ecdsa(3) OpenSSL ecdsa(3)NAMEecdsa - 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 func‐
tion 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 signa‐
ture created with the private EC key eckey.
ECDSA_sign_setup() may be used to precompute parts of the signing oper‐
ation. 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-com‐
puted values kinv and rp. The signature is returned in a newly allo‐
cated ECDSA_SIG structure (or NULL on error).
ECDSA_do_verify() verifies that the signature sig is a valid ECDSA sig‐
nature of the hash value dgst of size dgst_len using the public key
eckey.
RETURN VALUESECDSA_size() returns the maximum length signature or 0 on error.
ECDSA_sign_setup() and ECDSA_sign() return 1 if successful or -1 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 spe‐
cific)
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 (Dig‐
ital Signature Standard, DSS)
SEE ALSOdsa(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).
0.9.8k 2009-05-20 ecdsa(3)
