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<ul id="index">
  <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="#RETURN-VALUES">RETURN VALUES</a></li>
  <li><a href="#EXAMPLES">EXAMPLES</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_PKEY_derive_init, EVP_PKEY_derive_set_peer, EVP_PKEY_derive - derive public key algorithm shared secret</p>

<h1 id="SYNOPSIS">SYNOPSIS</h1>

<pre><code> #include &lt;openssl/evp.h&gt;

 int EVP_PKEY_derive_init(EVP_PKEY_CTX *ctx);
 int EVP_PKEY_derive_set_peer(EVP_PKEY_CTX *ctx, EVP_PKEY *peer);
 int EVP_PKEY_derive(EVP_PKEY_CTX *ctx, unsigned char *key, size_t *keylen);</code></pre>

<h1 id="DESCRIPTION">DESCRIPTION</h1>

<p>The EVP_PKEY_derive_init() function initializes a public key algorithm context using key <b>pkey</b> for shared secret derivation.</p>

<p>The EVP_PKEY_derive_set_peer() function sets the peer key: this will normally be a public key.</p>

<p>The EVP_PKEY_derive() derives a shared secret using <b>ctx</b>. If <b>key</b> is <b>NULL</b> then the maximum size of the output buffer is written to the <b>keylen</b> parameter. If <b>key</b> is not <b>NULL</b> then before the call the <b>keylen</b> parameter should contain the length of the <b>key</b> buffer, if the call is successful the shared secret is written to <b>key</b> and the amount of data written to <b>keylen</b>.</p>

<h1 id="NOTES">NOTES</h1>

<p>After the call to EVP_PKEY_derive_init() algorithm specific control operations can be performed to set any appropriate parameters for the operation.</p>

<p>The function EVP_PKEY_derive() can be called more than once on the same context if several operations are performed using the same parameters.</p>

<h1 id="RETURN-VALUES">RETURN VALUES</h1>

<p>EVP_PKEY_derive_init() and EVP_PKEY_derive() return 1 for success and 0 or a negative value for failure. In particular a return value of -2 indicates the operation is not supported by the public key algorithm.</p>

<h1 id="EXAMPLES">EXAMPLES</h1>

<p>Derive shared secret (for example DH or EC keys):</p>

<pre><code> #include &lt;openssl/evp.h&gt;
 #include &lt;openssl/rsa.h&gt;

 EVP_PKEY_CTX *ctx;
 ENGINE *eng;
 unsigned char *skey;
 size_t skeylen;
 EVP_PKEY *pkey, *peerkey;
 /* NB: assumes pkey, eng, peerkey have been already set up */

 ctx = EVP_PKEY_CTX_new(pkey, eng);
 if (!ctx)
     /* Error occurred */
 if (EVP_PKEY_derive_init(ctx) &lt;= 0)
     /* Error */
 if (EVP_PKEY_derive_set_peer(ctx, peerkey) &lt;= 0)
     /* Error */

 /* Determine buffer length */
 if (EVP_PKEY_derive(ctx, NULL, &amp;skeylen) &lt;= 0)
     /* Error */

 skey = OPENSSL_malloc(skeylen);

 if (!skey)
     /* malloc failure */

 if (EVP_PKEY_derive(ctx, skey, &amp;skeylen) &lt;= 0)
     /* Error */

 /* Shared secret is skey bytes written to buffer skey */</code></pre>

<h1 id="SEE-ALSO">SEE ALSO</h1>

<p><a href="../man3/EVP_PKEY_CTX_new.html">EVP_PKEY_CTX_new(3)</a>, <a href="../man3/EVP_PKEY_encrypt.html">EVP_PKEY_encrypt(3)</a>, <a href="../man3/EVP_PKEY_decrypt.html">EVP_PKEY_decrypt(3)</a>, <a href="../man3/EVP_PKEY_sign.html">EVP_PKEY_sign(3)</a>, <a href="../man3/EVP_PKEY_verify.html">EVP_PKEY_verify(3)</a>, <a href="../man3/EVP_PKEY_verify_recover.html">EVP_PKEY_verify_recover(3)</a>,</p>

<h1 id="HISTORY">HISTORY</h1>

<p>These functions were added in OpenSSL 1.0.0.</p>

<h1 id="COPYRIGHT">COPYRIGHT</h1>

<p>Copyright 2006-2019 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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