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

DESCRIPTION
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. Creation of the required EC_KEY objects is described in EC_KEY_new(3).

The ECDSA_SIG structure consists of two BIGNUMs for the r and s value of an 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 initializes 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 a BN_CTX structure (or NULL). The precomputed values are 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 a 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 signature is stored in sig and its length is returned in siglen. 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 a 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(), 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 given SHA-1 hash value using the named curve secp192k1.

First step: create an EC_KEY object. 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  = 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 */
    }

SEE ALSO
d2i_ECPKParameters(3), DSA_new(3), EC_GROUP_new(3), EC_KEY_new(3), ECDSA_set_ex_data(3), EVP_DigestSignInit(3), EVP_DigestVerifyInit(3), RSA_new(3)

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

HISTORY
The ECDSA implementation was first introduced in OpenSSL 0.9.8.

AUTHORS
Nils Larsch for the OpenSSL project.