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<title>EVP_KDF-KB</title>
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<ul id="index">
<li><a href="#NAME">NAME</a></li>
<li><a href="#DESCRIPTION">DESCRIPTION</a>
<ul>
<li><a href="#Identity">Identity</a></li>
<li><a href="#Supported-parameters">Supported parameters</a></li>
</ul>
</li>
<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>
<h1 id="NAME">NAME</h1>
<p>EVP_KDF-KB - The Key-Based EVP_KDF implementation</p>
<h1 id="DESCRIPTION">DESCRIPTION</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>
<h2 id="Identity">Identity</h2>
<p>"KBKDF" is the name for this implementation; it can be used with the EVP_KDF_fetch() function.</p>
<h2 id="Supported-parameters">Supported parameters</h2>
<p>The supported parameters are:</p>
<dl>
<dt id="mode-OSSL_KDF_PARAM_MODE-UTF8-string">"mode" (<b>OSSL_KDF_PARAM_MODE</b>) <UTF8 string></dt>
<dd>
<p>The mode parameter determines which flavor of KBKDF to use - currently the choices are "counter" and "feedback". "counter" is the default, and will be used if unspecified.</p>
</dd>
<dt id="mac-OSSL_KDF_PARAM_MAC-UTF8-string">"mac" (<b>OSSL_KDF_PARAM_MAC</b>) <UTF8 string></dt>
<dd>
<p>The value is either CMAC or HMAC.</p>
</dd>
<dt id="digest-OSSL_KDF_PARAM_DIGEST-UTF8-string">"digest" (<b>OSSL_KDF_PARAM_DIGEST</b>) <UTF8 string></dt>
<dd>
</dd>
<dt id="cipher-OSSL_KDF_PARAM_CIPHER-UTF8-string">"cipher" (<b>OSSL_KDF_PARAM_CIPHER</b>) <UTF8 string></dt>
<dd>
</dd>
<dt id="properties-OSSL_KDF_PARAM_PROPERTIES-UTF8-string">"properties" (<b>OSSL_KDF_PARAM_PROPERTIES</b>) <UTF8 string></dt>
<dd>
</dd>
<dt id="key-OSSL_KDF_PARAM_KEY-octet-string">"key" (<b>OSSL_KDF_PARAM_KEY</b>) <octet string></dt>
<dd>
</dd>
<dt id="salt-OSSL_KDF_PARAM_SALT-octet-string">"salt" (<b>OSSL_KDF_PARAM_SALT</b>) <octet string></dt>
<dd>
</dd>
<dt id="info-OSSL_KDF_PARAM_INFO-octet-string">"info (<b>OSSL_KDF_PARAM_INFO</b>) <octet string></dt>
<dd>
</dd>
<dt id="seed-OSSL_KDF_PARAM_SEED-octet-string">"seed" (<b>OSSL_KDF_PARAM_SEED</b>) <octet string></dt>
<dd>
<p>The seed parameter is unused in counter mode.</p>
</dd>
<dt id="use-l-OSSL_KDF_PARAM_KBKDF_USE_L-integer">"use-l" (<b>OSSL_KDF_PARAM_KBKDF_USE_L</b>) <integer></dt>
<dd>
<p>Set to <b>0</b> to disable use of the optional Fixed Input data 'L' (see SP800-108). The default value of <b>1</b> will be used if unspecified.</p>
</dd>
<dt id="use-separator-OSSL_KDF_PARAM_KBKDF_USE_SEPARATOR-integer">"use-separator" (<b>OSSL_KDF_PARAM_KBKDF_USE_SEPARATOR</b>) <integer></dt>
<dd>
<p>Set to <b>0</b> to disable use of the optional Fixed Input data 'zero separator' (see SP800-108) that is placed between the Label and Context. The default value of <b>1</b> will be used if unspecified.</p>
</dd>
</dl>
<p>Depending on whether mac is CMAC or HMAC, either digest or cipher is required (respectively) and the other is unused.</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>"mac", "digest", cipher" and "properties" are described in <a href="../man3/EVP_KDF.html">"PARAMETERS" in EVP_KDF(3)</a>.</p>
<h1 id="NOTES">NOTES</h1>
<p>A context for KBKDF can be obtained by calling:</p>
<pre><code> EVP_KDF *kdf = EVP_KDF_fetch(NULL, "KBKDF", NULL);
EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf);</code></pre>
<p>The output length of an KBKDF is specified via the <code>keylen</code> parameter to the <a href="../man3/EVP_KDF_derive.html">EVP_KDF_derive(3)</a> function.</p>
<p>Note that currently OpenSSL only implements counter and feedback modes. Other variants may be supported in the future.</p>
<h1 id="EXAMPLES">EXAMPLES</h1>
<p>This example derives 10 bytes using COUNTER-HMAC-SHA256, with KI "secret", Label "label", and Context "context".</p>
<pre><code> EVP_KDF *kdf;
EVP_KDF_CTX *kctx;
unsigned char out[10];
OSSL_PARAM params[6], *p = params;
kdf = EVP_KDF_fetch(NULL, "KBKDF", NULL);
kctx = EVP_KDF_CTX_new(kdf);
EVP_KDF_free(kdf);
*p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_DIGEST,
"SHA2-256", 0);
*p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_MAC,
"HMAC", 0);
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_KEY,
"secret", strlen("secret"));
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SALT,
"label", strlen("label"));
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_INFO,
"context", strlen("context"));
*p = OSSL_PARAM_construct_end();
if (EVP_KDF_derive(kctx, out, sizeof(out), params) <= 0)
error("EVP_KDF_derive");
EVP_KDF_CTX_free(kctx);</code></pre>
<p>This example derives 10 bytes using FEEDBACK-CMAC-AES256, with KI "secret", Label "label", and IV "sixteen bytes iv".</p>
<pre><code> EVP_KDF *kdf;
EVP_KDF_CTX *kctx;
unsigned char out[10];
OSSL_PARAM params[8], *p = params;
unsigned char *iv = "sixteen bytes iv";
kdf = EVP_KDF_fetch(NULL, "KBKDF", NULL);
kctx = EVP_KDF_CTX_new(kdf);
EVP_KDF_free(kdf);
*p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_CIPHER, "AES256", 0);
*p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_MAC, "CMAC", 0);
*p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_MODE, "FEEDBACK", 0);
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_KEY,
"secret", strlen("secret"));
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SALT,
"label", strlen("label"));
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_INFO,
"context", strlen("context"));
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SEED,
iv, strlen(iv));
*p = OSSL_PARAM_construct_end();
if (EVP_KDF_derive(kctx, out, sizeof(out), params) <= 0)
error("EVP_KDF_derive");
EVP_KDF_CTX_free(kctx);</code></pre>
<h1 id="CONFORMING-TO">CONFORMING TO</h1>
<p>NIST SP800-108, IETF RFC 6803, IETF RFC 8009.</p>
<h1 id="SEE-ALSO">SEE ALSO</h1>
<p><a href="../man3/EVP_KDF.html">EVP_KDF(3)</a>, <a href="../man3/EVP_KDF_CTX_free.html">EVP_KDF_CTX_free(3)</a>, <a href="../man3/EVP_KDF_CTX_get_kdf_size.html">EVP_KDF_CTX_get_kdf_size(3)</a>, <a href="../man3/EVP_KDF_derive.html">EVP_KDF_derive(3)</a>, <a href="../man3/EVP_KDF.html">"PARAMETERS" in EVP_KDF(3)</a></p>
<h1 id="HISTORY">HISTORY</h1>
<p>This functionality was added to OpenSSL 3.0.</p>
<h1 id="COPYRIGHT">COPYRIGHT</h1>
<p>Copyright 2019-2021 The OpenSSL Project Authors. All Rights Reserved. Copyright 2019 Red Hat, Inc.</p>
<p>Licensed under the Apache License 2.0 (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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