diff options
Diffstat (limited to 'libtomcrypt/src/pk/dsa/dsa_verify_hash.c')
| -rw-r--r-- | libtomcrypt/src/pk/dsa/dsa_verify_hash.c | 128 |
1 files changed, 128 insertions, 0 deletions
diff --git a/libtomcrypt/src/pk/dsa/dsa_verify_hash.c b/libtomcrypt/src/pk/dsa/dsa_verify_hash.c new file mode 100644 index 0000000..11e5c33 --- /dev/null +++ b/libtomcrypt/src/pk/dsa/dsa_verify_hash.c @@ -0,0 +1,128 @@ +/* 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 $ */ |