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ECDSA_SIG_NEW(3)                    OpenSSL                   ECDSA_SIG_NEW(3)
NAME
       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
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);
        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
       Note: these functions provide a low-level interface to ECDSA. Most
       applications should use the higher level EVP interface such as
       EVP_DigestSignInit(3) or EVP_DigestVerifyInit(3) 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 i2d_ECDSA_SIG(3) and d2i_ECDSA_SIG(3) 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).
RETURN VALUES
       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 ERR_get_error(3).
EXAMPLES
       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)
        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
       ANSI X9.62, US Federal Information Processing Standard FIPS 186-2
       (Digital Signature Standard, DSS)
SEE ALSO
       EC_KEY_new(3), EVP_DigestSignInit(3), EVP_DigestVerifyInit(3),
       i2d_ECDSA_SIG(3), d2i_ECDSA_SIG(3)
COPYRIGHT
       Copyright 2004-2020 The OpenSSL Project Authors. All Rights Reserved.
       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
       <https://www.openssl.org/source/license.html>;.
1.1.1k                            2021-03-25                  ECDSA_SIG_NEW(3)