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/* LibTomCrypt, modular cryptographic library -- Tom St Denis
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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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* The library is free for all purposes without any express
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* Tom St Denis, tomstdenis@iahu.ca, http://libtomcrypt.org
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int dsa_make_key(prng_state *prng, int wprng, int group_size, int modulus_size, dsa_key *key)
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if ((err = prng_is_valid(wprng)) != CRYPT_OK) {
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if (group_size >= MDSA_MAX_GROUP || group_size <= 15 ||
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group_size >= modulus_size || (modulus_size - group_size) >= MDSA_DELTA) {
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return CRYPT_INVALID_ARG;
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buf = XMALLOC(MDSA_DELTA);
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if ((err = mp_init_multi(&tmp, &tmp2, &key->g, &key->q, &key->p, &key->x, &key->y, NULL)) != MP_OKAY) {
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err = mpi_to_ltc_error(err);
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/* make our prime q */
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if ((err = rand_prime(&key->q, group_size*8, prng, wprng)) != CRYPT_OK) { goto __ERR; }
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if ((err = mp_mul_2(&key->q, &tmp)) != MP_OKAY) { goto error; }
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/* now make a random string and multply it against q */
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if (prng_descriptor[wprng].read(buf+1, modulus_size - group_size, prng) != (unsigned long)(modulus_size - group_size)) {
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err = CRYPT_ERROR_READPRNG;
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buf[modulus_size - group_size] &= ~1;
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if ((err = mp_read_unsigned_bin(&tmp2, buf, modulus_size - group_size+1)) != MP_OKAY) { goto error; }
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if ((err = mp_mul(&key->q, &tmp2, &key->p)) != MP_OKAY) { goto error; }
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if ((err = mp_add_d(&key->p, 1, &key->p)) != MP_OKAY) { goto error; }
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/* now loop until p is prime */
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if ((err = is_prime(&key->p, &res)) != CRYPT_OK) { goto __ERR; }
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if (res == MP_YES) break;
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/* add 2q to p and 2 to tmp2 */
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if ((err = mp_add(&tmp, &key->p, &key->p)) != MP_OKAY) { goto error; }
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if ((err = mp_add_d(&tmp2, 2, &tmp2)) != MP_OKAY) { goto error; }
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/* now p = (q * tmp2) + 1 is prime, find a value g for which g^tmp2 != 1 */
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if ((err = mp_add_d(&key->g, 1, &key->g)) != MP_OKAY) { goto error; }
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if ((err = mp_exptmod(&key->g, &tmp2, &key->p, &tmp)) != MP_OKAY) { goto error; }
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} while (mp_cmp_d(&tmp, 1) == MP_EQ);
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/* at this point tmp generates a group of order q mod p */
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mp_exch(&tmp, &key->g);
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/* so now we have our DH structure, generator g, order q, modulus p
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Now we need a random exponent [mod q] and it's power g^x mod p
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if (prng_descriptor[wprng].read(buf, group_size, prng) != (unsigned long)group_size) {
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err = CRYPT_ERROR_READPRNG;
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if ((err = mp_read_unsigned_bin(&key->x, buf, group_size)) != MP_OKAY) { goto error; }
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} while (mp_cmp_d(&key->x, 1) != MP_GT);
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if ((err = mp_exptmod(&key->g, &key->x, &key->p, &key->y)) != MP_OKAY) { goto error; }
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key->type = PK_PRIVATE;
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key->qord = group_size;
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/* shrink the ram required */
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if ((err = mp_shrink(&key->g)) != MP_OKAY) { goto error; }
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if ((err = mp_shrink(&key->p)) != MP_OKAY) { goto error; }
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if ((err = mp_shrink(&key->q)) != MP_OKAY) { goto error; }
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if ((err = mp_shrink(&key->x)) != MP_OKAY) { goto error; }
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if ((err = mp_shrink(&key->y)) != MP_OKAY) { goto error; }
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zeromem(buf, MDSA_DELTA);
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err = mpi_to_ltc_error(err);
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mp_clear_multi(&key->g, &key->q, &key->p, &key->x, &key->y, NULL);
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mp_clear_multi(&tmp, &tmp2, NULL);