diff options
Diffstat (limited to 'libtomcrypt/src/pk/dsa/dsa_verify_hash.c')
| -rw-r--r-- | libtomcrypt/src/pk/dsa/dsa_verify_hash.c | 126 |
1 files changed, 126 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..0e8ff22 --- /dev/null +++ b/libtomcrypt/src/pk/dsa/dsa_verify_hash.c @@ -0,0 +1,126 @@ +/* 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 + */ +#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( void *r, void *s, + const unsigned char *hash, unsigned long hashlen, + int *stat, dsa_key *key) +{ + void *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; + void *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: 1.13 $ */ +/* $Date: 2006/12/04 03:18:43 $ */ |