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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="#return_values">RETURN VALUES</a></li>
	<li><a href="#notes">NOTES</a></li>
	<li><a href="#see_also">SEE ALSO</a></li>
	<li><a href="#history">HISTORY</a></li>
	<li><a href="#copyright">COPYRIGHT</a></li>
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<h1><a name="name">NAME</a></h1>
<p>RAND_DRBG_generate,
RAND_DRBG_bytes
- generate random bytes using the given drbg instance</p>
<p>
</p>
<hr />
<h1><a name="synopsis">SYNOPSIS</a></h1>
<pre>
 #include &lt;openssl/rand_drbg.h&gt;</pre>
<pre>
 int RAND_DRBG_generate(RAND_DRBG *drbg,
                        unsigned char *out, size_t outlen,
                        int prediction_resistance,
                        const unsigned char *adin, size_t adinlen);</pre>
<pre>
 int RAND_DRBG_bytes(RAND_DRBG *drbg,
                     unsigned char *out, size_t outlen);</pre>
<p>
</p>
<hr />
<h1><a name="description">DESCRIPTION</a></h1>
<p><code>RAND_DRBG_generate()</code> generates <strong>outlen</strong> random bytes using the given
DRBG instance <strong>drbg</strong> and stores them in the buffer at <strong>out</strong>.</p>
<p>Before generating the output, the DRBG instance checks whether the maximum
number of generate requests (<em>reseed interval</em>) or the maximum timespan
(<em>reseed time interval</em>) since its last seeding have been reached.
If this is the case, the DRBG reseeds automatically.
Additionally, an immediate reseeding can be requested by setting the
<strong>prediction_resistance</strong> flag to 1. See NOTES section for more details.</p>
<p>The caller can optionally provide additional data to be used for reseeding
by passing a pointer <strong>adin</strong> to a buffer of length <strong>adinlen</strong>.
This additional data is mixed into the internal state of the random
generator but does not contribute to the entropy count.
The additional data can be omitted by setting <strong>adin</strong> to NULL and
<strong>adinlen</strong> to 0;</p>
<p><code>RAND_DRBG_bytes()</code> generates <strong>outlen</strong> random bytes using the given
DRBG instance <strong>drbg</strong> and stores them in the buffer at <strong>out</strong>.
This function is a wrapper around the <code>RAND_DRBG_generate()</code> call,
which collects some additional data from low entropy sources
(e.g., a high resolution timer) and calls
RAND_DRBG_generate(drbg, out, outlen, 0, adin, adinlen).</p>
<p>
</p>
<hr />
<h1><a name="return_values">RETURN VALUES</a></h1>
<p><code>RAND_DRBG_generate()</code> and <code>RAND_DRBG_bytes()</code> return 1 on success,
and 0 on failure.</p>
<p>
</p>
<hr />
<h1><a name="notes">NOTES</a></h1>
<p>The <em>reseed interval</em> and <em>reseed time interval</em> of the <strong>drbg</strong> are set to
reasonable default values, which in general do not have to be adjusted.
If necessary, they can be changed using <em>RAND_DRBG_set_reseed_interval(3)</em>
and <em>RAND_DRBG_set_reseed_time_interval(3)</em>, respectively.</p>
<p>A request for prediction resistance can only be satisfied by pulling fresh
entropy from one of the approved entropy sources listed in section 5.5.2 of
[NIST SP 800-90C].
Since the default DRBG implementation does not have access to such an approved
entropy source, a request for prediction resistance will always fail.
In other words, prediction resistance is currently not supported yet by the DRBG.</p>
<p>
</p>
<hr />
<h1><a name="see_also">SEE ALSO</a></h1>
<p><em>RAND_bytes(3)</em>,
<em>RAND_DRBG_set_reseed_interval(3)</em>,
<em>RAND_DRBG_set_reseed_time_interval(3)</em>,
<em>RAND_DRBG(7)</em></p>
<p>
</p>
<hr />
<h1><a name="history">HISTORY</a></h1>
<p>The RAND_DRBG functions were added in OpenSSL 1.1.1.</p>
<p>
</p>
<hr />
<h1><a name="copyright">COPYRIGHT</a></h1>
<p>Copyright 2017-2019 The OpenSSL Project Authors. All Rights Reserved.</p>
<p>Licensed under the OpenSSL license (the &quot;License&quot;).  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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