/* 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
*/
/* Implements ECC over Z/pZ for curve y^2 = x^3 + a*x + b
*
*/
#include "tomcrypt.h"
#ifdef LTC_MECC
/**
@file ecc_verify_hash.c
ECC Crypto, Tom St Denis
*/
static int ecc_verify_hash_ex(const unsigned char *sig, unsigned long siglen,
const unsigned char *hash, unsigned long hashlen,
int *stat, ecc_key *key, int sigformat)
{
ecc_point *mG, *mQ;
void *r, *s, *v, *w, *u1, *u2, *e, *p, *m, *a;
void *mp;
int err;
unsigned long pbits, pbytes, i, shift_right;
unsigned char ch, buf[MAXBLOCKSIZE];
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, &a, 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;
}
if (sigformat == 1) {
/* RFC7518 format */
if ((siglen % 2) == 1) {
err = CRYPT_INVALID_PACKET;
goto error;
}
i = siglen / 2;
if ((err = mp_read_unsigned_bin(r, (unsigned char *)sig, i)) != CRYPT_OK) { goto error; }
if ((err = mp_read_unsigned_bin(s, (unsigned char *)sig+i, i)) != CRYPT_OK) { goto error; }
}
else {
/* ASN.1 format */
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; }
/* get the a */
if ((err = mp_read_radix(a, (char *)key->dp->A, 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 - truncate if needed */
pbits = mp_count_bits(p);
pbytes = (pbits+7) >> 3;
if (pbits > hashlen*8) {
if ((err = mp_read_unsigned_bin(e, (unsigned char *)hash, hashlen)) != CRYPT_OK) { goto error; }
}
else if (pbits % 8 == 0) {
if ((err = mp_read_unsigned_bin(e, (unsigned char *)hash, pbytes)) != CRYPT_OK) { goto error; }
}
else {
shift_right = 8 - pbits % 8;
for (i=0, ch=0; i<pbytes; i++) {
buf[i] = ch;
ch = (hash[i] << (8-shift_right));
buf[i] = buf[i] ^ (hash[i] >> shift_right);
}
if ((err = mp_read_unsigned_bin(e, (unsigned char *)buf, pbytes)) != 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, a, m, 0)) != CRYPT_OK) { goto error; }
if ((err = ltc_mp.ecc_ptmul(u2, mQ, mQ, a, 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, a, 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, a, 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, a, NULL);
if (mp != NULL) {
mp_montgomery_free(mp);
}
return err;
}
/**
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)
{
return ecc_verify_hash_ex(sig, siglen, hash, hashlen, stat, key, 0);
}
/**
Verify an ECC signature in RFC7518 format
@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_rfc7518(const unsigned char *sig, unsigned long siglen,
const unsigned char *hash, unsigned long hashlen,
int *stat, ecc_key *key)
{
return ecc_verify_hash_ex(sig, siglen, hash, hashlen, stat, key, 1);
}
#endif