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<a name="TLS-handshake"></a>
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<p>
Next: <a href="Data-transfer-and-termination.html#Data-transfer-and-termination" accesskey="n" rel="next">Data transfer and termination</a>, Previous: <a href="Setting-up-the-transport-layer.html#Setting-up-the-transport-layer" accesskey="p" rel="prev">Setting up the transport layer</a>, Up: <a href="How-to-use-GnuTLS-in-applications.html#How-to-use-GnuTLS-in-applications" accesskey="u" rel="up">How to use GnuTLS in applications</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="TLS-handshake-1"></a>
<h3 class="section">6.6 TLS handshake</h3>
<p>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.
</p>
<dl>
<dt><a name="index-gnutls_005fhandshake"></a>Function: <em>int</em> <strong>gnutls_handshake</strong> <em>(gnutls_session_t <var>session</var>)</em></dt>
<dd><p><var>session</var>: is a <code>gnutls_session_t</code> structure.
</p>
<p>This function does the handshake of the TLS/SSL protocol, and
initializes the TLS connection.
</p>
<p>This function will fail if any problem is encountered, and will
return a negative error code. In case of a client, if the client
has asked to resume a session, but the server couldn’t, then a
full handshake will be performed.
</p>
<p>The non-fatal errors such as <code>GNUTLS_E_AGAIN</code> and
<code>GNUTLS_E_INTERRUPTED</code> interrupt the handshake procedure, which
should be resumed later. Call this function again, until it
returns 0; cf. <code>gnutls_record_get_direction()</code> and
<code>gnutls_error_is_fatal()</code> .
</p>
<p>If this function is called by a server after a rehandshake request
then <code>GNUTLS_E_GOT_APPLICATION_DATA</code> or
<code>GNUTLS_E_WARNING_ALERT_RECEIVED</code> may be returned. Note that these
are non fatal errors, only in the specific case of a rehandshake.
Their meaning is that the client rejected the rehandshake request or
in the case of <code>GNUTLS_E_GOT_APPLICATION_DATA</code> it might also mean that
some data were pending.
</p>
<p><strong>Returns:</strong> <code>GNUTLS_E_SUCCESS</code> on success, otherwise a negative error code.
</p></dd></dl>
<dl>
<dt><a name="index-gnutls_005fhandshake_005fset_005ftimeout"></a>Function: <em>void</em> <strong>gnutls_handshake_set_timeout</strong> <em>(gnutls_session_t <var>session</var>, unsigned int <var>ms</var>)</em></dt>
<dd><p><var>session</var>: is a <code>gnutls_session_t</code> structure.
</p>
<p><var>ms</var>: is a timeout value in milliseconds
</p>
<p>This function sets the timeout for the handshake process
to the provided value. Use an <code>ms</code> value of zero to disable
timeout.
</p>
<p>Note that in order for the timeout to be enforced
<code>gnutls_transport_set_pull_timeout_function()</code> must be set
(it is set by default in most systems).
</p></dd></dl>
<p>The handshake process doesn’t ensure the verification
of the peer’s identity. When certificates are in use,
this can be done, either after the handshake is complete, or during
the handshake if <a href="Core-TLS-API.html#gnutls_005fcertificate_005fset_005fverify_005ffunction">gnutls_certificate_set_verify_function</a>
has been used. In both cases the <a href="Core-TLS-API.html#gnutls_005fcertificate_005fverify_005fpeers2">gnutls_certificate_verify_peers2</a> function can be
used to verify the peer’s certificate (see <a href="Certificate-authentication.html#Certificate-authentication">Certificate authentication</a>
for more information).
</p>
<dl compact="compact">
<dt><code><var>int</var> <a href="Core-TLS-API.html#gnutls_005fcertificate_005fverify_005fpeers2">gnutls_certificate_verify_peers2</a> (gnutls_session_t <var>session</var>, unsigned int * <var>status</var>)</code></dt>
</dl>
<hr>
<div class="header">
<p>
Next: <a href="Data-transfer-and-termination.html#Data-transfer-and-termination" accesskey="n" rel="next">Data transfer and termination</a>, Previous: <a href="Setting-up-the-transport-layer.html#Setting-up-the-transport-layer" accesskey="p" rel="prev">Setting up the transport layer</a>, Up: <a href="How-to-use-GnuTLS-in-applications.html#How-to-use-GnuTLS-in-applications" accesskey="u" rel="up">How to use GnuTLS in applications</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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