87 lines
2.3 KiB
C
87 lines
2.3 KiB
C
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/* 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_key(dsa_key *key, int *stat)
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{
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mp_int tmp, tmp2;
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int res, err;
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_ARGCHK(key != NULL);
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_ARGCHK(stat != NULL);
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*stat = 0;
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/* first make sure key->q and key->p are prime */
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if ((err = is_prime(&key->q, &res)) != CRYPT_OK) {
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return err;
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}
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if (res == 0) {
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return CRYPT_OK;
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}
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if ((err = is_prime(&key->p, &res)) != CRYPT_OK) {
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return err;
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}
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if (res == 0) {
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return CRYPT_OK;
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}
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/* now make sure that g is not -1, 0 or 1 and <p */
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if (mp_cmp_d(&key->g, 0) == MP_EQ || mp_cmp_d(&key->g, 1) == MP_EQ) {
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return CRYPT_OK;
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}
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if ((err = mp_init_multi(&tmp, &tmp2, NULL)) != MP_OKAY) { goto error; }
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if ((err = mp_sub_d(&key->p, 1, &tmp)) != MP_OKAY) { goto error; }
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if (mp_cmp(&tmp, &key->g) == MP_EQ || mp_cmp(&key->g, &key->p) != MP_LT) {
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err = CRYPT_OK;
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goto done;
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}
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/* 1 < y < p-1 */
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if (!(mp_cmp_d(&key->y, 1) == MP_GT && mp_cmp(&key->y, &tmp) == MP_LT)) {
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err = CRYPT_OK;
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goto done;
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}
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/* now we have to make sure that g^q = 1, and that p-1/q gives 0 remainder */
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if ((err = mp_div(&tmp, &key->q, &tmp, &tmp2)) != MP_OKAY) { goto error; }
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if (mp_iszero(&tmp2) != MP_YES) {
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err = CRYPT_OK;
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goto done;
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}
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if ((err = mp_exptmod(&key->g, &key->q, &key->p, &tmp)) != MP_OKAY) { goto error; }
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if (mp_cmp_d(&tmp, 1) != MP_EQ) {
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err = CRYPT_OK;
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goto done;
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}
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/* now we have to make sure that y^q = 1, this makes sure y \in g^x mod p */
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if ((err = mp_exptmod(&key->y, &key->q, &key->p, &tmp)) != MP_OKAY) { goto error; }
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if (mp_cmp_d(&tmp, 1) != MP_EQ) {
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err = CRYPT_OK;
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goto done;
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}
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/* at this point we are out of tests ;-( */
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err = CRYPT_OK;
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*stat = 1;
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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(&tmp, &tmp2, NULL);
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return err;
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}
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#endif
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