NAME

SYNOPSIS

 #include <openssl/ecdsa.h>

 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);

The following functions have been deprecated since OpenSSL 3.0, and can be hidden entirely by defining OPENSSL_API_COMPAT with a suitable version value, see openssl_user_macros(7):

 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);

DESCRIPTION

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.

Non-NULL r and s values can be set on the sig by calling ECDSA_SIG_set0(). 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 by the caller.

See i2d_ECDSA_SIG(3) and d2i_ECDSA_SIG(3) for information about encoding and decoding ECDSA signatures to/from DER.

All of the functions described below are deprecated. Applications should use the higher level EVP interface such as EVP_DigestSignInit(3) or EVP_DigestVerifyInit(3) instead.

ECDSA_size() returns the maximum length of a DER encoded ECDSA signature created with the private EC key eckey. To obtain the actual signature size use EVP_PKEY_sign(3) with a NULL sig parameter.

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).

RETURN VALUES

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 ERR_get_error(3).

EXAMPLES

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

 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 */

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

 sig = ECDSA_do_sign(digest, 32, eckey);
 if (sig == NULL)
     /* error */

or using ECDSA_sign():

 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, &buf_len, eckey) == 0)
     /* error */

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

 ret = ECDSA_do_verify(digest, 32, sig, eckey);

or using ECDSA_verify():

 ret = ECDSA_verify(0, digest, 32, buffer, buf_len, eckey);

and finally evaluate the return value:

 if (ret == 1)
     /* signature ok */
 else if (ret == 0)
     /* incorrect signature */
 else
     /* error */

CONFORMING TO

SEE ALSO

HISTORY

COPYRIGHT

Licensed under the Apache License 2.0 (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 <https://www.openssl.org/source/license.html>.