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ecdsa(3)				     OpenSSL					 ecdsa(3)

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 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 = EC_KEY_new();
	if (eckey == NULL)
	       {
	       /* error */
	       }
	key->group = EC_GROUP_new_by_nid(NID_secp192k1);
	if (key->group == 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).

1.0.1e					    2013-02-11					 ecdsa(3)
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