the
     enumerated gnutls_x509_subject_alt_name_t.  For supported OIDs, it
     will return one of the virtual (GNUTLS_SAN_OTHERNAME_*) types, e.g.
     ‘GNUTLS_SAN_OTHERNAME_XMPP’ , and ‘GNUTLS_SAN_OTHERNAME’ for
     unknown OIDs.  It will return ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ if
     ‘ret_size’ is not large enough to hold the value.  In that case
     ‘ret_size’ will be updated with the required size.  If the
     certificate does not have an Alternative name with the specified
     sequence number and with the otherName type then
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ is returned.

*Since:* 2.10.0

gnutls_x509_crt_get_issuer_dn
-----------------------------

-- Function: int gnutls_x509_crt_get_issuer_dn (gnutls_x509_crt_t CERT,
          char * BUF, size_t * BUF_SIZE)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

BUF: a pointer to a structure to hold the name (may be null)

BUF_SIZE: initially holds the size of ‘buf’

This function will copy the name of the Certificate issuer in the
     provided buffer.  The name will be in the form
     "C=xxxx,O=yyyy,CN=zzzz" as described in RFC4514.  The output string
     will be ASCII or UTF-8 encoded, depending on the certificate data.

If ‘buf’ is null then only the size will be filled.

This function does not output a fully RFC4514 compliant string, if
     that is required see ‘gnutls_x509_crt_get_issuer_dn3()’ .

gnutls_x509_crt_get_issuer_dn2
------------------------------

-- Function: int gnutls_x509_crt_get_issuer_dn2 (gnutls_x509_crt_t
          CERT, gnutls_datum_t * DN)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

DN: a pointer to a structure to hold the name; must be freed using
     ‘gnutls_free()’

This function will allocate buffer and copy the name of issuer of
     the Certificate.  The name will be in the form
     "C=xxxx,O=yyyy,CN=zzzz" as described in RFC4514.  The output string
     will be ASCII or UTF-8 encoded, depending on the certificate data.

This function does not output a fully RFC4514 compliant string, if
     that is required see ‘gnutls_x509_crt_get_issuer_dn3()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.1.10

gnutls_x509_crt_get_issuer_dn3
------------------------------

-- Function: int gnutls_x509_crt_get_issuer_dn3 (gnutls_x509_crt_t
          CERT, gnutls_datum_t * DN, unsigned FLAGS)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

DN: a pointer to a structure to hold the name; must be freed using
     ‘gnutls_free()’

FLAGS: zero or ‘GNUTLS_X509_DN_FLAG_COMPAT’

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.5.7

gnutls_x509_crt_get_issuer_dn_by_oid
------------------------------------

-- Function: int gnutls_x509_crt_get_issuer_dn_by_oid
          (gnutls_x509_crt_t CERT, const char * OID, unsigned INDX,
          unsigned int RAW_FLAG, void * BUF, size_t * BUF_SIZE)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

OID: holds an Object Identified in null terminated string

INDX: In case multiple same OIDs exist in the RDN, this specifies
     which to send.  Use (0) to get the first one.

RAW_FLAG: If non-zero returns the raw DER data of the DN part.

BUF: a pointer to a structure to hold the name (may be null)

BUF_SIZE: initially holds the size of ‘buf’

This function will extract the part of the name of the Certificate
     issuer specified by the given OID. The output, if the raw flag is
     not used, will be encoded as described in RFC4514.  Thus a string
     that is ASCII or UTF-8 encoded, depending on the certificate data.

*Returns:* ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ if the provided buffer is
     not long enough, and in that case the ‘buf_size’ will be updated
     with the required size.  ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ if
     there are no data in the current index.  On success 0 is returned.

gnutls_x509_crt_get_issuer_dn_oid
---------------------------------

-- Function: int gnutls_x509_crt_get_issuer_dn_oid (gnutls_x509_crt_t
          CERT, unsigned INDX, void * OID, size_t * OID_SIZE)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

INDX: This specifies which OID to return.  Use (0) to get the first
     one.

OID: a pointer to a buffer to hold the OID (may be null)

OID_SIZE: initially holds the size of ‘oid’

This function will extract the OIDs of the name of the Certificate
     issuer specified by the given index.

If ‘oid’ is null then only the size will be filled.  The ‘oid’
     returned will be null terminated, although ‘oid_size’ will not
     account for the trailing null.

*Returns:* ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ if the provided buffer is
     not long enough, and in that case the ‘buf_size’ will be updated
     with the required size.  ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ if
     there are no data in the current index.  On success 0 is returned.

gnutls_x509_crt_get_issuer_unique_id
------------------------------------

-- Function: int gnutls_x509_crt_get_issuer_unique_id
          (gnutls_x509_crt_t CRT, char * BUF, size_t * BUF_SIZE)
     CRT: Holds the certificate

BUF: user allocated memory buffer, will hold the unique id

BUF_SIZE: size of user allocated memory buffer (on input), will
     hold actual size of the unique ID on return.

This function will extract the issuerUniqueID value (if present)
     for the given certificate.

If the user allocated memory buffer is not large enough to hold the
     full subjectUniqueID, then a GNUTLS_E_SHORT_MEMORY_BUFFER error
     will be returned, and buf_size will be set to the actual length.

This function had a bug prior to 3.4.8 that prevented the setting
     of ‘NULL’ ‘buf’ to discover the ‘buf_size’ .  To use this function
     safely with the older versions the ‘buf’ must be a valid buffer
     that can hold at least a single byte if ‘buf_size’ is zero.

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, otherwise a negative
     error code.

*Since:* 2.12.0

gnutls_x509_crt_get_key_id
--------------------------

-- Function: int gnutls_x509_crt_get_key_id (gnutls_x509_crt_t CRT,
          unsigned int FLAGS, unsigned char * OUTPUT_DATA, size_t *
          OUTPUT_DATA_SIZE)
     CRT: Holds the certificate

FLAGS: should be one of the flags from ‘gnutls_keyid_flags_t’

OUTPUT_DATA: will contain the key ID

OUTPUT_DATA_SIZE: holds the size of output_data (and will be
     replaced by the actual size of parameters)

This function will return a unique ID that depends on the public
     key parameters.  This ID can be used in checking whether a
     certificate corresponds to the given private key.

*Returns:* In case of failure a negative error code will be
     returned, and 0 on success.

gnutls_x509_crt_get_key_purpose_oid
-----------------------------------

-- Function: int gnutls_x509_crt_get_key_purpose_oid (gnutls_x509_crt_t
          CERT, unsigned INDX, void * OID, size_t * OID_SIZE, unsigned
          int * CRITICAL)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

INDX: This specifies which OID to return.  Use (0) to get the first
     one.

OID: a pointer to a buffer to hold the OID (may be null)

OID_SIZE: initially holds the size of ‘oid’

CRITICAL: output flag to indicate criticality of extension

This function will extract the key purpose OIDs of the Certificate
     specified by the given index.  These are stored in the Extended Key
     Usage extension (2.5.29.37) See the GNUTLS_KP_* definitions for
     human readable names.

If ‘oid’ is null then only the size will be filled.  The ‘oid’
     returned will be null terminated, although ‘oid_size’ will not
     account for the trailing null.

*Returns:* ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ if the provided buffer is
     not long enough, and in that case the *oid_size will be updated
     with the required size.  On success 0 is returned.

gnutls_x509_crt_get_key_usage
-----------------------------

-- Function: int gnutls_x509_crt_get_key_usage (gnutls_x509_crt_t CERT,
          unsigned int * KEY_USAGE, unsigned int * CRITICAL)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

KEY_USAGE: where the key usage bits will be stored

CRITICAL: will be non-zero if the extension is marked as critical

*Returns:* zero on success, or a negative error code in case of
     parsing error.  If the certificate does not contain the keyUsage
     extension ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ will be returned.

gnutls_x509_crt_get_name_constraints
------------------------------------

-- Function: int gnutls_x509_crt_get_name_constraints
          (gnutls_x509_crt_t CRT, gnutls_x509_name_constraints_t NC,
          unsigned int FLAGS, unsigned int * CRITICAL)
     CRT: should contain a ‘gnutls_x509_crt_t’ type

NC: The nameconstraints intermediate type

FLAGS: zero or ‘GNUTLS_EXT_FLAG_APPEND’

CRITICAL: the extension status

This function will return an intermediate type containing the name
     constraints of the provided CA certificate.  That structure can be
     used in combination with ‘gnutls_x509_name_constraints_check()’ to
     verify whether a server's name is in accordance with the
     constraints.

When the ‘flags’ is set to ‘GNUTLS_EXT_FLAG_APPEND’ , then if the
     ‘nc’ structure is empty this function will behave identically as if
     the flag was not set.  Otherwise if there are elements in the ‘nc’
     structure then the constraints will be merged with the existing
     constraints following RFC5280 p6.1.4 (excluded constraints will be
     appended, permitted will be intersected).

Note that ‘nc’ must be initialized prior to calling this function.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ if the extension is not
     present, otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_crt_get_pk_algorithm
--------------------------------

-- Function: int gnutls_x509_crt_get_pk_algorithm (gnutls_x509_crt_t
          CERT, unsigned int * BITS)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

BITS: if bits is non null it will hold the size of the parameters'
     in bits

This function will return the public key algorithm of an X.509
     certificate.

If bits is non null, it should have enough size to hold the
     parameters size in bits.  For RSA the bits returned is the modulus.
     For DSA the bits returned are of the public exponent.

Unknown/unsupported algorithms are mapped to ‘GNUTLS_PK_UNKNOWN’ .

*Returns:* a member of the ‘gnutls_pk_algorithm_t’ enumeration on
     success, or a negative error code on error.

gnutls_x509_crt_get_pk_dsa_raw
------------------------------

-- Function: int gnutls_x509_crt_get_pk_dsa_raw (gnutls_x509_crt_t CRT,
          gnutls_datum_t * P, gnutls_datum_t * Q, gnutls_datum_t * G,
          gnutls_datum_t * Y)
     CRT: Holds the certificate

P: will hold the p

Q: will hold the q

G: will hold the g

Y: will hold the y

This function will export the DSA public key's parameters found in
     the given certificate.  The new parameters will be allocated using
     ‘gnutls_malloc()’ and will be stored in the appropriate datum.

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, otherwise a negative
     error code.

gnutls_x509_crt_get_pk_ecc_raw
------------------------------

-- Function: int gnutls_x509_crt_get_pk_ecc_raw (gnutls_x509_crt_t CRT,
          gnutls_ecc_curve_t * CURVE, gnutls_datum_t * X, gnutls_datum_t
          * Y)
     CRT: Holds the certificate

CURVE: will hold the curve

X: will hold the x-coordinate

Y: will hold the y-coordinate

This function will export the ECC public key's parameters found in
     the given certificate.  The new parameters will be allocated using
     ‘gnutls_malloc()’ and will be stored in the appropriate datum.

In EdDSA curves the ‘y’ parameter will be ‘NULL’ and the other
     parameters will be in the native format for the curve.

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, otherwise a negative
     error code.

*Since:* 3.4.1

gnutls_x509_crt_get_pk_gost_raw
-------------------------------

-- Function: int gnutls_x509_crt_get_pk_gost_raw (gnutls_x509_crt_t
          CRT, gnutls_ecc_curve_t * CURVE, gnutls_digest_algorithm_t *
          DIGEST, gnutls_gost_paramset_t * PARAMSET, gnutls_datum_t * X,
          gnutls_datum_t * Y)
     CRT: Holds the certificate

CURVE: will hold the curve

DIGEST: will hold the digest

PARAMSET: will hold the GOST parameter set ID

X: will hold the x-coordinate

Y: will hold the y-coordinate

This function will export the GOST public key's parameters found in
     the given certificate.  The new parameters will be allocated using
     ‘gnutls_malloc()’ and will be stored in the appropriate datum.

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, otherwise a negative
     error code.

*Since:* 3.6.3

gnutls_x509_crt_get_pk_oid
--------------------------

-- Function: int gnutls_x509_crt_get_pk_oid (gnutls_x509_crt_t CERT,
          char * OID, size_t * OID_SIZE)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

OID: a pointer to a buffer to hold the OID (may be null)

OID_SIZE: initially holds the size of ‘oid’

This function will return the OID of the public key algorithm on
     that certificate.  This is function is useful in the case
     ‘gnutls_x509_crt_get_pk_algorithm()’ returned ‘GNUTLS_PK_UNKNOWN’ .

*Returns:* zero or a negative error code on error.

*Since:* 3.5.0

gnutls_x509_crt_get_pk_rsa_raw
------------------------------

-- Function: int gnutls_x509_crt_get_pk_rsa_raw (gnutls_x509_crt_t CRT,
          gnutls_datum_t * M, gnutls_datum_t * E)
     CRT: Holds the certificate

M: will hold the modulus

E: will hold the public exponent

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, otherwise a negative
     error code.

gnutls_x509_crt_get_policy
--------------------------

-- Function: int gnutls_x509_crt_get_policy (gnutls_x509_crt_t CRT,
          unsigned INDX, struct gnutls_x509_policy_st * POLICY, unsigned
          int * CRITICAL)
     CRT: should contain a ‘gnutls_x509_crt_t’ type

INDX: This specifies which policy to return.  Use (0) to get the
     first one.

POLICY: A pointer to a policy structure.

CRITICAL: will be non-zero if the extension is marked as critical

This function will extract the certificate policy (extension
     2.5.29.32) specified by the given index.

The policy returned by this function must be deinitialized by using
     ‘gnutls_x509_policy_release()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ if the extension is not
     present, otherwise a negative error value.

*Since:* 3.1.5

gnutls_x509_crt_get_private_key_usage_period
--------------------------------------------

-- Function: int gnutls_x509_crt_get_private_key_usage_period
          (gnutls_x509_crt_t CERT, time_t * ACTIVATION, time_t *
          EXPIRATION, unsigned int * CRITICAL)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

ACTIVATION: The activation time

EXPIRATION: The expiration time

CRITICAL: the extension status

This function will return the expiration and activation times of
     the private key of the certificate.  It relies on the PKIX
     extension 2.5.29.16 being present.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ if the extension is not
     present, otherwise a negative error value.

gnutls_x509_crt_get_proxy
-------------------------

-- Function: int gnutls_x509_crt_get_proxy (gnutls_x509_crt_t CERT,
          unsigned int * CRITICAL, int * PATHLEN, char **
          POLICYLANGUAGE, char ** POLICY, size_t * SIZEOF_POLICY)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

CRITICAL: will be non-zero if the extension is marked as critical

PATHLEN: pointer to output integer indicating path length (may be
     NULL), non-negative error codes indicate a present
     pCPathLenConstraint field and the actual value, -1 indicate that
     the field is absent.

POLICYLANGUAGE: output variable with OID of policy language

POLICY: output variable with policy data

SIZEOF_POLICY: output variable size of policy data

This function will get information from a proxy certificate.  It
     reads the ProxyCertInfo X.509 extension (1.3.6.1.5.5.7.1.14).

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

gnutls_x509_crt_get_raw_dn
--------------------------

-- Function: int gnutls_x509_crt_get_raw_dn (gnutls_x509_crt_t CERT,
          gnutls_datum_t * DN)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

DN: will hold the starting point of the DN

This function will return a pointer to the DER encoded DN structure
     and the length.  This points to allocated data that must be free'd
     using ‘gnutls_free()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.  or a negative error code on
     error.

gnutls_x509_crt_get_raw_issuer_dn
---------------------------------

-- Function: int gnutls_x509_crt_get_raw_issuer_dn (gnutls_x509_crt_t
          CERT, gnutls_datum_t * DN)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

DN: will hold the starting point of the DN

This function will return a pointer to the DER encoded DN structure
     and the length.  This points to allocated data that must be free'd
     using ‘gnutls_free()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.or a negative error code on error.

gnutls_x509_crt_get_serial
--------------------------

-- Function: int gnutls_x509_crt_get_serial (gnutls_x509_crt_t CERT,
          void * RESULT, size_t * RESULT_SIZE)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

RESULT: The place where the serial number will be copied

RESULT_SIZE: Holds the size of the result field.

This function will return the X.509 certificate's serial number.
     This is obtained by the X509 Certificate serialNumber field.
     Serial is not always a 32 or 64bit number.  Some CAs use large
     serial numbers, thus it may be wise to handle it as something
     uint8_t.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crt_get_signature
-----------------------------

-- Function: int gnutls_x509_crt_get_signature (gnutls_x509_crt_t CERT,
          char * SIG, size_t * SIG_SIZE)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

SIG: a pointer where the signature part will be copied (may be
     null).

SIG_SIZE: initially holds the size of ‘sig’

This function will extract the signature field of a certificate.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crt_get_signature_algorithm
---------------------------------------

-- Function: int gnutls_x509_crt_get_signature_algorithm
          (gnutls_x509_crt_t CERT)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

This function will return a value of the ‘gnutls_sign_algorithm_t’
     enumeration that is the signature algorithm that has been used to
     sign this certificate.

Since 3.6.0 this function never returns a negative error code.
     Error cases and unknown/unsupported signature algorithms are mapped
     to ‘GNUTLS_SIGN_UNKNOWN’ .

*Returns:* a ‘gnutls_sign_algorithm_t’ value

gnutls_x509_crt_get_signature_oid
---------------------------------

-- Function: int gnutls_x509_crt_get_signature_oid (gnutls_x509_crt_t
          CERT, char * OID, size_t * OID_SIZE)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

OID: a pointer to a buffer to hold the OID (may be null)

OID_SIZE: initially holds the size of ‘oid’

This function will return the OID of the signature algorithm that
     has been used to sign this certificate.  This is function is useful
     in the case ‘gnutls_x509_crt_get_signature_algorithm()’ returned
     ‘GNUTLS_SIGN_UNKNOWN’ .

*Returns:* zero or a negative error code on error.

*Since:* 3.5.0

gnutls_x509_crt_get_spki
------------------------

-- Function: int gnutls_x509_crt_get_spki (gnutls_x509_crt_t CERT,
          gnutls_x509_spki_t SPKI, unsigned int FLAGS)
     CERT: a certificate of type ‘gnutls_x509_crt_t’

SPKI: a SubjectPublicKeyInfo structure of type ‘gnutls_x509_spki_t’

FLAGS: must be zero

This function will return the public key information of an X.509
     certificate.  The provided ‘spki’ must be initialized.

*Since:* 3.6.0

gnutls_x509_crt_get_subject
---------------------------

-- Function: int gnutls_x509_crt_get_subject (gnutls_x509_crt_t CERT,
          gnutls_x509_dn_t * DN)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

DN: output variable with pointer to uint8_t DN.

Return the Certificate's Subject DN as a ‘gnutls_x509_dn_t’ data
     type, that can be decoded using ‘gnutls_x509_dn_get_rdn_ava()’ .

Note that ‘dn’ should be treated as constant.  Because it points
     into the ‘cert’ object, you should not use ‘dn’ after ‘cert’ is
     deallocated.

*Returns:* Returns 0 on success, or an error code.

gnutls_x509_crt_get_subject_alt_name
------------------------------------

-- Function: int gnutls_x509_crt_get_subject_alt_name
          (gnutls_x509_crt_t CERT, unsigned int SEQ, void * SAN, size_t
          * SAN_SIZE, unsigned int * CRITICAL)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

SEQ: specifies the sequence number of the alt name (0 for the first
     one, 1 for the second etc.)

SAN: is the place where the alternative name will be copied to

SAN_SIZE: holds the size of san.

CRITICAL: will be non-zero if the extension is marked as critical
     (may be null)

This function retrieves the Alternative Name (2.5.29.17), contained
     in the given certificate in the X509v3 Certificate Extensions.

*Returns:* the alternative subject name type on success, one of the
     enumerated ‘gnutls_x509_subject_alt_name_t’ .  It will return
     ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ if ‘san_size’ is not large enough to
     hold the value.  In that case ‘san_size’ will be updated with the
     required size.  If the certificate does not have an Alternative
     name with the specified sequence number then
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ is returned.

gnutls_x509_crt_get_subject_alt_name2
-------------------------------------

-- Function: int gnutls_x509_crt_get_subject_alt_name2
          (gnutls_x509_crt_t CERT, unsigned int SEQ, void * SAN, size_t
          * SAN_SIZE, unsigned int * SAN_TYPE, unsigned int * CRITICAL)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

SEQ: specifies the sequence number of the alt name (0 for the first
     one, 1 for the second etc.)

SAN: is the place where the alternative name will be copied to

SAN_SIZE: holds the size of ret.

SAN_TYPE: holds the type of the alternative name (one of
     gnutls_x509_subject_alt_name_t).

CRITICAL: will be non-zero if the extension is marked as critical
     (may be null)

This function will return the alternative names, contained in the
     given certificate.  It is the same as
     ‘gnutls_x509_crt_get_subject_alt_name()’ except for the fact that
     it will return the type of the alternative name in ‘san_type’ even
     if the function fails for some reason (i.e.  the buffer provided is
     not enough).

gnutls_x509_crt_get_subject_alt_othername_oid
---------------------------------------------

-- Function: int gnutls_x509_crt_get_subject_alt_othername_oid
          (gnutls_x509_crt_t CERT, unsigned int SEQ, void * OID, size_t
          * OID_SIZE)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

SEQ: specifies the sequence number of the alt name (0 for the first
     one, 1 for the second etc.)

OID: is the place where the otherName OID will be copied to

OID_SIZE: holds the size of ret.

This function will extract the type OID of an otherName Subject
     Alternative Name, contained in the given certificate, and return
     the type as an enumerated element.

This function is only useful if
     ‘gnutls_x509_crt_get_subject_alt_name()’ returned
     ‘GNUTLS_SAN_OTHERNAME’ .

If ‘oid’ is null then only the size will be filled.  The ‘oid’
     returned will be null terminated, although ‘oid_size’ will not
     account for the trailing null.

*Returns:* the alternative subject name type on success, one of the
     enumerated gnutls_x509_subject_alt_name_t.  For supported OIDs, it
     will return one of the virtual (GNUTLS_SAN_OTHERNAME_*) types, e.g.
     ‘GNUTLS_SAN_OTHERNAME_XMPP’ , and ‘GNUTLS_SAN_OTHERNAME’ for
     unknown OIDs.  It will return ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ if
     ‘ian_size’ is not large enough to hold the value.  In that case
     ‘ian_size’ will be updated with the required size.  If the
     certificate does not have an Alternative name with the specified
     sequence number and with the otherName type then
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ is returned.

gnutls_x509_crt_get_subject_key_id
----------------------------------

-- Function: int gnutls_x509_crt_get_subject_key_id (gnutls_x509_crt_t
          CERT, void * RET, size_t * RET_SIZE, unsigned int * CRITICAL)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

RET: The place where the identifier will be copied

RET_SIZE: Holds the size of the result field.

CRITICAL: will be non-zero if the extension is marked as critical
     (may be null)

This function will return the X.509v3 certificate's subject key
     identifier.  This is obtained by the X.509 Subject Key identifier
     extension field (2.5.29.14).

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ if the extension is not
     present, otherwise a negative error value.

gnutls_x509_crt_get_subject_unique_id
-------------------------------------

-- Function: int gnutls_x509_crt_get_subject_unique_id
          (gnutls_x509_crt_t CRT, char * BUF, size_t * BUF_SIZE)
     CRT: Holds the certificate

BUF: user allocated memory buffer, will hold the unique id

BUF_SIZE: size of user allocated memory buffer (on input), will
     hold actual size of the unique ID on return.

This function will extract the subjectUniqueID value (if present)
     for the given certificate.

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, otherwise a negative
     error code.

gnutls_x509_crt_get_tlsfeatures
-------------------------------

-- Function: int gnutls_x509_crt_get_tlsfeatures (gnutls_x509_crt_t
          CRT, gnutls_x509_tlsfeatures_t FEATURES, unsigned int FLAGS,
          unsigned int * CRITICAL)
     CRT: A X.509 certificate

FEATURES: If the function succeeds, the features will be stored in
     this variable.

FLAGS: zero or ‘GNUTLS_EXT_FLAG_APPEND’

CRITICAL: the extension status

This function will get the X.509 TLS features extension structure
     from the certificate.  The returned structure needs to be freed
     using ‘gnutls_x509_tlsfeatures_deinit()’ .

Note that ‘features’ must be initialized prior to calling this
     function.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.5.1

gnutls_x509_crt_get_version
---------------------------

-- Function: int gnutls_x509_crt_get_version (gnutls_x509_crt_t CERT)
     CERT: should contain a ‘gnutls_x509_crt_t’ type

This function will return the version of the specified Certificate.

*Returns:* version of certificate, or a negative error code on
     error.

gnutls_x509_crt_import
----------------------

-- Function: int gnutls_x509_crt_import (gnutls_x509_crt_t CERT, const
          gnutls_datum_t * DATA, gnutls_x509_crt_fmt_t FORMAT)
     CERT: The data to store the parsed certificate.

DATA: The DER or PEM encoded certificate.

FORMAT: One of DER or PEM

This function will convert the given DER or PEM encoded Certificate
     to the native gnutls_x509_crt_t format.  The output will be stored
     in ‘cert’ .

If the Certificate is PEM encoded it should have a header of "X509
     CERTIFICATE", or "CERTIFICATE".

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crt_import_url
--------------------------

-- Function: int gnutls_x509_crt_import_url (gnutls_x509_crt_t CRT,
          const char * URL, unsigned int FLAGS)
     CRT: A certificate of type ‘gnutls_x509_crt_t’

URL: A PKCS 11 url

FLAGS: One of GNUTLS_PKCS11_OBJ_* flags for PKCS‘11’ URLs or zero
     otherwise

This function will import a certificate present in a PKCS‘11’ token
     or any type of back-end that supports URLs.

In previous versions of gnutls this function was named
     gnutls_x509_crt_import_pkcs11_url, and the old name is an alias to
     this one.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.4.0

gnutls_x509_crt_init
--------------------

-- Function: int gnutls_x509_crt_init (gnutls_x509_crt_t * CERT)
     CERT: A pointer to the type to be initialized

This function will initialize an X.509 certificate structure.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crt_list_import
---------------------------

-- Function: int gnutls_x509_crt_list_import (gnutls_x509_crt_t *
          CERTS, unsigned int * CERT_MAX, const gnutls_datum_t * DATA,
          gnutls_x509_crt_fmt_t FORMAT, unsigned int FLAGS)
     CERTS: Indicates where the parsed list will be copied to.  Must not
     be initialized.

CERT_MAX: Initially must hold the maximum number of certs.  It will
     be updated with the number of certs available.

DATA: The PEM encoded certificate.

FORMAT: One of DER or PEM.

FLAGS: must be (0) or an OR'd sequence of
     gnutls_certificate_import_flags.

This function will convert the given PEM encoded certificate list
     to the native gnutls_x509_crt_t format.  The output will be stored
     in ‘certs’ .  They will be automatically initialized.

The flag ‘GNUTLS_X509_CRT_LIST_IMPORT_FAIL_IF_EXCEED’ will cause
     import to fail if the certificates in the provided buffer are more
     than the available structures.  The
     ‘GNUTLS_X509_CRT_LIST_FAIL_IF_UNSORTED’ flag will cause the
     function to fail if the provided list is not sorted from subject to
     issuer.

If the Certificate is PEM encoded it should have a header of "X509
     CERTIFICATE", or "CERTIFICATE".

*Returns:* the number of certificates read or a negative error
     value.

gnutls_x509_crt_list_import2
----------------------------

-- Function: int gnutls_x509_crt_list_import2 (gnutls_x509_crt_t **
          CERTS, unsigned int * SIZE, const gnutls_datum_t * DATA,
          gnutls_x509_crt_fmt_t FORMAT, unsigned int FLAGS)
     CERTS: Will hold the parsed certificate list.

SIZE: It will contain the size of the list.

DATA: The PEM encoded certificate.

FORMAT: One of DER or PEM.

FLAGS: must be (0) or an OR'd sequence of
     gnutls_certificate_import_flags.

This function will convert the given PEM encoded certificate list
     to the native gnutls_x509_crt_t format.  The output will be stored
     in ‘certs’ which will be allocated and initialized.

If the Certificate is PEM encoded it should have a header of "X509
     CERTIFICATE", or "CERTIFICATE".

To deinitialize ‘certs’ , you need to deinitialize each crt
     structure independently, and use ‘gnutls_free()’ at ‘certs’ .

*Returns:* ‘GNUTLS_E_SUCCESS’ on success, otherwise a negative
     error code.

*Since:* 3.0

gnutls_x509_crt_list_import_url
-------------------------------

-- Function: int gnutls_x509_crt_list_import_url (gnutls_x509_crt_t **
          CERTS, unsigned int * SIZE, const char * URL,
          gnutls_pin_callback_t PIN_FN, void * PIN_FN_USERDATA, unsigned
          int FLAGS)
     CERTS: Will hold the allocated certificate list.

SIZE: It will contain the size of the list.

URL: A PKCS 11 url

PIN_FN: a PIN callback if not globally set

PIN_FN_USERDATA: parameter for the PIN callback

FLAGS: One of GNUTLS_PKCS11_OBJ_* flags for PKCS‘11’ URLs or zero
     otherwise

This function will import a certificate chain present in a PKCS‘11’
     token or any type of back-end that supports URLs.  The certificates
     must be deinitialized afterwards using ‘gnutls_x509_crt_deinit()’
     and the returned pointer must be freed using ‘gnutls_free()’ .

The URI provided must be the first certificate in the chain;
     subsequent certificates will be retrieved using
     ‘gnutls_pkcs11_get_raw_issuer()’ or equivalent functionality for
     the supported URI.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.6.3

gnutls_x509_crt_list_verify
---------------------------

-- Function: int gnutls_x509_crt_list_verify (const gnutls_x509_crt_t *
          CERT_LIST, unsigned CERT_LIST_LENGTH, const gnutls_x509_crt_t
          * CA_LIST, unsigned CA_LIST_LENGTH, const gnutls_x509_crl_t *
          CRL_LIST, unsigned CRL_LIST_LENGTH, unsigned int FLAGS,
          unsigned int * VERIFY)
     CERT_LIST: is the certificate list to be verified

CERT_LIST_LENGTH: holds the number of certificate in cert_list

CA_LIST: is the CA list which will be used in verification

CA_LIST_LENGTH: holds the number of CA certificate in CA_list

CRL_LIST: holds a list of CRLs.

CRL_LIST_LENGTH: the length of CRL list.

FLAGS: Flags that may be used to change the verification algorithm.
     Use OR of the gnutls_certificate_verify_flags enumerations.

VERIFY: will hold the certificate verification output.

This function will try to verify the given certificate list and
     return its status.  The details of the verification are the same as
     in ‘gnutls_x509_trust_list_verify_crt2()’ .

You must check the peer's name in order to check if the verified
     certificate belongs to the actual peer.

The certificate verification output will be put in ‘verify’ and
     will be one or more of the gnutls_certificate_status_t enumerated
     elements bitwise or'd.  For a more detailed verification status use
     ‘gnutls_x509_crt_verify()’ per list element.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crt_print
---------------------

-- Function: int gnutls_x509_crt_print (gnutls_x509_crt_t CERT,
          gnutls_certificate_print_formats_t FORMAT, gnutls_datum_t *
          OUT)
     CERT: The data to be printed

FORMAT: Indicate the format to use

OUT: Newly allocated datum with null terminated string.

This function will pretty print a X.509 certificate, suitable for
     display to a human.

If the format is ‘GNUTLS_CRT_PRINT_FULL’ then all fields of the
     certificate will be output, on multiple lines.  The
     ‘GNUTLS_CRT_PRINT_ONELINE’ format will generate one line with some
     selected fields, which is useful for logging purposes.

The output ‘out’ needs to be deallocated using ‘gnutls_free()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crt_set_activation_time
-----------------------------------

-- Function: int gnutls_x509_crt_set_activation_time (gnutls_x509_crt_t
          CERT, time_t ACT_TIME)
     CERT: a certificate of type ‘gnutls_x509_crt_t’

ACT_TIME: The actual time

This function will set the time this certificate was or will be
     activated.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crt_set_authority_info_access
-----------------------------------------

-- Function: int gnutls_x509_crt_set_authority_info_access
          (gnutls_x509_crt_t CRT, int WHAT, gnutls_datum_t * DATA)
     CRT: Holds the certificate

WHAT: what data to get, a ‘gnutls_info_access_what_t’ type.

DATA: output data to be freed with ‘gnutls_free()’ .

This function sets the Authority Information Access (AIA)
     extension, see RFC 5280 section 4.2.2.1 for more information.

The type of data stored in ‘data’ is specified via ‘what’ which
     should be ‘gnutls_info_access_what_t’ values.

If ‘what’ is ‘GNUTLS_IA_OCSP_URI’ , ‘data’ will hold the OCSP URI.
     If ‘what’ is ‘GNUTLS_IA_CAISSUERS_URI’ , ‘data’ will hold the
     caIssuers URI.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.0

gnutls_x509_crt_set_authority_key_id
------------------------------------

-- Function: int gnutls_x509_crt_set_authority_key_id
          (gnutls_x509_crt_t CERT, const void * ID, size_t ID_SIZE)
     CERT: a certificate of type ‘gnutls_x509_crt_t’

ID: The key ID

ID_SIZE: Holds the size of the key ID field.

This function will set the X.509 certificate's authority key ID
     extension.  Only the keyIdentifier field can be set with this
     function.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crt_set_basic_constraints
-------------------------------------

-- Function: int gnutls_x509_crt_set_basic_constraints
          (gnutls_x509_crt_t CRT, unsigned int CA, int
          PATHLENCONSTRAINT)
     CRT: a certificate of type ‘gnutls_x509_crt_t’

CA: true(1) or false(0).  Depending on the Certificate authority
     status.

PATHLENCONSTRAINT: non-negative error codes indicate maximum length
     of path, and negative error codes indicate that the
     pathLenConstraints field should not be present.

This function will set the basicConstraints certificate extension.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crt_set_ca_status
-----------------------------

-- Function: int gnutls_x509_crt_set_ca_status (gnutls_x509_crt_t CRT,
          unsigned int CA)
     CRT: a certificate of type ‘gnutls_x509_crt_t’

CA: true(1) or false(0).  Depending on the Certificate authority
     status.

This function will set the basicConstraints certificate extension.
     Use ‘gnutls_x509_crt_set_basic_constraints()’ if you want to
     control the pathLenConstraint field too.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crt_set_crl_dist_points
-----------------------------------

-- Function: int gnutls_x509_crt_set_crl_dist_points (gnutls_x509_crt_t
          CRT, gnutls_x509_subject_alt_name_t TYPE, const void *
          DATA_STRING, unsigned int REASON_FLAGS)
     CRT: a certificate of type ‘gnutls_x509_crt_t’

TYPE: is one of the gnutls_x509_subject_alt_name_t enumerations

DATA_STRING: The data to be set

REASON_FLAGS: revocation reasons

This function will set the CRL distribution points certificate
     extension.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crt_set_crl_dist_points2
------------------------------------

-- Function: int gnutls_x509_crt_set_crl_dist_points2
          (gnutls_x509_crt_t CRT, gnutls_x509_subject_alt_name_t TYPE,
          const void * DATA, unsigned int DATA_SIZE, unsigned int
          REASON_FLAGS)
     CRT: a certificate of type ‘gnutls_x509_crt_t’

TYPE: is one of the gnutls_x509_subject_alt_name_t enumerations

DATA: The data to be set

DATA_SIZE: The data size

REASON_FLAGS: revocation reasons

This function will set the CRL distribution points certificate
     extension.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 2.6.0

gnutls_x509_crt_set_crq
-----------------------

-- Function: int gnutls_x509_crt_set_crq (gnutls_x509_crt_t CRT,
          gnutls_x509_crq_t CRQ)
     CRT: a certificate of type ‘gnutls_x509_crt_t’

CRQ: holds a certificate request

This function will set the name and public parameters as well as
     the extensions from the given certificate request to the
     certificate.  Only RSA keys are currently supported.

Note that this function will only set the ‘crq’ if it is self
     signed and the signature is correct.  See ‘gnutls_x509_crq_sign2()’
     .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crt_set_crq_extension_by_oid
----------------------------------------

-- Function: int gnutls_x509_crt_set_crq_extension_by_oid
          (gnutls_x509_crt_t CRT, gnutls_x509_crq_t CRQ, const char *
          OID, unsigned FLAGS)
     CRT: a certificate of type ‘gnutls_x509_crt_t’

CRQ: holds a certificate request

OID: the object identifier of the OID to copy

FLAGS: should be zero

This function will set the extension specify by ‘oid’ from the
     given request to the certificate.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.5.1

gnutls_x509_crt_set_crq_extensions
----------------------------------

-- Function: int gnutls_x509_crt_set_crq_extensions (gnutls_x509_crt_t
          CRT, gnutls_x509_crq_t CRQ)
     CRT: a certificate of type ‘gnutls_x509_crt_t’

CRQ: holds a certificate request

This function will set the extensions from the given request to the
     certificate.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 2.8.0

gnutls_x509_crt_set_dn
----------------------

-- Function: int gnutls_x509_crt_set_dn (gnutls_x509_crt_t CRT, const
          char * DN, const char ** ERR)
     CRT: a certificate of type ‘gnutls_x509_crt_t’

DN: a comma separated DN string (RFC4514)

ERR: indicates the error position (if any)

This function will set the DN on the provided certificate.  The
     input string should be plain ASCII or UTF-8 encoded.  On DN parsing
     error ‘GNUTLS_E_PARSING_ERROR’ is returned.

Note that DNs are not expected to hold DNS information, and thus no
     automatic IDNA conversions are attempted when using this function.
     If that is required (e.g., store a domain in CN), process the
     corresponding input with ‘gnutls_idna_map()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crt_set_dn_by_oid
-----------------------------

-- Function: int gnutls_x509_crt_set_dn_by_oid (gnutls_x509_crt_t CRT,
          const char * OID, unsigned int RAW_FLAG, const void * NAME,
          unsigned int SIZEOF_NAME)
     CRT: a certificate of type ‘gnutls_x509_crt_t’

OID: holds an Object Identifier in a null terminated string

RAW_FLAG: must be 0, or 1 if the data are DER encoded

NAME: a pointer to the name

SIZEOF_NAME: holds the size of ‘name’

This function will set the part of the name of the Certificate
     subject, specified by the given OID. The input string should be
     ASCII or UTF-8 encoded.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crt_set_expiration_time
-----------------------------------

-- Function: int gnutls_x509_crt_set_expiration_time (gnutls_x509_crt_t
          CERT, time_t EXP_TIME)
     CERT: a certificate of type ‘gnutls_x509_crt_t’

EXP_TIME: The actual time

This function will set the time this Certificate will expire.
     Setting an expiration time to (time_t)-1 will set to the no
     well-defined expiration date value.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crt_set_extension_by_oid
------------------------------------

-- Function: int gnutls_x509_crt_set_extension_by_oid
          (gnutls_x509_crt_t CRT, const char * OID, const void * BUF,
          size_t SIZEOF_BUF, unsigned int CRITICAL)
     CRT: a certificate of type ‘gnutls_x509_crt_t’

OID: holds an Object Identifier in null terminated string

BUF: a pointer to a DER encoded data

SIZEOF_BUF: holds the size of ‘buf’

CRITICAL: should be non-zero if the extension is to be marked as
     critical

This function will set an the extension, by the specified OID, in
     the certificate.  The extension data should be binary data DER
     encoded.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crt_set_flags
-------------------------

-- Function: void gnutls_x509_crt_set_flags (gnutls_x509_crt_t CERT,
          unsigned int FLAGS)
     CERT: A type ‘gnutls_x509_crt_t’

FLAGS: flags from the ‘gnutls_x509_crt_flags’

This function will set flags for the specified certificate.
     Currently this is useful for the
     ‘GNUTLS_X509_CRT_FLAG_IGNORE_SANITY’ which allows importing
     certificates even if they have known issues.

*Since:* 3.6.0

gnutls_x509_crt_set_inhibit_anypolicy
-------------------------------------

-- Function: int gnutls_x509_crt_set_inhibit_anypolicy
          (gnutls_x509_crt_t CRT, unsigned int SKIPCERTS)
     CRT: a certificate of type ‘gnutls_x509_crt_t’

SKIPCERTS: number of certificates after which anypolicy is no
     longer acceptable.

This function will set the Inhibit anyPolicy certificate extension.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crt_set_issuer_alt_name
-----------------------------------

-- Function: int gnutls_x509_crt_set_issuer_alt_name (gnutls_x509_crt_t
          CRT, gnutls_x509_subject_alt_name_t TYPE, const void * DATA,
          unsigned int DATA_SIZE, unsigned int FLAGS)
     CRT: a certificate of type ‘gnutls_x509_crt_t’

TYPE: is one of the gnutls_x509_subject_alt_name_t enumerations

DATA: The data to be set

DATA_SIZE: The size of data to be set

FLAGS: GNUTLS_FSAN_SET to clear previous data or GNUTLS_FSAN_APPEND
     to append.

This function will set the issuer alternative name certificate
     extension.  It can set the same types as
     ‘gnutls_x509_crt_set_subject_alt_name()’ .

Since version 3.5.7 the ‘GNUTLS_SAN_RFC822NAME’ ,
     ‘GNUTLS_SAN_DNSNAME’ , and ‘GNUTLS_SAN_OTHERNAME_XMPP’ are
     converted to ACE format when necessary.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_crt_set_issuer_alt_othername
----------------------------------------

-- Function: int gnutls_x509_crt_set_issuer_alt_othername
          (gnutls_x509_crt_t CRT, const char * OID, const void * DATA,
          unsigned int DATA_SIZE, unsigned int FLAGS)
     CRT: a certificate of type ‘gnutls_x509_crt_t’

OID: The other name OID

DATA: The data to be set

DATA_SIZE: The size of data to be set

FLAGS: GNUTLS_FSAN_SET to clear previous data or GNUTLS_FSAN_APPEND
     to append.

This function will set an "othername" to the issuer alternative
     name certificate extension.

The values set are set as binary values and are expected to have
     the proper DER encoding.  For convenience the flags
     ‘GNUTLS_FSAN_ENCODE_OCTET_STRING’ and
     ‘GNUTLS_FSAN_ENCODE_UTF8_STRING’ can be used to encode the provided
     data.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.5.0

gnutls_x509_crt_set_issuer_dn
-----------------------------

-- Function: int gnutls_x509_crt_set_issuer_dn (gnutls_x509_crt_t CRT,
          const char * DN, const char ** ERR)
     CRT: a certificate of type ‘gnutls_x509_crt_t’

DN: a comma separated DN string (RFC4514)

ERR: indicates the error position (if any)

This function will set the DN on the provided certificate.  The
     input string should be plain ASCII or UTF-8 encoded.  On DN parsing
     error ‘GNUTLS_E_PARSING_ERROR’ is returned.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crt_set_issuer_dn_by_oid
------------------------------------

-- Function: int gnutls_x509_crt_set_issuer_dn_by_oid
          (gnutls_x509_crt_t CRT, const char * OID, unsigned int
          RAW_FLAG, const void * NAME, unsigned int SIZEOF_NAME)
     CRT: a certificate of type ‘gnutls_x509_crt_t’

OID: holds an Object Identifier in a null terminated string

RAW_FLAG: must be 0, or 1 if the data are DER encoded

NAME: a pointer to the name

SIZEOF_NAME: holds the size of ‘name’

This function will set the part of the name of the Certificate
     issuer, specified by the given OID. The input string should be
     ASCII or UTF-8 encoded.

Normally you do not need to call this function, since the signing
     operation will copy the signer's name as the issuer of the
     certificate.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crt_set_issuer_unique_id
------------------------------------

-- Function: int gnutls_x509_crt_set_issuer_unique_id
          (gnutls_x509_crt_t CERT, const void * ID, size_t ID_SIZE)
     CERT: a certificate of type ‘gnutls_x509_crt_t’

ID: The unique ID

ID_SIZE: Holds the size of the unique ID.

This function will set the X.509 certificate's issuer unique ID
     field.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.4.7

gnutls_x509_crt_set_key
-----------------------

-- Function: int gnutls_x509_crt_set_key (gnutls_x509_crt_t CRT,
          gnutls_x509_privkey_t KEY)
     CRT: a certificate of type ‘gnutls_x509_crt_t’

KEY: holds a private key

This function will set the public parameters from the given private
     key to the certificate.

To export the public key (i.e., the SubjectPublicKeyInfo part),
     check ‘gnutls_pubkey_import_x509()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crt_set_key_purpose_oid
-----------------------------------

-- Function: int gnutls_x509_crt_set_key_purpose_oid (gnutls_x509_crt_t
          CERT, const void * OID, unsigned int CRITICAL)
     CERT: a certificate of type ‘gnutls_x509_crt_t’

OID: a pointer to a null terminated string that holds the OID

CRITICAL: Whether this extension will be critical or not

This function will set the key purpose OIDs of the Certificate.
     These are stored in the Extended Key Usage extension (2.5.29.37)
     See the GNUTLS_KP_* definitions for human readable names.

Subsequent calls to this function will append OIDs to the OID list.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

gnutls_x509_crt_set_key_usage
-----------------------------

-- Function: int gnutls_x509_crt_set_key_usage (gnutls_x509_crt_t CRT,
          unsigned int USAGE)
     CRT: a certificate of type ‘gnutls_x509_crt_t’

USAGE: an ORed sequence of the GNUTLS_KEY_* elements.

This function will set the keyUsage certificate extension.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crt_set_name_constraints
------------------------------------

-- Function: int gnutls_x509_crt_set_name_constraints
          (gnutls_x509_crt_t CRT, gnutls_x509_name_constraints_t NC,
          unsigned int CRITICAL)
     CRT: The certificate

NC: The nameconstraints structure

CRITICAL: whether this extension will be critical

This function will set the provided name constraints to the
     certificate extension list.  This extension is always marked as
     critical.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_crt_set_pin_function
--------------------------------

-- Function: void gnutls_x509_crt_set_pin_function (gnutls_x509_crt_t
          CRT, gnutls_pin_callback_t FN, void * USERDATA)
     CRT: The certificate structure

FN: the callback

USERDATA: data associated with the callback

This function will set a callback function to be used when it is
     required to access a protected object.  This function overrides the
     global function set using ‘gnutls_pkcs11_set_pin_function()’ .

Note that this callback is currently used only during the import of
     a PKCS ‘11’ certificate with ‘gnutls_x509_crt_import_url()’ .

*Since:* 3.1.0

gnutls_x509_crt_set_policy
--------------------------

-- Function: int gnutls_x509_crt_set_policy (gnutls_x509_crt_t CRT,
          const struct gnutls_x509_policy_st * POLICY, unsigned int
          CRITICAL)
     CRT: should contain a ‘gnutls_x509_crt_t’ type

POLICY: A pointer to a policy

CRITICAL: use non-zero if the extension is marked as critical

This function will set the certificate policy extension
     (2.5.29.32).  Multiple calls to this function append a new policy.

Note the maximum text size for the qualifier
     ‘GNUTLS_X509_QUALIFIER_NOTICE’ is 200 characters.  This function
     will fail with ‘GNUTLS_E_INVALID_REQUEST’ if this is exceeded.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.1.5

gnutls_x509_crt_set_private_key_usage_period
--------------------------------------------

-- Function: int gnutls_x509_crt_set_private_key_usage_period
          (gnutls_x509_crt_t CRT, time_t ACTIVATION, time_t EXPIRATION)
     CRT: a certificate of type ‘gnutls_x509_crt_t’

ACTIVATION: The activation time

EXPIRATION: The expiration time

This function will set the private key usage period extension
     (2.5.29.16).

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crt_set_proxy
-------------------------

-- Function: int gnutls_x509_crt_set_proxy (gnutls_x509_crt_t CRT, int
          PATHLENCONSTRAINT, const char * POLICYLANGUAGE, const char *
          POLICY, size_t SIZEOF_POLICY)
     CRT: a certificate of type ‘gnutls_x509_crt_t’

PATHLENCONSTRAINT: non-negative error codes indicate maximum length
     of path, and negative error codes indicate that the
     pathLenConstraints field should not be present.

POLICYLANGUAGE: OID describing the language of ‘policy’ .

POLICY: uint8_t byte array with policy language, can be ‘NULL’

SIZEOF_POLICY: size of ‘policy’ .

This function will set the proxyCertInfo extension.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crt_set_proxy_dn
----------------------------

-- Function: int gnutls_x509_crt_set_proxy_dn (gnutls_x509_crt_t CRT,
          gnutls_x509_crt_t EECRT, unsigned int RAW_FLAG, const void *
          NAME, unsigned int SIZEOF_NAME)
     CRT: a gnutls_x509_crt_t type with the new proxy cert

EECRT: the end entity certificate that will be issuing the proxy

RAW_FLAG: must be 0, or 1 if the CN is DER encoded

NAME: a pointer to the CN name, may be NULL (but MUST then be added
     later)

SIZEOF_NAME: holds the size of ‘name’

This function will set the subject in ‘crt’ to the end entity's
     ‘eecrt’ subject name, and add a single Common Name component ‘name’
     of size ‘sizeof_name’ .  This corresponds to the required proxy
     certificate naming style.  Note that if ‘name’ is ‘NULL’ , you MUST
     set it later by using ‘gnutls_x509_crt_set_dn_by_oid()’ or similar.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crt_set_serial
--------------------------

-- Function: int gnutls_x509_crt_set_serial (gnutls_x509_crt_t CERT,
          const void * SERIAL, size_t SERIAL_SIZE)
     CERT: a certificate of type ‘gnutls_x509_crt_t’

SERIAL: The serial number

SERIAL_SIZE: Holds the size of the serial field.

This function will set the X.509 certificate's serial number.
     While the serial number is an integer, it is often handled as an
     opaque field by several CAs.  For this reason this function accepts
     any kind of data as a serial number.  To be consistent with the
     X.509/PKIX specifications the provided ‘serial’ should be a
     big-endian positive number (i.e.  its leftmost bit should be zero).

The size of the serial is restricted to 20 bytes maximum by
     RFC5280.  This function allows writing more than 20 bytes but the
     generated certificates in that case may be rejected by other
     implementations.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crt_set_spki
------------------------

-- Function: int gnutls_x509_crt_set_spki (gnutls_x509_crt_t CRT, const
          gnutls_x509_spki_t SPKI, unsigned int FLAGS)
     CRT: a certificate of type ‘gnutls_x509_crt_t’

SPKI: a SubjectPublicKeyInfo structure of type ‘gnutls_x509_spki_t’

FLAGS: must be zero

This function will set the certificate's subject public key
     information explicitly.  This is intended to be used in the cases
     where a single public key (e.g., RSA) can be used for multiple
     signature algorithms (RSA PKCS1-1.5, and RSA-PSS).

To export the public key (i.e., the SubjectPublicKeyInfo part),
     check ‘gnutls_pubkey_import_x509()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.6.0

gnutls_x509_crt_set_subject_alt_name
------------------------------------

-- Function: int gnutls_x509_crt_set_subject_alt_name
          (gnutls_x509_crt_t CRT, gnutls_x509_subject_alt_name_t TYPE,
          const void * DATA, unsigned int DATA_SIZE, unsigned int FLAGS)
     CRT: a certificate of type ‘gnutls_x509_crt_t’

TYPE: is one of the gnutls_x509_subject_alt_name_t enumerations

DATA: The data to be set

DATA_SIZE: The size of data to be set

FLAGS: GNUTLS_FSAN_SET to clear previous data or GNUTLS_FSAN_APPEND
     to append.

This function will set the subject alternative name certificate
     extension.  It can set the following types: ‘GNUTLS_SAN_DNSNAME’ as
     a text string, ‘GNUTLS_SAN_RFC822NAME’ as a text string,
     ‘GNUTLS_SAN_URI’ as a text string, ‘GNUTLS_SAN_IPADDRESS’ as a
     binary IP address (4 or 16 bytes), ‘GNUTLS_SAN_OTHERNAME_XMPP’ as a
     UTF8 string (since 3.5.0).

Since version 3.5.7 the ‘GNUTLS_SAN_RFC822NAME’ ,
     ‘GNUTLS_SAN_DNSNAME’ , and ‘GNUTLS_SAN_OTHERNAME_XMPP’ are
     converted to ACE format when necessary.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 2.6.0

gnutls_x509_crt_set_subject_alt_othername
-----------------------------------------

-- Function: int gnutls_x509_crt_set_subject_alt_othername
          (gnutls_x509_crt_t CRT, const char * OID, const void * DATA,
          unsigned int DATA_SIZE, unsigned int FLAGS)
     CRT: a certificate of type ‘gnutls_x509_crt_t’

OID: The other name OID

DATA: The data to be set

DATA_SIZE: The size of data to be set

FLAGS: GNUTLS_FSAN_SET to clear previous data or GNUTLS_FSAN_APPEND
     to append.

This function will set an "othername" to the subject alternative
     name certificate extension.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.5.0

gnutls_x509_crt_set_subject_alternative_name
--------------------------------------------

-- Function: int gnutls_x509_crt_set_subject_alternative_name
          (gnutls_x509_crt_t CRT, gnutls_x509_subject_alt_name_t TYPE,
          const char * DATA_STRING)
     CRT: a certificate of type ‘gnutls_x509_crt_t’

TYPE: is one of the gnutls_x509_subject_alt_name_t enumerations

DATA_STRING: The data to be set, a (0) terminated string

This function will set the subject alternative name certificate
     extension.  This function assumes that data can be expressed as a
     null terminated string.

The name of the function is unfortunate since it is inconsistent
     with ‘gnutls_x509_crt_get_subject_alt_name()’ .

See ‘gnutls_x509_crt_set_subject_alt_name()’ for more information.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crt_set_subject_key_id
----------------------------------

-- Function: int gnutls_x509_crt_set_subject_key_id (gnutls_x509_crt_t
          CERT, const void * ID, size_t ID_SIZE)
     CERT: a certificate of type ‘gnutls_x509_crt_t’

ID: The key ID

ID_SIZE: Holds the size of the subject key ID field.

This function will set the X.509 certificate's subject key ID
     extension.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crt_set_subject_unique_id
-------------------------------------

-- Function: int gnutls_x509_crt_set_subject_unique_id
          (gnutls_x509_crt_t CERT, const void * ID, size_t ID_SIZE)
     CERT: a certificate of type ‘gnutls_x509_crt_t’

ID: The unique ID

ID_SIZE: Holds the size of the unique ID.

This function will set the X.509 certificate's subject unique ID
     field.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.4.7

gnutls_x509_crt_set_tlsfeatures
-------------------------------

-- Function: int gnutls_x509_crt_set_tlsfeatures (gnutls_x509_crt_t
          CRT, gnutls_x509_tlsfeatures_t FEATURES)
     CRT: A X.509 certificate

FEATURES: If the function succeeds, the features will be added to
     the certificate.

This function will set the certificates X.509 TLS extension from
     the given structure.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.5.1

gnutls_x509_crt_set_version
---------------------------

-- Function: int gnutls_x509_crt_set_version (gnutls_x509_crt_t CRT,
          unsigned int VERSION)
     CRT: a certificate of type ‘gnutls_x509_crt_t’

VERSION: holds the version number.  For X.509v1 certificates must
     be 1.

This function will set the version of the certificate.  This must
     be one for X.509 version 1, and so on.  Plain certificates without
     extensions must have version set to one.

To create well-formed certificates, you must specify version 3 if
     you use any certificate extensions.  Extensions are created by
     functions such as ‘gnutls_x509_crt_set_subject_alt_name()’ or
     ‘gnutls_x509_crt_set_key_usage()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crt_sign
--------------------

-- Function: int gnutls_x509_crt_sign (gnutls_x509_crt_t CRT,
          gnutls_x509_crt_t ISSUER, gnutls_x509_privkey_t ISSUER_KEY)
     CRT: a certificate of type ‘gnutls_x509_crt_t’

ISSUER: is the certificate of the certificate issuer

ISSUER_KEY: holds the issuer's private key

This function is the same a ‘gnutls_x509_crt_sign2()’ with no
     flags, and an appropriate hash algorithm.  The hash algorithm used
     may vary between versions of GnuTLS, and it is tied to the security
     level of the issuer's public key.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crt_sign2
---------------------

-- Function: int gnutls_x509_crt_sign2 (gnutls_x509_crt_t CRT,
          gnutls_x509_crt_t ISSUER, gnutls_x509_privkey_t ISSUER_KEY,
          gnutls_digest_algorithm_t DIG, unsigned int FLAGS)
     CRT: a certificate of type ‘gnutls_x509_crt_t’

ISSUER: is the certificate of the certificate issuer

ISSUER_KEY: holds the issuer's private key

DIG: The message digest to use, ‘GNUTLS_DIG_SHA256’ is a safe
     choice

FLAGS: must be 0

This function will sign the certificate with the issuer's private
     key, and will copy the issuer's information into the certificate.

This must be the last step in a certificate generation since all
     the previously set parameters are now signed.

A known limitation of this function is, that a newly-signed
     certificate will not be fully functional (e.g., for signature
     verification), until it is exported an re-imported.

After GnuTLS 3.6.1 the value of ‘dig’ may be ‘GNUTLS_DIG_UNKNOWN’ ,
     and in that case, a suitable but reasonable for the key algorithm
     will be selected.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crt_verify
----------------------

-- Function: int gnutls_x509_crt_verify (gnutls_x509_crt_t CERT, const
          gnutls_x509_crt_t * CA_LIST, unsigned CA_LIST_LENGTH, unsigned
          int FLAGS, unsigned int * VERIFY)
     CERT: is the certificate to be verified

CA_LIST: is one certificate that is considered to be trusted one

CA_LIST_LENGTH: holds the number of CA certificate in CA_list

FLAGS: Flags that may be used to change the verification algorithm.
     Use OR of the gnutls_certificate_verify_flags enumerations.

VERIFY: will hold the certificate verification output.

This function will try to verify the given certificate and return
     its status.  Note that a verification error does not imply a
     negative return status.  In that case the ‘verify’ status is set.

The details of the verification are the same as in
     ‘gnutls_x509_trust_list_verify_crt2()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_crt_verify_data2
----------------------------

-- Function: int gnutls_x509_crt_verify_data2 (gnutls_x509_crt_t CRT,
          gnutls_sign_algorithm_t ALGO, unsigned int FLAGS, const
          gnutls_datum_t * DATA, const gnutls_datum_t * SIGNATURE)
     CRT: Holds the certificate to verify with

ALGO: The signature algorithm used

FLAGS: Zero or an OR list of ‘gnutls_certificate_verify_flags’

DATA: holds the signed data

SIGNATURE: contains the signature

This function will verify the given signed data, using the
     parameters from the certificate.

*Returns:* In case of a verification failure
     ‘GNUTLS_E_PK_SIG_VERIFY_FAILED’ is returned, ‘GNUTLS_E_EXPIRED’ or
     ‘GNUTLS_E_NOT_YET_ACTIVATED’ on expired or not yet activated
     certificate and zero or positive code on success.

Note that since GnuTLS 3.5.6 this function introduces checks in the
     end certificate ( ‘crt’ ), including time checks and key usage
     checks.

*Since:* 3.4.0

gnutls_x509_ct_sct_get
----------------------

-- Function: int gnutls_x509_ct_sct_get (const gnutls_x509_ct_scts_t
          SCTS, unsigned IDX, time_t * TIMESTAMP, gnutls_datum_t *
          LOGID, gnutls_sign_algorithm_t * SIGALG, gnutls_datum_t *
          SIGNATURE)
     SCTS: A list of SCTs

IDX: The index of the target SCT in the list

TIMESTAMP: The timestamp of the SCT

LOGID: The LogID field of the SCT; must be freed with
     ‘gnutls_free()’

SIGALG: The signature algorithm

SIGNATURE: The signature of the SCT; must be freed with
     ‘gnutls_free()’

This function will return a specific SCT (Signed Certificate
     Timestamp) stored in the SCT list ‘scts’ .

The datums holding the SCT's LogId and signature will be allocated
     using ‘gnutls_malloc()’ .

*Returns:* ‘GNUTLS_E_SUCCESS’ (0) will be returned on success,
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ if ‘idx’ exceeds the number
     of SCTs in the list or a negative error value.

gnutls_x509_ct_sct_get_version
------------------------------

-- Function: int gnutls_x509_ct_sct_get_version (gnutls_x509_ct_scts_t
          SCTS, unsigned IDX, unsigned int * VERSION_OUT)
     SCTS: A list of SCTs

IDX: The index of the target SCT in the list

VERSION_OUT: The version of the target SCT.

This function obtains the version of the SCT at the given position
     in the SCT list.

The version of that SCT will be placed on ‘version_out’ .

Return : ‘GNUTLS_E_SUCCESS’ (0) is returned on success,
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ if ‘idx’ exceeds the number
     of SCTs in the list and ‘GNUTLS_E_INVALID_REQUEST’ if the SCT's
     version is different than 1, as that's currently the only defined
     version.

gnutls_x509_dn_deinit
---------------------

-- Function: void gnutls_x509_dn_deinit (gnutls_x509_dn_t DN)
     DN: a DN uint8_t object pointer.

This function deallocates the DN object as returned by
     ‘gnutls_x509_dn_import()’ .

*Since:* 2.4.0

gnutls_x509_dn_export
---------------------

-- Function: int gnutls_x509_dn_export (gnutls_x509_dn_t DN,
          gnutls_x509_crt_fmt_t FORMAT, void * OUTPUT_DATA, size_t *
          OUTPUT_DATA_SIZE)
     DN: Holds the uint8_t DN object

FORMAT: the format of output params.  One of PEM or DER.

OUTPUT_DATA: will contain a DN PEM or DER encoded

OUTPUT_DATA_SIZE: holds the size of output_data (and will be
     replaced by the actual size of parameters)

This function will export the DN to DER or PEM format.

If the buffer provided is not long enough to hold the output, then
     * ‘output_data_size’ is updated and ‘GNUTLS_E_SHORT_MEMORY_BUFFER’
     will be returned.

If the structure is PEM encoded, it will have a header of "BEGIN
     NAME".

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_dn_export2
----------------------

-- Function: int gnutls_x509_dn_export2 (gnutls_x509_dn_t DN,
          gnutls_x509_crt_fmt_t FORMAT, gnutls_datum_t * OUT)
     DN: Holds the uint8_t DN object

FORMAT: the format of output params.  One of PEM or DER.

OUT: will contain a DN PEM or DER encoded

This function will export the DN to DER or PEM format.

The output buffer is allocated using ‘gnutls_malloc()’ .

If the structure is PEM encoded, it will have a header of "BEGIN
     NAME".

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.1.3

gnutls_x509_dn_get_rdn_ava
--------------------------

-- Function: int gnutls_x509_dn_get_rdn_ava (gnutls_x509_dn_t DN, int
          IRDN, int IAVA, gnutls_x509_ava_st * AVA)
     DN: a pointer to DN

IRDN: index of RDN

IAVA: index of AVA.

AVA: Pointer to structure which will hold output information.

Get pointers to data within the DN. The format of the ‘ava’
     structure is shown below.

struct gnutls_x509_ava_st { gnutls_datum_t oid; gnutls_datum_t
     value; unsigned long value_tag; };

The X.509 distinguished name is a sequence of sequences of strings
     and this is what the ‘irdn’ and ‘iava’ indexes model.

Note that ‘ava’ will contain pointers into the ‘dn’ structure which
     in turns points to the original certificate.  Thus you should not
     modify any data or deallocate any of those.

This is a low-level function that requires the caller to do the
     value conversions when necessary (e.g.  from UCS-2).

*Returns:* Returns 0 on success, or an error code.

gnutls_x509_dn_get_str
----------------------

-- Function: int gnutls_x509_dn_get_str (gnutls_x509_dn_t DN,
          gnutls_datum_t * STR)
     DN: a pointer to DN

STR: a datum that will hold the name

This function will allocate buffer and copy the name in the
     provided DN. The name will be in the form "C=xxxx,O=yyyy,CN=zzzz"
     as described in RFC4514.  The output string will be ASCII or UTF-8
     encoded, depending on the certificate data.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.4.2

gnutls_x509_dn_get_str2
-----------------------

-- Function: int gnutls_x509_dn_get_str2 (gnutls_x509_dn_t DN,
          gnutls_datum_t * STR, unsigned FLAGS)
     DN: a pointer to DN

STR: a datum that will hold the name

FLAGS: zero or ‘GNUTLS_X509_DN_FLAG_COMPAT’

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.5.7

gnutls_x509_dn_import
---------------------

-- Function: int gnutls_x509_dn_import (gnutls_x509_dn_t DN, const
          gnutls_datum_t * DATA)
     DN: the structure that will hold the imported DN

DATA: should contain a DER encoded RDN sequence

This function parses an RDN sequence and stores the result to a
     ‘gnutls_x509_dn_t’ type.  The data must have been initialized with
     ‘gnutls_x509_dn_init()’ .  You may use
     ‘gnutls_x509_dn_get_rdn_ava()’ to decode the DN.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 2.4.0

gnutls_x509_dn_init
-------------------

-- Function: int gnutls_x509_dn_init (gnutls_x509_dn_t * DN)
     DN: the object to be initialized

This function initializes a ‘gnutls_x509_dn_t’ type.

The object returned must be deallocated using
     ‘gnutls_x509_dn_deinit()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 2.4.0

gnutls_x509_dn_oid_known
------------------------

-- Function: int gnutls_x509_dn_oid_known (const char * OID)
     OID: holds an Object Identifier in a null terminated string

This function will inform about known DN OIDs.  This is useful
     since functions like ‘gnutls_x509_crt_set_dn_by_oid()’ use the
     information on known OIDs to properly encode their input.  Object
     Identifiers that are not known are not encoded by these functions,
     and their input is stored directly into the ASN.1 structure.  In
     that case of unknown OIDs, you have the responsibility of DER
     encoding your data.

*Returns:* 1 on known OIDs and 0 otherwise.

gnutls_x509_dn_oid_name
-----------------------

-- Function: const char * gnutls_x509_dn_oid_name (const char * OID,
          unsigned int FLAGS)
     OID: holds an Object Identifier in a null terminated string

FLAGS: 0 or GNUTLS_X509_DN_OID_*

This function will return the name of a known DN OID. If
     ‘GNUTLS_X509_DN_OID_RETURN_OID’ is specified this function will
     return the given OID if no descriptive name has been found.

*Returns:* A null terminated string or NULL otherwise.

*Since:* 3.0

gnutls_x509_dn_set_str
----------------------

-- Function: int gnutls_x509_dn_set_str (gnutls_x509_dn_t DN, const
          char * STR, const char ** ERR)
     DN: a pointer to DN

STR: a comma separated DN string (RFC4514)

ERR: indicates the error position (if any)

This function will set the DN on the provided DN structure.  The
     input string should be plain ASCII or UTF-8 encoded.  On DN parsing
     error ‘GNUTLS_E_PARSING_ERROR’ is returned.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.5.3

gnutls_x509_ext_ct_export_scts
------------------------------

-- Function: int gnutls_x509_ext_ct_export_scts (const
          gnutls_x509_ct_scts_t SCTS, gnutls_datum_t * EXT)
     SCTS: An initialized SCT list

EXT: The DER-encoded extension data; must be freed with
     ‘gnutls_free()’

This function will convert the provided list of SCTs to a
     DER-encoded SignedCertificateTimestampList extension
     (1.3.6.1.4.1.11129.2.4.2).  The output data in ‘ext’ will be
     allocated using ‘gnutls_malloc()’ .

*Returns:* ‘GNUTLS_E_SUCCESS’ (0) on success or a negative error
     value.

gnutls_x509_ext_ct_import_scts
------------------------------

-- Function: int gnutls_x509_ext_ct_import_scts (const gnutls_datum_t *
          EXT, gnutls_x509_ct_scts_t SCTS, unsigned int FLAGS)
     EXT: a DER-encoded extension

SCTS: The SCT list

FLAGS: should be zero

This function will read a SignedCertificateTimestampList structure
     from the DER data of the X.509 Certificate Transparency SCT
     extension (OID 1.3.6.1.4.1.11129.2.4.2).

The list of SCTs (Signed Certificate Timestamps) is placed on
     ‘scts’ , which must be previously initialized with
     ‘gnutls_x509_ext_ct_scts_init()’ .

*Returns:* ‘GNUTLS_E_SUCCESS’ (0) on success or a negative error
     value.

gnutls_x509_ext_ct_scts_deinit
------------------------------

-- Function: void gnutls_x509_ext_ct_scts_deinit (gnutls_x509_ct_scts_t
          SCTS)
     SCTS: The SCT list

This function will deinitialize a Certificate Transparency SCT
     list.

gnutls_x509_ext_ct_scts_init
----------------------------

-- Function: int gnutls_x509_ext_ct_scts_init (gnutls_x509_ct_scts_t *
          SCTS)
     SCTS: The SCT list

This function will initialize a Certificate Transparency SCT list.

*Returns:* ‘GNUTLS_E_SUCCESS’ (0) on success, otherwise a negative
     error value.

gnutls_x509_ext_deinit
----------------------

-- Function: void gnutls_x509_ext_deinit (gnutls_x509_ext_st * EXT)
     EXT: The extensions structure

This function will deinitialize an extensions structure.

*Since:* 3.3.8

gnutls_x509_ext_export_aia
--------------------------

-- Function: int gnutls_x509_ext_export_aia (gnutls_x509_aia_t AIA,
          gnutls_datum_t * EXT)
     AIA: The authority info access

EXT: The DER-encoded extension data; must be freed using
     ‘gnutls_free()’ .

This function will DER encode the Authority Information Access
     (AIA) extension; see RFC 5280 section 4.2.2.1 for more information
     on the extension.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_ext_export_authority_key_id
---------------------------------------

-- Function: int gnutls_x509_ext_export_authority_key_id
          (gnutls_x509_aki_t AKI, gnutls_datum_t * EXT)
     AKI: An initialized authority key identifier

EXT: The DER-encoded extension data; must be freed using
     ‘gnutls_free()’ .

This function will convert the provided key identifier to a
     DER-encoded PKIX AuthorityKeyIdentifier extension.  The output data
     in ‘ext’ will be allocated using ‘gnutls_malloc()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_ext_export_basic_constraints
----------------------------------------

-- Function: int gnutls_x509_ext_export_basic_constraints (unsigned int
          CA, int PATHLEN, gnutls_datum_t * EXT)
     CA: non-zero for a CA

PATHLEN: The path length constraint (set to -1 for no constraint)

EXT: The DER-encoded extension data; must be freed using
     ‘gnutls_free()’ .

This function will convert the parameters provided to a basic
     constraints DER encoded extension (2.5.29.19).  The ‘ext’ data will
     be allocated using ‘gnutls_malloc()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_ext_export_crl_dist_points
--------------------------------------

-- Function: int gnutls_x509_ext_export_crl_dist_points
          (gnutls_x509_crl_dist_points_t CDP, gnutls_datum_t * EXT)
     CDP: A pointer to an initialized CRL distribution points.

EXT: The DER-encoded extension data; must be freed using
     ‘gnutls_free()’ .

This function will convert the provided policies, to a certificate
     policy DER encoded extension (2.5.29.31).

The ‘ext’ data will be allocated using ‘gnutls_malloc()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_ext_export_inhibit_anypolicy
----------------------------------------

-- Function: int gnutls_x509_ext_export_inhibit_anypolicy (unsigned int
          SKIPCERTS, gnutls_datum_t * EXT)
     SKIPCERTS: number of certificates after which anypolicy is no
     longer acceptable.

EXT: The DER-encoded extension data; must be freed using
     ‘gnutls_free()’ .

This function will convert the ‘skipcerts’ value to a DER encoded
     Inhibit AnyPolicy PKIX extension.  The ‘ext’ data will be allocated
     using ‘gnutls_malloc()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.6.0

gnutls_x509_ext_export_key_purposes
-----------------------------------

-- Function: int gnutls_x509_ext_export_key_purposes
          (gnutls_x509_key_purposes_t P, gnutls_datum_t * EXT)
     P: The key purposes

EXT: The DER-encoded extension data; must be freed using
     ‘gnutls_free()’ .

This function will convert the key purposes type to a DER-encoded
     PKIX ExtKeyUsageSyntax (2.5.29.37) extension.  The output data in
     ‘ext’ will be allocated using ‘gnutls_malloc()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_ext_export_key_usage
--------------------------------

-- Function: int gnutls_x509_ext_export_key_usage (unsigned int USAGE,
          gnutls_datum_t * EXT)
     USAGE: an ORed sequence of the GNUTLS_KEY_* elements.

EXT: The DER-encoded extension data; must be freed using
     ‘gnutls_free()’ .

This function will convert the keyUsage bit string to a DER encoded
     PKIX extension.  The ‘ext’ data will be allocated using
     ‘gnutls_malloc()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_ext_export_name_constraints
---------------------------------------

-- Function: int gnutls_x509_ext_export_name_constraints
          (gnutls_x509_name_constraints_t NC, gnutls_datum_t * EXT)
     NC: The nameconstraints

EXT: The DER-encoded extension data; must be freed using
     ‘gnutls_free()’ .

This function will convert the provided name constraints type to a
     DER-encoded PKIX NameConstraints (2.5.29.30) extension.  The output
     data in ‘ext’ will be allocated using ‘gnutls_malloc()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_ext_export_policies
-------------------------------

-- Function: int gnutls_x509_ext_export_policies
          (gnutls_x509_policies_t POLICIES, gnutls_datum_t * EXT)
     POLICIES: A pointer to an initialized policies.

EXT: The DER-encoded extension data; must be freed using
     ‘gnutls_free()’ .

This function will convert the provided policies, to a certificate
     policy DER encoded extension (2.5.29.32).

The ‘ext’ data will be allocated using ‘gnutls_malloc()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_ext_export_private_key_usage_period
-----------------------------------------------

-- Function: int gnutls_x509_ext_export_private_key_usage_period
          (time_t ACTIVATION, time_t EXPIRATION, gnutls_datum_t * EXT)
     ACTIVATION: The activation time

EXPIRATION: The expiration time

EXT: The DER-encoded extension data; must be freed using
     ‘gnutls_free()’ .

This function will convert the periods provided to a private key
     usage DER encoded extension (2.5.29.16).  The ‘ext’ data will be
     allocated using ‘gnutls_malloc()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_ext_export_proxy
----------------------------

-- Function: int gnutls_x509_ext_export_proxy (int PATHLENCONSTRAINT,
          const char * POLICYLANGUAGE, const char * POLICY, size_t
          SIZEOF_POLICY, gnutls_datum_t * EXT)
     PATHLENCONSTRAINT: A negative value will remove the path length
     constraint, while non-negative values will be set as the length of
     the pathLenConstraints field.

POLICYLANGUAGE: OID describing the language of ‘policy’ .

POLICY: uint8_t byte array with policy language, can be ‘NULL’

SIZEOF_POLICY: size of ‘policy’ .

EXT: The DER-encoded extension data; must be freed using
     ‘gnutls_free()’ .

This function will convert the parameters provided to a
     proxyCertInfo extension.

The ‘ext’ data will be allocated using ‘gnutls_malloc()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_ext_export_subject_alt_names
----------------------------------------

-- Function: int gnutls_x509_ext_export_subject_alt_names
          (gnutls_subject_alt_names_t SANS, gnutls_datum_t * EXT)
     SANS: The alternative names

EXT: The DER-encoded extension data; must be freed using
     ‘gnutls_free()’ .

This function will convert the provided alternative names structure
     to a DER-encoded SubjectAltName PKIX extension.  The output data in
     ‘ext’ will be allocated using ‘gnutls_malloc()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_ext_export_subject_key_id
-------------------------------------

-- Function: int gnutls_x509_ext_export_subject_key_id (const
          gnutls_datum_t * ID, gnutls_datum_t * EXT)
     ID: The key identifier

EXT: The DER-encoded extension data; must be freed using
     ‘gnutls_free()’ .

This function will convert the provided key identifier to a
     DER-encoded PKIX SubjectKeyIdentifier extension.  The output data
     in ‘ext’ will be allocated using ‘gnutls_malloc()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_ext_export_tlsfeatures
----------------------------------

-- Function: int gnutls_x509_ext_export_tlsfeatures
          (gnutls_x509_tlsfeatures_t F, gnutls_datum_t * EXT)
     F: The features structure

EXT: The DER-encoded extension data; must be freed using
     ‘gnutls_free()’ .

This function will convert the provided TLS features structure
     structure to a DER-encoded TLS features PKIX extension.  The output
     data in ‘ext’ will be allocated using ‘gnutls_malloc()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.5.1

gnutls_x509_ext_import_aia
--------------------------

-- Function: int gnutls_x509_ext_import_aia (const gnutls_datum_t *
          EXT, gnutls_x509_aia_t AIA, unsigned int FLAGS)
     EXT: The DER-encoded extension data

AIA: The authority info access

FLAGS: should be zero

This function extracts the Authority Information Access (AIA)
     extension from the provided DER-encoded data; see RFC 5280 section
     4.2.2.1 for more information on the extension.  The AIA extension
     holds a sequence of AccessDescription (AD) data.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_ext_import_authority_key_id
---------------------------------------

-- Function: int gnutls_x509_ext_import_authority_key_id (const
          gnutls_datum_t * EXT, gnutls_x509_aki_t AKI, unsigned int
          FLAGS)
     EXT: a DER encoded extension

AKI: An initialized authority key identifier type

FLAGS: should be zero

This function will return the subject key ID stored in the provided
     AuthorityKeyIdentifier extension.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ if the extension is not
     present, otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_ext_import_basic_constraints
----------------------------------------

-- Function: int gnutls_x509_ext_import_basic_constraints (const
          gnutls_datum_t * EXT, unsigned int * CA, int * PATHLEN)
     EXT: the DER encoded extension data

CA: will be non zero if the CA status is true

PATHLEN: the path length constraint; will be set to -1 for no limit

This function will return the CA status and path length constraint
     as written in the PKIX extension 2.5.29.19.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_ext_import_crl_dist_points
--------------------------------------

-- Function: int gnutls_x509_ext_import_crl_dist_points (const
          gnutls_datum_t * EXT, gnutls_x509_crl_dist_points_t CDP,
          unsigned int FLAGS)
     EXT: the DER encoded extension data

CDP: A pointer to an initialized CRL distribution points.

FLAGS: should be zero

This function will extract the CRL distribution points extension
     (2.5.29.31) and store it into the provided type.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_ext_import_inhibit_anypolicy
----------------------------------------

-- Function: int gnutls_x509_ext_import_inhibit_anypolicy (const
          gnutls_datum_t * EXT, unsigned int * SKIPCERTS)
     EXT: the DER encoded extension data

SKIPCERTS: will hold the number of certificates after which
     anypolicy is no longer acceptable.

This function will return certificate's value of SkipCerts, by
     reading the DER data of the Inhibit anyPolicy X.509 extension
     (2.5.29.54).

The ‘skipcerts’ value is the number of additional certificates that
     may appear in the path before the anyPolicy
     (‘GNUTLS_X509_OID_POLICY_ANY’ ) is no longer acceptable.

*Returns:* zero, or a negative error code in case of parsing error.
     If the certificate does not contain the Inhibit anyPolicy extension
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ will be returned.

*Since:* 3.6.0

gnutls_x509_ext_import_key_purposes
-----------------------------------

-- Function: int gnutls_x509_ext_import_key_purposes (const
          gnutls_datum_t * EXT, gnutls_x509_key_purposes_t P, unsigned
          int FLAGS)
     EXT: The DER-encoded extension data

P: The key purposes

FLAGS: should be zero

This function will extract the key purposes in the provided
     DER-encoded ExtKeyUsageSyntax PKIX extension, to a
     ‘gnutls_x509_key_purposes_t’ type.  The data must be initialized.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_ext_import_key_usage
--------------------------------

-- Function: int gnutls_x509_ext_import_key_usage (const gnutls_datum_t
          * EXT, unsigned int * KEY_USAGE)
     EXT: the DER encoded extension data

KEY_USAGE: where the key usage bits will be stored

This function will return certificate's key usage, by reading the
     DER data of the keyUsage X.509 extension (2.5.29.15).  The key
     usage value will ORed values of the: ‘GNUTLS_KEY_DIGITAL_SIGNATURE’
     , ‘GNUTLS_KEY_NON_REPUDIATION’ , ‘GNUTLS_KEY_KEY_ENCIPHERMENT’ ,
     ‘GNUTLS_KEY_DATA_ENCIPHERMENT’ , ‘GNUTLS_KEY_KEY_AGREEMENT’ ,
     ‘GNUTLS_KEY_KEY_CERT_SIGN’ , ‘GNUTLS_KEY_CRL_SIGN’ ,
     ‘GNUTLS_KEY_ENCIPHER_ONLY’ , ‘GNUTLS_KEY_DECIPHER_ONLY’ .

*Since:* 3.3.0

gnutls_x509_ext_import_name_constraints
---------------------------------------

-- Function: int gnutls_x509_ext_import_name_constraints (const
          gnutls_datum_t * EXT, gnutls_x509_name_constraints_t NC,
          unsigned int FLAGS)
     EXT: a DER encoded extension

NC: The nameconstraints

FLAGS: zero or ‘GNUTLS_NAME_CONSTRAINTS_FLAG_APPEND’

This function will return an intermediate type containing the name
     constraints of the provided NameConstraints extension.  That can be
     used in combination with ‘gnutls_x509_name_constraints_check()’ to
     verify whether a server's name is in accordance with the
     constraints.

When the ‘flags’ is set to ‘GNUTLS_NAME_CONSTRAINTS_FLAG_APPEND’ ,
     then if the ‘nc’ type is empty this function will behave
     identically as if the flag was not set.  Otherwise if there are
     elements in the ‘nc’ structure then the constraints will be merged
     with the existing constraints following RFC5280 p6.1.4 (excluded
     constraints will be appended, permitted will be intersected).

Note that ‘nc’ must be initialized prior to calling this function.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ if the extension is not
     present, otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_ext_import_policies
-------------------------------

-- Function: int gnutls_x509_ext_import_policies (const gnutls_datum_t
          * EXT, gnutls_x509_policies_t POLICIES, unsigned int FLAGS)
     EXT: the DER encoded extension data

POLICIES: A pointer to an initialized policies.

FLAGS: should be zero

This function will extract the certificate policy extension
     (2.5.29.32) and store it the provided policies.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_ext_import_private_key_usage_period
-----------------------------------------------

-- Function: int gnutls_x509_ext_import_private_key_usage_period (const
          gnutls_datum_t * EXT, time_t * ACTIVATION, time_t *
          EXPIRATION)
     EXT: the DER encoded extension data

ACTIVATION: Will hold the activation time

EXPIRATION: Will hold the expiration time

This function will return the expiration and activation times of
     the private key as written in the PKIX extension 2.5.29.16.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_ext_import_proxy
----------------------------

-- Function: int gnutls_x509_ext_import_proxy (const gnutls_datum_t *
          EXT, int * PATHLEN, char ** POLICYLANGUAGE, char ** POLICY,
          size_t * SIZEOF_POLICY)
     EXT: the DER encoded extension data

POLICYLANGUAGE: output variable with OID of policy language

POLICY: output variable with policy data

SIZEOF_POLICY: output variable with size of policy data

This function will return the information from a proxy certificate
     extension.  It reads the ProxyCertInfo X.509 extension
     (1.3.6.1.5.5.7.1.14).  The ‘policyLanguage’ and ‘policy’ values
     must be deinitialized using ‘gnutls_free()’ after use.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_ext_import_subject_alt_names
----------------------------------------

-- Function: int gnutls_x509_ext_import_subject_alt_names (const
          gnutls_datum_t * EXT, gnutls_subject_alt_names_t SANS,
          unsigned int FLAGS)
     EXT: The DER-encoded extension data

SANS: The alternative names

FLAGS: should be zero

This function will export the alternative names in the provided
     DER-encoded SubjectAltName PKIX extension, to a
     ‘gnutls_subject_alt_names_t’ type.  ‘sans’ must be initialized.

This function will succeed even if there no subject alternative
     names in the structure.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_ext_import_subject_key_id
-------------------------------------

-- Function: int gnutls_x509_ext_import_subject_key_id (const
          gnutls_datum_t * EXT, gnutls_datum_t * ID)
     EXT: a DER encoded extension

ID: will contain the subject key ID

This function will return the subject key ID stored in the provided
     SubjectKeyIdentifier extension.  The ID will be allocated using
     ‘gnutls_malloc()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ if the extension is not
     present, otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_ext_import_tlsfeatures
----------------------------------

-- Function: int gnutls_x509_ext_import_tlsfeatures (const
          gnutls_datum_t * EXT, gnutls_x509_tlsfeatures_t F, unsigned
          int FLAGS)
     EXT: The DER-encoded extension data

F: The features structure

FLAGS: zero or ‘GNUTLS_EXT_FLAG_APPEND’

This function will export the features in the provided DER-encoded
     TLS Features PKIX extension, to a ‘gnutls_x509_tlsfeatures_t’ type.
     ‘f’ must be initialized.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.5.1

gnutls_x509_ext_print
---------------------

-- Function: int gnutls_x509_ext_print (gnutls_x509_ext_st * EXTS,
          unsigned int EXTS_SIZE, gnutls_certificate_print_formats_t
          FORMAT, gnutls_datum_t * OUT)
     EXTS: The data to be printed

EXTS_SIZE: the number of available structures

FORMAT: Indicate the format to use

OUT: Newly allocated datum with null terminated string.

This function will pretty print X.509 certificate extensions,
     suitable for display to a human.

The output ‘out’ needs to be deallocated using ‘gnutls_free()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_key_purpose_deinit
------------------------------

-- Function: void gnutls_x509_key_purpose_deinit
          (gnutls_x509_key_purposes_t P)
     P: The key purposes

This function will deinitialize a key purposes type.

*Since:* 3.3.0

gnutls_x509_key_purpose_get
---------------------------

-- Function: int gnutls_x509_key_purpose_get
          (gnutls_x509_key_purposes_t P, unsigned IDX, gnutls_datum_t *
          OID)
     P: The key purposes

IDX: The index of the key purpose to retrieve

OID: Will hold the object identifier of the key purpose (to be
     treated as constant)

This function will retrieve the specified by the index key purpose
     in the purposes type.  The object identifier will be a null
     terminated string.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ if the index is out of
     bounds, otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_key_purpose_init
----------------------------

-- Function: int gnutls_x509_key_purpose_init
          (gnutls_x509_key_purposes_t * P)
     P: The key purposes

This function will initialize an alternative names type.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_key_purpose_set
---------------------------

-- Function: int gnutls_x509_key_purpose_set
          (gnutls_x509_key_purposes_t P, const char * OID)
     P: The key purposes

OID: The object identifier of the key purpose

This function will store the specified key purpose in the purposes.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0), otherwise a negative
     error value.

*Since:* 3.3.0

gnutls_x509_name_constraints_add_excluded
-----------------------------------------

-- Function: int gnutls_x509_name_constraints_add_excluded
          (gnutls_x509_name_constraints_t NC,
          gnutls_x509_subject_alt_name_t TYPE, const gnutls_datum_t *
          NAME)
     NC: The nameconstraints

TYPE: The type of the constraints

NAME: The data of the constraints

This function will add a name constraint to the list of excluded
     constraints.  The constraints ‘type’ can be any of the following
     types: ‘GNUTLS_SAN_DNSNAME’ , ‘GNUTLS_SAN_RFC822NAME’ ,
     ‘GNUTLS_SAN_DN’ , ‘GNUTLS_SAN_URI’ , ‘GNUTLS_SAN_IPADDRESS’ .  For
     the latter, an IP address in network byte order is expected,
     followed by its network mask (which is 4 bytes in IPv4 or 16-bytes
     in IPv6).

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_name_constraints_add_permitted
------------------------------------------

-- Function: int gnutls_x509_name_constraints_add_permitted
          (gnutls_x509_name_constraints_t NC,
          gnutls_x509_subject_alt_name_t TYPE, const gnutls_datum_t *
          NAME)
     NC: The nameconstraints

TYPE: The type of the constraints

NAME: The data of the constraints

This function will add a name constraint to the list of permitted
     constraints.  The constraints ‘type’ can be any of the following
     types: ‘GNUTLS_SAN_DNSNAME’ , ‘GNUTLS_SAN_RFC822NAME’ ,
     ‘GNUTLS_SAN_DN’ , ‘GNUTLS_SAN_URI’ , ‘GNUTLS_SAN_IPADDRESS’ .  For
     the latter, an IP address in network byte order is expected,
     followed by its network mask.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_name_constraints_check
----------------------------------

-- Function: unsigned gnutls_x509_name_constraints_check
          (gnutls_x509_name_constraints_t NC,
          gnutls_x509_subject_alt_name_t TYPE, const gnutls_datum_t *
          NAME)
     NC: the extracted name constraints

TYPE: the type of the constraint to check (of type
     gnutls_x509_subject_alt_name_t)

NAME: the name to be checked

This function will check the provided name against the constraints
     in ‘nc’ using the RFC5280 rules.  Currently this function is
     limited to DNS names, emails and IP addresses (of type
     ‘GNUTLS_SAN_DNSNAME’ , ‘GNUTLS_SAN_RFC822NAME’ and
     ‘GNUTLS_SAN_IPADDRESS’ ).

*Returns:* zero if the provided name is not acceptable, and
     non-zero otherwise.

*Since:* 3.3.0

gnutls_x509_name_constraints_check_crt
--------------------------------------

-- Function: unsigned gnutls_x509_name_constraints_check_crt
          (gnutls_x509_name_constraints_t NC,
          gnutls_x509_subject_alt_name_t TYPE, gnutls_x509_crt_t CERT)
     NC: the extracted name constraints

TYPE: the type of the constraint to check (of type
     gnutls_x509_subject_alt_name_t)

CERT: the certificate to be checked

This function will check the provided certificate names against the
     constraints in ‘nc’ using the RFC5280 rules.  It will traverse all
     the certificate's names and alternative names.

Currently this function is limited to DNS names and emails (of type
     ‘GNUTLS_SAN_DNSNAME’ and ‘GNUTLS_SAN_RFC822NAME’ ).

*Returns:* zero if the provided name is not acceptable, and
     non-zero otherwise.

*Since:* 3.3.0

gnutls_x509_name_constraints_deinit
-----------------------------------

-- Function: void gnutls_x509_name_constraints_deinit
          (gnutls_x509_name_constraints_t NC)
     NC: The nameconstraints

This function will deinitialize a name constraints type.

*Since:* 3.3.0

gnutls_x509_name_constraints_get_excluded
-----------------------------------------

-- Function: int gnutls_x509_name_constraints_get_excluded
          (gnutls_x509_name_constraints_t NC, unsigned IDX, unsigned *
          TYPE, gnutls_datum_t * NAME)
     NC: the extracted name constraints

IDX: the index of the constraint

TYPE: the type of the constraint (of type
     gnutls_x509_subject_alt_name_t)

NAME: the name in the constraint (of the specific type)

The name should be treated as constant and valid for the lifetime
     of ‘nc’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ if the extension is not
     present, otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_name_constraints_get_permitted
------------------------------------------

-- Function: int gnutls_x509_name_constraints_get_permitted
          (gnutls_x509_name_constraints_t NC, unsigned IDX, unsigned *
          TYPE, gnutls_datum_t * NAME)
     NC: the extracted name constraints

IDX: the index of the constraint

TYPE: the type of the constraint (of type
     gnutls_x509_subject_alt_name_t)

NAME: the name in the constraint (of the specific type)

The name should be treated as constant and valid for the lifetime
     of ‘nc’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ if the extension is not
     present, otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_name_constraints_init
---------------------------------

-- Function: int gnutls_x509_name_constraints_init
          (gnutls_x509_name_constraints_t * NC)
     NC: The nameconstraints

This function will initialize a name constraints type.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_othername_to_virtual
--------------------------------

-- Function: int gnutls_x509_othername_to_virtual (const char * OID,
          const gnutls_datum_t * OTHERNAME, unsigned int * VIRT_TYPE,
          gnutls_datum_t * VIRT)
     OID: The othername object identifier

OTHERNAME: The othername data

VIRT_TYPE: GNUTLS_SAN_OTHERNAME_XXX

VIRT: allocated printable data

This function will parse and convert the othername data to a
     virtual type supported by gnutls.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.8

gnutls_x509_policies_deinit
---------------------------

-- Function: void gnutls_x509_policies_deinit (gnutls_x509_policies_t
          POLICIES)
     POLICIES: The authority key identifier

This function will deinitialize an authority key identifier type.

*Since:* 3.3.0

gnutls_x509_policies_get
------------------------

-- Function: int gnutls_x509_policies_get (gnutls_x509_policies_t
          POLICIES, unsigned int SEQ, struct gnutls_x509_policy_st *
          POLICY)
     POLICIES: The policies

SEQ: The index of the name to get

POLICY: Will hold the policy

This function will return a specific policy as stored in the
     ‘policies’ type.  The returned values should be treated as constant
     and valid for the lifetime of ‘policies’ .

The any policy OID is available as the ‘GNUTLS_X509_OID_POLICY_ANY’
     macro.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ if the index is out of
     bounds, otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_policies_init
-------------------------

-- Function: int gnutls_x509_policies_init (gnutls_x509_policies_t *
          POLICIES)
     POLICIES: The authority key ID

This function will initialize an authority key ID type.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.3.0

gnutls_x509_policies_set
------------------------

-- Function: int gnutls_x509_policies_set (gnutls_x509_policies_t
          POLICIES, const struct gnutls_x509_policy_st * POLICY)
     POLICIES: An initialized policies

POLICY: Contains the policy to set

This function will store the specified policy in the provided
     ‘policies’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0), otherwise a negative
     error value.

*Since:* 3.3.0

gnutls_x509_policy_release
--------------------------

-- Function: void gnutls_x509_policy_release (struct
          gnutls_x509_policy_st * POLICY)
     POLICY: a certificate policy

This function will deinitialize all memory associated with the
     provided ‘policy’ .  The policy is allocated using
     ‘gnutls_x509_crt_get_policy()’ .

*Since:* 3.1.5

gnutls_x509_privkey_cpy
-----------------------

-- Function: int gnutls_x509_privkey_cpy (gnutls_x509_privkey_t DST,
          gnutls_x509_privkey_t SRC)
     DST: The destination key, which should be initialized.

SRC: The source key

This function will copy a private key from source to destination
     key.  Destination has to be initialized.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_privkey_deinit
--------------------------

-- Function: void gnutls_x509_privkey_deinit (gnutls_x509_privkey_t
          KEY)
     KEY: The key to be deinitialized

This function will deinitialize a private key structure.

gnutls_x509_privkey_export
--------------------------

-- Function: int gnutls_x509_privkey_export (gnutls_x509_privkey_t KEY,
          gnutls_x509_crt_fmt_t FORMAT, void * OUTPUT_DATA, size_t *
          OUTPUT_DATA_SIZE)
     KEY: Holds the key

FORMAT: the format of output params.  One of PEM or DER.

OUTPUT_DATA: will contain a private key PEM or DER encoded

OUTPUT_DATA_SIZE: holds the size of output_data (and will be
     replaced by the actual size of parameters)

This function will export the private key to a PKCS‘1’ structure
     for RSA or RSA-PSS keys, and integer sequence for DSA keys.  Other
     keys types will be exported in PKCS‘8’ form.

If the structure is PEM encoded, it will have a header of "BEGIN
     RSA PRIVATE KEY".

It is recommended to use ‘gnutls_x509_privkey_export_pkcs8()’
     instead of this function, when a consistent output format is
     required.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_privkey_export2
---------------------------

-- Function: int gnutls_x509_privkey_export2 (gnutls_x509_privkey_t
          KEY, gnutls_x509_crt_fmt_t FORMAT, gnutls_datum_t * OUT)
     KEY: Holds the key

FORMAT: the format of output params.  One of PEM or DER.

OUT: will contain a private key PEM or DER encoded

This function will export the private key to a PKCS‘1’ structure
     for RSA or RSA-PSS keys, and integer sequence for DSA keys.  Other
     keys types will be exported in PKCS‘8’ form.

The output buffer is allocated using ‘gnutls_malloc()’ .

It is recommended to use ‘gnutls_x509_privkey_export2_pkcs8()’
     instead of this function, when a consistent output format is
     required.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

Since 3.1.3

gnutls_x509_privkey_export2_pkcs8
---------------------------------

-- Function: int gnutls_x509_privkey_export2_pkcs8
          (gnutls_x509_privkey_t KEY, gnutls_x509_crt_fmt_t FORMAT,
          const char * PASSWORD, unsigned int FLAGS, gnutls_datum_t *
          OUT)
     KEY: Holds the key

FORMAT: the format of output params.  One of PEM or DER.

PASSWORD: the password that will be used to encrypt the key.

FLAGS: an ORed sequence of gnutls_pkcs_encrypt_flags_t

OUT: will contain a private key PEM or DER encoded

This function will export the private key to a PKCS8 structure.
     Both RSA and DSA keys can be exported.  For DSA keys we use PKCS
     ‘11’ definitions.  If the flags do not specify the encryption
     cipher, then the default 3DES (PBES2) will be used.

The ‘password’ can be either ASCII or UTF-8 in the default PBES2
     encryption schemas, or ASCII for the PKCS12 schemas.

The output buffer is allocated using ‘gnutls_malloc()’ .

If the structure is PEM encoded, it will have a header of "BEGIN
     ENCRYPTED PRIVATE KEY" or "BEGIN PRIVATE KEY" if encryption is not
     used.

*Returns:* In case of failure a negative error code will be
     returned, and 0 on success.

Since 3.1.3

gnutls_x509_privkey_export_dsa_raw
----------------------------------

-- Function: int gnutls_x509_privkey_export_dsa_raw
          (gnutls_x509_privkey_t KEY, gnutls_datum_t * P, gnutls_datum_t
          * Q, gnutls_datum_t * G, gnutls_datum_t * Y, gnutls_datum_t *
          X)
     KEY: a key

P: will hold the p

Q: will hold the q

G: will hold the g

Y: will hold the y

X: will hold the x

This function will export the DSA private key's parameters found in
     the given structure.  The new parameters will be allocated using
     ‘gnutls_malloc()’ and will be stored in the appropriate datum.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_privkey_export_ecc_raw
----------------------------------

-- Function: int gnutls_x509_privkey_export_ecc_raw
          (gnutls_x509_privkey_t KEY, gnutls_ecc_curve_t * CURVE,
          gnutls_datum_t * X, gnutls_datum_t * Y, gnutls_datum_t * K)
     KEY: a key

CURVE: will hold the curve

X: will hold the x-coordinate

Y: will hold the y-coordinate

K: will hold the private key

This function will export the ECC private key's parameters found in
     the given structure.  The new parameters will be allocated using
     ‘gnutls_malloc()’ and will be stored in the appropriate datum.

In EdDSA curves the ‘y’ parameter will be ‘NULL’ and the other
     parameters will be in the native format for the curve.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.0

gnutls_x509_privkey_export_gost_raw
-----------------------------------

-- Function: int gnutls_x509_privkey_export_gost_raw
          (gnutls_x509_privkey_t KEY, gnutls_ecc_curve_t * CURVE,
          gnutls_digest_algorithm_t * DIGEST, gnutls_gost_paramset_t *
          PARAMSET, gnutls_datum_t * X, gnutls_datum_t * Y,
          gnutls_datum_t * K)
     KEY: a key

CURVE: will hold the curve

DIGEST: will hold the digest

PARAMSET: will hold the GOST parameter set ID

X: will hold the x-coordinate

Y: will hold the y-coordinate

K: will hold the private key

This function will export the GOST private key's parameters found
     in the given structure.  The new parameters will be allocated using
     ‘gnutls_malloc()’ and will be stored in the appropriate datum.

*Note:* parameters will be stored with least significant byte
     first.  On version 3.6.3 this was incorrectly returned in
     big-endian format.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.6.3

gnutls_x509_privkey_export_pkcs8
--------------------------------

-- Function: int gnutls_x509_privkey_export_pkcs8
          (gnutls_x509_privkey_t KEY, gnutls_x509_crt_fmt_t FORMAT,
          const char * PASSWORD, unsigned int FLAGS, void * OUTPUT_DATA,
          size_t * OUTPUT_DATA_SIZE)
     KEY: Holds the key

FORMAT: the format of output params.  One of PEM or DER.

PASSWORD: the password that will be used to encrypt the key.

FLAGS: an ORed sequence of gnutls_pkcs_encrypt_flags_t

OUTPUT_DATA: will contain a private key PEM or DER encoded

OUTPUT_DATA_SIZE: holds the size of output_data (and will be
     replaced by the actual size of parameters)

The ‘password’ can be either ASCII or UTF-8 in the default PBES2
     encryption schemas, or ASCII for the PKCS12 schemas.

If the buffer provided is not long enough to hold the output, then
     *output_data_size is updated and GNUTLS_E_SHORT_MEMORY_BUFFER will
     be returned.

If the structure is PEM encoded, it will have a header of "BEGIN
     ENCRYPTED PRIVATE KEY" or "BEGIN PRIVATE KEY" if encryption is not
     used.

*Returns:* In case of failure a negative error code will be
     returned, and 0 on success.

gnutls_x509_privkey_export_rsa_raw
----------------------------------

-- Function: int gnutls_x509_privkey_export_rsa_raw
          (gnutls_x509_privkey_t KEY, gnutls_datum_t * M, gnutls_datum_t
          * E, gnutls_datum_t * D, gnutls_datum_t * P, gnutls_datum_t *
          Q, gnutls_datum_t * U)
     KEY: a key

M: will hold the modulus

E: will hold the public exponent

D: will hold the private exponent

P: will hold the first prime (p)

Q: will hold the second prime (q)

U: will hold the coefficient

This function will export the RSA private key's parameters found in
     the given structure.  The new parameters will be allocated using
     ‘gnutls_malloc()’ and will be stored in the appropriate datum.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_privkey_export_rsa_raw2
-----------------------------------

-- Function: int gnutls_x509_privkey_export_rsa_raw2
          (gnutls_x509_privkey_t KEY, gnutls_datum_t * M, gnutls_datum_t
          * E, gnutls_datum_t * D, gnutls_datum_t * P, gnutls_datum_t *
          Q, gnutls_datum_t * U, gnutls_datum_t * E1, gnutls_datum_t *
          E2)
     KEY: a key

M: will hold the modulus

E: will hold the public exponent

D: will hold the private exponent

P: will hold the first prime (p)

Q: will hold the second prime (q)

U: will hold the coefficient

E1: will hold e1 = d mod (p-1)

E2: will hold e2 = d mod (q-1)

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 2.12.0

gnutls_x509_privkey_fix
-----------------------

-- Function: int gnutls_x509_privkey_fix (gnutls_x509_privkey_t KEY)
     KEY: a key

This function will recalculate the secondary parameters in a key.
     In RSA keys, this can be the coefficient and exponent1,2.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_privkey_generate
----------------------------

-- Function: int gnutls_x509_privkey_generate (gnutls_x509_privkey_t
          KEY, gnutls_pk_algorithm_t ALGO, unsigned int BITS, unsigned
          int FLAGS)
     KEY: an initialized key

ALGO: is one of the algorithms in ‘gnutls_pk_algorithm_t’ .

BITS: the size of the parameters to generate

FLAGS: Must be zero or flags from ‘gnutls_privkey_flags_t’ .

This function will generate a random private key.  Note that this
     function must be called on an initialized private key.

Note that when generating an elliptic curve key, the curve can be
     substituted in the place of the bits parameter using the
     ‘GNUTLS_CURVE_TO_BITS()’ macro.  The input to the macro is any
     curve from ‘gnutls_ecc_curve_t’ .

For DSA keys, if the subgroup size needs to be specified check the
     ‘GNUTLS_SUBGROUP_TO_BITS()’ macro.

It is recommended to do not set the number of ‘bits’ directly, use
     ‘gnutls_sec_param_to_pk_bits()’ instead .

See also ‘gnutls_privkey_generate()’ ,
     ‘gnutls_x509_privkey_generate2()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_privkey_generate2
-----------------------------

-- Function: int gnutls_x509_privkey_generate2 (gnutls_x509_privkey_t
          KEY, gnutls_pk_algorithm_t ALGO, unsigned int BITS, unsigned
          int FLAGS, const gnutls_keygen_data_st * DATA, unsigned
          DATA_SIZE)
     KEY: a key

ALGO: is one of the algorithms in ‘gnutls_pk_algorithm_t’ .

BITS: the size of the modulus

FLAGS: Must be zero or flags from ‘gnutls_privkey_flags_t’ .

DATA: Allow specifying ‘gnutls_keygen_data_st’ types such as the
     seed to be used.

DATA_SIZE: The number of ‘data’ available.

This function will generate a random private key.  Note that this
     function must be called on an initialized private key.

Note that when generating an elliptic curve key, the curve can be
     substituted in the place of the bits parameter using the
     ‘GNUTLS_CURVE_TO_BITS()’ macro.

See also ‘gnutls_privkey_generate2()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_privkey_get_key_id
------------------------------

-- Function: int gnutls_x509_privkey_get_key_id (gnutls_x509_privkey_t
          KEY, unsigned int FLAGS, unsigned char * OUTPUT_DATA, size_t *
          OUTPUT_DATA_SIZE)
     KEY: a key

FLAGS: should be one of the flags from ‘gnutls_keyid_flags_t’

OUTPUT_DATA: will contain the key ID

OUTPUT_DATA_SIZE: holds the size of output_data (and will be
     replaced by the actual size of parameters)

This function will return a unique ID that depends on the public
     key parameters.  This ID can be used in checking whether a
     certificate corresponds to the given key.

If the buffer provided is not long enough to hold the output, then
     * ‘output_data_size’ is updated and ‘GNUTLS_E_SHORT_MEMORY_BUFFER’
     will be returned.  The output will normally be a SHA-1 hash output,
     which is 20 bytes.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_privkey_get_pk_algorithm
------------------------------------

-- Function: int gnutls_x509_privkey_get_pk_algorithm
          (gnutls_x509_privkey_t KEY)
     KEY: should contain a ‘gnutls_x509_privkey_t’ type

This function will return the public key algorithm of a private
     key.

*Returns:* a member of the ‘gnutls_pk_algorithm_t’ enumeration on
     success, or a negative error code on error.

gnutls_x509_privkey_get_pk_algorithm2
-------------------------------------

-- Function: int gnutls_x509_privkey_get_pk_algorithm2
          (gnutls_x509_privkey_t KEY, unsigned int * BITS)
     KEY: should contain a ‘gnutls_x509_privkey_t’ type

BITS: The number of bits in the public key algorithm

This function will return the public key algorithm of a private
     key.

*Returns:* a member of the ‘gnutls_pk_algorithm_t’ enumeration on
     success, or a negative error code on error.

gnutls_x509_privkey_get_seed
----------------------------

-- Function: int gnutls_x509_privkey_get_seed (gnutls_x509_privkey_t
          KEY, gnutls_digest_algorithm_t * DIGEST, void * SEED, size_t *
          SEED_SIZE)
     KEY: should contain a ‘gnutls_x509_privkey_t’ type

DIGEST: if non-NULL it will contain the digest algorithm used for
     key generation (if applicable)

SEED: where seed will be copied to

SEED_SIZE: originally holds the size of ‘seed’ , will be updated
     with actual size

This function will return the seed that was used to generate the
     given private key.  That function will succeed only if the key was
     generated as a provable key.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.5.0

gnutls_x509_privkey_get_spki
----------------------------

-- Function: int gnutls_x509_privkey_get_spki (gnutls_x509_privkey_t
          KEY, gnutls_x509_spki_t SPKI, unsigned int FLAGS)
     KEY: should contain a ‘gnutls_x509_privkey_t’ type

SPKI: a SubjectPublicKeyInfo structure of type ‘gnutls_x509_spki_t’

FLAGS: must be zero

This function will return the public key information of a private
     key.  The provided ‘spki’ must be initialized.

*Returns:* Zero on success, or a negative error code on error.

gnutls_x509_privkey_import
--------------------------

-- Function: int gnutls_x509_privkey_import (gnutls_x509_privkey_t KEY,
          const gnutls_datum_t * DATA, gnutls_x509_crt_fmt_t FORMAT)
     KEY: The data to store the parsed key

DATA: The DER or PEM encoded certificate.

FORMAT: One of DER or PEM

This function will convert the given DER or PEM encoded key to the
     native ‘gnutls_x509_privkey_t’ format.  The output will be stored
     in ‘key’ .

If the key is PEM encoded it should have a header that contains
     "PRIVATE KEY". Note that this function falls back to PKCS ‘8’
     decoding without password, if the default format fails to import.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_privkey_import2
---------------------------

DATA: The DER or PEM encoded key.

FORMAT: One of DER or PEM

PASSWORD: A password (optional)

FLAGS: an ORed sequence of gnutls_pkcs_encrypt_flags_t

This function will import the given DER or PEM encoded key, to the
     native ‘gnutls_x509_privkey_t’ format, irrespective of the input
     format.  The input format is auto-detected.

The supported formats are basic unencrypted key, PKCS8, PKCS12, and
     the openssl format.

If the provided key is encrypted but no password was given, then
     ‘GNUTLS_E_DECRYPTION_FAILED’ is returned.  Since GnuTLS 3.4.0 this
     function will utilize the PIN callbacks if any.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_privkey_import_dh_raw
---------------------------------

-- Function: int gnutls_x509_privkey_import_dh_raw
          (gnutls_x509_privkey_t KEY, const gnutls_dh_params_t PARAMS,
          const gnutls_datum_t * Y, const gnutls_datum_t * X)
     KEY: The data to store the parsed key

PARAMS: holds the ‘gnutls_dh_params_t’

Y: holds the y (optional)

X: holds the x

This function will convert the given Diffie-Hellman raw parameters
     to the native ‘gnutls_x509_privkey_t’ format.  The output will be
     stored in ‘key’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_privkey_import_dsa_raw
----------------------------------

-- Function: int gnutls_x509_privkey_import_dsa_raw
          (gnutls_x509_privkey_t KEY, const gnutls_datum_t * P, const
          gnutls_datum_t * Q, const gnutls_datum_t * G, const
          gnutls_datum_t * Y, const gnutls_datum_t * X)
     KEY: The data to store the parsed key

P: holds the p

Q: holds the q

G: holds the g

Y: holds the y (optional)

X: holds the x

This function will convert the given DSA raw parameters to the
     native ‘gnutls_x509_privkey_t’ format.  The output will be stored
     in ‘key’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_privkey_import_ecc_raw
----------------------------------

-- Function: int gnutls_x509_privkey_import_ecc_raw
          (gnutls_x509_privkey_t KEY, gnutls_ecc_curve_t CURVE, const
          gnutls_datum_t * X, const gnutls_datum_t * Y, const
          gnutls_datum_t * K)
     KEY: The data to store the parsed key

CURVE: holds the curve

X: holds the x-coordinate

Y: holds the y-coordinate

K: holds the k

This function will convert the given elliptic curve parameters to
     the native ‘gnutls_x509_privkey_t’ format.  The output will be
     stored in ‘key’ .  For EdDSA keys, the ‘x’ and ‘k’ values must be
     in the native to curve format.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.0

gnutls_x509_privkey_import_gost_raw
-----------------------------------

-- Function: int gnutls_x509_privkey_import_gost_raw
          (gnutls_x509_privkey_t KEY, gnutls_ecc_curve_t CURVE,
          gnutls_digest_algorithm_t DIGEST, gnutls_gost_paramset_t
          PARAMSET, const gnutls_datum_t * X, const gnutls_datum_t * Y,
          const gnutls_datum_t * K)
     KEY: The data to store the parsed key

CURVE: holds the curve

DIGEST: will hold the digest

PARAMSET: will hold the GOST parameter set ID

X: holds the x-coordinate

Y: holds the y-coordinate

K: holds the k (private key)

This function will convert the given GOST private key's parameters
     to the native ‘gnutls_x509_privkey_t’ format.  The output will be
     stored in ‘key’ .  ‘digest’ should be one of GNUTLS_DIG_GOSR_94,
     GNUTLS_DIG_STREEBOG_256 or GNUTLS_DIG_STREEBOG_512.  If ‘paramset’
     is set to GNUTLS_GOST_PARAMSET_UNKNOWN default one will be selected
     depending on ‘digest’ .

*Note:* parameters should be stored with least significant byte
     first.  On version 3.6.3 big-endian format was used incorrectly.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.6.3

gnutls_x509_privkey_import_openssl
----------------------------------

-- Function: int gnutls_x509_privkey_import_openssl
          (gnutls_x509_privkey_t KEY, const gnutls_datum_t * DATA, const
          char * PASSWORD)
     KEY: The data to store the parsed key

DATA: The DER or PEM encoded key.

PASSWORD: the password to decrypt the key (if it is encrypted).

This function will convert the given PEM encrypted to the native
     gnutls_x509_privkey_t format.  The output will be stored in ‘key’ .

The ‘password’ should be in ASCII. If the password is not provided
     or wrong then ‘GNUTLS_E_DECRYPTION_FAILED’ will be returned.

If the Certificate is PEM encoded it should have a header of
     "PRIVATE KEY" and the "DEK-Info" header.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_privkey_import_pkcs8
--------------------------------

-- Function: int gnutls_x509_privkey_import_pkcs8
          (gnutls_x509_privkey_t KEY, const gnutls_datum_t * DATA,
          gnutls_x509_crt_fmt_t FORMAT, const char * PASSWORD, unsigned
          int FLAGS)
     KEY: The data to store the parsed key

DATA: The DER or PEM encoded key.

FORMAT: One of DER or PEM

PASSWORD: the password to decrypt the key (if it is encrypted).

FLAGS: 0 if encrypted or GNUTLS_PKCS_PLAIN if not encrypted.

This function will convert the given DER or PEM encoded PKCS8 2.0
     encrypted key to the native gnutls_x509_privkey_t format.  The
     output will be stored in ‘key’ .  Both RSA and DSA keys can be
     imported, and flags can only be used to indicate an unencrypted
     key.

The ‘password’ can be either ASCII or UTF-8 in the default PBES2
     encryption schemas, or ASCII for the PKCS12 schemas.

If the Certificate is PEM encoded it should have a header of
     "ENCRYPTED PRIVATE KEY", or "PRIVATE KEY". You only need to specify
     the flags if the key is DER encoded, since in that case the
     encryption status cannot be auto-detected.

If the ‘GNUTLS_PKCS_PLAIN’ flag is specified and the supplied data
     are encrypted then ‘GNUTLS_E_DECRYPTION_FAILED’ is returned.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_privkey_import_rsa_raw
----------------------------------

-- Function: int gnutls_x509_privkey_import_rsa_raw
          (gnutls_x509_privkey_t KEY, const gnutls_datum_t * M, const
          gnutls_datum_t * E, const gnutls_datum_t * D, const
          gnutls_datum_t * P, const gnutls_datum_t * Q, const
          gnutls_datum_t * U)
     KEY: The data to store the parsed key

M: holds the modulus

E: holds the public exponent

D: holds the private exponent

P: holds the first prime (p)

Q: holds the second prime (q)

U: holds the coefficient

This function will convert the given RSA raw parameters to the
     native ‘gnutls_x509_privkey_t’ format.  The output will be stored
     in ‘key’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_privkey_import_rsa_raw2
-----------------------------------

-- Function: int gnutls_x509_privkey_import_rsa_raw2
          (gnutls_x509_privkey_t KEY, const gnutls_datum_t * M, const
          gnutls_datum_t * E, const gnutls_datum_t * D, const
          gnutls_datum_t * P, const gnutls_datum_t * Q, const
          gnutls_datum_t * U, const gnutls_datum_t * E1, const
          gnutls_datum_t * E2)
     KEY: The data to store the parsed key

M: holds the modulus

E: holds the public exponent

D: holds the private exponent

P: holds the first prime (p)

Q: holds the second prime (q)

U: holds the coefficient (optional)

E1: holds e1 = d mod (p-1) (optional)

E2: holds e2 = d mod (q-1) (optional)

This function will convert the given RSA raw parameters to the
     native ‘gnutls_x509_privkey_t’ format.  The output will be stored
     in ‘key’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_privkey_init
------------------------

-- Function: int gnutls_x509_privkey_init (gnutls_x509_privkey_t * KEY)
     KEY: A pointer to the type to be initialized

This function will initialize a private key type.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_privkey_sec_param
-----------------------------

-- Function: gnutls_sec_param_t gnutls_x509_privkey_sec_param
          (gnutls_x509_privkey_t KEY)
     KEY: a key

This function will return the security parameter appropriate with
     this private key.

*Returns:* On success, a valid security parameter is returned
     otherwise ‘GNUTLS_SEC_PARAM_UNKNOWN’ is returned.

*Since:* 2.12.0

gnutls_x509_privkey_set_flags
-----------------------------

-- Function: void gnutls_x509_privkey_set_flags (gnutls_x509_privkey_t
          KEY, unsigned int FLAGS)
     KEY: A key of type ‘gnutls_x509_privkey_t’

FLAGS: flags from the ‘gnutls_privkey_flags’

This function will set flags for the specified private key, after
     it is generated.  Currently this is useful for the
     ‘GNUTLS_PRIVKEY_FLAG_EXPORT_COMPAT’ to allow exporting a "provable"
     private key in backwards compatible way.

*Since:* 3.5.0

gnutls_x509_privkey_set_pin_function
------------------------------------

-- Function: void gnutls_x509_privkey_set_pin_function
          (gnutls_x509_privkey_t PRIVKEY, gnutls_pin_callback_t FN, void
          * USERDATA)
     PRIVKEY: The certificate structure

FN: the callback

USERDATA: data associated with the callback

Note that this callback is used when decrypting a key.

*Since:* 3.4.0

gnutls_x509_privkey_set_spki
----------------------------

-- Function: int gnutls_x509_privkey_set_spki (gnutls_x509_privkey_t
          KEY, const gnutls_x509_spki_t SPKI, unsigned int FLAGS)
     KEY: should contain a ‘gnutls_x509_privkey_t’ type

SPKI: a SubjectPublicKeyInfo structure of type ‘gnutls_x509_spki_t’

FLAGS: must be zero

This function will return the public key information of a private
     key.  The provided ‘spki’ must be initialized.

*Returns:* Zero on success, or a negative error code on error.

gnutls_x509_privkey_sign_data
-----------------------------

-- Function: int gnutls_x509_privkey_sign_data (gnutls_x509_privkey_t
          KEY, gnutls_digest_algorithm_t DIGEST, unsigned int FLAGS,
          const gnutls_datum_t * DATA, void * SIGNATURE, size_t *
          SIGNATURE_SIZE)
     KEY: a key

DIGEST: should be a digest algorithm

FLAGS: should be 0 for now

DATA: holds the data to be signed

SIGNATURE: will contain the signature

SIGNATURE_SIZE: holds the size of signature (and will be replaced
     by the new size)

If the buffer provided is not long enough to hold the output, then
     * ‘signature_size’ is updated and ‘GNUTLS_E_SHORT_MEMORY_BUFFER’
     will be returned.

Use ‘gnutls_x509_crt_get_preferred_hash_algorithm()’ to determine
     the hash algorithm.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_privkey_verify_params
---------------------------------

-- Function: int gnutls_x509_privkey_verify_params
          (gnutls_x509_privkey_t KEY)
     KEY: a key

This function will verify the private key parameters.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_x509_privkey_verify_seed
-------------------------------

-- Function: int gnutls_x509_privkey_verify_seed (gnutls_x509_privkey_t
          KEY, gnutls_digest_algorithm_t DIGEST, const void * SEED,
          size_t SEED_SIZE)
     KEY: should contain a ‘gnutls_x509_privkey_t’ type

DIGEST: it contains the digest algorithm used for key generation
     (if applicable)

SEED: the seed of the key to be checked with

SEED_SIZE: holds the size of ‘seed’

This function will verify that the given private key was generated
     from the provided seed.  If ‘seed’ is ‘NULL’ then the seed stored
     in the ‘key’ 's structure will be used for verification.

*Returns:* In case of a verification failure
     ‘GNUTLS_E_PRIVKEY_VERIFICATION_ERROR’ is returned, and zero or
     positive code on success.

*Since:* 3.5.0

gnutls_x509_rdn_get
-------------------

-- Function: int gnutls_x509_rdn_get (const gnutls_datum_t * IDN, char
          * BUF, size_t * BUF_SIZE)
     IDN: should contain a DER encoded RDN sequence

BUF: a pointer to a structure to hold the peer's name

BUF_SIZE: holds the size of ‘buf’

This function will return the name of the given RDN sequence.  The
     name will be in the form "C=xxxx,O=yyyy,CN=zzzz" as described in
     RFC4514.

This function does not output a fully RFC4514 compliant string, if
     that is required see ‘gnutls_x509_rdn_get2()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned, or
     ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ is returned and * ‘buf_size’ is
     updated if the provided buffer is not long enough, otherwise a
     negative error value.

gnutls_x509_rdn_get2
--------------------

-- Function: int gnutls_x509_rdn_get2 (const gnutls_datum_t * IDN,
          gnutls_datum_t * STR, unsigned FLAGS)
     IDN: should contain a DER encoded RDN sequence

STR: a datum that will hold the name

FLAGS: zero of ‘GNUTLS_X509_DN_FLAG_COMPAT’

This function will return the name of the given RDN sequence.  The
     name will be in the form "C=xxxx,O=yyyy,CN=zzzz" as described in
     RFC4514.

gnutls_x509_rdn_get_by_oid
--------------------------

-- Function: int gnutls_x509_rdn_get_by_oid (const gnutls_datum_t *
          IDN, const char * OID, unsigned INDX, unsigned int RAW_FLAG,
          void * BUF, size_t * BUF_SIZE)
     IDN: should contain a DER encoded RDN sequence

OID: an Object Identifier

INDX: In case multiple same OIDs exist in the RDN indicates which
     to send.  Use 0 for the first one.

RAW_FLAG: If non-zero then the raw DER data are returned.

BUF: a pointer to a structure to hold the peer's name

BUF_SIZE: holds the size of ‘buf’

This function will return the name of the given Object identifier,
     of the RDN sequence.  The name will be encoded using the rules from
     RFC4514.

gnutls_x509_rdn_get_oid
-----------------------

-- Function: int gnutls_x509_rdn_get_oid (const gnutls_datum_t * IDN,
          unsigned INDX, void * BUF, size_t * BUF_SIZE)
     IDN: should contain a DER encoded RDN sequence

INDX: Indicates which OID to return.  Use 0 for the first one.

BUF: a pointer to a structure to hold the peer's name OID

BUF_SIZE: holds the size of ‘buf’

This function will return the specified Object identifier, of the
     RDN sequence.

*Since:* 2.4.0

gnutls_x509_spki_deinit
-----------------------

-- Function: void gnutls_x509_spki_deinit (gnutls_x509_spki_t SPKI)
     SPKI: the SubjectPublicKeyInfo structure

This function will deinitialize a SubjectPublicKeyInfo structure.

*Since:* 3.6.0

gnutls_x509_spki_get_rsa_oaep_params
------------------------------------

-- Function: int gnutls_x509_spki_get_rsa_oaep_params
          (gnutls_x509_spki_t SPKI, gnutls_digest_algorithm_t * DIG,
          gnutls_datum_t * LABEL)
     SPKI: the SubjectPublicKeyInfo structure

DIG: if non-NULL, it will hold the digest algorithm

LABEL: if non-NULL, it will hold the pointer to label

This function will get the public key algorithm parameters of
     RSA-OAEP type.

*Returns:* zero if the parameters are present or a negative value
     on error.

*Since:* 3.8.4

gnutls_x509_spki_get_rsa_pss_params
-----------------------------------

-- Function: int gnutls_x509_spki_get_rsa_pss_params
          (gnutls_x509_spki_t SPKI, gnutls_digest_algorithm_t * DIG,
          unsigned int * SALT_SIZE)
     SPKI: the SubjectPublicKeyInfo structure

DIG: if non-NULL, it will hold the digest algorithm

SALT_SIZE: if non-NULL, it will hold the salt size

This function will get the public key algorithm parameters of
     RSA-PSS type.

*Returns:* zero if the parameters are present or a negative value
     on error.

*Since:* 3.6.0

gnutls_x509_spki_init
---------------------

-- Function: int gnutls_x509_spki_init (gnutls_x509_spki_t * SPKI)
     SPKI: A pointer to the type to be initialized

This function will initialize a SubjectPublicKeyInfo structure used
     in PKIX. The structure is used to set additional parameters in the
     public key information field of a certificate.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.6.0

gnutls_x509_spki_set_rsa_oaep_params
------------------------------------

-- Function: int gnutls_x509_spki_set_rsa_oaep_params
          (gnutls_x509_spki_t SPKI, gnutls_digest_algorithm_t DIG, const
          gnutls_datum_t * LABEL)
     SPKI: the SubjectPublicKeyInfo structure

DIG: a digest algorithm of type ‘gnutls_digest_algorithm_t’

LABEL: optional label

This function will set the public key parameters for an RSA-OAEP
     algorithm, in the SubjectPublicKeyInfo structure.

*Returns:* zero if the parameters are present or a negative value
     on error.

*Since:* 3.8.4

gnutls_x509_spki_set_rsa_pss_params
-----------------------------------

-- Function: void gnutls_x509_spki_set_rsa_pss_params
          (gnutls_x509_spki_t SPKI, gnutls_digest_algorithm_t DIG,
          unsigned int SALT_SIZE)
     SPKI: the SubjectPublicKeyInfo structure

DIG: a digest algorithm of type ‘gnutls_digest_algorithm_t’

SALT_SIZE: the size of salt string

This function will set the public key parameters for an RSA-PSS
     algorithm, in the SubjectPublicKeyInfo structure.

*Since:* 3.6.0

gnutls_x509_tlsfeatures_add
---------------------------

-- Function: int gnutls_x509_tlsfeatures_add (gnutls_x509_tlsfeatures_t
          F, unsigned int FEATURE)
     F: The TLS features

FEATURE: The feature to add

This function will append a feature to the X.509 TLS features
     extension structure.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.5.1

gnutls_x509_tlsfeatures_check_crt
---------------------------------

-- Function: unsigned gnutls_x509_tlsfeatures_check_crt
          (gnutls_x509_tlsfeatures_t FEAT, gnutls_x509_crt_t CERT)
     FEAT: a set of TLSFeatures

CERT: the certificate to be checked

This function will check the provided certificate against the
     TLSFeatures set in ‘feat’ using the RFC7633 p.4.2.2 rules.  It will
     check whether the certificate contains the features in ‘feat’ or a
     superset.

*Returns:* non-zero if the provided certificate complies, and zero
     otherwise.

*Since:* 3.5.1

gnutls_x509_tlsfeatures_deinit
------------------------------

-- Function: void gnutls_x509_tlsfeatures_deinit
          (gnutls_x509_tlsfeatures_t F)
     F: The TLS features

This function will deinitialize a X.509 TLS features extension
     structure

*Since:* 3.5.1

gnutls_x509_tlsfeatures_get
---------------------------

-- Function: int gnutls_x509_tlsfeatures_get (gnutls_x509_tlsfeatures_t
          F, unsigned IDX, unsigned int * FEATURE)
     F: The TLS features

IDX: The index of the feature to get

FEATURE: If the function succeeds, the feature will be stored in
     this variable

This function will get a feature from the X.509 TLS features
     extension structure.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.5.1

gnutls_x509_tlsfeatures_init
----------------------------

-- Function: int gnutls_x509_tlsfeatures_init
          (gnutls_x509_tlsfeatures_t * F)
     F: The TLS features

This function will initialize a X.509 TLS features extension
     structure

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.5.1

gnutls_x509_trust_list_add_cas
------------------------------

-- Function: int gnutls_x509_trust_list_add_cas
          (gnutls_x509_trust_list_t LIST, const gnutls_x509_crt_t *
          CLIST, unsigned CLIST_SIZE, unsigned int FLAGS)
     LIST: The list

CLIST: A list of CAs

CLIST_SIZE: The length of the CA list

FLAGS: flags from ‘gnutls_trust_list_flags_t’

This function will add the given certificate authorities to the
     trusted list.  The CAs in ‘clist’ must not be deinitialized during
     the lifetime of ‘list’ .

If the flag ‘GNUTLS_TL_NO_DUPLICATES’ is specified, then this
     function will ensure that no duplicates will be present in the
     final trust list.

If the flag ‘GNUTLS_TL_NO_DUPLICATE_KEY’ is specified, then this
     function will ensure that no certificates with the same key are
     present in the final trust list.

If either ‘GNUTLS_TL_NO_DUPLICATE_KEY’ or ‘GNUTLS_TL_NO_DUPLICATES’
     are given, ‘gnutls_x509_trust_list_deinit()’ must be called with
     parameter ‘all’ being 1.

*Returns:* The number of added elements is returned; that includes
     duplicate entries.

*Since:* 3.0.0

gnutls_x509_trust_list_add_crls
-------------------------------

CRL_LIST: A list of CRLs

CRL_SIZE: The length of the CRL list

FLAGS: flags from ‘gnutls_trust_list_flags_t’

VERIFICATION_FLAGS: gnutls_certificate_verify_flags if flags
     specifies GNUTLS_TL_VERIFY_CRL

This function will add the given certificate revocation lists to
     the trusted list.  The CRLs in ‘crl_list’ must not be deinitialized
     during the lifetime of ‘list’ .

If the flag ‘GNUTLS_TL_NO_DUPLICATES’ is given,
     ‘gnutls_x509_trust_list_deinit()’ must be called with parameter
     ‘all’ being 1.

If flag ‘GNUTLS_TL_VERIFY_CRL’ is given the CRLs will be verified
     before being added, and if verification fails, they will be
     skipped.

*Returns:* The number of added elements is returned; that includes
     duplicate entries.

*Since:* 3.0

gnutls_x509_trust_list_add_named_crt
------------------------------------

CERT: A certificate

NAME: An identifier for the certificate

NAME_SIZE: The size of the identifier

FLAGS: should be 0.

In principle this function can be used to set individual "server"
     certificates that are trusted by the user for that specific server
     but for no other purposes.

The certificate ‘cert’ must not be deinitialized during the
     lifetime of the ‘list’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.0.0

gnutls_x509_trust_list_add_system_trust
---------------------------------------

-- Function: int gnutls_x509_trust_list_add_system_trust
          (gnutls_x509_trust_list_t LIST, unsigned int TL_FLAGS,
          unsigned int TL_VFLAGS)
     LIST: The structure of the list

TL_FLAGS: GNUTLS_TL_*

TL_VFLAGS: gnutls_certificate_verify_flags if flags specifies
     GNUTLS_TL_VERIFY_CRL

This function adds the system's default trusted certificate
     authorities to the trusted list.  Note that on unsupported systems
     this function returns ‘GNUTLS_E_UNIMPLEMENTED_FEATURE’ .

This function implies the flag ‘GNUTLS_TL_NO_DUPLICATES’ .

*Returns:* The number of added elements or a negative error code on
     error.

*Since:* 3.1

gnutls_x509_trust_list_add_trust_dir
------------------------------------

-- Function: int gnutls_x509_trust_list_add_trust_dir
          (gnutls_x509_trust_list_t LIST, const char * CA_DIR, const
          char * CRL_DIR, gnutls_x509_crt_fmt_t TYPE, unsigned int
          TL_FLAGS, unsigned int TL_VFLAGS)
     LIST: The list

CA_DIR: A directory containing the CAs (optional)

CRL_DIR: A directory containing a list of CRLs (optional)

TYPE: The format of the certificates

TL_FLAGS: flags from ‘gnutls_trust_list_flags_t’

TL_VFLAGS: gnutls_certificate_verify_flags if flags specifies
     GNUTLS_TL_VERIFY_CRL

This function will add the given certificate authorities to the
     trusted list.  Only directories are accepted by this function.

*Returns:* The number of added elements is returned.

*Since:* 3.3.6

gnutls_x509_trust_list_add_trust_file
-------------------------------------

CA_FILE: A file containing a list of CAs (optional)

CRL_FILE: A file containing a list of CRLs (optional)

TYPE: The format of the certificates

TL_FLAGS: flags from ‘gnutls_trust_list_flags_t’

TL_VFLAGS: gnutls_certificate_verify_flags if flags specifies
     GNUTLS_TL_VERIFY_CRL

*Returns:* The number of added elements is returned.

*Since:* 3.1

gnutls_x509_trust_list_add_trust_mem
------------------------------------

CAS: A buffer containing a list of CAs (optional)

CRLS: A buffer containing a list of CRLs (optional)

TYPE: The format of the certificates

TL_FLAGS: flags from ‘gnutls_trust_list_flags_t’

TL_VFLAGS: gnutls_certificate_verify_flags if flags specifies
     GNUTLS_TL_VERIFY_CRL

This function will add the given certificate authorities to the
     trusted list.

If this function is used ‘gnutls_x509_trust_list_deinit()’ must be
     called with parameter ‘all’ being 1.

*Returns:* The number of added elements is returned.

*Since:* 3.1

gnutls_x509_trust_list_deinit
-----------------------------

-- Function: void gnutls_x509_trust_list_deinit
          (gnutls_x509_trust_list_t LIST, unsigned int ALL)
     LIST: The list to be deinitialized

ALL: if non-zero it will deinitialize all the certificates and CRLs
     contained in the structure.

This function will deinitialize a trust list.  Note that the ‘all’
     flag should be typically non-zero unless you have specified your
     certificates using ‘gnutls_x509_trust_list_add_cas()’ and you want
     to prevent them from being deinitialized by this function.

*Since:* 3.0.0

gnutls_x509_trust_list_get_issuer
---------------------------------

-- Function: int gnutls_x509_trust_list_get_issuer
          (gnutls_x509_trust_list_t LIST, gnutls_x509_crt_t CERT,
          gnutls_x509_crt_t * ISSUER, unsigned int FLAGS)
     LIST: The list

CERT: is the certificate to find issuer for

ISSUER: Will hold the issuer if any.  Should be treated as constant
     unless ‘GNUTLS_TL_GET_COPY’ is set in ‘flags’ .

FLAGS: flags from ‘gnutls_trust_list_flags_t’ (‘GNUTLS_TL_GET_COPY’
     is applicable)

This function will find the issuer of the given certificate.  If
     the flag ‘GNUTLS_TL_GET_COPY’ is specified a copy of the issuer
     will be returned which must be freed using
     ‘gnutls_x509_crt_deinit()’ .  In that case the provided ‘issuer’
     must not be initialized.

Note that the flag ‘GNUTLS_TL_GET_COPY’ is required for this
     function to work with PKCS‘11’ trust lists in a thread-safe way.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.0

gnutls_x509_trust_list_get_issuer_by_dn
---------------------------------------

-- Function: int gnutls_x509_trust_list_get_issuer_by_dn
          (gnutls_x509_trust_list_t LIST, const gnutls_datum_t * DN,
          gnutls_x509_crt_t * ISSUER, unsigned int FLAGS)
     LIST: The list

DN: is the issuer's DN

ISSUER: Will hold the issuer if any.  Should be deallocated after
     use.

FLAGS: Use zero

This function will find the issuer with the given name, and return
     a copy of the issuer, which must be freed using
     ‘gnutls_x509_crt_deinit()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.4.0

gnutls_x509_trust_list_get_issuer_by_subject_key_id
---------------------------------------------------

-- Function: int gnutls_x509_trust_list_get_issuer_by_subject_key_id
          (gnutls_x509_trust_list_t LIST, const gnutls_datum_t * DN,
          const gnutls_datum_t * SPKI, gnutls_x509_crt_t * ISSUER,
          unsigned int FLAGS)
     LIST: The list

DN: is the issuer's DN (may be ‘NULL’ )

SPKI: is the subject key ID

ISSUER: Will hold the issuer if any.  Should be deallocated after
     use.

FLAGS: Use zero

This function will find the issuer with the given name and subject
     key ID, and return a copy of the issuer, which must be freed using
     ‘gnutls_x509_crt_deinit()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.4.2

gnutls_x509_trust_list_get_ptr
------------------------------

-- Function: void * gnutls_x509_trust_list_get_ptr
          (gnutls_x509_trust_list_t TLIST)
     TLIST: is a ‘gnutls_x509_trust_list_t’ type.

Get user pointer for tlist.  Useful in callback function
     gnutls_x509_trust_list_set_getissuer_function.  This is the pointer
     set with ‘gnutls_x509_trust_list_set_ptr()’ .

*Returns:* the user given pointer from the tlist structure, or
     ‘NULL’ if it was never set.

*Since:* 3.7.0

gnutls_x509_trust_list_init
---------------------------

-- Function: int gnutls_x509_trust_list_init (gnutls_x509_trust_list_t
          * LIST, unsigned int SIZE)
     LIST: A pointer to the type to be initialized

SIZE: The size of the internal hash table.  Use (0) for default
     size.

This function will initialize an X.509 trust list structure.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.0.0

gnutls_x509_trust_list_iter_deinit
----------------------------------

-- Function: void gnutls_x509_trust_list_iter_deinit
          (gnutls_x509_trust_list_iter_t ITER)
     ITER: The iterator structure to be deinitialized

This function will deinitialize an iterator structure.

*Since:* 3.4.0

gnutls_x509_trust_list_iter_get_ca
----------------------------------

-- Function: int gnutls_x509_trust_list_iter_get_ca
          (gnutls_x509_trust_list_t LIST, gnutls_x509_trust_list_iter_t
          * ITER, gnutls_x509_crt_t * CRT)
     LIST: The list

ITER: A pointer to an iterator (initially the iterator should be
     ‘NULL’ )

CRT: where the certificate will be copied

This function obtains a certificate in the trust list and advances
     the iterator to the next certificate.  The certificate returned in
     ‘crt’ must be deallocated with ‘gnutls_x509_crt_deinit()’ .

When past the last element is accessed
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ is returned and the
     iterator is reset.

The iterator is deinitialized and reset to ‘NULL’ automatically by
     this function after iterating through all elements until
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ is returned.  If the
     iteration is aborted early, it must be manually deinitialized using
     ‘gnutls_x509_trust_list_iter_deinit()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.4.0

gnutls_x509_trust_list_remove_cas
---------------------------------

-- Function: int gnutls_x509_trust_list_remove_cas
          (gnutls_x509_trust_list_t LIST, const gnutls_x509_crt_t *
          CLIST, unsigned CLIST_SIZE)
     LIST: The list

CLIST: A list of CAs

CLIST_SIZE: The length of the CA list

This function will remove the given certificate authorities from
     the trusted list.

Note that this function can accept certificates and authorities not
     yet known.  In that case they will be kept in a separate block list
     that will be used during certificate verification.  Unlike
     ‘gnutls_x509_trust_list_add_cas()’ there is no deinitialization
     restriction for certificate list provided in this function.

*Returns:* The number of removed elements is returned.

*Since:* 3.1.10

gnutls_x509_trust_list_remove_trust_file
----------------------------------------

-- Function: int gnutls_x509_trust_list_remove_trust_file
          (gnutls_x509_trust_list_t LIST, const char * CA_FILE,
          gnutls_x509_crt_fmt_t TYPE)
     LIST: The list

CA_FILE: A file containing a list of CAs

TYPE: The format of the certificates

This function will remove the given certificate authorities from
     the trusted list, and add them into a block list when needed.  PKCS
     11 URLs are also accepted, instead of files, by this function.

See also ‘gnutls_x509_trust_list_remove_cas()’ .

*Returns:* The number of added elements is returned.

*Since:* 3.1.10

gnutls_x509_trust_list_remove_trust_mem
---------------------------------------

-- Function: int gnutls_x509_trust_list_remove_trust_mem
          (gnutls_x509_trust_list_t LIST, const gnutls_datum_t * CAS,
          gnutls_x509_crt_fmt_t TYPE)
     LIST: The list

CAS: A buffer containing a list of CAs (optional)

TYPE: The format of the certificates

This function will remove the provided certificate authorities from
     the trusted list, and add them into a block list when needed.

See also ‘gnutls_x509_trust_list_remove_cas()’ .

*Returns:* The number of removed elements is returned.

*Since:* 3.1.10

gnutls_x509_trust_list_set_getissuer_function
---------------------------------------------

-- Function: void gnutls_x509_trust_list_set_getissuer_function
          (gnutls_x509_trust_list_t TLIST,
          gnutls_x509_trust_list_getissuer_function * FUNC)
     TLIST: is a ‘gnutls_x509_trust_list_t’ type.

FUNC: is the callback function

This function sets a callback to be called when the peer's
     certificate chain is incomplete due a missing intermediate
     certificate.  The callback may provide the missing certificate for
     use during verification.

The callback's function prototype is defined in gnutls/x509.h as:

int (*callback)(gnutls_x509_trust_list_t list, const
     gnutls_x509_crt_t cert, gnutls_x509_crt_t **issuers, unsigned int
     *issuers_size);

If the callback function is provided then gnutls will call it
     during the certificate verification procedure.  The callback may
     wish to use ‘gnutls_x509_crt_get_authority_info_access()’ to get a
     URI from which to attempt to download the missing issuer
     certificate, if available.

On a successful call, the callback shall set '*issuers' and
     '*issuers_size' even if the result is empty; in that case
     '*issuers' will point to ‘NULL’ and '*issuers_size' will be 0.
     Otherwise, the '*issuers' array shall be allocated using
     ‘gnutls_x509_crt_list_import2()’ .  The ownership of both the array
     and the elements is transferred to the caller and thus the
     application does not need to maintain the memory after the call.

The callback function should return 0 if the attempt to retrieve
     the issuer certificates for 'crt' succeeded, or non-zero to
     indicate any error occurred during the attempt.  In the latter
     case, '*issuers' and '*issuers_size' are not set.

*Since:* 3.7.0

gnutls_x509_trust_list_set_ptr
------------------------------

-- Function: void gnutls_x509_trust_list_set_ptr
          (gnutls_x509_trust_list_t TLIST, void * PTR)
     TLIST: is a ‘gnutls_x509_trust_list_t’ type.

PTR: is the user pointer

This function will set (associate) the user given pointer ‘ptr’ to
     the tlist structure.  This pointer can be accessed with
     ‘gnutls_x509_trust_list_get_ptr()’ .  Useful in the callback
     function gnutls_x509_trust_list_set_getissuer_function.

*Since:* 3.7.0

gnutls_x509_trust_list_verify_crt
---------------------------------

CERT_LIST: is the certificate list to be verified

CERT_LIST_SIZE: is the certificate list size

FLAGS: Flags that may be used to change the verification algorithm.
     Use OR of the gnutls_certificate_verify_flags enumerations.

VOUTPUT: will hold the certificate verification output.

FUNC: If non-null will be called on each chain element verification
     with the output.

This function will try to verify the given certificate and return
     its status.  The ‘voutput’ parameter will hold an OR'ed sequence of
     ‘gnutls_certificate_status_t’ flags.

The details of the verification are the same as in
     ‘gnutls_x509_trust_list_verify_crt2()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.0

gnutls_x509_trust_list_verify_crt2
----------------------------------

CERT_LIST: is the certificate list to be verified

CERT_LIST_SIZE: is the certificate list size

DATA: an array of typed data

ELEMENTS: the number of data elements

FLAGS: Flags that may be used to change the verification algorithm.
     Use OR of the gnutls_certificate_verify_flags enumerations.

VOUTPUT: will hold the certificate verification output.

FUNC: If non-null will be called on each chain element verification
     with the output.

This function will attempt to verify the given certificate chain
     and return its status.  The ‘voutput’ parameter will hold an OR'ed
     sequence of ‘gnutls_certificate_status_t’ flags.

*Since:* 3.3.8

gnutls_x509_trust_list_verify_named_crt
---------------------------------------

CERT: is the certificate to be verified

NAME: is the certificate's name

NAME_SIZE: is the certificate's name size

FLAGS: Flags that may be used to change the verification algorithm.
     Use OR of the gnutls_certificate_verify_flags enumerations.

VOUTPUT: will hold the certificate verification output.

FUNC: If non-null will be called on each chain element verification
     with the output.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.0.0

File: gnutls.info,  Node: PKCS 7 API,  Next: OCSP API,  Prev: X509 certificate API,  Up: API reference

E.4 PKCS 7 API
==============

The following functions are to be used for PKCS 7 structures handling.
Their prototypes lie in ‘gnutls/pkcs7.h’.

gnutls_pkcs7_add_attr
---------------------

-- Function: int gnutls_pkcs7_add_attr (gnutls_pkcs7_attrs_t * LIST,
          const char * OID, gnutls_datum_t * DATA, unsigned FLAGS)
     LIST: A list of existing attributes or pointer to ‘NULL’ for the
     first one

OID: the OID of the attribute to be set

DATA: the raw (DER-encoded) data of the attribute to be set

FLAGS: zero or ‘GNUTLS_PKCS7_ATTR_ENCODE_OCTET_STRING’

This function will set a PKCS ‘7’ attribute in the provided list.
     If this function fails, the previous list would be deallocated.

Note that any attributes set with this function must either be DER
     or BER encoded, unless a special flag is present.

*Returns:* On success, the new list head, otherwise ‘NULL’ .

*Since:* 3.4.2

gnutls_pkcs7_attrs_deinit
-------------------------

-- Function: void gnutls_pkcs7_attrs_deinit (gnutls_pkcs7_attrs_t LIST)
     LIST: A list of existing attributes

This function will clear a PKCS ‘7’ attribute list.

*Since:* 3.4.2

gnutls_pkcs7_deinit
-------------------

-- Function: void gnutls_pkcs7_deinit (gnutls_pkcs7_t PKCS7)
     PKCS7: the type to be deinitialized

This function will deinitialize a PKCS7 type.

gnutls_pkcs7_delete_crl
-----------------------

-- Function: int gnutls_pkcs7_delete_crl (gnutls_pkcs7_t PKCS7, int
          INDX)
     PKCS7: The pkcs7 type

INDX: the index of the crl to delete

This function will delete a crl from a PKCS7 or RFC2630 crl set.
     Index starts from 0.  Returns 0 on success.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_pkcs7_delete_crt
-----------------------

-- Function: int gnutls_pkcs7_delete_crt (gnutls_pkcs7_t PKCS7, int
          INDX)
     PKCS7: The pkcs7 type

INDX: the index of the certificate to delete

This function will delete a certificate from a PKCS7 or RFC2630
     certificate set.  Index starts from 0.  Returns 0 on success.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_pkcs7_export
-------------------

-- Function: int gnutls_pkcs7_export (gnutls_pkcs7_t PKCS7,
          gnutls_x509_crt_fmt_t FORMAT, void * OUTPUT_DATA, size_t *
          OUTPUT_DATA_SIZE)
     PKCS7: The pkcs7 type

FORMAT: the format of output params.  One of PEM or DER.

OUTPUT_DATA: will contain a structure PEM or DER encoded

OUTPUT_DATA_SIZE: holds the size of output_data (and will be
     replaced by the actual size of parameters)

This function will export the pkcs7 structure to DER or PEM format.

If the buffer provided is not long enough to hold the output, then
     * ‘output_data_size’ is updated and ‘GNUTLS_E_SHORT_MEMORY_BUFFER’
     will be returned.

If the structure is PEM encoded, it will have a header of "BEGIN
     PKCS7".

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_pkcs7_export2
--------------------

-- Function: int gnutls_pkcs7_export2 (gnutls_pkcs7_t PKCS7,
          gnutls_x509_crt_fmt_t FORMAT, gnutls_datum_t * OUT)
     PKCS7: The pkcs7 type

FORMAT: the format of output params.  One of PEM or DER.

OUT: will contain a structure PEM or DER encoded

This function will export the pkcs7 structure to DER or PEM format.

The output buffer is allocated using ‘gnutls_malloc()’ .

If the structure is PEM encoded, it will have a header of "BEGIN
     PKCS7".

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.1.3

gnutls_pkcs7_get_attr
---------------------

-- Function: int gnutls_pkcs7_get_attr (gnutls_pkcs7_attrs_t LIST,
          unsigned IDX, char ** OID, gnutls_datum_t * DATA, unsigned
          FLAGS)
     LIST: A list of existing attributes or ‘NULL’ for the first one

IDX: the index of the attribute to get

OID: the OID of the attribute (read-only)

DATA: the raw data of the attribute

FLAGS: zero or ‘GNUTLS_PKCS7_ATTR_ENCODE_OCTET_STRING’

This function will get a PKCS ‘7’ attribute from the provided list.
     The OID is a constant string, but data will be allocated and must
     be deinitialized by the caller.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ is returned if there are no
     data in the current index.

*Since:* 3.4.2

gnutls_pkcs7_get_crl_count
--------------------------

-- Function: int gnutls_pkcs7_get_crl_count (gnutls_pkcs7_t PKCS7)
     PKCS7: The pkcs7 type

This function will return the number of certificates in the PKCS7
     or RFC2630 crl set.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_pkcs7_get_crl_raw
------------------------

-- Function: int gnutls_pkcs7_get_crl_raw (gnutls_pkcs7_t PKCS7,
          unsigned INDX, void * CRL, size_t * CRL_SIZE)
     PKCS7: The pkcs7 type

INDX: contains the index of the crl to extract

CRL: the contents of the crl will be copied there (may be null)

CRL_SIZE: should hold the size of the crl

This function will return a crl of the PKCS7 or RFC2630 crl set.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.  If the provided buffer is not
     long enough, then ‘crl_size’ is updated and
     ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ is returned.  After the last crl has
     been read ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ will be returned.

gnutls_pkcs7_get_crl_raw2
-------------------------

-- Function: int gnutls_pkcs7_get_crl_raw2 (gnutls_pkcs7_t PKCS7,
          unsigned INDX, gnutls_datum_t * CRL)
     PKCS7: The pkcs7 type

INDX: contains the index of the crl to extract

CRL: will contain the contents of the CRL in an allocated buffer

This function will return a DER encoded CRL of the PKCS7 or RFC2630
     crl set.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.  After the last crl has been read
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ will be returned.

*Since:* 3.4.2

gnutls_pkcs7_get_crt_count
--------------------------

-- Function: int gnutls_pkcs7_get_crt_count (gnutls_pkcs7_t PKCS7)
     PKCS7: should contain a ‘gnutls_pkcs7_t’ type

This function will return the number of certificates in the PKCS7
     or RFC2630 certificate set.

*Returns:* On success, a positive number is returned, otherwise a
     negative error value.

gnutls_pkcs7_get_crt_raw
------------------------

-- Function: int gnutls_pkcs7_get_crt_raw (gnutls_pkcs7_t PKCS7,
          unsigned INDX, void * CERTIFICATE, size_t * CERTIFICATE_SIZE)
     PKCS7: should contain a gnutls_pkcs7_t type

INDX: contains the index of the certificate to extract

CERTIFICATE: the contents of the certificate will be copied there
     (may be null)

CERTIFICATE_SIZE: should hold the size of the certificate

This function will return a certificate of the PKCS7 or RFC2630
     certificate set.

After the last certificate has been read
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ will be returned.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.  If the provided buffer is not
     long enough, then ‘certificate_size’ is updated and
     ‘GNUTLS_E_SHORT_MEMORY_BUFFER’ is returned.

gnutls_pkcs7_get_crt_raw2
-------------------------

-- Function: int gnutls_pkcs7_get_crt_raw2 (gnutls_pkcs7_t PKCS7,
          unsigned INDX, gnutls_datum_t * CERT)
     PKCS7: should contain a gnutls_pkcs7_t type

INDX: contains the index of the certificate to extract

CERT: will hold the contents of the certificate; must be
     deallocated with ‘gnutls_free()’

This function will return a certificate of the PKCS7 or RFC2630
     certificate set.

After the last certificate has been read
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ will be returned.

*Since:* 3.4.2

gnutls_pkcs7_get_embedded_data
------------------------------

-- Function: int gnutls_pkcs7_get_embedded_data (gnutls_pkcs7_t PKCS7,
          unsigned FLAGS, gnutls_datum_t * DATA)
     PKCS7: should contain a gnutls_pkcs7_t type

FLAGS: must be zero or ‘GNUTLS_PKCS7_EDATA_GET_RAW’

DATA: will hold the embedded data in the provided structure

This function will return the data embedded in the signature of the
     PKCS7 structure.  If no data are available then
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ will be returned.

The returned data must be de-allocated using ‘gnutls_free()’ .

Note, that this function returns the exact same data that are
     authenticated.  If the ‘GNUTLS_PKCS7_EDATA_GET_RAW’ flag is
     provided, the returned data will be including the wrapping
     tag/value as they are encoded in the structure.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.4.8

gnutls_pkcs7_get_embedded_data_oid
----------------------------------

-- Function: const char * gnutls_pkcs7_get_embedded_data_oid
          (gnutls_pkcs7_t PKCS7)
     PKCS7: should contain a gnutls_pkcs7_t type

This function will return the OID of the data embedded in the
     signature of the PKCS7 structure.  If no data are available then
     ‘NULL’ will be returned.  The returned value will be valid during
     the lifetime of the ‘pkcs7’ structure.

*Returns:* On success, a pointer to an OID string, ‘NULL’ on error.

*Since:* 3.5.5

gnutls_pkcs7_get_signature_count
--------------------------------

-- Function: int gnutls_pkcs7_get_signature_count (gnutls_pkcs7_t
          PKCS7)
     PKCS7: should contain a ‘gnutls_pkcs7_t’ type

This function will return the number of signatures in the PKCS7
     structure.

*Returns:* On success, a positive number is returned, otherwise a
     negative error value.

*Since:* 3.4.3

gnutls_pkcs7_get_signature_info
-------------------------------

-- Function: int gnutls_pkcs7_get_signature_info (gnutls_pkcs7_t PKCS7,
          unsigned IDX, gnutls_pkcs7_signature_info_st * INFO)
     PKCS7: should contain a ‘gnutls_pkcs7_t’ type

IDX: the index of the signature info to check

INFO: will contain the output signature

This function will return information about the signature
     identified by idx in the provided PKCS ‘7’ structure.  The
     information should be deinitialized using
     ‘gnutls_pkcs7_signature_info_deinit()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.4.2

gnutls_pkcs7_import
-------------------

-- Function: int gnutls_pkcs7_import (gnutls_pkcs7_t PKCS7, const
          gnutls_datum_t * DATA, gnutls_x509_crt_fmt_t FORMAT)
     PKCS7: The data to store the parsed PKCS7.

DATA: The DER or PEM encoded PKCS7.

FORMAT: One of DER or PEM

This function will convert the given DER or PEM encoded PKCS7 to
     the native ‘gnutls_pkcs7_t’ format.  The output will be stored in
     ‘pkcs7’ .  Any signed data that may be present inside the ‘pkcs7’
     structure, like certificates set by ‘gnutls_pkcs7_set_crt()’ , will
     be freed and overwritten by this function.

If the PKCS7 is PEM encoded it should have a header of "PKCS7".

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_pkcs7_init
-----------------

-- Function: int gnutls_pkcs7_init (gnutls_pkcs7_t * PKCS7)
     PKCS7: A pointer to the type to be initialized

This function will initialize a PKCS7 structure.  PKCS7 structures
     usually contain lists of X.509 Certificates and X.509 Certificate
     revocation lists.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_pkcs7_print
------------------

-- Function: int gnutls_pkcs7_print (gnutls_pkcs7_t PKCS7,
          gnutls_certificate_print_formats_t FORMAT, gnutls_datum_t *
          OUT)
     PKCS7: The PKCS7 struct to be printed

FORMAT: Indicate the format to use

OUT: Newly allocated datum with null terminated string.

This function will pretty print a signed PKCS ‘7’ structure,
     suitable for display to a human.

Currently the supported formats are ‘GNUTLS_CRT_PRINT_FULL’ and
     ‘GNUTLS_CRT_PRINT_COMPACT’ .

The output ‘out’ needs to be deallocated using ‘gnutls_free()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_pkcs7_print_signature_info
---------------------------------

-- Function: int gnutls_pkcs7_print_signature_info
          (gnutls_pkcs7_signature_info_st * INFO,
          gnutls_certificate_print_formats_t FORMAT, gnutls_datum_t *
          OUT)
     INFO: The PKCS7 signature info struct to be printed

FORMAT: Indicate the format to use

OUT: Newly allocated datum with null terminated string.

This function will pretty print a PKCS ‘7’ signature info
     structure, suitable for display to a human.

Currently the supported formats are ‘GNUTLS_CRT_PRINT_FULL’ and
     ‘GNUTLS_CRT_PRINT_COMPACT’ .

The output ‘out’ needs to be deallocated using ‘gnutls_free()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.6.14

gnutls_pkcs7_set_crl
--------------------

-- Function: int gnutls_pkcs7_set_crl (gnutls_pkcs7_t PKCS7,
          gnutls_x509_crl_t CRL)
     PKCS7: The pkcs7 type

CRL: the DER encoded crl to be added

This function will add a parsed CRL to the PKCS7 or RFC2630 crl
     set.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_pkcs7_set_crl_raw
------------------------

-- Function: int gnutls_pkcs7_set_crl_raw (gnutls_pkcs7_t PKCS7, const
          gnutls_datum_t * CRL)
     PKCS7: The pkcs7 type

CRL: the DER encoded crl to be added

This function will add a crl to the PKCS7 or RFC2630 crl set.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_pkcs7_set_crt
--------------------

-- Function: int gnutls_pkcs7_set_crt (gnutls_pkcs7_t PKCS7,
          gnutls_x509_crt_t CRT)
     PKCS7: The pkcs7 type

CRT: the certificate to be copied.

This function will add a parsed certificate to the PKCS7 or RFC2630
     certificate set.  This is a wrapper function over
     ‘gnutls_pkcs7_set_crt_raw()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_pkcs7_set_crt_raw
------------------------

-- Function: int gnutls_pkcs7_set_crt_raw (gnutls_pkcs7_t PKCS7, const
          gnutls_datum_t * CRT)
     PKCS7: The pkcs7 type

CRT: the DER encoded certificate to be added

This function will add a certificate to the PKCS7 or RFC2630
     certificate set.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_pkcs7_sign
-----------------

SIGNER: the certificate to sign the structure

SIGNER_KEY: the key to sign the structure

DATA: The data to be signed or ‘NULL’ if the data are already
     embedded

SIGNED_ATTRS: Any additional attributes to be included in the
     signed ones (or ‘NULL’ )

UNSIGNED_ATTRS: Any additional attributes to be included in the
     unsigned ones (or ‘NULL’ )

DIG: The digest algorithm to use for signing

FLAGS: Should be zero or one of ‘GNUTLS_PKCS7’ flags

This function will add a signature in the provided PKCS ‘7’
     structure for the provided data.  Multiple signatures can be made
     with different signers.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

*Since:* 3.4.2

gnutls_pkcs7_signature_info_deinit
----------------------------------

-- Function: void gnutls_pkcs7_signature_info_deinit
          (gnutls_pkcs7_signature_info_st * INFO)
     INFO: should point to a ‘gnutls_pkcs7_signature_info_st’ structure

This function will deinitialize any allocated value in the provided
     ‘gnutls_pkcs7_signature_info_st’ .

*Since:* 3.4.2

gnutls_pkcs7_verify
-------------------

-- Function: int gnutls_pkcs7_verify (gnutls_pkcs7_t PKCS7,
          gnutls_x509_trust_list_t TL, gnutls_typed_vdata_st * VDATA,
          unsigned int VDATA_SIZE, unsigned IDX, const gnutls_datum_t *
          DATA, unsigned FLAGS)
     PKCS7: should contain a ‘gnutls_pkcs7_t’ type

TL: A list of trusted certificates

VDATA: an array of typed data

VDATA_SIZE: the number of data elements

IDX: the index of the signature info to check

DATA: The data to be verified or ‘NULL’

FLAGS: Zero or an OR list of ‘gnutls_certificate_verify_flags’

This function will verify the provided data against the signature
     present in the SignedData of the PKCS ‘7’ structure.  If the data
     provided are NULL then the data in the encapsulatedContent field
     will be used instead.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.  A verification error results to
     a ‘GNUTLS_E_PK_SIG_VERIFY_FAILED’ and the lack of encapsulated data
     to verify to a ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ .

*Since:* 3.4.2

gnutls_pkcs7_verify_direct
--------------------------

-- Function: int gnutls_pkcs7_verify_direct (gnutls_pkcs7_t PKCS7,
          gnutls_x509_crt_t SIGNER, unsigned IDX, const gnutls_datum_t *
          DATA, unsigned FLAGS)
     PKCS7: should contain a ‘gnutls_pkcs7_t’ type

SIGNER: the certificate believed to have signed the structure

IDX: the index of the signature info to check

DATA: The data to be verified or ‘NULL’

FLAGS: Zero or an OR list of ‘gnutls_certificate_verify_flags’

Note that, unlike ‘gnutls_pkcs7_verify()’ this function does not
     verify the key purpose of the signer.  It is expected for the
     caller to verify the intended purpose of the ‘signer’ -e.g., via
     ‘gnutls_x509_crt_get_key_purpose_oid()’ , or
     ‘gnutls_x509_crt_check_key_purpose()’ .

Note also, that since GnuTLS 3.5.6 this function introduces checks
     in the end certificate ( ‘signer’ ), including time checks and key
     usage checks.

*Since:* 3.4.2

File: gnutls.info,  Node: OCSP API,  Next: PKCS 12 API,  Prev: PKCS 7 API,  Up: API reference

E.5 OCSP API
============

The following functions are for OCSP certificate status checking.  Their
prototypes lie in ‘gnutls/ocsp.h’.

gnutls_ocsp_req_add_cert
------------------------

-- Function: int gnutls_ocsp_req_add_cert (gnutls_ocsp_req_t REQ,
          gnutls_digest_algorithm_t DIGEST, gnutls_x509_crt_t ISSUER,
          gnutls_x509_crt_t CERT)
     REQ: should contain a ‘gnutls_ocsp_req_t’ type

DIGEST: hash algorithm, a ‘gnutls_digest_algorithm_t’ value

ISSUER: issuer of ‘subject’ certificate

CERT: certificate to request status for

This function will add another request to the OCSP request for a
     particular certificate.  The issuer name hash, issuer key hash, and
     serial number fields is populated as follows.  The issuer name and
     the serial number is taken from ‘cert’ .  The issuer key is taken
     from ‘issuer’ .  The hashed values will be hashed using the
     ‘digest’ algorithm, normally ‘GNUTLS_DIG_SHA1’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

gnutls_ocsp_req_add_cert_id
---------------------------

-- Function: int gnutls_ocsp_req_add_cert_id (gnutls_ocsp_req_t REQ,
          gnutls_digest_algorithm_t DIGEST, const gnutls_datum_t *
          ISSUER_NAME_HASH, const gnutls_datum_t * ISSUER_KEY_HASH,
          const gnutls_datum_t * SERIAL_NUMBER)
     REQ: should contain a ‘gnutls_ocsp_req_t’ type

DIGEST: hash algorithm, a ‘gnutls_digest_algorithm_t’ value

ISSUER_NAME_HASH: hash of issuer's DN

ISSUER_KEY_HASH: hash of issuer's public key

SERIAL_NUMBER: serial number of certificate to check

This function will add another request to the OCSP request for a
     particular certificate having the issuer name hash of
     ‘issuer_name_hash’ and issuer key hash of ‘issuer_key_hash’ (both
     hashed using ‘digest’ ) and serial number ‘serial_number’ .

The information needed corresponds to the CertID structure:

<informalexample><programlisting> CertID	::= SEQUENCE {
     hashAlgorithm AlgorithmIdentifier, issuerNameHash OCTET STRING, -
     Hash of Issuer's DN issuerKeyHash OCTET STRING, - Hash of Issuers
     public key serialNumber	CertificateSerialNumber }
     </programlisting></informalexample>

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

gnutls_ocsp_req_deinit
----------------------

-- Function: void gnutls_ocsp_req_deinit (gnutls_ocsp_req_t REQ)
     REQ: The data to be deinitialized

This function will deinitialize a OCSP request structure.

gnutls_ocsp_req_export
----------------------

-- Function: int gnutls_ocsp_req_export (gnutls_ocsp_req_const_t REQ,
          gnutls_datum_t * DATA)
     REQ: Holds the OCSP request

DATA: newly allocate buffer holding DER encoded OCSP request

This function will export the OCSP request to DER format.

*Returns:* In case of failure a negative error code will be
     returned, and 0 on success.

gnutls_ocsp_req_get_cert_id
---------------------------

-- Function: int gnutls_ocsp_req_get_cert_id (gnutls_ocsp_req_const_t
          REQ, unsigned INDX, gnutls_digest_algorithm_t * DIGEST,
          gnutls_datum_t * ISSUER_NAME_HASH, gnutls_datum_t *
          ISSUER_KEY_HASH, gnutls_datum_t * SERIAL_NUMBER)
     REQ: should contain a ‘gnutls_ocsp_req_t’ type

INDX: Specifies which extension OID to get.  Use (0) to get the
     first one.

DIGEST: output variable with ‘gnutls_digest_algorithm_t’ hash
     algorithm

ISSUER_NAME_HASH: output buffer with hash of issuer's DN

ISSUER_KEY_HASH: output buffer with hash of issuer's public key

SERIAL_NUMBER: output buffer with serial number of certificate to
     check

This function will return the certificate information of the ‘indx’
     'ed request in the OCSP request.  The information returned
     corresponds to the CertID structure:

Each of the pointers to output variables may be NULL to indicate
     that the caller is not interested in that value.

gnutls_ocsp_req_get_extension
-----------------------------

-- Function: int gnutls_ocsp_req_get_extension (gnutls_ocsp_req_const_t
          REQ, unsigned INDX, gnutls_datum_t * OID, unsigned int *
          CRITICAL, gnutls_datum_t * DATA)
     REQ: should contain a ‘gnutls_ocsp_req_t’ type

INDX: Specifies which extension OID to get.  Use (0) to get the
     first one.

OID: will hold newly allocated buffer with OID of extension, may be
     NULL

CRITICAL: output variable with critical flag, may be NULL.

DATA: will hold newly allocated buffer with extension data, may be
     NULL

This function will return all information about the requested
     extension in the OCSP request.  The information returned is the
     OID, the critical flag, and the data itself.  The extension OID
     will be stored as a string.  Any of ‘oid’ , ‘critical’ , and ‘data’
     may be NULL which means that the caller is not interested in
     getting that information back.

The caller needs to deallocate memory by calling ‘gnutls_free()’ on
     ‘oid’ ->data and ‘data’ ->data.

Since 3.7.0 ‘oid’ ->size does not account for the terminating null
     byte.

gnutls_ocsp_req_get_nonce
-------------------------

-- Function: int gnutls_ocsp_req_get_nonce (gnutls_ocsp_req_const_t
          REQ, unsigned int * CRITICAL, gnutls_datum_t * NONCE)
     REQ: should contain a ‘gnutls_ocsp_req_t’ type

CRITICAL: whether nonce extension is marked critical, or NULL

NONCE: will hold newly allocated buffer with nonce data

This function will return the OCSP request nonce extension data.

The caller needs to deallocate memory by calling ‘gnutls_free()’ on
     ‘nonce’ ->data.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

gnutls_ocsp_req_get_version
---------------------------

-- Function: int gnutls_ocsp_req_get_version (gnutls_ocsp_req_const_t
          REQ)
     REQ: should contain a ‘gnutls_ocsp_req_t’ type

This function will return the version of the OCSP request.
     Typically this is always 1 indicating version 1.

*Returns:* version of OCSP request, or a negative error code on
     error.

gnutls_ocsp_req_import
----------------------

-- Function: int gnutls_ocsp_req_import (gnutls_ocsp_req_t REQ, const
          gnutls_datum_t * DATA)
     REQ: The data to store the parsed request.

DATA: DER encoded OCSP request.

This function will convert the given DER encoded OCSP request to
     the native ‘gnutls_ocsp_req_t’ format.  The output will be stored
     in ‘req’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_ocsp_req_init
--------------------

-- Function: int gnutls_ocsp_req_init (gnutls_ocsp_req_t * REQ)
     REQ: A pointer to the type to be initialized

This function will initialize an OCSP request structure.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_ocsp_req_print
---------------------

-- Function: int gnutls_ocsp_req_print (gnutls_ocsp_req_const_t REQ,
          gnutls_ocsp_print_formats_t FORMAT, gnutls_datum_t * OUT)
     REQ: The data to be printed

FORMAT: Indicate the format to use

OUT: Newly allocated datum with (0) terminated string.

This function will pretty print a OCSP request, suitable for
     display to a human.

If the format is ‘GNUTLS_OCSP_PRINT_FULL’ then all fields of the
     request will be output, on multiple lines.

The output ‘out’ ->data needs to be deallocate using
     ‘gnutls_free()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_ocsp_req_randomize_nonce
-------------------------------

-- Function: int gnutls_ocsp_req_randomize_nonce (gnutls_ocsp_req_t
          REQ)
     REQ: should contain a ‘gnutls_ocsp_req_t’ type

This function will add or update an nonce extension to the OCSP
     request with a newly generated random value.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

gnutls_ocsp_req_set_extension
-----------------------------

-- Function: int gnutls_ocsp_req_set_extension (gnutls_ocsp_req_t REQ,
          const char * OID, unsigned int CRITICAL, const gnutls_datum_t
          * DATA)
     REQ: should contain a ‘gnutls_ocsp_req_t’ type

OID: buffer with OID of extension as a string.

CRITICAL: critical flag, normally false.

DATA: the extension data

This function will add an extension to the OCSP request.  Calling
     this function multiple times for the same OID will overwrite values
     from earlier calls.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

gnutls_ocsp_req_set_nonce
-------------------------

-- Function: int gnutls_ocsp_req_set_nonce (gnutls_ocsp_req_t REQ,
          unsigned int CRITICAL, const gnutls_datum_t * NONCE)
     REQ: should contain a ‘gnutls_ocsp_req_t’ type

CRITICAL: critical flag, normally false.

NONCE: the nonce data

This function will add an nonce extension to the OCSP request.
     Calling this function multiple times will overwrite values from
     earlier calls.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

gnutls_ocsp_resp_check_crt
--------------------------

-- Function: int gnutls_ocsp_resp_check_crt (gnutls_ocsp_resp_const_t
          RESP, unsigned int INDX, gnutls_x509_crt_t CRT)
     RESP: should contain a ‘gnutls_ocsp_resp_t’ type

INDX: Specifies response number to get.  Use (0) to get the first
     one.

CRT: The certificate to check

This function will check whether the OCSP response is about the
     provided certificate.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

*Since:* 3.1.3

gnutls_ocsp_resp_deinit
-----------------------

-- Function: void gnutls_ocsp_resp_deinit (gnutls_ocsp_resp_t RESP)
     RESP: The data to be deinitialized

This function will deinitialize a OCSP response structure.

gnutls_ocsp_resp_export
-----------------------

-- Function: int gnutls_ocsp_resp_export (gnutls_ocsp_resp_const_t
          RESP, gnutls_datum_t * DATA)
     RESP: Holds the OCSP response

DATA: newly allocate buffer holding DER encoded OCSP response

This function will export the OCSP response to DER format.

*Returns:* In case of failure a negative error code will be
     returned, and 0 on success.

gnutls_ocsp_resp_export2
------------------------

-- Function: int gnutls_ocsp_resp_export2 (gnutls_ocsp_resp_const_t
          RESP, gnutls_datum_t * DATA, gnutls_x509_crt_fmt_t FMT)
     RESP: Holds the OCSP response

DATA: newly allocate buffer holding DER or PEM encoded OCSP
     response

FMT: DER or PEM

This function will export the OCSP response to DER or PEM format.

*Returns:* In case of failure a negative error code will be
     returned, and 0 on success.

*Since:* 3.6.3

gnutls_ocsp_resp_get_certs
--------------------------

-- Function: int gnutls_ocsp_resp_get_certs (gnutls_ocsp_resp_const_t
          RESP, gnutls_x509_crt_t ** CERTS, size_t * NCERTS)
     RESP: should contain a ‘gnutls_ocsp_resp_t’ type

CERTS: newly allocated array with ‘gnutls_x509_crt_t’ certificates

NCERTS: output variable with number of allocated certs.

This function will extract the X.509 certificates found in the
     Basic OCSP Response.  The ‘certs’ output variable will hold a newly
     allocated zero-terminated array with X.509 certificates.

Every certificate in the array needs to be de-allocated with
     ‘gnutls_x509_crt_deinit()’ and the array itself must be freed using
     ‘gnutls_free()’ .

Both the ‘certs’ and ‘ncerts’ variables may be NULL. Then the
     function will work as normal but will not return the NULL:d
     information.  This can be used to get the number of certificates
     only, or to just get the certificate array without its size.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_ocsp_resp_get_extension
------------------------------

-- Function: int gnutls_ocsp_resp_get_extension
          (gnutls_ocsp_resp_const_t RESP, unsigned INDX, gnutls_datum_t
          * OID, unsigned int * CRITICAL, gnutls_datum_t * DATA)
     RESP: should contain a ‘gnutls_ocsp_resp_t’ type

INDX: Specifies which extension OID to get.  Use (0) to get the
     first one.

OID: will hold newly allocated buffer with OID of extension, may be
     NULL

CRITICAL: output variable with critical flag, may be NULL.

DATA: will hold newly allocated buffer with extension data, may be
     NULL

This function will return all information about the requested
     extension in the OCSP response.  The information returned is the
     OID, the critical flag, and the data itself.  The extension OID
     will be stored as a string.  Any of ‘oid’ , ‘critical’ , and ‘data’
     may be NULL which means that the caller is not interested in
     getting that information back.

The caller needs to deallocate memory by calling ‘gnutls_free()’ on
     ‘oid’ ->data and ‘data’ ->data.

Since 3.7.0 ‘oid’ ->size does not account for the terminating null
     byte.

gnutls_ocsp_resp_get_nonce
--------------------------

-- Function: int gnutls_ocsp_resp_get_nonce (gnutls_ocsp_resp_const_t
          RESP, unsigned int * CRITICAL, gnutls_datum_t * NONCE)
     RESP: should contain a ‘gnutls_ocsp_resp_t’ type

CRITICAL: whether nonce extension is marked critical

NONCE: will hold newly allocated buffer with nonce data

This function will return the Basic OCSP Response nonce extension
     data.

The caller needs to deallocate memory by calling ‘gnutls_free()’ on
     ‘nonce’ ->data.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

gnutls_ocsp_resp_get_produced
-----------------------------

-- Function: time_t gnutls_ocsp_resp_get_produced
          (gnutls_ocsp_resp_const_t RESP)
     RESP: should contain a ‘gnutls_ocsp_resp_t’ type

This function will return the time when the OCSP response was
     signed.

*Returns:* signing time, or (time_t)-1 on error.

gnutls_ocsp_resp_get_responder
------------------------------

-- Function: int gnutls_ocsp_resp_get_responder
          (gnutls_ocsp_resp_const_t RESP, gnutls_datum_t * DN)
     RESP: should contain a ‘gnutls_ocsp_resp_t’ type

DN: newly allocated buffer with name

This function will extract the name of the Basic OCSP Response in
     the provided buffer.  The name will be in the form
     "C=xxxx,O=yyyy,CN=zzzz" as described in RFC2253.  The output string
     will be ASCII or UTF-8 encoded, depending on the certificate data.

If the responder ID is not a name but a hash, this function will
     return zero and the ‘dn’ elements will be set to ‘NULL’ .

The caller needs to deallocate memory by calling ‘gnutls_free()’ on
     ‘dn’ ->data.

This function does not output a fully RFC4514 compliant string, if
     that is required see ‘gnutls_ocsp_resp_get_responder2()’ .

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.  When no data exist it
     will return success and set ‘dn’ elements to zero.

gnutls_ocsp_resp_get_responder2
-------------------------------

-- Function: int gnutls_ocsp_resp_get_responder2
          (gnutls_ocsp_resp_const_t RESP, gnutls_datum_t * DN, unsigned
          FLAGS)
     RESP: should contain a ‘gnutls_ocsp_resp_t’ type

DN: newly allocated buffer with name

FLAGS: zero or ‘GNUTLS_X509_DN_FLAG_COMPAT’

If the responder ID is not a name but a hash, this function will
     return zero and the ‘dn’ elements will be set to ‘NULL’ .

The caller needs to deallocate memory by calling ‘gnutls_free()’ on
     ‘dn’ ->data.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.  When no data exist it
     will return ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ .

gnutls_ocsp_resp_get_responder_raw_id
-------------------------------------

-- Function: int gnutls_ocsp_resp_get_responder_raw_id
          (gnutls_ocsp_resp_const_t RESP, unsigned TYPE, gnutls_datum_t
          * RAW)
     RESP: should contain a ‘gnutls_ocsp_resp_t’ type

TYPE: should be ‘GNUTLS_OCSP_RESP_ID_KEY’ or
     ‘GNUTLS_OCSP_RESP_ID_DN’

RAW: newly allocated buffer with the raw ID

This function will extract the raw key (or DN) ID of the Basic OCSP
     Response in the provided buffer.  If the responder ID is not a key
     ID then this function will return
     ‘GNUTLS_E_REQUESTED_DATA_NOT_AVAILABLE’ .

The caller needs to deallocate memory by calling ‘gnutls_free()’ on
     ‘dn’ ->data.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error code is returned.

gnutls_ocsp_resp_get_response
-----------------------------

-- Function: int gnutls_ocsp_resp_get_response
          (gnutls_ocsp_resp_const_t RESP, gnutls_datum_t *
          RESPONSE_TYPE_OID, gnutls_datum_t * RESPONSE)
     RESP: should contain a ‘gnutls_ocsp_resp_t’ type

RESPONSE_TYPE_OID: newly allocated output buffer with response type
     OID

RESPONSE: newly allocated output buffer with DER encoded response

This function will extract the response type OID in and the
     response data from an OCSP response.  Normally the
     ‘response_type_oid’ is always "1.3.6.1.5.5.7.48.1.1" which means
     the ‘response’ should be decoded as a Basic OCSP Response, but
     technically other response types could be used.

This function is typically only useful when you want to extract the
     response type OID of an response for diagnostic purposes.
     Otherwise ‘gnutls_ocsp_resp_import()’ will decode the basic OCSP
     response part and the caller need not worry about that aspect.

Since 3.7.0 ‘response_type_oid’ ->size does not account for the
     terminating null byte.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_ocsp_resp_get_signature
------------------------------

-- Function: int gnutls_ocsp_resp_get_signature
          (gnutls_ocsp_resp_const_t RESP, gnutls_datum_t * SIG)
     RESP: should contain a ‘gnutls_ocsp_resp_t’ type

SIG: newly allocated output buffer with signature data

This function will extract the signature field of a OCSP response.

*Returns:* On success, ‘GNUTLS_E_SUCCESS’ (0) is returned,
     otherwise a negative error value.

gnutls_ocsp_resp_get_signature_algorithm
----------------------------------------

-- Function: int gnutls_ocsp_resp_get_signature_algorithm
          (gnutls_ocsp_resp_const_t RESP)
     RESP: should contain a ‘gnutls_ocsp_resp_t’ type

This function will return a value of the ‘gnutls_sign_algorithm_t’
     enumeration that is the signature algorithm that has been used to
     sign the OCSP response.

*Returns:* a ‘gnutls_sign_algorithm_t’ value, or a negative error
     code on error.

gnutls_ocsp_resp_get_single
---------------------------