NAME

       ecdsa - Elliptic Curve Digital Signature Algorithm

SYNOPSIS

        #include <openssl/ecdsa.h>

        ECDSA_SIG*     ECDSA_SIG_new(void);
        void           ECDSA_SIG_free(ECDSA_SIG *sig);
        int            i2d_ECDSA_SIG(const ECDSA_SIG *sig, unsigned char **pp);
        ECDSA_SIG*     d2i_ECDSA_SIG(ECDSA_SIG **sig, const unsigned char **pp,
                       long len);

        ECDSA_SIG*     ECDSA_do_sign(const unsigned char *dgst, int dgst_len,
                               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_do_verify(const unsigned char *dgst, int dgst_len,
                               const ECDSA_SIG *sig, EC_KEY* eckey);
        int            ECDSA_sign_setup(EC_KEY *eckey, BN_CTX *ctx,
                               BIGNUM **kinv, BIGNUM **rp);
        int            ECDSA_sign(int type, const unsigned char *dgst,
                               int dgstlen, unsigned char *sig,
                               unsigned int *siglen, EC_KEY *eckey);
        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);
        int            ECDSA_verify(int type, const unsigned char *dgst,
                               int dgstlen, const unsigned char *sig,
                               int siglen, EC_KEY *eckey);
        int            ECDSA_size(const EC_KEY *eckey);

        const ECDSA_METHOD*    ECDSA_OpenSSL(void);
        void           ECDSA_set_default_method(const ECDSA_METHOD *meth);
        const ECDSA_METHOD*    ECDSA_get_default_method(void);
        int            ECDSA_set_method(EC_KEY *eckey,const ECDSA_METHOD *meth);

        int            ECDSA_get_ex_new_index(long argl, void *argp,
                               CRYPTO_EX_new *new_func,
                               CRYPTO_EX_dup *dup_func,
                               CRYPTO_EX_free *free_func);
        int            ECDSA_set_ex_data(EC_KEY *d, int idx, void *arg);
        void*          ECDSA_get_ex_data(EC_KEY *d, int idx);

DESCRIPTION

       The ECDSA_SIG structure consists of two BIGNUMs for the r and s value of a ECDSA signature
       (see X9.62 or FIPS 186-2).

        struct
               {
               BIGNUM *r;
               BIGNUM *s;
        } ECDSA_SIG;

       ECDSA_SIG_new() allocates a new ECDSA_SIG structure (note: this function also allocates
       the BIGNUMs) and initialize it.

       ECDSA_SIG_free() frees the ECDSA_SIG structure sig.

       i2d_ECDSA_SIG() creates the DER encoding of the ECDSA signature sig and writes the encoded
       signature to *pp (note: if pp is NULL i2d_ECDSA_SIG returns the expected length in bytes
       of the DER encoded signature). i2d_ECDSA_SIG returns the length of the DER encoded
       signature (or 0 on error).

       d2i_ECDSA_SIG() decodes a DER encoded ECDSA signature and returns the decoded signature in
       a newly allocated ECDSA_SIG structure.  *sig points to the buffer containing the DER
       encoded signature of size len.

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

       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() is wrapper function for ECDSA_sign_ex with kinv and rp set to NULL.

       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
       signatures is stored in sig and it's length is returned in sig_len. Note: sig must point
       to ECDSA_size bytes of memory. The parameter type is ignored.

       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_sign() is wrapper function for ECDSA_do_sign_ex with kinv and rp set to NULL.

       ECDSA_do_sign_ex() computes a digital signature of the dgst_len bytes hash value dgst
       using the private key eckey and the optional pre-computed values kinv and rp. The
       signature is returned in a newly allocated ECDSA_SIG structure (or NULL on error).

       ECDSA_do_verify() verifies that the signature sig is a valid ECDSA signature of the hash
       value dgst of size dgst_len using the public key eckey.

RETURN VALUES

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

       ECDSA_sign_setup() and ECDSA_sign() return 1 if successful or 0 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 a ECDSA signature of given SHA-1 hash value using the named curve secp192k1.

       First step: create a 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_secp192k1);
        if (eckey == NULL)
               {
               /* error */
               }
        if (!EC_KEY_generate_key(eckey))
               {
               /* error */
               }

       Second step: compute the ECDSA signature of a SHA-1 hash value using ECDSA_do_sign

        sig = ECDSA_do_sign(digest, 20, 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);
               {
               /* error */
               }

       Third step: verify the created ECDSA signature using ECDSA_do_verify

        ret = ECDSA_do_verify(digest, 20, sig, eckey);

       or using ECDSA_verify

        ret = ECDSA_verify(0, digest, 20, buffer, buf_len, eckey);

       and finally evaluate the return value:

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

CONFORMING TO

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

SEE ALSO

       dsa(3), rsa(3)

HISTORY

       The ecdsa implementation was first introduced in OpenSSL 0.9.8

AUTHOR

       Nils Larsch for the OpenSSL project (http://www.openssl.org).