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<title>EVP_KDF-SS</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="#Auxiliary-function">Auxiliary function</a></li>
<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-SS - The Single Step / One Step EVP_KDF implementation</p>
<h1 id="DESCRIPTION">DESCRIPTION</h1>
<p>The EVP_KDF-SS algorithm implements the Single Step key derivation function (SSKDF). SSKDF derives a key using input such as a shared secret key (that was generated during the execution of a key establishment scheme) and fixedinfo. SSKDF is also informally referred to as 'Concat KDF'.</p>
<h2 id="Auxiliary-function">Auxiliary function</h2>
<p>The implementation uses a selectable auxiliary function H, which can be one of:</p>
<dl>
<dt id="H-x-hash-x-digest-md"><b>H(x) = hash(x, digest=md)</b></dt>
<dd>
</dd>
<dt id="H-x-HMAC_hash-x-key-salt-digest-md"><b>H(x) = HMAC_hash(x, key=salt, digest=md)</b></dt>
<dd>
</dd>
<dt id="H-x-KMACxxx-x-key-salt-custom-KDF-outlen-mac_size"><b>H(x) = KMACxxx(x, key=salt, custom="KDF", outlen=mac_size)</b></dt>
<dd>
</dd>
</dl>
<p>Both the HMAC and KMAC implementations set the key using the 'salt' value. The hash and HMAC also require the digest to be set.</p>
<h2 id="Identity">Identity</h2>
<p>"SSKDF" 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="properties-OSSL_KDF_PARAM_PROPERTIES-UTF8-string">"properties" (<b>OSSL_KDF_PARAM_PROPERTIES</b>) <UTF8 string></dt>
<dd>
</dd>
<dt id="digest-OSSL_KDF_PARAM_DIGEST-UTF8-string">"digest" (<b>OSSL_KDF_PARAM_DIGEST</b>) <UTF8 string></dt>
<dd>
</dd>
<dt id="mac-OSSL_KDF_PARAM_MAC-UTF8-string">"mac" (<b>OSSL_KDF_PARAM_MAC</b>) <UTF8 string></dt>
<dd>
</dd>
<dt id="maclen-OSSL_KDF_PARAM_MAC_SIZE-unsigned-integer">"maclen" (<b>OSSL_KDF_PARAM_MAC_SIZE</b>) <unsigned integer></dt>
<dd>
</dd>
<dt id="salt-OSSL_KDF_PARAM_SALT-octet-string">"salt" (<b>OSSL_KDF_PARAM_SALT</b>) <octet string></dt>
<dd>
<p>These parameters work as described in <a href="../man3/EVP_KDF.html">"PARAMETERS" in EVP_KDF(3)</a>.</p>
</dd>
<dt id="key-EVP_KDF_CTRL_SET_KEY-octet-string">"key" (<b>EVP_KDF_CTRL_SET_KEY</b>) <octet string></dt>
<dd>
<p>This parameter set the shared secret that is used for key derivation.</p>
</dd>
<dt id="info-OSSL_KDF_PARAM_INFO-octet-string">"info" (<b>OSSL_KDF_PARAM_INFO</b>) <octet string></dt>
<dd>
<p>This parameter sets an optional value for fixedinfo, also known as otherinfo.</p>
</dd>
</dl>
<h1 id="NOTES">NOTES</h1>
<p>A context for SSKDF can be obtained by calling:</p>
<pre><code> EVP_KDF *kdf = EVP_KDF_fetch(NULL, "SSKDF", NULL);
EVP_KDF_CTX *kctx = EVP_KDF_CTX_new(kdf);</code></pre>
<p>The output length of an SSKDF is specified via the <i>keylen</i> parameter to the <a href="../man3/EVP_KDF_derive.html">EVP_KDF_derive(3)</a> function.</p>
<h1 id="EXAMPLES">EXAMPLES</h1>
<p>This example derives 10 bytes using H(x) = SHA-256, with the secret key "secret" and fixedinfo value "label":</p>
<pre><code> EVP_KDF *kdf;
EVP_KDF_CTX *kctx;
unsigned char out[10];
OSSL_PARAM params[4], *p = params;
kdf = EVP_KDF_fetch(NULL, "SSKDF", NULL);
kctx = EVP_KDF_CTX_new(kdf);
EVP_KDF_free(kdf);
*p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_DIGEST,
SN_sha256, strlen(SN_sha256));
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_KEY,
"secret", (size_t)6);
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_INFO,
"label", (size_t)5);
*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 H(x) = HMAC(SHA-256), with the secret key "secret", fixedinfo value "label" and salt "salt":</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, "SSKDF", NULL);
kctx = EVP_KDF_CTX_new(kdf);
EVP_KDF_free(kdf);
*p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_MAC,
SN_hmac, strlen(SN_hmac));
*p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_DIGEST,
SN_sha256, strlen(SN_sha256));
*p++ = OSSL_PARAM_construct_octet_string(EVP_KDF_CTRL_SET_KEY,
"secret", (size_t)6);
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_INFO,
"label", (size_t)5);
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SALT,
"salt", (size_t)4);
*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 H(x) = KMAC128(x,salt,outlen), with the secret key "secret" fixedinfo value "label", salt of "salt" and KMAC outlen of 20:</p>
<pre><code> EVP_KDF *kdf;
EVP_KDF_CTX *kctx;
unsigned char out[10];
OSSL_PARAM params[7], *p = params;
kdf = EVP_KDF_fetch(NULL, "SSKDF", NULL);
kctx = EVP_KDF_CTX_new(kdf);
EVP_KDF_free(kdf);
*p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_MAC,
SN_kmac128, strlen(SN_kmac128));
*p++ = OSSL_PARAM_construct_utf8_string(OSSL_KDF_PARAM_DIGEST,
SN_sha256, strlen(SN_sha256));
*p++ = OSSL_PARAM_construct_octet_string(EVP_KDF_CTRL_SET_KEY,
"secret", (size_t)6);
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_INFO,
"label", (size_t)5);
*p++ = OSSL_PARAM_construct_octet_string(OSSL_KDF_PARAM_SALT,
"salt", (size_t)4);
*p++ = OSSL_PARAM_construct_size_t(OSSL_KDF_PARAM_MAC_SIZE, (size_t)20);
*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 SP800-56Cr1.</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_new.html">EVP_KDF_CTX_new(3)</a>, <a href="../man3/EVP_KDF_CTX_free.html">EVP_KDF_CTX_free(3)</a>, <a href="../man3/EVP_KDF_CTX_set_params.html">EVP_KDF_CTX_set_params(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 (c) 2019, Oracle and/or its affiliates. All rights reserved.</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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