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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="#removed_functionality">REMOVED FUNCTIONALITY</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>BN_CTX_new, BN_CTX_secure_new, BN_CTX_free - allocate and free BN_CTX structures</p>
<p>
</p>
<hr />
<h1><a name="synopsis">SYNOPSIS</a></h1>
<pre>
#include <openssl/bn.h></pre>
<pre>
BN_CTX *BN_CTX_new(void);</pre>
<pre>
BN_CTX *BN_CTX_secure_new(void);</pre>
<pre>
void BN_CTX_free(BN_CTX *c);</pre>
<p>
</p>
<hr />
<h1><a name="description">DESCRIPTION</a></h1>
<p>A <strong>BN_CTX</strong> is a structure that holds <strong>BIGNUM</strong> temporary variables used by
library functions. Since dynamic memory allocation to create <strong>BIGNUM</strong>s
is rather expensive when used in conjunction with repeated subroutine
calls, the <strong>BN_CTX</strong> structure is used.</p>
<p><code>BN_CTX_new()</code> allocates and initializes a <strong>BN_CTX</strong> structure.
<code>BN_CTX_secure_new()</code> allocates and initializes a <strong>BN_CTX</strong> structure
but uses the secure heap (see <em>CRYPTO_secure_malloc(3)</em>) to hold the
<strong>BIGNUM</strong>s.</p>
<p><code>BN_CTX_free()</code> frees the components of the <strong>BN_CTX</strong> and the structure itself.
Since <code>BN_CTX_start()</code> is required in order to obtain <strong>BIGNUM</strong>s from the
<strong>BN_CTX</strong>, in most cases <code>BN_CTX_end()</code> must be called before the <strong>BN_CTX</strong> may
be freed by <code>BN_CTX_free()</code>. If <strong>c</strong> is NULL, nothing is done.</p>
<p>A given <strong>BN_CTX</strong> must only be used by a single thread of execution. No
locking is performed, and the internal pool allocator will not properly handle
multiple threads of execution.</p>
<p>
</p>
<hr />
<h1><a name="return_values">RETURN VALUES</a></h1>
<p><code>BN_CTX_new()</code> and <code>BN_CTX_secure_new()</code> return a pointer to the <strong>BN_CTX</strong>.
If the allocation fails,
they return <strong>NULL</strong> and sets an error code that can be obtained by
<em>ERR_get_error(3)</em>.</p>
<p><code>BN_CTX_free()</code> has no return values.</p>
<p>
</p>
<hr />
<h1><a name="removed_functionality">REMOVED FUNCTIONALITY</a></h1>
<pre>
void BN_CTX_init(BN_CTX *c);</pre>
<p><code>BN_CTX_init()</code> is no longer available as of OpenSSL 1.1.0. Applications should
replace use of BN_CTX_init with BN_CTX_new instead:</p>
<pre>
BN_CTX *ctx;
ctx = BN_CTX_new();
if (!ctx)
/* error */
...
BN_CTX_free(ctx);</pre>
<p>
</p>
<hr />
<h1><a name="see_also">SEE ALSO</a></h1>
<p><em>ERR_get_error(3)</em>, <em>BN_add(3)</em>,
<em>BN_CTX_start(3)</em></p>
<p>
</p>
<hr />
<h1><a name="history">HISTORY</a></h1>
<p><code>BN_CTX_init()</code> was removed in OpenSSL 1.1.0.</p>
<p>
</p>
<hr />
<h1><a name="copyright">COPYRIGHT</a></h1>
<p>Copyright 2000-2017 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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