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✏️ Editing: ECDSA_size.html

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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="#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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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

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

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

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);

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);

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);

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);</code></pre>

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

Note: these functions provide a low-level interface to ECDSA. Most applications should use the higher level EVP interface such as <a href="../man3/EVP_DigestSignInit.html">EVP_DigestSignInit(3)</a> or <a href="../man3/EVP_DigestVerifyInit.html">EVP_DigestVerifyInit(3)</a> instead.

ECDSA_SIG is an opaque structure consisting of two BIGNUMs for the r and s value of an ECDSA signature (see X9.62 or FIPS 186-2).

ECDSA_SIG_new() allocates an empty ECDSA_SIG structure. Note: before OpenSSL 1.1.0 the: the r and s components were initialised.

ECDSA_SIG_free() frees the ECDSA_SIG structure sig.

ECDSA_SIG_get0() returns internal pointers the r and s values contained in sig and stores them in *pr and *ps, respectively. The pointer pr or ps can be NULL, in which case the corresponding value is not returned.

The values r, s can also be retrieved separately by the corresponding function ECDSA_SIG_get0_r() and ECDSA_SIG_get0_s(), respectively.

The r and s values can be set by calling ECDSA_SIG_set0() and passing the new values for r and s 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.

See <a href="../man3/i2d_ECDSA_SIG.html">i2d_ECDSA_SIG(3)</a> and <a href="../man3/d2i_ECDSA_SIG.html">d2i_ECDSA_SIG(3)</a> for information about encoding and decoding ECDSA signatures to/from DER.

ECDSA_size() returns the maximum length of a DER encoded ECDSA signature created with the private EC key eckey.

ECDSA_sign() computes a digital signature of the dgstlen bytes hash value dgst using the private EC key eckey. The DER encoded signatures is stored in sig and its length is returned in sig_len. Note: sig must point to ECDSA_size(eckey) bytes of memory. The parameter type is currently ignored. ECDSA_sign() is wrapper function for ECDSA_sign_ex() with kinv and rp set to NULL.

ECDSA_do_sign() is similar to ECDSA_sign() except the signature is returned as a newly allocated ECDSA_SIG structure (or NULL on error). ECDSA_do_sign() is a wrapper function for ECDSA_do_sign_ex() with kinv and rp set to NULL.

ECDSA_verify() verifies that the signature in sig of size siglen is a valid ECDSA signature of the hash value dgst of size dgstlen using the public key eckey. The parameter type is ignored.

ECDSA_do_verify() is similar to ECDSA_verify() except the signature is presented in the form of a pointer to an ECDSA_SIG structure.

The remaining functions utilise the internal kinv and r 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 kinv or r is not NULL.

ECDSA_sign_setup() may be used to precompute parts of the signing operation. eckey is the private EC key and ctx is a pointer to BN_CTX structure (or NULL). The precomputed values or returned in kinv and rp and can be used in a later call to ECDSA_sign_ex() or ECDSA_do_sign_ex().

ECDSA_sign_ex() computes a digital signature of the dgstlen bytes hash value dgst using the private EC key eckey and the optional pre-computed values kinv and rp. The DER encoded signature is stored in sig and its length is returned in sig_len. Note: sig must point to ECDSA_size(eckey) bytes of memory. The parameter type is ignored.

ECDSA_do_sign_ex() is similar to ECDSA_sign_ex() except the signature is returned as a newly allocated ECDSA_SIG structure (or NULL on error).

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

ECDSA_SIG_new() returns NULL if the allocation fails.

ECDSA_SIG_set0() returns 1 on success or 0 on failure.

ECDSA_SIG_get0_r() and ECDSA_SIG_get0_s() return the corresponding value, or NULL if it is unset.

ECDSA_size() returns the maximum length signature or 0 on error.

ECDSA_sign(), ECDSA_sign_ex() and ECDSA_sign_setup() return 1 if successful or 0 on error.

ECDSA_do_sign() and ECDSA_do_sign_ex() return a pointer to an allocated ECDSA_SIG structure or NULL on error.

ECDSA_verify() and ECDSA_do_verify() return 1 for a valid signature, 0 for an invalid signature and -1 on error. The error codes can be obtained by <a href="../man3/ERR_get_error.html">ERR_get_error(3)</a>.

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

Creating an ECDSA signature of a given SHA-256 hash value using the named curve prime256v1 (aka P-256).

First step: create an EC_KEY object (note: this part is not ECDSA specific)

<pre><code> int ret;
 ECDSA_SIG *sig;
 EC_KEY *eckey;

eckey = EC_KEY_new_by_curve_name(NID_X9_62_prime256v1);
 if (eckey == NULL)
 /* error */
 if (EC_KEY_generate_key(eckey) == 0)
 /* error */</code></pre>

Second step: compute the ECDSA signature of a SHA-256 hash value using ECDSA_do_sign():

<pre><code> sig = ECDSA_do_sign(digest, 32, eckey);
 if (sig == NULL)
 /* error */</code></pre>

or using ECDSA_sign():

<pre><code> unsigned char *buffer, *pp;
 int buf_len;

buf_len = ECDSA_size(eckey);
 buffer = OPENSSL_malloc(buf_len);
 pp = buffer;
 if (ECDSA_sign(0, dgst, dgstlen, pp, &amp;buf_len, eckey) == 0)
 /* error */</code></pre>

Third step: verify the created ECDSA signature using ECDSA_do_verify():

<pre><code> ret = ECDSA_do_verify(digest, 32, sig, eckey);</code></pre>

or using ECDSA_verify():

<pre><code> ret = ECDSA_verify(0, digest, 32, buffer, buf_len, eckey);</code></pre>

and finally evaluate the return value:

<pre><code> if (ret == 1)
 /* signature ok */
 else if (ret == 0)
 /* incorrect signature */
 else
 /* error */</code></pre>

<h1 id="CONFORMING-TO">CONFORMING TO</h1>

ANSI X9.62, US Federal Information Processing Standard FIPS 186-2 (Digital Signature Standard, DSS)

<a href="../man3/EC_KEY_new.html">EC_KEY_new(3)</a>, <a href="../man3/EVP_DigestSignInit.html">EVP_DigestSignInit(3)</a>, <a href="../man3/EVP_DigestVerifyInit.html">EVP_DigestVerifyInit(3)</a>, <a href="../man3/i2d_ECDSA_SIG.html">i2d_ECDSA_SIG(3)</a>, <a href="../man3/d2i_ECDSA_SIG.html">d2i_ECDSA_SIG(3)</a>

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

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>.

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MR SKB