Update and clarify ECDSA documentation.

=head1 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

ECDSA_SIG_new, ECDSA_SIG_free, i2d_ECDSA_SIG, d2i_ECDSA_SIG, ECDSA_size,

ECDSA_sign, ECDSA_do_sign, ECDSA_verify, ECDSA_do_verify, ECDSA_sign_setup,

ECDSA_sign_ex, ECDSA_do_sign_ex - low level elliptic curve digital signature

algorithm (ECDSA) functions.

=head1 SYNOPSIS

 ECDSA_SIG *ECDSA_SIG_new(void);

 void ECDSA_SIG_free(ECDSA_SIG *sig);

 void ECDSA_SIG_get0(BIGNUM **pr, BIGNUM **ps, 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 *d2i_ECDSA_SIG(ECDSA_SIG **sig, const unsigned char **pp, long len);

 int ECDSA_size(const EC_KEY *eckey);

 int ECDSA_sign(int type, const unsigned char *dgst, int dgstlen,

                unsigned char *sig, unsigned 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_verify(int type, const unsigned char *dgst, int dgstlen,

                  const unsigned char *sig, int siglen, 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);

 ECDSA_SIG *ECDSA_do_sign_ex(const unsigned char *dgst, int dgstlen,

                             const BIGNUM *kinv, const BIGNUM *rp,

                             EC_KEY *eckey);

 int ECDSA_sign_setup(EC_KEY *eckey, BN_CTX *ctx, BIGNUM **kinv, BIGNUM **rp);

 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);

=head1 DESCRIPTION

The B<ECDSA_SIG> structure consists of two BIGNUMs for the

r and s value of a ECDSA signature (see X9.62 or FIPS 186-2).

Note: these functions provide a low level interface to ECDSA. Most

applications should use the higher level B<EVP> interface such as

L<EVP_DigestSignInit(3)> or L<EVP_DigestVerifyInit(3)> instead.

 struct

	{

	BIGNUM *r;

	BIGNUM *s;

 } ECDSA_SIG;

B<ECDSA_SIG> is an opaque structure consisting of two BIGNUMs for the

B<r> and B<s> value of an ECDSA signature (see X9.62 or FIPS 186-2).

ECDSA_SIG_new() allocates a new B<ECDSA_SIG> structure (note: this

function also allocates the BIGNUMs) and initialize it.

function also allocates the BIGNUMs) and initializes it.

ECDSA_SIG_free() frees the B<ECDSA_SIG> structure B<sig>.

i2d_ECDSA_SIG() creates the DER encoding of the ECDSA signature

B<sig> and writes the encoded signature to B<*pp> (note: if B<pp>

is NULL B<i2d_ECDSA_SIG> returns the expected length in bytes of 

the DER encoded signature). B<i2d_ECDSA_SIG> returns the length

of the DER encoded signature (or 0 on error).

ECDSA_SIG_get0() returns internal pointers the B<r> and B<s> values contained

in B<sig>. The values can then be examined or initialised.

d2i_ECDSA_SIG() decodes a DER encoded ECDSA signature and returns

the decoded signature in a newly allocated B<ECDSA_SIG> structure.

B<*sig> points to the buffer containing the DER encoded signature

of size B<len>.

i2d_ECDSA_SIG() creates the DER encoding of the ECDSA signature B<sig> and

writes the encoded signature to B<*pp> (note: if B<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).

ECDSA_size() returns the maximum length of a DER encoded

ECDSA signature created with the private EC key B<eckey>.

d2i_ECDSA_SIG() decodes a DER encoded ECDSA signature and returns the decoded

signature in a newly allocated B<ECDSA_SIG> structure. B<*sig> points to the

buffer containing the DER encoded signature of size B<len>.

ECDSA_sign_setup() may be used to precompute parts of the

signing operation. B<eckey> is the private EC key and B<ctx>

is a pointer to B<BN_CTX> structure (or NULL). The precomputed

values or returned in B<kinv> and B<rp> and can be used in a

later call to B<ECDSA_sign_ex> or B<ECDSA_do_sign_ex>.

ECDSA_size() returns the maximum length of a DER encoded ECDSA signature

created with the private EC key B<eckey>.

ECDSA_sign() is wrapper function for ECDSA_sign_ex with B<kinv>

ECDSA_sign() computes a digital signature of the B<dgstlen> bytes hash value

B<dgst> using the private EC key B<eckey>. The DER encoded signatures is

stored in B<sig> and it's length is returned in B<sig_len>. Note: B<sig> must

point to ECDSA_size(eckey) bytes of memory. The parameter B<type> is currently

ignored. ECDSA_sign() is wrapper function for ECDSA_sign_ex() with B<kinv>

and B<rp> set to NULL.

ECDSA_sign_ex() computes a digital signature of the B<dgstlen> bytes

hash value B<dgst> using the private EC key B<eckey> and the optional

pre-computed values B<kinv> and B<rp>. The DER encoded signatures is

stored in B<sig> and it's length is returned in B<sig_len>. Note: B<sig>

must point to B<ECDSA_size> bytes of memory. The parameter B<type>

is ignored.

ECDSA_do_sign() is similar to ECDSA_sign() except the signature is returned

as a newly allocated B<ECDSA_SIG> structure (or NULL on error). ECDSA_do_sign()

is a wrapper function for ECDSA_do_sign_ex() with B<kinv> and B<rp> set to

NULL.

ECDSA_verify() verifies that the signature in B<sig> of size

B<siglen> is a valid ECDSA signature of the hash value

B<dgst> of size B<dgstlen> using the public key B<eckey>.

The parameter B<type> is ignored.

ECDSA_verify() verifies that the signature in B<sig> of size B<siglen> is a

valid ECDSA signature of the hash value B<dgst> of size B<dgstlen> using the

public key B<eckey>.  The parameter B<type> is ignored.

ECDSA_do_sign() is wrapper function for ECDSA_do_sign_ex with B<kinv>

and B<rp> set to NULL.

ECDSA_do_verify() is similar to ECDSA_verify() except the signature is

presented in the form of a pointer to an B<ECDSA_SIG> structure.

ECDSA_do_sign_ex() computes a digital signature of the B<dgst_len>

bytes hash value B<dgst> using the private key B<eckey> and the

optional pre-computed values B<kinv> and B<rp>. The signature is

returned in a newly allocated B<ECDSA_SIG> structure (or NULL on error).

The remaining functions utilise the internal B<kinv> and B<r> values used

during signature computation. Most applications will never need to call these

and some external ECDSA ENGINE implementations may not support them at all if

either B<kinv> or B<r> is not B<NULL>.

ECDSA_do_verify() verifies that the signature B<sig> is a valid

ECDSA signature of the hash value B<dgst> of size B<dgst_len>

using the public key B<eckey>.

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

B<eckey> is the private EC key and B<ctx> is a pointer to B<BN_CTX> structure

(or NULL). The precomputed values or returned in B<kinv> and B<rp> and can be

used in a later call to ECDSA_sign_ex() or ECDSA_do_sign_ex().

ECDSA_sign_ex() computes a digital signature of the B<dgstlen> bytes hash value

B<dgst> using the private EC key B<eckey> and the optional pre-computed values

B<kinv> and B<rp>. The DER encoded signatures is stored in B<sig> and it's

length is returned in B<sig_len>. Note: B<sig> must point to ECDSA_size(eckey)

bytes of memory. The parameter B<type> is ignored.

ECDSA_do_sign_ex() is similar to ECDSA_sign_ex() except the signature is

returned as a newly allocated B<ECDSA_SIG> structure (or NULL on error).

=head1 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_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

B<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.

=head1 EXAMPLES

Creating a ECDSA signature of given SHA-1 hash value using the

named curve secp192k1.

Creating an ECDSA signature of a given SHA-256 hash value using the

named curve prime256v1 (aka P-256).

First step: create a EC_KEY object (note: this part is B<not> ECDSA

specific)

 int        ret;

 ECDSA_SIG *sig;

 EC_KEY    *eckey;

 eckey = EC_KEY_new_by_curve_name(NID_secp192k1);

 if (eckey == NULL)

	{

 eckey = EC_KEY_new_by_curve_name(NID_X9_62_prime256v1);

 if (eckey == NULL) {

    /* error */

 }

 if (!EC_KEY_generate_key(eckey))

	{

 if (EC_KEY_generate_key(eckey) == 0) {

    /* error */

 }

Second step: compute the ECDSA signature of a SHA-1 hash value 

using B<ECDSA_do_sign> 

Second step: compute the ECDSA signature of a SHA-256 hash value

using ECDSA_do_sign():

 sig = ECDSA_do_sign(digest, 20, eckey);

 if (sig == NULL)

	{

 sig = ECDSA_do_sign(digest, 32, eckey);

 if (sig == NULL) {

    /* error */

 }

or using B<ECDSA_sign>

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);

	{

 if (ECDSA_sign(0, dgst, dgstlen, pp, &buf_len, eckey) == 0) {

    /* error */

 }

Third step: verify the created ECDSA signature using B<ECDSA_do_verify>

Third step: verify the created ECDSA signature using ECDSA_do_verify():

 ret = ECDSA_do_verify(digest, 20, sig, eckey);

 ret = ECDSA_do_verify(digest, 32, sig, eckey);

or using B<ECDSA_verify>

or using ECDSA_verify():

 ret = ECDSA_verify(0, digest, 20, buffer, buf_len, eckey);

 ret = ECDSA_verify(0, digest, 32, buffer, buf_len, eckey);

and finally evaluate the return value:

 if (ret == -1)

	{

	/* error */

	}

 else if (ret == 0)

	{

	/* incorrect signature */

	}

 else	/* ret == 1 */

	{

 if (ret == 1) {

    /* signature ok */

 } else if (ret == 0) {

    /* incorrect signature */

 } else {

    /* error */

 }

=head1 CONFORMING TO

=head1 SEE ALSO

L<dsa(3)>, L<rsa(3)>

L<dsa(3)>,

L<rsa(3)>,

L<EVP_DigestSignInit(3)>,

L<EVP_DigestVerifyInit(3)>

=cut