Add ECDSA documentation.

=pod

=head1 NAME

ecdsa - Elliptic Curve Digital Signature Algorithm

=head1 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_DATA*	ECDSA_DATA_new(void);

 ECDSA_DATA*	ECDSA_DATA_new_method(ENGINE *eng);

 void		ECDSA_DATA_free(ECDSA_DATA *data);

 ECDSA_DATA*	ecdsa_check(EC_KEY *eckey);

 ECDSA_SIG*	ECDSA_do_sign(const unsigned char *dgst, int dgst_len,

			EC_KEY *eckey);

 int		ECDSA_do_verify(const unsigned char *dgst, int dgst_len,

			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_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);

=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).

 struct

	{

	BIGNUM *r;

	BIGNUM *s;

 } ECDSA_SIG;

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

function also allocates the BIGNUMs) and initialize 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).

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>.

The B<ECDSA_DATA> structure extends the B<EC_KEY_METH_DATA>

structure with ECDSA specific data.

 struct

	{

	/* EC_KEY_METH_DATA part */

	int  (*init)(EC_KEY *);

	void (*finish)(EC_KEY *);

	/* method (ECDSA) specific part */

	BIGNUM	*kinv;	/* signing pre-calc */

	BIGNUM	*r;	/* signing pre-calc */

	...

	} 

 ECDSA_DATA;

B<kinv> and B<r> are used to store precomputed values (see

B<ECDSA_sign_setup>). 

ECDSA_DATA_new() returns a newly allocated and initialized

B<ECDSA_DATA> structure (or NULL on error). 

ECDSA_DATA_free() frees the B<ECDSA_DATA> structure B<data>.

ecdsa_check() returns the pointer to the B<ECDSA_DATA>

structure in B<EC_KEY-E<gt>meth_data> (if B<EC_KEY-E<gt>meth_data>

is not a pointer to a B<ECDSA_DATA> structure then the old

data is freed and a new B<ECDSA_DATA> structure is allocated

using B<ECDSA_DATA_new>).

ECDSA_size() returns the maximum length of a DER encoded

ECDSA signature created with the private EC 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 B<ECDSA_sign> or B<ECDSA_do_sign> when placed in

B<ECDSA_DATA-E<gt>kinv> and B<ECDSA_DATA-E<gt>r>.

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

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

the DER encoding of the created signature in B<sig>. The length

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

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

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

The parameter B<type> is ignored.

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

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

returns the signature in a newly allocated B<ECDSA_SIG> structure

(or NULL on error).

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>.

=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 -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 L<ERR_get_error(3)|ERR_get_error(3)>.

=head1 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 B<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 B<ECDSA_do_sign> 

 sig = ECDSA_do_sign(digest, 20, eckey);

 if (sig == NULL)

	{

	/* error */

	}

or using B<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 B<ECDSA_do_verify>

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

or using B<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 */

	}

=head1 CONFORMING TO

ANSI X9.62, US Federal Information Processing Standard FIPS 186-2

(Digital Signature Standard, DSS)

=head1 SEE ALSO

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

=head1 HISTORY

The ecdsa implementation was first introduced in OpenSSL 0.9.8

=head1 AUTHOR

Nils Larsch for the OpenSSL project (http://www.openssl.org).

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