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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<!-- This manual is last updated 25 May 2013 for version
3.2.1 of GnuTLS.

Copyright (C) 2001-2013 Free Software Foundation, Inc.\\
Copyright (C) 2001-2013 Nikos Mavrogiannopoulos

Permission is granted to copy, distribute and/or modify this document
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<h1 class="settitle" align="center">GnuTLS 3.2.1</h1>


















<a name="SEC_Contents"></a>
<h2 class="contents-heading">Table of Contents</h2>

<div class="contents">

<ul class="no-bullet">
  <li><a name="toc-Preface-1" href="Preface.html#Preface">1 Preface</a></li>
  <li><a name="toc-Introduction-to-GnuTLS-1" href="Introduction-to-GnuTLS.html#Introduction-to-GnuTLS">2 Introduction to GnuTLS</a>
  <ul class="no-bullet">
    <li><a name="toc-Downloading-and-installing-1" href="Downloading-and-installing.html#Downloading-and-installing">2.1 Downloading and installing</a></li>
    <li><a name="toc-Overview" href="Document-overview.html#Document-overview">2.2 Overview</a></li>
  </ul></li>
  <li><a name="toc-Introduction-to-TLS-and-DTLS" href="Introduction-to-TLS.html#Introduction-to-TLS">3 Introduction to <acronym>TLS</acronym> and <acronym>DTLS</acronym></a>
  <ul class="no-bullet">
    <li><a name="toc-TLS-layers-1" href="TLS-layers.html#TLS-layers">3.1 TLS layers</a></li>
    <li><a name="toc-The-transport-layer-1" href="The-transport-layer.html#The-transport-layer">3.2 The transport layer</a></li>
    <li><a name="toc-The-TLS-record-protocol-1" href="The-TLS-record-protocol.html#The-TLS-record-protocol">3.3 The TLS record protocol</a>
    <ul class="no-bullet">
      <li><a name="toc-Encryption-algorithms-used-in-the-record-layer-1" href="Encryption-algorithms-used-in-the-record-layer.html#Encryption-algorithms-used-in-the-record-layer">3.3.1 Encryption algorithms used in the record layer</a></li>
      <li><a name="toc-Compression-algorithms-used-in-the-record-layer-1" href="Compression-algorithms-used-in-the-record-layer.html#Compression-algorithms-used-in-the-record-layer">3.3.2 Compression algorithms used in the record layer</a></li>
      <li><a name="toc-Weaknesses-and-countermeasures-1" href="Weaknesses-and-countermeasures.html#Weaknesses-and-countermeasures">3.3.3 Weaknesses and countermeasures</a></li>
      <li><a name="toc-On-record-padding" href="On-Record-Padding.html#On-Record-Padding">3.3.4 On record padding</a></li>
    </ul></li>
    <li><a name="toc-The-TLS-alert-protocol" href="The-TLS-Alert-Protocol.html#The-TLS-Alert-Protocol">3.4 The TLS alert protocol</a></li>
    <li><a name="toc-The-TLS-handshake-protocol" href="The-TLS-Handshake-Protocol.html#The-TLS-Handshake-Protocol">3.5 The TLS handshake protocol</a>
    <ul class="no-bullet">
      <li><a name="toc-TLS-ciphersuites" href="TLS-Cipher-Suites.html#TLS-Cipher-Suites">3.5.1 TLS ciphersuites</a></li>
      <li><a name="toc-Authentication-1" href="Authentication.html#Authentication">3.5.2 Authentication</a></li>
      <li><a name="toc-Client-authentication" href="Client-Authentication.html#Client-Authentication">3.5.3 Client authentication</a></li>
      <li><a name="toc-Resuming-sessions" href="Resuming-Sessions.html#Resuming-Sessions">3.5.4 Resuming sessions</a></li>
    </ul></li>
    <li><a name="toc-TLS-extensions" href="TLS-Extensions.html#TLS-Extensions">3.6 TLS extensions</a>
    <ul class="no-bullet">
      <li><a name="toc-Maximum-fragment-length-negotiation-1" href="Maximum-fragment-length-negotiation.html#Maximum-fragment-length-negotiation">3.6.1 Maximum fragment length negotiation</a></li>
      <li><a name="toc-Server-name-indication-1" href="Server-name-indication.html#Server-name-indication">3.6.2 Server name indication</a></li>
      <li><a name="toc-Session-tickets-1" href="Session-tickets.html#Session-tickets">3.6.3 Session tickets</a></li>
      <li><a name="toc-HeartBeat-1" href="HeartBeat.html#HeartBeat">3.6.4 HeartBeat</a></li>
      <li><a name="toc-Safe-renegotiation-1" href="Safe-renegotiation.html#Safe-renegotiation">3.6.5 Safe renegotiation</a></li>
      <li><a name="toc-OCSP-status-request-1" href="OCSP-status-request.html#OCSP-status-request">3.6.6 OCSP status request</a></li>
      <li><a name="toc-SRTP-1" href="SRTP.html#SRTP">3.6.7 SRTP</a></li>
      <li><a name="toc-Application-Layer-Protocol-Negotiation-_0028ALPN_0029-1" href="Application-Layer-Protocol-Negotiation-_0028ALPN_0029.html#Application-Layer-Protocol-Negotiation-_0028ALPN_0029">3.6.8 Application Layer Protocol Negotiation (ALPN)</a></li>
    </ul></li>
    <li><a name="toc-How-to-use-TLS-in-application-protocols-1" href="How-to-use-TLS-in-application-protocols.html#How-to-use-TLS-in-application-protocols">3.7 How to use <acronym>TLS</acronym> in application protocols</a>
    <ul class="no-bullet">
      <li><a name="toc-Separate-ports-1" href="Separate-ports.html#Separate-ports">3.7.1 Separate ports</a></li>
      <li><a name="toc-Upward-negotiation-1" href="Upward-negotiation.html#Upward-negotiation">3.7.2 Upward negotiation</a></li>
    </ul></li>
    <li><a name="toc-On-SSL-2-and-older-protocols-1" href="On-SSL-2-and-older-protocols.html#On-SSL-2-and-older-protocols">3.8 On SSL 2 and older protocols</a></li>
  </ul></li>
  <li><a name="toc-Authentication-methods-1" href="Authentication-methods.html#Authentication-methods">4 Authentication methods</a>
  <ul class="no-bullet">
    <li><a name="toc-Certificate-authentication-1" href="Certificate-authentication.html#Certificate-authentication">4.1 Certificate authentication</a>
    <ul class="no-bullet">
      <li><a name="toc-X_002e509-certificates-1" href="X_002e509-certificates.html#X_002e509-certificates">4.1.1 <acronym>X.509</acronym> certificates</a>
      <ul class="no-bullet">
        <li><a name="toc-X_002e509-certificate-structure-1" href="X_002e509-certificate-structure.html#X_002e509-certificate-structure">4.1.1.1 <acronym>X.509</acronym> certificate structure</a></li>
        <li><a name="toc-Importing-an-X_002e509-certificate-1" href="Importing-an-X_002e509-certificate.html#Importing-an-X_002e509-certificate">4.1.1.2 Importing an X.509 certificate</a></li>
        <li><a name="toc-X_002e509-distinguished-names-1" href="X_002e509-distinguished-names.html#X_002e509-distinguished-names">4.1.1.3 X.509 distinguished names</a></li>
        <li><a name="toc-Accessing-public-and-private-keys" href="X_002e509-public-and-private-keys.html#X_002e509-public-and-private-keys">4.1.1.4 Accessing public and private keys</a></li>
        <li><a name="toc-Verifying-X_002e509-certificate-paths-1" href="Verifying-X_002e509-certificate-paths.html#Verifying-X_002e509-certificate-paths">4.1.1.5 Verifying <acronym>X.509</acronym> certificate paths</a></li>
        <li><a name="toc-Verifying-a-certificate-in-the-context-of-TLS-session-1" href="Verifying-a-certificate-in-the-context-of-TLS-session.html#Verifying-a-certificate-in-the-context-of-TLS-session">4.1.1.6 Verifying a certificate in the context of TLS session</a></li>
      </ul></li>
      <li><a name="toc-OpenPGP-certificates-1" href="OpenPGP-certificates.html#OpenPGP-certificates">4.1.2 <acronym>OpenPGP</acronym> certificates</a>
      <ul class="no-bullet">
        <li><a name="toc-OpenPGP-certificate-structure" href="OpenPGP-certificates.html#OpenPGP-certificate-structure">4.1.2.1 <acronym>OpenPGP</acronym> certificate structure</a></li>
        <li><a name="toc-Verifying-an-OpenPGP-certificate" href="OpenPGP-certificates.html#Verifying-an-OpenPGP-certificate">4.1.2.2 Verifying an <acronym>OpenPGP</acronym> certificate</a></li>
        <li><a name="toc-Verifying-a-certificate-in-the-context-of-a-TLS-session" href="OpenPGP-certificates.html#Verifying-a-certificate-in-the-context-of-a-TLS-session">4.1.2.3 Verifying a certificate in the context of a TLS session</a></li>
      </ul></li>
      <li><a name="toc-Advanced-certificate-verification-1" href="Advanced-certificate-verification.html#Advanced-certificate-verification">4.1.3 Advanced certificate verification</a>
      <ul class="no-bullet">
        <li><a name="toc-Verifying-a-certificate-using-trust-on-first-use-authentication-1" href="Verifying-a-certificate-using-trust-on-first-use-authentication.html#Verifying-a-certificate-using-trust-on-first-use-authentication">4.1.3.1 Verifying a certificate using trust on first use authentication</a></li>
        <li><a name="toc-Verifying-a-certificate-using-DANE-_0028DNSSEC_0029" href="Verifying-a-certificate-using-DANE.html#Verifying-a-certificate-using-DANE">4.1.3.2 Verifying a certificate using DANE (DNSSEC)</a></li>
      </ul></li>
      <li><a name="toc-Digital-signatures-1" href="Digital-signatures.html#Digital-signatures">4.1.4 Digital signatures</a>
      <ul class="no-bullet">
        <li><a name="toc-Trading-security-for-interoperability" href="Digital-signatures.html#Trading-security-for-interoperability">4.1.4.1 Trading security for interoperability</a></li>
      </ul></li>
    </ul></li>
    <li><a name="toc-More-on-certificate-authentication-1" href="More-on-certificate-authentication.html#More-on-certificate-authentication">4.2 More on certificate authentication</a>
    <ul class="no-bullet">
      <li><a name="toc-PKCS-_002310-certificate-requests" href="PKCS-10-certificate-requests.html#PKCS-10-certificate-requests">4.2.1 <acronym>PKCS</acronym> #10 certificate requests</a></li>
      <li><a name="toc-PKIX-certificate-revocation-lists-1" href="PKIX-certificate-revocation-lists.html#PKIX-certificate-revocation-lists">4.2.2 PKIX certificate revocation lists</a></li>
      <li><a name="toc-OCSP-certificate-status-checking-1" href="OCSP-certificate-status-checking.html#OCSP-certificate-status-checking">4.2.3 <acronym>OCSP</acronym> certificate status checking</a></li>
      <li><a name="toc-Managing-encrypted-keys-1" href="Managing-encrypted-keys.html#Managing-encrypted-keys">4.2.4 Managing encrypted keys</a></li>
      <li><a name="toc-Invoking-certtool" href="certtool-Invocation.html#certtool-Invocation">4.2.5 Invoking certtool</a></li>
      <li><a name="toc-Invoking-ocsptool" href="ocsptool-Invocation.html#ocsptool-Invocation">4.2.6 Invoking ocsptool</a></li>
      <li><a name="toc-Invoking-danetool" href="danetool-Invocation.html#danetool-Invocation">4.2.7 Invoking danetool</a></li>
    </ul></li>
    <li><a name="toc-Shared_002dkey-and-anonymous-authentication-1" href="Shared_002dkey-and-anonymous-authentication.html#Shared_002dkey-and-anonymous-authentication">4.3 Shared-key and anonymous authentication</a>
    <ul class="no-bullet">
      <li><a name="toc-SRP-authentication-1" href="SRP-authentication.html#SRP-authentication">4.3.1 SRP authentication</a>
      <ul class="no-bullet">
        <li><a name="toc-Authentication-using-SRP-1" href="Authentication-using-SRP.html#Authentication-using-SRP">4.3.1.1 Authentication using <acronym>SRP</acronym></a></li>
        <li><a name="toc-Invoking-srptool" href="srptool-Invocation.html#srptool-Invocation">4.3.1.2 Invoking srptool</a></li>
      </ul></li>
      <li><a name="toc-PSK-authentication-1" href="PSK-authentication.html#PSK-authentication">4.3.2 PSK authentication</a>
      <ul class="no-bullet">
        <li><a name="toc-Authentication-using-PSK-1" href="Authentication-using-PSK.html#Authentication-using-PSK">4.3.2.1 Authentication using <acronym>PSK</acronym></a></li>
        <li><a name="toc-Invoking-psktool" href="psktool-Invocation.html#psktool-Invocation">4.3.2.2 Invoking psktool</a></li>
      </ul></li>
      <li><a name="toc-Anonymous-authentication-1" href="Anonymous-authentication.html#Anonymous-authentication">4.3.3 Anonymous authentication</a></li>
    </ul></li>
    <li><a name="toc-Selecting-an-appropriate-authentication-method-1" href="Selecting-an-appropriate-authentication-method.html#Selecting-an-appropriate-authentication-method">4.4 Selecting an appropriate authentication method</a>
    <ul class="no-bullet">
      <li><a name="toc-Two-peers-with-an-out_002dof_002dband-channel" href="Selecting-an-appropriate-authentication-method.html#Two-peers-with-an-out_002dof_002dband-channel">4.4.1 Two peers with an out-of-band channel</a></li>
      <li><a name="toc-Two-peers-without-an-out_002dof_002dband-channel" href="Selecting-an-appropriate-authentication-method.html#Two-peers-without-an-out_002dof_002dband-channel">4.4.2 Two peers without an out-of-band channel</a></li>
      <li><a name="toc-Two-peers-and-a-trusted-third-party" href="Selecting-an-appropriate-authentication-method.html#Two-peers-and-a-trusted-third-party">4.4.3 Two peers and a trusted third party</a></li>
    </ul></li>
  </ul></li>
  <li><a name="toc-Hardware-security-modules-and-abstract-key-types-1" href="Hardware-security-modules-and-abstract-key-types.html#Hardware-security-modules-and-abstract-key-types">5 Hardware security modules and abstract key types</a>
  <ul class="no-bullet">
    <li><a name="toc-Abstract-key-types-1" href="Abstract-key-types.html#Abstract-key-types">5.1 Abstract key types</a>
    <ul class="no-bullet">
      <li><a name="toc-Public-keys" href="Abstract-public-keys.html#Abstract-public-keys">5.1.1 Public keys</a></li>
      <li><a name="toc-Private-keys" href="Abstract-private-keys.html#Abstract-private-keys">5.1.2 Private keys</a></li>
      <li><a name="toc-Operations-1" href="Operations.html#Operations">5.1.3 Operations</a></li>
    </ul></li>
    <li><a name="toc-Smart-cards-and-HSMs-1" href="Smart-cards-and-HSMs.html#Smart-cards-and-HSMs">5.2 Smart cards and HSMs</a>
    <ul class="no-bullet">
      <li><a name="toc-Initialization-1" href="PKCS11-Initialization.html#PKCS11-Initialization">5.2.1 Initialization</a></li>
      <li><a name="toc-Accessing-objects-that-require-a-PIN-1" href="Accessing-objects-that-require-a-PIN.html#Accessing-objects-that-require-a-PIN">5.2.2 Accessing objects that require a PIN</a></li>
      <li><a name="toc-Reading-objects-1" href="Reading-objects.html#Reading-objects">5.2.3 Reading objects</a></li>
      <li><a name="toc-Writing-objects-1" href="Writing-objects.html#Writing-objects">5.2.4 Writing objects</a></li>
      <li><a name="toc-Using-a-PKCS-_002311-token-with-TLS" href="Using-a-PKCS11-token-with-TLS.html#Using-a-PKCS11-token-with-TLS">5.2.5 Using a <acronym>PKCS</acronym> #11 token with TLS</a></li>
      <li><a name="toc-Invoking-p11tool" href="p11tool-Invocation.html#p11tool-Invocation">5.2.6 Invoking p11tool</a></li>
    </ul></li>
    <li><a name="toc-Trusted-Platform-Module-_0028TPM_0029" href="Trusted-Platform-Module.html#Trusted-Platform-Module">5.3 Trusted Platform Module (TPM)</a>
    <ul class="no-bullet">
      <li><a name="toc-Keys-in-TPM-1" href="Keys-in-TPM.html#Keys-in-TPM">5.3.1 Keys in TPM</a></li>
      <li><a name="toc-Key-generation-1" href="Key-generation.html#Key-generation">5.3.2 Key generation</a></li>
      <li><a name="toc-Using-keys-1" href="Using-keys.html#Using-keys">5.3.3 Using keys</a></li>
      <li><a name="toc-Invoking-tpmtool" href="tpmtool-Invocation.html#tpmtool-Invocation">5.3.4 Invoking tpmtool</a></li>
    </ul></li>
  </ul></li>
  <li><a name="toc-How-to-use-GnuTLS-in-applications-1" href="How-to-use-GnuTLS-in-applications.html#How-to-use-GnuTLS-in-applications">6 How to use <acronym>GnuTLS</acronym> in applications</a>
  <ul class="no-bullet">
    <li><a name="toc-Introduction" href="Introduction-to-the-library.html#Introduction-to-the-library">6.1 Introduction</a>
    <ul class="no-bullet">
      <li><a name="toc-General-idea-1" href="General-idea.html#General-idea">6.1.1 General idea</a></li>
      <li><a name="toc-Error-handling-1" href="Error-handling.html#Error-handling">6.1.2 Error handling</a></li>
      <li><a name="toc-Common-types-1" href="Common-types.html#Common-types">6.1.3 Common types</a></li>
      <li><a name="toc-Debugging-and-auditing-1" href="Debugging-and-auditing.html#Debugging-and-auditing">6.1.4 Debugging and auditing</a></li>
      <li><a name="toc-Thread-safety-1" href="Thread-safety.html#Thread-safety">6.1.5 Thread safety</a></li>
      <li><a name="toc-Callback-functions-1" href="Callback-functions.html#Callback-functions">6.1.6 Callback functions</a></li>
    </ul></li>
    <li><a name="toc-Preparation-1" href="Preparation.html#Preparation">6.2 Preparation</a>
    <ul class="no-bullet">
      <li><a name="toc-Headers-1" href="Headers.html#Headers">6.2.1 Headers</a></li>
      <li><a name="toc-Initialization-2" href="Initialization.html#Initialization">6.2.2 Initialization</a></li>
      <li><a name="toc-Version-check-1" href="Version-check.html#Version-check">6.2.3 Version check</a></li>
      <li><a name="toc-Building-the-source-1" href="Building-the-source.html#Building-the-source">6.2.4 Building the source</a></li>
    </ul></li>
    <li><a name="toc-Session-initialization-1" href="Session-initialization.html#Session-initialization">6.3 Session initialization</a></li>
    <li><a name="toc-Associating-the-credentials-1" href="Associating-the-credentials.html#Associating-the-credentials">6.4 Associating the credentials</a>
    <ul class="no-bullet">
      <li><a name="toc-Certificates" href="Certificate-credentials.html#Certificate-credentials">6.4.1 Certificates</a></li>
      <li><a name="toc-SRP" href="SRP-credentials.html#SRP-credentials">6.4.2 SRP</a></li>
      <li><a name="toc-PSK" href="PSK-credentials.html#PSK-credentials">6.4.3 PSK</a></li>
      <li><a name="toc-Anonymous" href="Anonymous-credentials.html#Anonymous-credentials">6.4.4 Anonymous</a></li>
    </ul></li>
    <li><a name="toc-Setting-up-the-transport-layer-1" href="Setting-up-the-transport-layer.html#Setting-up-the-transport-layer">6.5 Setting up the transport layer</a>
    <ul class="no-bullet">
      <li><a name="toc-Asynchronous-operation-1" href="Asynchronous-operation.html#Asynchronous-operation">6.5.1 Asynchronous operation</a></li>
      <li><a name="toc-DTLS-sessions-1" href="DTLS-sessions.html#DTLS-sessions">6.5.2 DTLS sessions</a></li>
    </ul></li>
    <li><a name="toc-TLS-handshake-1" href="TLS-handshake.html#TLS-handshake">6.6 TLS handshake</a></li>
    <li><a name="toc-Data-transfer-and-termination-1" href="Data-transfer-and-termination.html#Data-transfer-and-termination">6.7 Data transfer and termination</a></li>
    <li><a name="toc-Buffered-data-transfer-1" href="Buffered-data-transfer.html#Buffered-data-transfer">6.8 Buffered data transfer</a></li>
    <li><a name="toc-Handling-alerts-1" href="Handling-alerts.html#Handling-alerts">6.9 Handling alerts</a></li>
    <li><a name="toc-Priority-strings" href="Priority-Strings.html#Priority-Strings">6.10 Priority strings</a></li>
    <li><a name="toc-Selecting-cryptographic-key-sizes-1" href="Selecting-cryptographic-key-sizes.html#Selecting-cryptographic-key-sizes">6.11 Selecting cryptographic key sizes</a></li>
    <li><a name="toc-Advanced-topics-1" href="Advanced-topics.html#Advanced-topics">6.12 Advanced topics</a>
    <ul class="no-bullet">
      <li><a name="toc-Session-resumption-1" href="Session-resumption.html#Session-resumption">6.12.1 Session resumption</a></li>
      <li><a name="toc-Certificate-verification-1" href="Certificate-verification.html#Certificate-verification">6.12.2 Certificate verification</a>
      <ul class="no-bullet">
        <li><a name="toc-Trust-on-first-use" href="Certificate-verification.html#Trust-on-first-use">6.12.2.1 Trust on first use</a></li>
        <li><a name="toc-DANE-verification" href="Certificate-verification.html#DANE-verification">6.12.2.2 DANE verification</a></li>
      </ul></li>
      <li><a name="toc-Parameter-generation-1" href="Parameter-generation.html#Parameter-generation">6.12.3 Parameter generation</a></li>
      <li><a name="toc-Keying-material-exporters" href="Keying-Material-Exporters.html#Keying-Material-Exporters">6.12.4 Keying material exporters</a></li>
      <li><a name="toc-Channel-bindings" href="Channel-Bindings.html#Channel-Bindings">6.12.5 Channel bindings</a></li>
      <li><a name="toc-Interoperability-1" href="Interoperability.html#Interoperability">6.12.6 Interoperability</a></li>
      <li><a name="toc-Compatibility-with-the-OpenSSL-library-1" href="Compatibility-with-the-OpenSSL-library.html#Compatibility-with-the-OpenSSL-library">6.12.7 Compatibility with the OpenSSL library</a></li>
    </ul></li>
  </ul></li>
  <li><a name="toc-GnuTLS-application-examples-1" href="GnuTLS-application-examples.html#GnuTLS-application-examples">7 GnuTLS application examples</a>
  <ul class="no-bullet">
    <li><a name="toc-Client-examples-1" href="Client-examples.html#Client-examples">7.1 Client examples</a>
    <ul class="no-bullet">
      <li><a name="toc-Simple-client-example-with-X_002e509-certificate-support-1" href="Simple-client-example-with-X_002e509-certificate-support.html#Simple-client-example-with-X_002e509-certificate-support">7.1.1 Simple client example with <acronym>X.509</acronym> certificate support</a></li>
      <li><a name="toc-Simple-client-example-with-SSH_002dstyle-certificate-verification-1" href="Simple-client-example-with-SSH_002dstyle-certificate-verification.html#Simple-client-example-with-SSH_002dstyle-certificate-verification">7.1.2 Simple client example with SSH-style certificate verification</a></li>
      <li><a name="toc-Simple-client-example-with-anonymous-authentication-1" href="Simple-client-example-with-anonymous-authentication.html#Simple-client-example-with-anonymous-authentication">7.1.3 Simple client example with anonymous authentication</a></li>
      <li><a name="toc-Simple-datagram-TLS-client-example" href="Simple-Datagram-TLS-client-example.html#Simple-Datagram-TLS-client-example">7.1.4 Simple datagram <acronym>TLS</acronym> client example</a></li>
      <li><a name="toc-Obtaining-session-information-1" href="Obtaining-session-information.html#Obtaining-session-information">7.1.5 Obtaining session information</a></li>
      <li><a name="toc-Using-a-callback-to-select-the-certificate-to-use-1" href="Using-a-callback-to-select-the-certificate-to-use.html#Using-a-callback-to-select-the-certificate-to-use">7.1.6 Using a callback to select the certificate to use</a></li>
      <li><a name="toc-Verifying-a-certificate-1" href="Verifying-a-certificate.html#Verifying-a-certificate">7.1.7 Verifying a certificate</a></li>
      <li><a name="toc-Using-a-smart-card-with-TLS" href="Client-using-a-smart-card-with-TLS.html#Client-using-a-smart-card-with-TLS">7.1.8 Using a smart card with TLS</a></li>
      <li><a name="toc-Client-with-resume-capability-example" href="Client-with-Resume-capability-example.html#Client-with-Resume-capability-example">7.1.9 Client with resume capability example</a></li>
      <li><a name="toc-Simple-client-example-with-SRP-authentication-1" href="Simple-client-example-with-SRP-authentication.html#Simple-client-example-with-SRP-authentication">7.1.10 Simple client example with <acronym>SRP</acronym> authentication</a></li>
      <li><a name="toc-Simple-client-example-using-the-C_002b_002b-API" href="Simple-client-example-in-C_002b_002b.html#Simple-client-example-in-C_002b_002b">7.1.11 Simple client example using the C++ API</a></li>
      <li><a name="toc-Helper-functions-for-TCP-connections-1" href="Helper-functions-for-TCP-connections.html#Helper-functions-for-TCP-connections">7.1.12 Helper functions for TCP connections</a></li>
      <li><a name="toc-Helper-functions-for-UDP-connections-1" href="Helper-functions-for-UDP-connections.html#Helper-functions-for-UDP-connections">7.1.13 Helper functions for UDP connections</a></li>
    </ul></li>
    <li><a name="toc-Server-examples-1" href="Server-examples.html#Server-examples">7.2 Server examples</a>
    <ul class="no-bullet">
      <li><a name="toc-Echo-server-with-X_002e509-authentication-1" href="Echo-server-with-X_002e509-authentication.html#Echo-server-with-X_002e509-authentication">7.2.1 Echo server with <acronym>X.509</acronym> authentication</a></li>
      <li><a name="toc-Echo-server-with-OpenPGP-authentication-1" href="Echo-server-with-OpenPGP-authentication.html#Echo-server-with-OpenPGP-authentication">7.2.2 Echo server with <acronym>OpenPGP</acronym> authentication</a></li>
      <li><a name="toc-Echo-server-with-SRP-authentication-1" href="Echo-server-with-SRP-authentication.html#Echo-server-with-SRP-authentication">7.2.3 Echo server with <acronym>SRP</acronym> authentication</a></li>
      <li><a name="toc-Echo-server-with-anonymous-authentication-1" href="Echo-server-with-anonymous-authentication.html#Echo-server-with-anonymous-authentication">7.2.4 Echo server with anonymous authentication</a></li>
      <li><a name="toc-DTLS-echo-server-with-X_002e509-authentication-1" href="DTLS-echo-server-with-X_002e509-authentication.html#DTLS-echo-server-with-X_002e509-authentication">7.2.5 DTLS echo server with <acronym>X.509</acronym> authentication</a></li>
    </ul></li>
    <li><a name="toc-OCSP-example-1" href="OCSP-example.html#OCSP-example">7.3 OCSP example</a></li>
    <li><a name="toc-Miscellaneous-examples-1" href="Miscellaneous-examples.html#Miscellaneous-examples">7.4 Miscellaneous examples</a>
    <ul class="no-bullet">
      <li><a name="toc-Checking-for-an-alert-1" href="Checking-for-an-alert.html#Checking-for-an-alert">7.4.1 Checking for an alert</a></li>
      <li><a name="toc-X_002e509-certificate-parsing-example-1" href="X_002e509-certificate-parsing-example.html#X_002e509-certificate-parsing-example">7.4.2 <acronym>X.509</acronym> certificate parsing example</a></li>
      <li><a name="toc-Listing-the-ciphersuites-in-a-priority-string-1" href="Listing-the-ciphersuites-in-a-priority-string.html#Listing-the-ciphersuites-in-a-priority-string">7.4.3 Listing the ciphersuites in a priority string</a></li>
      <li><a name="toc-PKCS-_002312-structure-generation-example" href="PKCS12-structure-generation-example.html#PKCS12-structure-generation-example">7.4.4 PKCS #12 structure generation example</a></li>
    </ul></li>
    <li><a name="toc-XSSL-examples-1" href="XSSL-examples.html#XSSL-examples">7.5 XSSL examples</a>
    <ul class="no-bullet">
      <li><a name="toc-Example-client-with-X_002e509-certificate-authentication-1" href="Example-client-with-X_002e509-certificate-authentication.html#Example-client-with-X_002e509-certificate-authentication">7.5.1 Example client with X.509 certificate authentication</a></li>
      <li><a name="toc-Example-client-with-X_002e509-certificate-authentication-and-TOFU-1" href="Example-client-with-X_002e509-certificate-authentication-and-TOFU.html#Example-client-with-X_002e509-certificate-authentication-and-TOFU">7.5.2 Example client with X.509 certificate authentication and TOFU</a></li>
    </ul></li>
  </ul></li>
  <li><a name="toc-Using-GnuTLS-as-a-cryptographic-library-1" href="Using-GnuTLS-as-a-cryptographic-library.html#Using-GnuTLS-as-a-cryptographic-library">8 Using GnuTLS as a cryptographic library</a>
  <ul class="no-bullet">
    <li><a name="toc-Symmetric-algorithms-1" href="Symmetric-algorithms.html#Symmetric-algorithms">8.1 Symmetric algorithms</a></li>
    <li><a name="toc-Public-key-algorithms-1" href="Public-key-algorithms.html#Public-key-algorithms">8.2 Public key algorithms</a></li>
    <li><a name="toc-Hash-and-HMAC-functions-1" href="Hash-and-HMAC-functions.html#Hash-and-HMAC-functions">8.3 Hash and HMAC functions</a></li>
    <li><a name="toc-Random-number-generation-1" href="Random-number-generation.html#Random-number-generation">8.4 Random number generation</a></li>
  </ul></li>
  <li><a name="toc-Other-included-programs-1" href="Other-included-programs.html#Other-included-programs">9 Other included programs</a>
  <ul class="no-bullet">
    <li><a name="toc-Invoking-gnutls_002dcli" href="gnutls_002dcli-Invocation.html#gnutls_002dcli-Invocation">9.1 Invoking gnutls-cli</a></li>
    <li><a name="toc-Invoking-gnutls_002dserv" href="gnutls_002dserv-Invocation.html#gnutls_002dserv-Invocation">9.2 Invoking gnutls-serv</a></li>
    <li><a name="toc-Invoking-gnutls_002dcli_002ddebug" href="gnutls_002dcli_002ddebug-Invocation.html#gnutls_002dcli_002ddebug-Invocation">9.3 Invoking gnutls-cli-debug</a></li>
  </ul></li>
  <li><a name="toc-Internal-Architecture-of-GnuTLS" href="Internal-architecture-of-GnuTLS.html#Internal-architecture-of-GnuTLS">10 Internal Architecture of GnuTLS</a>
  <ul class="no-bullet">
    <li><a name="toc-The-TLS-Protocol-1" href="The-TLS-Protocol.html#The-TLS-Protocol">10.1 The TLS Protocol</a></li>
    <li><a name="toc-TLS-Handshake-Protocol-1" href="TLS-Handshake-Protocol.html#TLS-Handshake-Protocol">10.2 TLS Handshake Protocol</a></li>
    <li><a name="toc-TLS-Authentication-Methods-1" href="TLS-Authentication-Methods.html#TLS-Authentication-Methods">10.3 TLS Authentication Methods</a></li>
    <li><a name="toc-TLS-Extension-Handling-1" href="TLS-Extension-Handling.html#TLS-Extension-Handling">10.4 TLS Extension Handling</a></li>
    <li><a name="toc-Cryptographic-Backend-1" href="Cryptographic-Backend.html#Cryptographic-Backend">10.5 Cryptographic Backend</a></li>
  </ul></li>
  <li><a name="toc-Upgrading-from-previous-versions-1" href="Upgrading-from-previous-versions.html#Upgrading-from-previous-versions">Appendix A Upgrading from previous versions</a></li>
  <li><a name="toc-Support-1" href="Support.html#Support">Appendix B Support</a>
  <ul class="no-bullet">
    <li><a name="toc-Getting-Help" href="Getting-help.html#Getting-help">B.1 Getting Help</a></li>
    <li><a name="toc-Commercial-Support-1" href="Commercial-Support.html#Commercial-Support">B.2 Commercial Support</a></li>
    <li><a name="toc-Bug-Reports-1" href="Bug-Reports.html#Bug-Reports">B.3 Bug Reports</a></li>
    <li><a name="toc-Contributing-1" href="Contributing.html#Contributing">B.4 Contributing</a></li>
    <li><a name="toc-Certification-1" href="Certification.html#Certification">B.5 Certification</a></li>
  </ul></li>
  <li><a name="toc-Error-Codes-and-Descriptions" href="Error-codes.html#Error-codes">Appendix C Error Codes and Descriptions</a></li>
  <li><a name="toc-Supported-Ciphersuites" href="Supported-ciphersuites.html#Supported-ciphersuites">Appendix D Supported Ciphersuites</a></li>
  <li><a name="toc-API-reference-1" href="API-reference.html#API-reference">Appendix E API reference</a>
  <ul class="no-bullet">
    <li><a name="toc-Core-TLS-API-1" href="Core-TLS-API.html#Core-TLS-API">E.1 Core TLS API</a></li>
    <li><a name="toc-High-level-TLS-API-1" href="High-level-TLS-API.html#High-level-TLS-API">E.2 High level TLS API</a></li>
    <li><a name="toc-Datagram-TLS-API-1" href="Datagram-TLS-API.html#Datagram-TLS-API">E.3 Datagram TLS API</a></li>
    <li><a name="toc-X_002e509-certificate-API" href="X509-certificate-API.html#X509-certificate-API">E.4 <acronym>X.509</acronym> certificate API</a></li>
    <li><a name="toc-OCSP-API-1" href="OCSP-API.html#OCSP-API">E.5 <acronym>OCSP</acronym> API</a></li>
    <li><a name="toc-OpenPGP-API-1" href="OpenPGP-API.html#OpenPGP-API">E.6 <acronym>OpenPGP</acronym> API</a></li>
    <li><a name="toc-PKCS-12-API-1" href="PKCS-12-API.html#PKCS-12-API">E.7 PKCS 12 API</a></li>
    <li><a name="toc-Hardware-token-via-PKCS-11-API" href="PKCS-11-API.html#PKCS-11-API">E.8 Hardware token via PKCS 11 API</a></li>
    <li><a name="toc-TPM-API-1" href="TPM-API.html#TPM-API">E.9 TPM API</a></li>
    <li><a name="toc-Abstract-key-API-1" href="Abstract-key-API.html#Abstract-key-API">E.10 Abstract key API</a></li>
    <li><a name="toc-DANE-API-1" href="DANE-API.html#DANE-API">E.11 DANE API</a></li>
    <li><a name="toc-Cryptographic-API-1" href="Cryptographic-API.html#Cryptographic-API">E.12 Cryptographic API</a></li>
    <li><a name="toc-Compatibility-API-1" href="Compatibility-API.html#Compatibility-API">E.13 Compatibility API</a></li>
  </ul></li>
  <li><a name="toc-Copying-Information-1" href="Copying-Information.html#Copying-Information">Appendix F Copying Information</a></li>
  <li><a name="toc-Bibliography-1" href="Bibliography.html#Bibliography">Bibliography</a></li>
  <li><a name="toc-Function-and-Data-Index-1" href="Function-and-Data-Index.html#Function-and-Data-Index">Function and Data Index</a></li>
  <li><a name="toc-Concept-Index-1" href="Concept-Index.html#Concept-Index">Concept Index</a></li>
</ul>
</div>


<a name="Top"></a>
<div class="header">
<p>
Next: <a href="Preface.html#Preface" accesskey="n" rel="next">Preface</a>, Up: <a href="../dir/index.html" accesskey="u" rel="up">(dir)</a> &nbsp; [<a href="#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Function-and-Data-Index.html#Function-and-Data-Index" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="GnuTLS"></a>
<h1 class="top">GnuTLS</h1>

<p>This manual is last updated 25 May 2013 for version
3.2.1 of GnuTLS.
</p>
<p>Copyright &copy; 2001-2013 Free Software Foundation, Inc.\\
Copyright &copy; 2001-2013 Nikos Mavrogiannopoulos
</p>
<blockquote>
<p>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 no Back-Cover Texts.  A
copy of the license is included in the section entitled &ldquo;GNU Free
Documentation License&rdquo;.
</p></blockquote>


<table class="menu" border="0" cellspacing="0">
<tr><td align="left" valign="top">&bull; <a href="Preface.html#Preface" accesskey="1">Preface</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Introduction-to-GnuTLS.html#Introduction-to-GnuTLS" accesskey="2">Introduction to GnuTLS</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Introduction-to-TLS.html#Introduction-to-TLS" accesskey="3">Introduction to TLS</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Authentication-methods.html#Authentication-methods" accesskey="4">Authentication methods</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Hardware-security-modules-and-abstract-key-types.html#Hardware-security-modules-and-abstract-key-types" accesskey="5">Hardware security modules and abstract key types</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="How-to-use-GnuTLS-in-applications.html#How-to-use-GnuTLS-in-applications" accesskey="6">How to use GnuTLS in applications</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="GnuTLS-application-examples.html#GnuTLS-application-examples" accesskey="7">GnuTLS application examples</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Using-GnuTLS-as-a-cryptographic-library.html#Using-GnuTLS-as-a-cryptographic-library" accesskey="8">Using GnuTLS as a cryptographic library</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Other-included-programs.html#Other-included-programs" accesskey="9">Other included programs</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">&bull; <a href="Internal-architecture-of-GnuTLS.html#Internal-architecture-of-GnuTLS">Internal architecture of GnuTLS</a>:</td><td>&nbsp;&nbsp;</td><td align="left" valign="top">
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