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/* LibTomCrypt, modular cryptographic library -- Tom St Denis
*
* LibTomCrypt is a library that provides various cryptographic
* algorithms in a highly modular and flexible manner.
*
* The library is free for all purposes without any express
* guarantee it works.
*
* Tom St Denis, tomstdenis@gmail.com, http://libtom.org
*/
#include "tomcrypt.h"
/**
@file dsa_verify_hash.c
DSA implementation, verify a signature, Tom St Denis
*/
#ifdef LTC_MDSA
/**
Verify a DSA signature
@param r DSA "r" parameter
@param s DSA "s" parameter
@param hash The hash that was signed
@param hashlen The length of the hash that was signed
@param stat [out] The result of the signature verification, 1==valid, 0==invalid
@param key The corresponding public DH key
@return CRYPT_OK if successful (even if the signature is invalid)
*/
int dsa_verify_hash_raw(mp_int_t r, mp_int_t s,
const unsigned char *hash, unsigned long hashlen,
int *stat, dsa_key * key)
{
mp_int w, v, u1, u2;
int err;
LTC_ARGCHK(r != NULL);
LTC_ARGCHK(s != NULL);
LTC_ARGCHK(stat != NULL);
LTC_ARGCHK(key != NULL);
/* default to invalid signature */
*stat = 0;
/* init our variables */
if ((err = mp_init_multi(&w, &v, &u1, &u2, NULL)) != CRYPT_OK) {
return err;
}
/* neither r or s can be null or >q */
if (mp_iszero(r) == LTC_MP_YES || mp_iszero(s) == LTC_MP_YES
|| mp_cmp(r, &key->q) != LTC_MP_LT
|| mp_cmp(s, &key->q) != LTC_MP_LT) {
err = CRYPT_INVALID_PACKET;
goto error;
}
/* w = 1/s mod q */
if ((err = mp_invmod(s, &key->q, &w)) != CRYPT_OK) {
goto error;
}
/* u1 = m * w mod q */
if ((err =
mp_read_unsigned_bin(&u1, (unsigned char *)hash,
hashlen)) != CRYPT_OK) {
goto error;
}
if ((err = mp_mulmod(&u1, &w, &key->q, &u1)) != CRYPT_OK) {
goto error;
}
/* u2 = r*w mod q */
if ((err = mp_mulmod(r, &w, &key->q, &u2)) != CRYPT_OK) {
goto error;
}
/* v = g^u1 * y^u2 mod p mod q */
if ((err = mp_exptmod(&key->g, &u1, &key->p, &u1)) != CRYPT_OK) {
goto error;
}
if ((err = mp_exptmod(&key->y, &u2, &key->p, &u2)) != CRYPT_OK) {
goto error;
}
if ((err = mp_mulmod(&u1, &u2, &key->p, &v)) != CRYPT_OK) {
goto error;
}
if ((err = mp_mod(&v, &key->q, &v)) != CRYPT_OK) {
goto error;
}
/* if r = v then we're set */
if (mp_cmp(r, &v) == LTC_MP_EQ) {
*stat = 1;
}
err = CRYPT_OK;
error:
mp_clear_multi(&w, &v, &u1, &u2, NULL);
return err;
}
/**
Verify a DSA signature
@param sig The signature
@param siglen The length of the signature (octets)
@param hash The hash that was signed
@param hashlen The length of the hash that was signed
@param stat [out] The result of the signature verification, 1==valid, 0==invalid
@param key The corresponding public DH key
@return CRYPT_OK if successful (even if the signature is invalid)
*/
int dsa_verify_hash(const unsigned char *sig, unsigned long siglen,
const unsigned char *hash, unsigned long hashlen,
int *stat, dsa_key * key)
{
int err;
mp_int r, s;
if ((err = mp_init_multi(&r, &s, NULL)) != CRYPT_OK) {
return CRYPT_MEM;
}
/* decode the sequence */
if ((err = der_decode_sequence_multi(sig, siglen,
LTC_ASN1_INTEGER, 1UL, &r,
LTC_ASN1_INTEGER, 1UL, &s,
LTC_ASN1_EOL, 0UL,
NULL)) != CRYPT_OK) {
goto LBL_ERR;
}
/* do the op */
err = dsa_verify_hash_raw(&r, &s, hash, hashlen, stat, key);
LBL_ERR:
mp_clear_multi(&r, &s, NULL);
return err;
}
#endif
/* $Source: /cvs/libtom/libtomcrypt/src/pk/dsa/dsa_verify_hash.c,v $ */
/* $Revision: 1.15 $ */
/* $Date: 2007/05/12 14:32:35 $ */
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