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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://libtomcrypt.com
*/
/* Implements ECC over Z/pZ for curve y^2 = x^3 - 3x + b
*
* All curves taken from NIST recommendation paper of July 1999
* Available at http://csrc.nist.gov/cryptval/dss.htm
*/
#include "tomcrypt.h"
/**
@file ecc_verify_hash.c
ECC Crypto, Tom St Denis
*/
#ifdef MECC
/* verify
*
* w = s^-1 mod n
* u1 = xw
* u2 = rw
* X = u1*G + u2*Q
* v = X_x1 mod n
* accept if v == r
*/
/**
Verify an ECC signature
@param sig The signature to verify
@param siglen The length of the signature (octets)
@param hash The hash (message digest) that was signed
@param hashlen The length of the hash (octets)
@param stat Result of signature, 1==valid, 0==invalid
@param key The corresponding public ECC key
@return CRYPT_OK if successful (even if the signature is not valid)
*/
int ecc_verify_hash(const unsigned char *sig, unsigned long siglen,
const unsigned char *hash, unsigned long hashlen,
int *stat, ecc_key *key)
{
ecc_point *mG, *mQ;
void *r, *s, *v, *w, *u1, *u2, *e, *p, *m;
void *mp;
int err;
LTC_ARGCHK(sig != NULL);
LTC_ARGCHK(hash != NULL);
LTC_ARGCHK(stat != NULL);
LTC_ARGCHK(key != NULL);
/* default to invalid signature */
*stat = 0;
mp = NULL;
/* is the IDX valid ? */
if (ltc_ecc_is_valid_idx(key->idx) != 1) {
return CRYPT_PK_INVALID_TYPE;
}
/* allocate ints */
if ((err = mp_init_multi(&r, &s, &v, &w, &u1, &u2, &p, &e, &m, NULL)) != CRYPT_OK) {
return CRYPT_MEM;
}
/* allocate points */
mG = ltc_ecc_new_point();
mQ = ltc_ecc_new_point();
if (mQ == NULL || mG == NULL) {
err = CRYPT_MEM;
goto error;
}
/* parse header */
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 error;
}
/* get the order */
if ((err = mp_read_radix(p, (char *)key->dp->order, 16)) != CRYPT_OK) { goto error; }
/* get the modulus */
if ((err = mp_read_radix(m, (char *)key->dp->prime, 16)) != CRYPT_OK) { goto error; }
/* check for zero */
if (mp_iszero(r) || mp_iszero(s) || mp_cmp(r, p) != LTC_MP_LT || mp_cmp(s, p) != LTC_MP_LT) {
err = CRYPT_INVALID_PACKET;
goto error;
}
/* read hash */
if ((err = mp_read_unsigned_bin(e, (unsigned char *)hash, (int)hashlen)) != CRYPT_OK) { goto error; }
/* w = s^-1 mod n */
if ((err = mp_invmod(s, p, w)) != CRYPT_OK) { goto error; }
/* u1 = ew */
if ((err = mp_mulmod(e, w, p, u1)) != CRYPT_OK) { goto error; }
/* u2 = rw */
if ((err = mp_mulmod(r, w, p, u2)) != CRYPT_OK) { goto error; }
/* find mG and mQ */
if ((err = mp_read_radix(mG->x, (char *)key->dp->Gx, 16)) != CRYPT_OK) { goto error; }
if ((err = mp_read_radix(mG->y, (char *)key->dp->Gy, 16)) != CRYPT_OK) { goto error; }
if ((err = mp_set(mG->z, 1)) != CRYPT_OK) { goto error; }
if ((err = mp_copy(key->pubkey.x, mQ->x)) != CRYPT_OK) { goto error; }
if ((err = mp_copy(key->pubkey.y, mQ->y)) != CRYPT_OK) { goto error; }
if ((err = mp_copy(key->pubkey.z, mQ->z)) != CRYPT_OK) { goto error; }
/* compute u1*mG + u2*mQ = mG */
if (ltc_mp.ecc_mul2add == NULL) {
if ((err = ltc_mp.ecc_ptmul(u1, mG, mG, m, 0)) != CRYPT_OK) { goto error; }
if ((err = ltc_mp.ecc_ptmul(u2, mQ, mQ, m, 0)) != CRYPT_OK) { goto error; }
/* find the montgomery mp */
if ((err = mp_montgomery_setup(m, &mp)) != CRYPT_OK) { goto error; }
/* add them */
if ((err = ltc_mp.ecc_ptadd(mQ, mG, mG, m, mp)) != CRYPT_OK) { goto error; }
/* reduce */
if ((err = ltc_mp.ecc_map(mG, m, mp)) != CRYPT_OK) { goto error; }
} else {
/* use Shamir's trick to compute u1*mG + u2*mQ using half of the doubles */
if ((err = ltc_mp.ecc_mul2add(mG, u1, mQ, u2, mG, m)) != CRYPT_OK) { goto error; }
}
/* v = X_x1 mod n */
if ((err = mp_mod(mG->x, p, v)) != CRYPT_OK) { goto error; }
/* does v == r */
if (mp_cmp(v, r) == LTC_MP_EQ) {
*stat = 1;
}
/* clear up and return */
err = CRYPT_OK;
error:
ltc_ecc_del_point(mG);
ltc_ecc_del_point(mQ);
mp_clear_multi(r, s, v, w, u1, u2, p, e, m, NULL);
if (mp != NULL) {
mp_montgomery_free(mp);
}
return err;
}
#endif
/* $Source: /cvs/libtom/libtomcrypt/src/pk/ecc/ecc_verify_hash.c,v $ */
/* $Revision: 1.12 $ */
/* $Date: 2006/12/04 05:07:59 $ */
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