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ECDSA_size(3)




ecdsa(3)                     OpenSSL                     ecdsa(3)


NAME

     ECDSA_SIG_new, ECDSA_SIG_free, i2d_ECDSA_SIG, d2i_ECDSA_SIG,
     ECDSA_size, ECDSA_sign_setup, ECDSA_sign, ECDSA_sign_ex,
     ECDSA_verify, ECDSA_do_sign, ECDSA_do_sign_ex,
     ECDSA_do_verify - 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).

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ecdsa(3)                     OpenSSL                     ecdsa(3)

      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

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ecdsa(3)                     OpenSSL                     ecdsa(3)

     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_SIG_new() returns NULL if the allocation fails.

     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

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ecdsa(3)                     OpenSSL                     ecdsa(3)

      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).

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