98 lines
2.9 KiB
C
98 lines
2.9 KiB
C
/* LibTomCrypt, modular cryptographic library -- Tom St Denis
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*
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* LibTomCrypt is a library that provides various cryptographic
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* algorithms in a highly modular and flexible manner.
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*
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* The library is free for all purposes without any express
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* guarantee it works.
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*
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* Tom St Denis, tomstdenis@iahu.ca, http://libtomcrypt.org
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*/
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#include "mycrypt.h"
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#ifdef MDSA
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int dsa_verify_hash(const unsigned char *sig, unsigned long siglen,
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const unsigned char *hash, unsigned long inlen,
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int *stat, dsa_key *key)
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{
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mp_int r, s, w, v, u1, u2;
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unsigned long x, y;
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int err;
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_ARGCHK(sig != NULL);
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_ARGCHK(hash != NULL);
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_ARGCHK(stat != NULL);
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_ARGCHK(key != NULL);
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/* default to invalid signature */
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*stat = 0;
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if (siglen < PACKET_SIZE+2+2) {
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return CRYPT_INVALID_PACKET;
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}
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/* is the message format correct? */
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if ((err = packet_valid_header((unsigned char *)sig, PACKET_SECT_DSA, PACKET_SUB_SIGNED)) != CRYPT_OK) {
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return err;
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}
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/* skip over header */
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y = PACKET_SIZE;
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/* init our variables */
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if ((err = mp_init_multi(&r, &s, &w, &v, &u1, &u2, NULL)) != MP_OKAY) {
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return mpi_to_ltc_error(err);
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}
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/* read in r followed by s */
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x = ((unsigned)sig[y]<<8)|((unsigned)sig[y+1]);
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y += 2;
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if (y + x > siglen) {
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err = CRYPT_INVALID_PACKET;
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goto done;
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}
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if ((err = mp_read_unsigned_bin(&r, (unsigned char *)sig+y, x)) != MP_OKAY) { goto error; }
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y += x;
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/* load s */
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x = ((unsigned)sig[y]<<8)|((unsigned)sig[y+1]);
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y += 2;
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if (y + x > siglen) {
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err = CRYPT_INVALID_PACKET;
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goto done;
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}
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if ((err = mp_read_unsigned_bin(&s, (unsigned char *)sig+y, x)) != MP_OKAY) { goto error; }
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/* w = 1/s mod q */
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if ((err = mp_invmod(&s, &key->q, &w)) != MP_OKAY) { goto error; }
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/* u1 = m * w mod q */
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if ((err = mp_read_unsigned_bin(&u1, (unsigned char *)hash, inlen)) != MP_OKAY) { goto error; }
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if ((err = mp_mulmod(&u1, &w, &key->q, &u1)) != MP_OKAY) { goto error; }
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/* u2 = r*w mod q */
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if ((err = mp_mulmod(&r, &w, &key->q, &u2)) != MP_OKAY) { goto error; }
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/* v = g^u1 * y^u2 mod p mod q */
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if ((err = mp_exptmod(&key->g, &u1, &key->p, &u1)) != MP_OKAY) { goto error; }
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if ((err = mp_exptmod(&key->y, &u2, &key->p, &u2)) != MP_OKAY) { goto error; }
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if ((err = mp_mulmod(&u1, &u2, &key->p, &v)) != MP_OKAY) { goto error; }
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if ((err = mp_mod(&v, &key->q, &v)) != MP_OKAY) { goto error; }
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/* if r = v then we're set */
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if (mp_cmp(&r, &v) == MP_EQ) {
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*stat = 1;
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}
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err = CRYPT_OK;
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goto done;
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error : err = mpi_to_ltc_error(err);
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done : mp_clear_multi(&r, &s, &w, &v, &u1, &u2, NULL);
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return err;
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}
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#endif
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