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<title>EVP_PKEY_verify_recover</title>
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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_verify_recover_init, EVP_PKEY_verify_recover - recover signature using a public key algorithm</p>
<h1 id="SYNOPSIS">SYNOPSIS</h1>
<pre><code> #include <openssl/evp.h>
int EVP_PKEY_verify_recover_init(EVP_PKEY_CTX *ctx);
int EVP_PKEY_verify_recover(EVP_PKEY_CTX *ctx,
unsigned char *rout, size_t *routlen,
const unsigned char *sig, size_t siglen);</code></pre>
<h1 id="DESCRIPTION">DESCRIPTION</h1>
<p>The EVP_PKEY_verify_recover_init() function initializes a public key algorithm context using key <b>pkey</b> for a verify recover operation.</p>
<p>The EVP_PKEY_verify_recover() function recovers signed data using <b>ctx</b>. The signature is specified using the <b>sig</b> and <b>siglen</b> parameters. If <b>rout</b> is <b>NULL</b> then the maximum size of the output buffer is written to the <b>routlen</b> parameter. If <b>rout</b> is not <b>NULL</b> then before the call the <b>routlen</b> parameter should contain the length of the <b>rout</b> buffer, if the call is successful recovered data is written to <b>rout</b> and the amount of data written to <b>routlen</b>.</p>
<h1 id="NOTES">NOTES</h1>
<p>Normally an application is only interested in whether a signature verification operation is successful in those cases the EVP_verify() function should be used.</p>
<p>Sometimes however it is useful to obtain the data originally signed using a signing operation. Only certain public key algorithms can recover a signature in this way (for example RSA in PKCS padding mode).</p>
<p>After the call to EVP_PKEY_verify_recover_init() algorithm specific control operations can be performed to set any appropriate parameters for the operation.</p>
<p>The function EVP_PKEY_verify_recover() 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_verify_recover_init() and EVP_PKEY_verify_recover() 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>Recover digest originally signed using PKCS#1 and SHA256 digest:</p>
<pre><code> #include <openssl/evp.h>
#include <openssl/rsa.h>
EVP_PKEY_CTX *ctx;
unsigned char *rout, *sig;
size_t routlen, siglen;
EVP_PKEY *verify_key;
/*
* NB: assumes verify_key, sig and siglen are already set up
* and that verify_key is an RSA public key
*/
ctx = EVP_PKEY_CTX_new(verify_key, NULL /* no engine */);
if (!ctx)
/* Error occurred */
if (EVP_PKEY_verify_recover_init(ctx) <= 0)
/* Error */
if (EVP_PKEY_CTX_set_rsa_padding(ctx, RSA_PKCS1_PADDING) <= 0)
/* Error */
if (EVP_PKEY_CTX_set_signature_md(ctx, EVP_sha256()) <= 0)
/* Error */
/* Determine buffer length */
if (EVP_PKEY_verify_recover(ctx, NULL, &routlen, sig, siglen) <= 0)
/* Error */
rout = OPENSSL_malloc(routlen);
if (!rout)
/* malloc failure */
if (EVP_PKEY_verify_recover(ctx, rout, &routlen, sig, siglen) <= 0)
/* Error */
/* Recovered data is routlen bytes written to buffer rout */</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_derive.html">EVP_PKEY_derive(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 2013-2019 The OpenSSL Project Authors. All Rights Reserved.</p>
<p>Licensed under the OpenSSL license (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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