130 lines
5.3 KiB
HTML
130 lines
5.3 KiB
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<title>EVP_SignInit</title>
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<meta http-equiv="content-type" content="text/html; charset=utf-8" />
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<link rev="made" href="mailto:root@localhost" />
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<body style="background-color: white">
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<!-- INDEX BEGIN -->
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<div name="index">
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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="#bugs">BUGS</a></li>
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<li><a href="#see_also">SEE ALSO</a></li>
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<li><a href="#copyright">COPYRIGHT</a></li>
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</ul>
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</div>
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<!-- INDEX END -->
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<p>
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</p>
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<hr />
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<h1><a name="name">NAME</a></h1>
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<p>EVP_SignInit, EVP_SignInit_ex, EVP_SignUpdate, EVP_SignFinal
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- EVP signing functions</p>
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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_SignInit_ex(EVP_MD_CTX *ctx, const EVP_MD *type, ENGINE *impl);
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int EVP_SignUpdate(EVP_MD_CTX *ctx, const void *d, unsigned int cnt);
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int EVP_SignFinal(EVP_MD_CTX *ctx, unsigned char *sig, unsigned int *s, EVP_PKEY *pkey);</pre>
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<pre>
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void EVP_SignInit(EVP_MD_CTX *ctx, const EVP_MD *type);</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
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signatures.</p>
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<p><code>EVP_SignInit_ex()</code> sets up signing context <em>ctx</em> to use digest
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<em>type</em> from <strong>ENGINE</strong> <em>impl</em>. <em>ctx</em> must be created with
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<code>EVP_MD_CTX_new()</code> before calling this function.</p>
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<p><code>EVP_SignUpdate()</code> hashes <em>cnt</em> bytes of data at <em>d</em> into the
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signature context <em>ctx</em>. This function can be called several times on the
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same <em>ctx</em> to include additional data.</p>
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<p><code>EVP_SignFinal()</code> signs the data in <em>ctx</em> using the private key <em>pkey</em> and
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places the signature in <em>sig</em>. <em>sig</em> must be at least <code>EVP_PKEY_size(pkey)</code>
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bytes in size. <em>s</em> is an OUT parameter, and not used as an IN parameter.
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The number of bytes of data written (i.e. the length of the signature)
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will be written to the integer at <em>s</em>, at most <code>EVP_PKEY_size(pkey)</code> bytes
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will be written.</p>
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<p><code>EVP_SignInit()</code> initializes a signing context <em>ctx</em> to use the default
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implementation of digest <em>type</em>.</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_SignInit_ex()</code>, <code>EVP_SignUpdate()</code> and <code>EVP_SignFinal()</code> return 1
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for success and 0 for failure.</p>
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<p>The error codes can be obtained by <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>When signing with DSA private keys 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.
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This requirement does not hold for RSA signatures.</p>
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<p>The call to <code>EVP_SignFinal()</code> internally finalizes a copy of the digest context.
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This means that calls to <code>EVP_SignUpdate()</code> and <code>EVP_SignFinal()</code> can be called
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later to digest and sign 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="bugs">BUGS</a></h1>
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<p>Older versions of this documentation wrongly stated that calls to
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<code>EVP_SignUpdate()</code> could not be made after calling <code>EVP_SignFinal()</code>.</p>
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<p>Since the private key is passed in the call to <code>EVP_SignFinal()</code> any error
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relating to the private key (for example an unsuitable key and digest
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combination) will not be indicated until after potentially large amounts of
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data have been passed through <code>EVP_SignUpdate()</code>.</p>
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<p>It is not possible to change the signing parameters using these function.</p>
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<p>The previous two bugs are fixed in the newer EVP_SignDigest*() function.</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_PKEY_size(3)</em>, <em>EVP_PKEY_bits(3)</em>, <em>EVP_PKEY_security_bits(3)</em>,
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<em>EVP_VerifyInit(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>openssl-dgst(1)</em></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 2000-2018 The OpenSSL Project Authors. All Rights Reserved.</p>
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<p>Licensed under the Apache License 2.0 (the "License"). You may not use
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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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</body>
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</html>
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