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<title>GnuTLS 3.5.4: Certificate authentication</title>
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<a name="Certificate-authentication"></a>
<div class="header">
<p>
Next: <a href="More-on-certificate-authentication.html#More-on-certificate-authentication" accesskey="n" rel="next">More on certificate authentication</a>, Up: <a href="Authentication-methods.html#Authentication-methods" accesskey="u" rel="up">Authentication methods</a> [<a href="index.html#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="Certificate-authentication-1"></a>
<h3 class="section">4.1 Certificate authentication</h3>
<a name="index-certificate-authentication"></a>
<p>The most known authentication method of <acronym>TLS</acronym> are certificates.
The PKIX [<em>PKIX</em>] public key infrastructure is daily used by anyone
using a browser today. <acronym>GnuTLS</acronym> supports both
<acronym>X.509</acronym> certificates [<em>PKIX</em>] and <acronym>OpenPGP</acronym>
certificates using a common API.
</p>
<p>The key exchange algorithms supported by certificate authentication are
shown in <a href="#tab_003akey_002dexchange">Table 4.1</a>.
</p>
<div class="float"><a name="tab_003akey_002dexchange"></a>
<table>
<thead><tr><th width="20%">Key exchange</th><th width="70%">Description</th></tr></thead>
<tr><td width="20%">RSA</td><td width="70%">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.</td></tr>
<tr><td width="20%">DHE_RSA</td><td width="70%">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.</td></tr>
<tr><td width="20%">ECDHE_RSA</td><td width="70%">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.</td></tr>
<tr><td width="20%">DHE_DSS</td><td width="70%">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).</td></tr>
<tr><td width="20%">ECDHE_ECDSA</td><td width="70%">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.</td></tr>
</table>
<div class="float-caption"><p><strong>Table 4.1: </strong>Supported key exchange algorithms.</p></div></div>
<table class="menu" border="0" cellspacing="0">
<tr><td align="left" valign="top">• <a href="X_002e509-certificates.html#X_002e509-certificates" accesskey="1">X.509 certificates</a>:</td><td> </td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">• <a href="OpenPGP-certificates.html#OpenPGP-certificates" accesskey="2">OpenPGP certificates</a>:</td><td> </td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">• <a href="Advanced-certificate-verification.html#Advanced-certificate-verification" accesskey="3">Advanced certificate verification</a>:</td><td> </td><td align="left" valign="top">
</td></tr>
<tr><td align="left" valign="top">• <a href="Digital-signatures.html#Digital-signatures" accesskey="4">Digital signatures</a>:</td><td> </td><td align="left" valign="top">
</td></tr>
</table>
<hr>
<div class="header">
<p>
Next: <a href="More-on-certificate-authentication.html#More-on-certificate-authentication" accesskey="n" rel="next">More on certificate authentication</a>, Up: <a href="Authentication-methods.html#Authentication-methods" accesskey="u" rel="up">Authentication methods</a> [<a href="index.html#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>
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