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<title>EVP_KDF-KB</title>
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<!-- INDEX BEGIN -->
<div name="index">
<p><a name="__index__"></a></p>
<ul>
<li><a href="#name">NAME</a></li>
<li><a href="#description">DESCRIPTION</a></li>
<ul>
<li><a href="#identity">Identity</a></li>
<li><a href="#supported_parameters">Supported parameters</a></li>
</ul>
<li><a href="#notes">NOTES</a></li>
<li><a href="#examples">EXAMPLES</a></li>
<li><a href="#conforming_to">CONFORMING TO</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>
</ul>
<hr name="index" />
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<!-- INDEX END -->
<p>
</p>
<hr />
<h1><a name="name">NAME</a></h1>
<p>EVP_KDF-KB - The Key-Based EVP_KDF implementation</p>
<p>
</p>
<hr />
<h1><a name="description">DESCRIPTION</a></h1>
<p>The EVP_KDF-KB algorithm implements the Key-Based key derivation function
(KBKDF). KBKDF derives a key from repeated application of a keyed MAC to an
input secret (and other optional values).</p>
<p>
</p>
<h2><a name="identity">Identity</a></h2>
<p>&quot;KBKDF&quot; is the name for this implementation; it can be used with the
<code>EVP_KDF_fetch()</code> function.</p>
<p>
</p>
<h2><a name="supported_parameters">Supported parameters</a></h2>
<p>The supported parameters are:</p>
<dl>
<dt><strong><a name="properties_ossl_kdf_param_properties_utf8_string" class="item">&quot;properties&quot; (<strong>OSSL_KDF_PARAM_PROPERTIES</strong>) &lt;UTF8 string&gt;</a></strong></dt>
<dt><strong><a name="mode_ossl_kdf_param_mode_utf8_string" class="item">&quot;mode&quot; (<strong>OSSL_KDF_PARAM_MODE</strong>) &lt;UTF8 string&gt;</a></strong></dt>
<dt><strong><a name="mac_ossl_kdf_param_mac_utf8_string" class="item">&quot;mac&quot; (<strong>OSSL_KDF_PARAM_MAC</strong>) &lt;UTF8 string&gt;</a></strong></dt>
<dt><strong><a name="digest_ossl_kdf_param_digest_utf8_string" class="item">&quot;digest&quot; (<strong>OSSL_KDF_PARAM_DIGEST</strong>) &lt;UTF8 string&gt;</a></strong></dt>
<dt><strong><a name="cipher_ossl_kdf_param_digest_utf8_string" class="item">&quot;cipher&quot; (<strong>OSSL_KDF_PARAM_DIGEST</strong>) &lt;UTF8 string&gt;</a></strong></dt>
<dt><strong><a name="key_ossl_kdf_param_key_octet_string" class="item">&quot;key&quot; (<strong>OSSL_KDF_PARAM_KEY</strong>) &lt;octet string&gt;</a></strong></dt>
<dt><strong><a name="salt_ossl_kdf_param_salt_octet_string" class="item">&quot;salt&quot; (<strong>OSSL_KDF_PARAM_SALT</strong>) &lt;octet string&gt;</a></strong></dt>
<dt><strong><a name="info" class="item">&quot;info (<strong>OSSL_KDF_PARAM_INFO</strong>) &lt;octet string&gt;</a></strong></dt>
<dt><strong><a name="seed_ossl_kdf_param_seed_octet_string" class="item">&quot;seed&quot; (<strong>OSSL_KDF_PARAM_SEED</strong>) &lt;octet string&gt;</a></strong></dt>
</dl>
<p>The mode parameter determines which flavor of KBKDF to use - currently the
choices are &quot;counter&quot; and &quot;feedback&quot;. Counter is the default, and will be
used if unspecified. The seed parameter is unused in counter mode.</p>
<p>The parameters key, salt, info, and seed correspond to KI, Label, Context, and
IV (respectively) in SP800-108. As in that document, salt, info, and seed are
optional and may be omitted.</p>
<p>Depending on whether mac is CMAC or HMAC, either digest or cipher is required
(respectively) and the other is unused.</p>
<p>
</p>
<hr />
<h1><a name="notes">NOTES</a></h1>
<p>A context for KBKDF can be obtained by calling:</p>
<pre>
EVP_KDF *kdf = EVP_KDF_fetch(NULL, &quot;KBKDF&quot;, NULL);
EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf);</pre>
<p>The output length of an KBKDF is specified via the <code>keylen</code>
parameter to the <em>EVP_KDF_derive(3)</em> function.</p>
<p>Note that currently OpenSSL only implements counter and feedback modes. Other
variants may be supported in the future.</p>
<p>
</p>
<hr />
<h1><a name="examples">EXAMPLES</a></h1>
<p>This example derives 10 bytes using COUNTER-HMAC-SHA256, with KI &quot;secret&quot;,
Label &quot;label&quot;, and Context &quot;context&quot;.</p>
<pre>
EVP_KDF *kdf;
EVP_KDF_CTX *kctx;
unsigned char out[10];
OSSL_PARAM params[6], *p = params;</pre>
<pre>
kdf = EVP_KDF_fetch(NULL, &quot;KBKDF&quot;, NULL);
kctx = EVP_KDF_CTX_new(kdf);
EVP_KDF_free(kdf);</pre>
<pre>
*p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_DIGEST,
&quot;SHA2-256&quot;, 0);
*p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_MAC,
&quot;HMAC&quot;, 0);
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_KEY,
&quot;secret&quot;, strlen(&quot;secret&quot;))
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SALT,
&quot;label&quot;, strlen(&quot;label&quot;));
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_INFO,
&quot;context&quot;, strlen(&quot;context&quot;));
*p = OSSL_PARAM_construct_end();
if (EVP_KDF_CTX_set_params(kctx, params) &lt;= 0)
error(&quot;EVP_KDF_CTX_set_params&quot;);
else if (EVP_KDF_derive(kctx, out, sizeof(out)) &lt;= 0)
error(&quot;EVP_KDF_derive&quot;);</pre>
<pre>
EVP_KDF_CTX_free(kctx);</pre>
<p>This example derives 10 bytes using FEEDBACK-CMAC-AES256, with KI &quot;secret&quot;,
Label &quot;label&quot;, and IV &quot;sixteen bytes iv&quot;.</p>
<pre>
EVP_KDF *kdf;
EVP_KDF_CTX *kctx;
unsigned char out[10];
OSSL_PARAM params[8], *p = params;
unsigned char *iv = &quot;sixteen bytes iv&quot;;</pre>
<pre>
kdf = EVP_KDF_fetch(NULL, &quot;KBKDF&quot;, NULL);
kctx = EVP_KDF_CTX_new(kdf);
EVP_KDF_free(kdf);</pre>
<pre>
*p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_CIPHER, &quot;AES256&quot;, 0);
*p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_MAC, &quot;CMAC&quot;, 0);
*p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_MODE, &quot;FEEDBACK&quot;, 0);
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_KEY,
&quot;secret&quot;, strlen(&quot;secret&quot;));
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SALT,
&quot;label&quot;, strlen(&quot;label&quot;));
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_INFO,
&quot;context&quot;, strlen(&quot;context&quot;));
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SEED,
iv, strlen(iv));
*p = OSSL_PARAM_construct_end();
if (EVP_KDF_CTX_set_params(kctx, params) &lt;= 0)
error(&quot;EVP_KDF_CTX_set_params&quot;);
else if (EVP_KDF_derive(kctx, out, sizeof(out)) &lt;= 0)
error(&quot;EVP_KDF_derive&quot;);</pre>
<pre>
EVP_KDF_CTX_free(kctx);</pre>
<p>
</p>
<hr />
<h1><a name="conforming_to">CONFORMING TO</a></h1>
<p>NIST SP800-108, IETF <a href="http://www.ietf.org/rfc/rfc6803.txt" class="rfc">RFC 6803</a>, IETF <a href="http://www.ietf.org/rfc/rfc8009.txt" class="rfc">RFC 8009</a>.</p>
<p>
</p>
<hr />
<h1><a name="see_also">SEE ALSO</a></h1>
<p><em>EVP_KDF(3)</em>,
<em>EVP_KDF_CTX_free(3)</em>,
<em>EVP_KDF_size(3)</em>,
<em>EVP_KDF_derive(3)</em>,
<em>EVP_KDF(3)/PARAMETERS</em></p>
<p>
</p>
<hr />
<h1><a name="history">HISTORY</a></h1>
<p>This functionality was added to OpenSSL 3.0.</p>
<p>
</p>
<hr />
<h1><a name="copyright">COPYRIGHT</a></h1>
<p>Copyright 2019 The OpenSSL Project Authors. All Rights Reserved.
Copyright 2019 Red Hat, Inc.</p>
<p>Licensed under the Apache License 2.0 (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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