ECDSA_size (3)

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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 structure consists of two BIGNUMs for the r and s value of a signature (see X9.62 or ).

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

ECDSA_SIG_new() allocates a new

structure (note: this function also allocates the BIGNUMs) and initialize it.

ECDSA_SIG_free() frees the

structure sig.

i2d_ECDSA_SIG() creates the

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

d2i_ECDSA_SIG() decodes a

encoded signature and returns the decoded signature in a newly allocated structure. *sig points to the buffer containing the encoded signature of size len.

ECDSA_size() returns the maximum length of a

encoded signature created with the private key eckey.

ECDSA_sign_setup() may be used to precompute parts of the signing operation. eckey is the private

key and ctx is a pointer to structure (or ). 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

ECDSA_sign_ex() computes a digital signature of the dgstlen bytes hash value dgst using the private

key eckey and the optional pre-computed values kinv and rp. The 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

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

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

structure (or on error).

ECDSA_do_verify() verifies that the signature sig is a valid

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 signature of given hash value using the named curve secp192k1.

First step: create a

object (note: this part is not 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

signature of a 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

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

Federal Information Processing Standard (Digital Signature Standard, )

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 (www.openssl.org