2020-03-02 16:50:34 +00:00
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<title>EVP_DigestVerifyInit</title>
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<!-- INDEX BEGIN -->
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<p><a name="__index__"></a></p>
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<ul>
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<li><a href="#name">NAME</a></li>
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<li><a href="#synopsis">SYNOPSIS</a></li>
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<li><a href="#description">DESCRIPTION</a></li>
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<li><a href="#return_values">RETURN VALUES</a></li>
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<li><a href="#notes">NOTES</a></li>
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<li><a href="#see_also">SEE ALSO</a></li>
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<li><a href="#history">HISTORY</a></li>
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<li><a href="#copyright">COPYRIGHT</a></li>
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<h1><a name="name">NAME</a></h1>
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2020-03-02 17:19:21 +00:00
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<p>EVP_DigestVerifyInit, EVP_DigestVerifyUpdate, EVP_DigestVerifyFinal,
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EVP_DigestVerify - EVP signature verification functions</p>
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2020-03-02 16:50:34 +00:00
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<p>
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</p>
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<hr />
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<h1><a name="synopsis">SYNOPSIS</a></h1>
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<pre>
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#include <openssl/evp.h></pre>
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<pre>
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int EVP_DigestVerifyInit(EVP_MD_CTX *ctx, EVP_PKEY_CTX **pctx,
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const EVP_MD *type, ENGINE *e, EVP_PKEY *pkey);
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int EVP_DigestVerifyUpdate(EVP_MD_CTX *ctx, const void *d, size_t cnt);
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int EVP_DigestVerifyFinal(EVP_MD_CTX *ctx, const unsigned char *sig,
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size_t siglen);
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int EVP_DigestVerify(EVP_MD_CTX *ctx, const unsigned char *sigret,
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size_t siglen, const unsigned char *tbs, size_t tbslen);</pre>
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<p>
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</p>
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<hr />
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<h1><a name="description">DESCRIPTION</a></h1>
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<p>The EVP signature routines are a high level interface to digital signatures.</p>
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<p><code>EVP_DigestVerifyInit()</code> sets up verification context <strong>ctx</strong> to use digest
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<strong>type</strong> from ENGINE <strong>e</strong> and public key <strong>pkey</strong>. <strong>ctx</strong> must be created
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with <code>EVP_MD_CTX_new()</code> before calling this function. If <strong>pctx</strong> is not NULL, the
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EVP_PKEY_CTX of the verification operation will be written to <strong>*pctx</strong>: this
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can be used to set alternative verification options. Note that any existing
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value in <strong>*pctx</strong> is overwritten. The EVP_PKEY_CTX value returned must not be freed
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directly by the application if <strong>ctx</strong> is not assigned an EVP_PKEY_CTX value before
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being passed to <code>EVP_DigestVerifyInit()</code> (which means the EVP_PKEY_CTX is created
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inside <code>EVP_DigestVerifyInit()</code> and it will be freed automatically when the
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EVP_MD_CTX is freed).</p>
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<p>No <strong>EVP_PKEY_CTX</strong> will be created by <code>EVP_DigestSignInit()</code> if the passed <strong>ctx</strong>
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has already been assigned one via <em>EVP_MD_CTX_set_pkey_ctx(3)</em>. See also <em>SM2(7)</em>.</p>
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<p><code>EVP_DigestVerifyUpdate()</code> hashes <strong>cnt</strong> bytes of data at <strong>d</strong> into the
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verification context <strong>ctx</strong>. This function can be called several times on the
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same <strong>ctx</strong> to include additional data. This function is currently implemented
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using a macro.</p>
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<p><code>EVP_DigestVerifyFinal()</code> verifies the data in <strong>ctx</strong> against the signature in
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<strong>sig</strong> of length <strong>siglen</strong>.</p>
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<p><code>EVP_DigestVerify()</code> verifies <strong>tbslen</strong> bytes at <strong>tbs</strong> against the signature
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in <strong>sig</strong> of length <strong>siglen</strong>.</p>
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<p>
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</p>
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<hr />
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<h1><a name="return_values">RETURN VALUES</a></h1>
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<p><code>EVP_DigestVerifyInit()</code> and <code>EVP_DigestVerifyUpdate()</code> return 1 for success and 0
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for failure.</p>
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<p><code>EVP_DigestVerifyFinal()</code> and <code>EVP_DigestVerify()</code> return 1 for success; any other
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value indicates failure. A return value of zero indicates that the signature
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did not verify successfully (that is, <strong>tbs</strong> did not match the original data or
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the signature had an invalid form), while other values indicate a more serious
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error (and sometimes also indicate an invalid signature form).</p>
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<p>The error codes can be obtained from <em>ERR_get_error(3)</em>.</p>
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<p>
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</p>
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<hr />
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<h1><a name="notes">NOTES</a></h1>
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<p>The <strong>EVP</strong> interface to digital signatures should almost always be used in
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preference to the low level interfaces. This is because the code then becomes
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transparent to the algorithm used and much more flexible.</p>
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<p><code>EVP_DigestVerify()</code> is a one shot operation which verifies a single block of
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data in one function. For algorithms that support streaming it is equivalent
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to calling <code>EVP_DigestVerifyUpdate()</code> and <code>EVP_DigestVerifyFinal()</code>. For
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algorithms which do not support streaming (e.g. PureEdDSA) it is the only way
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to verify data.</p>
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<p>In previous versions of OpenSSL there was a link between message digest types
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and public key algorithms. This meant that "clone" digests such as EVP_dss1()
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needed to be used to sign using SHA1 and DSA. This is no longer necessary and
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the use of clone digest is now discouraged.</p>
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<p>For some key types and parameters the random number generator must be seeded.
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If the automatic seeding or reseeding of the OpenSSL CSPRNG fails due to
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external circumstances (see <em>RAND(7)</em>), the operation will fail.</p>
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<p>The call to <code>EVP_DigestVerifyFinal()</code> internally finalizes a copy of the digest
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context. This means that <code>EVP_VerifyUpdate()</code> and <code>EVP_VerifyFinal()</code> can
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be called later to digest and verify additional data.</p>
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<p>Since only a copy of the digest context is ever finalized, the context must
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be cleaned up after use by calling <code>EVP_MD_CTX_free()</code> or a memory leak
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will occur.</p>
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<p>
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</p>
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<hr />
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<h1><a name="see_also">SEE ALSO</a></h1>
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<p><em>EVP_DigestSignInit(3)</em>,
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<em>EVP_DigestInit(3)</em>,
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<em>evp(7)</em>, <em>HMAC(3)</em>, <em>MD2(3)</em>,
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<em>MD5(3)</em>, <em>MDC2(3)</em>, <em>RIPEMD160(3)</em>,
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<em>SHA1(3)</em>, <em>dgst(1)</em>,
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<em>RAND(7)</em></p>
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<p>
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</p>
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<hr />
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<h1><a name="history">HISTORY</a></h1>
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<p><code>EVP_DigestVerifyInit()</code>, <code>EVP_DigestVerifyUpdate()</code> and <code>EVP_DigestVerifyFinal()</code>
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were added in OpenSSL 1.0.0.</p>
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<p>
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</p>
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<hr />
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<h1><a name="copyright">COPYRIGHT</a></h1>
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<p>Copyright 2006-2019 The OpenSSL Project Authors. All Rights Reserved.</p>
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<p>Licensed under the OpenSSL license (the "License"). You may not use
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2020-03-02 16:50:34 +00:00
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this file except in compliance with the License. You can obtain a copy
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in the file LICENSE in the source distribution or at
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<a href="https://www.openssl.org/source/license.html">https://www.openssl.org/source/license.html</a>.</p>
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