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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="#key_derivation_algorithm">KEY DERIVATION ALGORITHM</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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<hr />
<h1><a name="name">NAME</a></h1>
<p>EVP_BytesToKey - password based encryption routine</p>
<p>
</p>
<hr />
<h1><a name="synopsis">SYNOPSIS</a></h1>
<pre>
 #include &lt;openssl/evp.h&gt;</pre>
<pre>
 int EVP_BytesToKey(const EVP_CIPHER *type, const EVP_MD *md,
                    const unsigned char *salt,
                    const unsigned char *data, int datal, int count,
                    unsigned char *key, unsigned char *iv);</pre>
<p>
</p>
<hr />
<h1><a name="description">DESCRIPTION</a></h1>
<p><code>EVP_BytesToKey()</code> derives a key and IV from various parameters. <strong>type</strong> is
the cipher to derive the key and IV for. <strong>md</strong> is the message digest to use.
The <strong>salt</strong> parameter is used as a salt in the derivation: it should point to
an 8 byte buffer or NULL if no salt is used. <strong>data</strong> is a buffer containing
<strong>datal</strong> bytes which is used to derive the keying data. <strong>count</strong> is the
iteration count to use. The derived key and IV will be written to <strong>key</strong>
and <strong>iv</strong> respectively.</p>
<p>
</p>
<hr />
<h1><a name="notes">NOTES</a></h1>
<p>A typical application of this function is to derive keying material for an
encryption algorithm from a password in the <strong>data</strong> parameter.</p>
<p>Increasing the <strong>count</strong> parameter slows down the algorithm which makes it
harder for an attacker to perform a brute force attack using a large number
of candidate passwords.</p>
<p>If the total key and IV length is less than the digest length and
<strong>MD5</strong> is used then the derivation algorithm is compatible with PKCS#5 v1.5
otherwise a non standard extension is used to derive the extra data.</p>
<p>Newer applications should use a more modern algorithm such as PBKDF2 as
defined in PKCS#5v2.1 and provided by PKCS5_PBKDF2_HMAC.</p>
<p>
</p>
<hr />
<h1><a name="key_derivation_algorithm">KEY DERIVATION ALGORITHM</a></h1>
<p>The key and IV is derived by concatenating D_1, D_2, etc until
enough data is available for the key and IV. D_i is defined as:</p>
<pre>
        D_i = HASH^count(D_(i-1) || data || salt)</pre>
<p>where || denotes concatenation, D_0 is empty, HASH is the digest
algorithm in use, HASH^1(data) is simply HASH(data), HASH^2(data)
is HASH(HASH(data)) and so on.</p>
<p>The initial bytes are used for the key and the subsequent bytes for
the IV.</p>
<p>
</p>
<hr />
<h1><a name="return_values">RETURN VALUES</a></h1>
<p>If <strong>data</strong> is NULL, then <code>EVP_BytesToKey()</code> returns the number of bytes
needed to store the derived key.
Otherwise, <code>EVP_BytesToKey()</code> returns the size of the derived key in bytes,
or 0 on error.</p>
<p>
</p>
<hr />
<h1><a name="see_also">SEE ALSO</a></h1>
<p><em>evp(7)</em>, <em>RAND_bytes(3)</em>,
<em>PKCS5_PBKDF2_HMAC(3)</em>,
<em>EVP_EncryptInit(3)</em></p>
<p>
</p>
<hr />
<h1><a name="copyright">COPYRIGHT</a></h1>
<p>Copyright 2001-2016 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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