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<ul>
<li><a href="#name">NAME</a></li>
<li><a href="#synopsis">SYNOPSIS</a></li>
<li><a href="#description">DESCRIPTION</a></li>
<li><a href="#return_values">RETURN VALUES</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="#copyright">COPYRIGHT</a></li>
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<hr />
<h1><a name="name">NAME</a></h1>
<p>ECDSA_SIG_get0, ECDSA_SIG_get0_r, ECDSA_SIG_get0_s, ECDSA_SIG_set0,
ECDSA_SIG_new, ECDSA_SIG_free, ECDSA_size, ECDSA_sign, ECDSA_do_sign,
ECDSA_verify, ECDSA_do_verify, ECDSA_sign_setup, ECDSA_sign_ex,
ECDSA_do_sign_ex - low-level elliptic curve digital signature algorithm (ECDSA)
functions</p>
<p>
</p>
<hr />
<h1><a name="synopsis">SYNOPSIS</a></h1>
<pre>
#include <openssl/ecdsa.h></pre>
<pre>
ECDSA_SIG *ECDSA_SIG_new(void);
void ECDSA_SIG_free(ECDSA_SIG *sig);
void ECDSA_SIG_get0(const ECDSA_SIG *sig, const BIGNUM **pr, const BIGNUM **ps);
const BIGNUM *ECDSA_SIG_get0_r(const ECDSA_SIG *sig);
const BIGNUM *ECDSA_SIG_get0_s(const ECDSA_SIG *sig);
int ECDSA_SIG_set0(ECDSA_SIG *sig, BIGNUM *r, BIGNUM *s);
int ECDSA_size(const EC_KEY *eckey);</pre>
<pre>
int ECDSA_sign(int type, const unsigned char *dgst, int dgstlen,
unsigned char *sig, unsigned int *siglen, EC_KEY *eckey);
ECDSA_SIG *ECDSA_do_sign(const unsigned char *dgst, int dgst_len,
EC_KEY *eckey);</pre>
<pre>
int ECDSA_verify(int type, const unsigned char *dgst, int dgstlen,
const unsigned char *sig, int siglen, EC_KEY *eckey);
int ECDSA_do_verify(const unsigned char *dgst, int dgst_len,
const ECDSA_SIG *sig, EC_KEY* eckey);</pre>
<pre>
ECDSA_SIG *ECDSA_do_sign_ex(const unsigned char *dgst, int dgstlen,
const BIGNUM *kinv, const BIGNUM *rp,
EC_KEY *eckey);
int ECDSA_sign_setup(EC_KEY *eckey, BN_CTX *ctx, BIGNUM **kinv, BIGNUM **rp);
int ECDSA_sign_ex(int type, const unsigned char *dgst, int dgstlen,
unsigned char *sig, unsigned int *siglen,
const BIGNUM *kinv, const BIGNUM *rp, EC_KEY *eckey);</pre>
<p>
</p>
<hr />
<h1><a name="description">DESCRIPTION</a></h1>
<p>Note: these functions provide a low-level interface to ECDSA. Most
applications should use the higher level <strong>EVP</strong> interface such as
<em>EVP_DigestSignInit(3)</em> or <em>EVP_DigestVerifyInit(3)</em> instead.</p>
<p><strong>ECDSA_SIG</strong> is an opaque structure consisting of two BIGNUMs for the
<strong>r</strong> and <strong>s</strong> value of an ECDSA signature (see X9.62 or FIPS 186-2).</p>
<p><code>ECDSA_SIG_new()</code> allocates an empty <strong>ECDSA_SIG</strong> structure. Note: before
OpenSSL 1.1.0 the: the <strong>r</strong> and <strong>s</strong> components were initialised.</p>
<p><code>ECDSA_SIG_free()</code> frees the <strong>ECDSA_SIG</strong> structure <strong>sig</strong>.</p>
<p>ECDSA_SIG_get0() returns internal pointers the <strong>r</strong> and <strong>s</strong> values contained
in <strong>sig</strong> and stores them in <strong>*pr</strong> and <strong>*ps</strong>, respectively.
The pointer <strong>pr</strong> or <strong>ps</strong> can be NULL, in which case the corresponding value
is not returned.</p>
<p>The values <strong>r</strong>, <strong>s</strong> can also be retrieved separately by the corresponding
function ECDSA_SIG_get0_r() and ECDSA_SIG_get0_s(), respectively.</p>
<p>The <strong>r</strong> and <strong>s</strong> values can be set by calling ECDSA_SIG_set0() and passing the
new values for <strong>r</strong> and <strong>s</strong> as parameters to the function. Calling this
function transfers the memory management of the values to the ECDSA_SIG object,
and therefore the values that have been passed in should not be freed directly
after this function has been called.</p>
<p>See <em>i2d_ECDSA_SIG(3)</em> and <em>d2i_ECDSA_SIG(3)</em> for information about encoding
and decoding ECDSA signatures to/from DER.</p>
<p><code>ECDSA_size()</code> returns the maximum length of a DER encoded ECDSA signature
created with the private EC key <strong>eckey</strong>.</p>
<p><code>ECDSA_sign()</code> computes a digital signature of the <strong>dgstlen</strong> bytes hash value
<strong>dgst</strong> using the private EC key <strong>eckey</strong>. The DER encoded signatures is
stored in <strong>sig</strong> and its length is returned in <strong>sig_len</strong>. Note: <strong>sig</strong> must
point to ECDSA_size(eckey) bytes of memory. The parameter <strong>type</strong> is currently
ignored. <code>ECDSA_sign()</code> is wrapper function for <code>ECDSA_sign_ex()</code> with <strong>kinv</strong>
and <strong>rp</strong> set to NULL.</p>
<p><code>ECDSA_do_sign()</code> is similar to <code>ECDSA_sign()</code> except the signature is returned
as a newly allocated <strong>ECDSA_SIG</strong> structure (or NULL on error). <code>ECDSA_do_sign()</code>
is a wrapper function for <code>ECDSA_do_sign_ex()</code> with <strong>kinv</strong> and <strong>rp</strong> set to
NULL.</p>
<p><code>ECDSA_verify()</code> verifies that the signature in <strong>sig</strong> of size <strong>siglen</strong> is a
valid ECDSA signature of the hash value <strong>dgst</strong> of size <strong>dgstlen</strong> using the
public key <strong>eckey</strong>. The parameter <strong>type</strong> is ignored.</p>
<p><code>ECDSA_do_verify()</code> is similar to <code>ECDSA_verify()</code> except the signature is
presented in the form of a pointer to an <strong>ECDSA_SIG</strong> structure.</p>
<p>The remaining functions utilise the internal <strong>kinv</strong> and <strong>r</strong> values used
during signature computation. Most applications will never need to call these
and some external ECDSA ENGINE implementations may not support them at all if
either <strong>kinv</strong> or <strong>r</strong> is not <strong>NULL</strong>.</p>
<p><code>ECDSA_sign_setup()</code> may be used to precompute parts of the signing operation.
<strong>eckey</strong> is the private EC key and <strong>ctx</strong> is a pointer to <strong>BN_CTX</strong> structure
(or NULL). The precomputed values or returned in <strong>kinv</strong> and <strong>rp</strong> and can be
used in a later call to <code>ECDSA_sign_ex()</code> or <code>ECDSA_do_sign_ex()</code>.</p>
<p><code>ECDSA_sign_ex()</code> computes a digital signature of the <strong>dgstlen</strong> bytes hash value
<strong>dgst</strong> using the private EC key <strong>eckey</strong> and the optional pre-computed values
<strong>kinv</strong> and <strong>rp</strong>. The DER encoded signature is stored in <strong>sig</strong> and its
length is returned in <strong>sig_len</strong>. Note: <strong>sig</strong> must point to ECDSA_size(eckey)
bytes of memory. The parameter <strong>type</strong> is ignored.</p>
<p><code>ECDSA_do_sign_ex()</code> is similar to <code>ECDSA_sign_ex()</code> except the signature is
returned as a newly allocated <strong>ECDSA_SIG</strong> structure (or NULL on error).</p>
<p>
</p>
<hr />
<h1><a name="return_values">RETURN VALUES</a></h1>
<p><code>ECDSA_SIG_new()</code> returns NULL if the allocation fails.</p>
<p>ECDSA_SIG_set0() returns 1 on success or 0 on failure.</p>
<p>ECDSA_SIG_get0_r() and ECDSA_SIG_get0_s() return the corresponding value,
or NULL if it is unset.</p>
<p><code>ECDSA_size()</code> returns the maximum length signature or 0 on error.</p>
<p><code>ECDSA_sign()</code>, <code>ECDSA_sign_ex()</code> and <code>ECDSA_sign_setup()</code> return 1 if successful
or 0 on error.</p>
<p><code>ECDSA_do_sign()</code> and <code>ECDSA_do_sign_ex()</code> return a pointer to an allocated
<strong>ECDSA_SIG</strong> structure or NULL on error.</p>
<p><code>ECDSA_verify()</code> and <code>ECDSA_do_verify()</code> return 1 for a valid
signature, 0 for an invalid signature and -1 on error.
The error codes can be obtained by <em>ERR_get_error(3)</em>.</p>
<p>
</p>
<hr />
<h1><a name="examples">EXAMPLES</a></h1>
<p>Creating an ECDSA signature of a given SHA-256 hash value using the
named curve prime256v1 (aka P-256).</p>
<p>First step: create an EC_KEY object (note: this part is <strong>not</strong> ECDSA
specific)</p>
<pre>
int ret;
ECDSA_SIG *sig;
EC_KEY *eckey;</pre>
<pre>
eckey = EC_KEY_new_by_curve_name(NID_X9_62_prime256v1);
if (eckey == NULL)
/* error */
if (EC_KEY_generate_key(eckey) == 0)
/* error */</pre>
<p>Second step: compute the ECDSA signature of a SHA-256 hash value
using ECDSA_do_sign():</p>
<pre>
sig = ECDSA_do_sign(digest, 32, eckey);
if (sig == NULL)
/* error */</pre>
<p>or using ECDSA_sign():</p>
<pre>
unsigned char *buffer, *pp;
int buf_len;</pre>
<pre>
buf_len = ECDSA_size(eckey);
buffer = OPENSSL_malloc(buf_len);
pp = buffer;
if (ECDSA_sign(0, dgst, dgstlen, pp, &buf_len, eckey) == 0)
/* error */</pre>
<p>Third step: verify the created ECDSA signature using ECDSA_do_verify():</p>
<pre>
ret = ECDSA_do_verify(digest, 32, sig, eckey);</pre>
<p>or using ECDSA_verify():</p>
<pre>
ret = ECDSA_verify(0, digest, 32, buffer, buf_len, eckey);</pre>
<p>and finally evaluate the return value:</p>
<pre>
if (ret == 1)
/* signature ok */
else if (ret == 0)
/* incorrect signature */
else
/* error */</pre>
<p>
</p>
<hr />
<h1><a name="conforming_to">CONFORMING TO</a></h1>
<p>ANSI X9.62, US Federal Information Processing Standard FIPS 186-2
(Digital Signature Standard, DSS)</p>
<p>
</p>
<hr />
<h1><a name="see_also">SEE ALSO</a></h1>
<p><em>EC_KEY_new(3)</em>,
<em>EVP_DigestSignInit(3)</em>,
<em>EVP_DigestVerifyInit(3)</em>,
<em>i2d_ECDSA_SIG(3)</em>,
<em>d2i_ECDSA_SIG(3)</em></p>
<p>
</p>
<hr />
<h1><a name="copyright">COPYRIGHT</a></h1>
<p>Copyright 2004-2020 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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