| /* 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.org |
| */ |
| #include "tomcrypt.h" |
| |
| /** |
| @file dsa_verify_hash.c |
| DSA implementation, verify a signature, Tom St Denis |
| */ |
| |
| |
| #ifdef 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 *r, mp_int *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)) != MP_OKAY) { |
| return mpi_to_ltc_error(err); |
| } |
| |
| /* neither r or s can be null or >q*/ |
| if (mp_iszero(r) == MP_YES || mp_iszero(s) == MP_YES || mp_cmp(r, &key->q) != MP_LT || mp_cmp(s, &key->q) != MP_LT) { |
| err = CRYPT_INVALID_PACKET; |
| goto done; |
| } |
| |
| /* w = 1/s mod q */ |
| if ((err = mp_invmod(s, &key->q, &w)) != MP_OKAY) { goto error; } |
| |
| /* u1 = m * w mod q */ |
| if ((err = mp_read_unsigned_bin(&u1, (unsigned char *)hash, hashlen)) != MP_OKAY) { goto error; } |
| if ((err = mp_mulmod(&u1, &w, &key->q, &u1)) != MP_OKAY) { goto error; } |
| |
| /* u2 = r*w mod q */ |
| if ((err = mp_mulmod(r, &w, &key->q, &u2)) != MP_OKAY) { goto error; } |
| |
| /* v = g^u1 * y^u2 mod p mod q */ |
| if ((err = mp_exptmod(&key->g, &u1, &key->p, &u1)) != MP_OKAY) { goto error; } |
| if ((err = mp_exptmod(&key->y, &u2, &key->p, &u2)) != MP_OKAY) { goto error; } |
| if ((err = mp_mulmod(&u1, &u2, &key->p, &v)) != MP_OKAY) { goto error; } |
| if ((err = mp_mod(&v, &key->q, &v)) != MP_OKAY) { goto error; } |
| |
| /* if r = v then we're set */ |
| if (mp_cmp(r, &v) == MP_EQ) { |
| *stat = 1; |
| } |
| |
| err = CRYPT_OK; |
| goto done; |
| |
| error : err = mpi_to_ltc_error(err); |
| done : 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: 1.8 $ */ |
| /* $Date: 2005/05/15 21:48:59 $ */ |