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<title>SSL_get_client_random</title>
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<ul>
<li><a href="#name">NAME</a></li>
<li><a href="#synopsis">SYNOPSIS</a></li>
<li><a href="#description">DESCRIPTION</a></li>
<li><a href="#notes">NOTES</a></li>
<li><a href="#return_values">RETURN VALUES</a></li>
<li><a href="#see_also">SEE ALSO</a></li>
<li><a href="#copyright">COPYRIGHT</a></li>
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<h1><a name="name">NAME</a></h1>
<p>SSL_get_client_random,
SSL_get_server_random,
SSL_SESSION_get_master_key,
SSL_SESSION_set1_master_key
- get internal TLS/SSL random values and get/set master key</p>
<p>
</p>
<hr />
<h1><a name="synopsis">SYNOPSIS</a></h1>
<pre>
#include <openssl/ssl.h></pre>
<pre>
size_t SSL_get_client_random(const SSL *ssl, unsigned char *out, size_t outlen);
size_t SSL_get_server_random(const SSL *ssl, unsigned char *out, size_t outlen);
size_t SSL_SESSION_get_master_key(const SSL_SESSION *session,
unsigned char *out, size_t outlen);
int SSL_SESSION_set1_master_key(SSL_SESSION *sess, const unsigned char *in,
size_t len);</pre>
<p>
</p>
<hr />
<h1><a name="description">DESCRIPTION</a></h1>
<p><code>SSL_get_client_random()</code> extracts the random value sent from the client
to the server during the initial SSL/TLS handshake. It copies as many
bytes as it can of this value into the buffer provided in <strong>out</strong>,
which must have at least <strong>outlen</strong> bytes available. It returns the
total number of bytes that were actually copied. If <strong>outlen</strong> is
zero, <code>SSL_get_client_random()</code> copies nothing, and returns the
total size of the client_random value.</p>
<p><code>SSL_get_server_random()</code> behaves the same, but extracts the random value
sent from the server to the client during the initial SSL/TLS handshake.</p>
<p><code>SSL_SESSION_get_master_key()</code> behaves the same, but extracts the master
secret used to guarantee the security of the SSL/TLS session. This one
can be dangerous if misused; see NOTES below.</p>
<p>SSL_SESSION_set1_master_key() sets the master key value associated with the
SSL_SESSION <strong>sess</strong>. For example, this could be used to set up a session based
PSK (see <em>SSL_CTX_set_psk_use_session_callback(3)</em>). The master key of length
<strong>len</strong> should be provided at <strong>in</strong>. The supplied master key is copied by the
function, so the caller is responsible for freeing and cleaning any memory
associated with <strong>in</strong>. The caller must ensure that the length of the key is
suitable for the ciphersuite associated with the SSL_SESSION.</p>
<p>
</p>
<hr />
<h1><a name="notes">NOTES</a></h1>
<p>You probably shouldn't use these functions.</p>
<p>These functions expose internal values from the TLS handshake, for
use in low-level protocols. You probably should not use them, unless
you are implementing something that needs access to the internal protocol
details.</p>
<p>Despite the names of <code>SSL_get_client_random()</code> and <code>SSL_get_server_random()</code>, they
ARE NOT random number generators. Instead, they return the mostly-random values that
were already generated and used in the TLS protocol. Using them
in place of <code>RAND_bytes()</code> would be grossly foolish.</p>
<p>The security of your TLS session depends on keeping the master key secret:
do not expose it, or any information about it, to anybody.
If you need to calculate another secret value that depends on the master
secret, you should probably use <code>SSL_export_keying_material()</code> instead, and
forget that you ever saw these functions.</p>
<p>In current versions of the TLS protocols, the length of client_random
(and also server_random) is always SSL3_RANDOM_SIZE bytes. Support for
other outlen arguments to the SSL_get_*_random() functions is provided
in case of the unlikely event that a future version or variant of TLS
uses some other length there.</p>
<p>Finally, though the "client_random" and "server_random" values are called
"random", many TLS implementations will generate four bytes of those
values based on their view of the current time.</p>
<p>
</p>
<hr />
<h1><a name="return_values">RETURN VALUES</a></h1>
<p>SSL_SESSION_set1_master_key() returns 1 on success or 0 on failure.</p>
<p>For the other functions, if <strong>outlen</strong> is greater than 0 then these functions
return the number of bytes actually copied, which will be less than or equal to
<strong>outlen</strong>. If <strong>outlen</strong> is 0 then these functions return the maximum number
of bytes they would copy -- that is, the length of the underlying field.</p>
<p>
</p>
<hr />
<h1><a name="see_also">SEE ALSO</a></h1>
<p><em>ssl(7)</em>,
<em>RAND_bytes(3)</em>,
<em>SSL_export_keying_material(3)</em>,
<em>SSL_CTX_set_psk_use_session_callback(3)</em></p>
<p>
</p>
<hr />
<h1><a name="copyright">COPYRIGHT</a></h1>
<p>Copyright 2015-2017 The OpenSSL Project Authors. All Rights Reserved.</p>
<p>Licensed under the OpenSSL license (the "License"). You may not use
this file except in compliance with the License. You can obtain a copy
in the file LICENSE in the source distribution or at
<a href="https://www.openssl.org/source/license.html">https://www.openssl.org/source/license.html</a>.</p>
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