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Update and clarify ECDSA documentation.

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Reviewed-by: Richard Levitte <levitte@openssl.org>
This commit is contained in:
Dr. Stephen Henson
2016-03-14 16:45:51 +00:00
committed by Richard Levitte
parent c91a0a8343
commit 580b557b13
1 changed files with 114 additions and 116 deletions
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196
doc/crypto/ecdsa.pod
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@@ -2,7 +2,10 @@
=head1 NAME =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 =head1 SYNOPSIS
@@ -10,105 +13,106 @@ ECDSA_SIG_new, ECDSA_SIG_free, i2d_ECDSA_SIG, d2i_ECDSA_SIG, ECDSA_size, ECDSA_s
ECDSA_SIG *ECDSA_SIG_new(void); ECDSA_SIG *ECDSA_SIG_new(void);
void ECDSA_SIG_free(ECDSA_SIG *sig); 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); int i2d_ECDSA_SIG(const ECDSA_SIG *sig, unsigned char **pp);
ECDSA_SIG* d2i_ECDSA_SIG(ECDSA_SIG **sig, const unsigned char **pp, ECDSA_SIG *d2i_ECDSA_SIG(ECDSA_SIG **sig, const unsigned char **pp, long len);
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, ECDSA_SIG *ECDSA_do_sign(const unsigned char *dgst, int dgst_len,
EC_KEY *eckey); 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);
ECDSA_SIG *ECDSA_do_sign_ex(const unsigned char *dgst, int dgstlen, ECDSA_SIG *ECDSA_do_sign_ex(const unsigned char *dgst, int dgstlen,
const BIGNUM *kinv, const BIGNUM *rp, const BIGNUM *kinv, const BIGNUM *rp,
EC_KEY *eckey); EC_KEY *eckey);
int ECDSA_do_verify(const unsigned char *dgst, int dgst_len, int ECDSA_sign_setup(EC_KEY *eckey, BN_CTX *ctx, BIGNUM **kinv, BIGNUM **rp);
const ECDSA_SIG *sig, EC_KEY* eckey); int ECDSA_sign_ex(int type, const unsigned char *dgst, int dgstlen,
int ECDSA_sign_setup(EC_KEY *eckey, BN_CTX *ctx, unsigned char *sig, unsigned int *siglen,
BIGNUM **kinv, BIGNUM **rp); const BIGNUM *kinv, const BIGNUM *rp, EC_KEY *eckey);
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);
=head1 DESCRIPTION =head1 DESCRIPTION
The B<ECDSA_SIG> structure consists of two BIGNUMs for the Note: these functions provide a low level interface to ECDSA. Most
r and s value of a ECDSA signature (see X9.62 or FIPS 186-2). applications should use the higher level B<EVP> interface such as
L<EVP_DigestSignInit(3)> or L<EVP_DigestVerifyInit(3)> instead.
struct 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).
BIGNUM *r;
BIGNUM *s;
} ECDSA_SIG;
ECDSA_SIG_new() allocates a new B<ECDSA_SIG> structure (note: this 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>. ECDSA_SIG_free() frees the B<ECDSA_SIG> structure B<sig>.
i2d_ECDSA_SIG() creates the DER encoding of the ECDSA signature ECDSA_SIG_get0() returns internal pointers the B<r> and B<s> values contained
B<sig> and writes the encoded signature to B<*pp> (note: if B<pp> in B<sig>. The values can then be examined or initialised.
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 i2d_ECDSA_SIG() creates the DER encoding of the ECDSA signature B<sig> and
the decoded signature in a newly allocated B<ECDSA_SIG> structure. writes the encoded signature to B<*pp> (note: if B<pp> is NULL i2d_ECDSA_SIG()
B<*sig> points to the buffer containing the DER encoded signature returns the expected length in bytes of the DER encoded signature).
of size B<len>. 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 d2i_ECDSA_SIG() decodes a DER encoded ECDSA signature and returns the decoded
ECDSA signature created with the private EC key B<eckey>. 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 ECDSA_size() returns the maximum length of a DER encoded ECDSA signature
signing operation. B<eckey> is the private EC key and B<ctx> created with the private EC key B<eckey>.
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_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. and B<rp> set to NULL.
ECDSA_sign_ex() computes a digital signature of the B<dgstlen> bytes ECDSA_do_sign() is similar to ECDSA_sign() except the signature is returned
hash value B<dgst> using the private EC key B<eckey> and the optional as a newly allocated B<ECDSA_SIG> structure (or NULL on error). ECDSA_do_sign()
pre-computed values B<kinv> and B<rp>. The DER encoded signatures is is a wrapper function for ECDSA_do_sign_ex() with B<kinv> and B<rp> set to
stored in B<sig> and it's length is returned in B<sig_len>. Note: B<sig> NULL.
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 ECDSA_verify() verifies that the signature in B<sig> of size B<siglen> is a
B<siglen> is a valid ECDSA signature of the hash value valid ECDSA signature of the hash value B<dgst> of size B<dgstlen> using the
B<dgst> of size B<dgstlen> using the public key B<eckey>. public key B<eckey>. The parameter B<type> is ignored.
The parameter B<type> is ignored.
ECDSA_do_sign() is wrapper function for ECDSA_do_sign_ex with B<kinv> ECDSA_do_verify() is similar to ECDSA_verify() except the signature is
and B<rp> set to NULL. 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> The remaining functions utilise the internal B<kinv> and B<r> values used
bytes hash value B<dgst> using the private key B<eckey> and the during signature computation. Most applications will never need to call these
optional pre-computed values B<kinv> and B<rp>. The signature is and some external ECDSA ENGINE implementations may not support them at all if
returned in a newly allocated B<ECDSA_SIG> structure (or NULL on error). either B<kinv> or B<r> is not B<NULL>.
ECDSA_do_verify() verifies that the signature B<sig> is a valid ECDSA_sign_setup() may be used to precompute parts of the signing operation.
ECDSA signature of the hash value B<dgst> of size B<dgst_len> B<eckey> is the private EC key and B<ctx> is a pointer to B<BN_CTX> structure
using the public key B<eckey>. (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 =head1 RETURN VALUES
ECDSA_size() returns the maximum length signature or 0 on error. ECDSA_size() returns the maximum length signature or 0 on error.
ECDSA_sign_setup() and ECDSA_sign() return 1 if successful or 0 ECDSA_sign(), ECDSA_sign_ex() and ECDSA_sign_setup() return 1 if successful
on error. 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 ECDSA_verify() and ECDSA_do_verify() return 1 for a valid
signature, 0 for an invalid signature and -1 on error. signature, 0 for an invalid signature and -1 on error.
@@ -116,8 +120,8 @@ The error codes can be obtained by L<ERR_get_error(3)>.
=head1 EXAMPLES =head1 EXAMPLES
Creating a ECDSA signature of given SHA-1 hash value using the Creating an ECDSA signature of a given SHA-256 hash value using the
named curve secp192k1. named curve prime256v1 (aka P-256).
First step: create a EC_KEY object (note: this part is B<not> ECDSA First step: create a EC_KEY object (note: this part is B<not> ECDSA
specific) specific)
@@ -125,58 +129,49 @@ specific)
int ret; int ret;
ECDSA_SIG *sig; ECDSA_SIG *sig;
EC_KEY *eckey; EC_KEY *eckey;
eckey = EC_KEY_new_by_curve_name(NID_secp192k1); eckey = EC_KEY_new_by_curve_name(NID_X9_62_prime256v1);
if (eckey == NULL) if (eckey == NULL) {
{
/* error */ /* error */
} }
if (!EC_KEY_generate_key(eckey)) if (EC_KEY_generate_key(eckey) == 0) {
{
/* error */ /* error */
} }
Second step: compute the ECDSA signature of a SHA-1 hash value Second step: compute the ECDSA signature of a SHA-256 hash value
using B<ECDSA_do_sign> using ECDSA_do_sign():
sig = ECDSA_do_sign(digest, 20, eckey); sig = ECDSA_do_sign(digest, 32, eckey);
if (sig == NULL) if (sig == NULL) {
{
/* error */ /* error */
} }
or using B<ECDSA_sign> or using ECDSA_sign():
unsigned char *buffer, *pp; unsigned char *buffer, *pp;
int buf_len; int buf_len;
buf_len = ECDSA_size(eckey); buf_len = ECDSA_size(eckey);
buffer = OPENSSL_malloc(buf_len); buffer = OPENSSL_malloc(buf_len);
pp = buffer; pp = buffer;
if (!ECDSA_sign(0, dgst, dgstlen, pp, &buf_len, eckey); if (ECDSA_sign(0, dgst, dgstlen, pp, &buf_len, eckey) == 0) {
{
/* error */ /* 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: and finally evaluate the return value:
if (ret == -1) if (ret == 1) {
{
/* error */
}
else if (ret == 0)
{
/* incorrect signature */
}
else /* ret == 1 */
{
/* signature ok */ /* signature ok */
} else if (ret == 0) {
/* incorrect signature */
} else {
/* error */
} }
=head1 CONFORMING TO =head1 CONFORMING TO
@@ -186,6 +181,9 @@ ANSI X9.62, US Federal Information Processing Standard FIPS 186-2
=head1 SEE ALSO =head1 SEE ALSO
L<dsa(3)>, L<rsa(3)> L<dsa(3)>,
L<rsa(3)>,
L<EVP_DigestSignInit(3)>,
L<EVP_DigestVerifyInit(3)>
=cut =cut