void bn_gen_prime_basic(bn_t a, int bits) {
while (1) {
do {
bn_rand(a, BN_POS, bits);
} while (bn_bits(a) != bits);
if (bn_is_prime(a)) {
return;
}
}
}
void bn_gen_prime_safep(bn_t a, int bits) {
while (1) {
do {
bn_rand(a, BN_POS, bits);
} while (bn_bits(a) != bits);
/* Check if (a - 1)/2 is prime. */
bn_sub_dig(a, a, 1);
bn_rsh(a, a, 1);
if (bn_is_prime(a)) {
/* Restore a. */
bn_lsh(a, a, 1);
bn_add_dig(a, a, 1);
if (bn_is_prime(a)) {
/* Should be prime now. */
return;
}
}
}
}
int fp_param_set_any_dense() {
bn_t modulus;
int result = STS_OK;
bn_null(modulus);
TRY {
bn_new(modulus);
bn_gen_prime(modulus, FP_BITS);
if (!bn_is_prime(modulus)) {
result = STS_ERR;
} else {
fp_prime_set_dense(modulus);
}
}
CATCH_ANY {
THROW(ERR_CAUGHT);
}
FINALLY {
bn_free(modulus);
}
return result;
}
int cp_bdpe_gen(bdpe_t pub, bdpe_t prv, dig_t block, int bits) {
bn_t t, r;
int result = STS_OK;
bn_null(t);
bn_null(r);
TRY {
bn_new(t);
bn_new(r);
prv->t = pub->t = block;
/* Make sure that block size is prime. */
bn_set_dig(t, block);
if (bn_is_prime_basic(t) == 0) {
THROW(ERR_NO_VALID);
}
/* Generate prime q such that gcd(block, (q - 1)) = 1. */
do {
bn_gen_prime(prv->q, bits / 2);
bn_sub_dig(prv->q, prv->q, 1);
bn_gcd_dig(t, prv->q, block);
bn_add_dig(prv->q, prv->q, 1);
} while (bn_cmp_dig(t, 1) != CMP_EQ);
/* Generate different primes p and q. */
do {
/* Compute p = block * (x * block + b) + 1, 0 < b < block random. */
bn_rand(prv->p, BN_POS, bits / 2 - 2 * util_bits_dig(block));
bn_mul_dig(prv->p, prv->p, block);
bn_rand(t, BN_POS, util_bits_dig(block));
bn_add_dig(prv->p, prv->p, t->dp[0]);
/* We know that block divides (p-1). */
bn_gcd_dig(t, prv->p, block);
bn_mul_dig(prv->p, prv->p, block);
bn_add_dig(prv->p, prv->p, 1);
} while (bn_cmp_dig(t, 1) != CMP_EQ || bn_is_prime(prv->p) == 0);
/* Compute t = (p-1)*(q-1). */
bn_sub_dig(prv->q, prv->q, 1);
bn_sub_dig(prv->p, prv->p, 1);
bn_mul(t, prv->p, prv->q);
bn_div_dig(t, t, block);
/* Restore factors p and q and compute n = p * q. */
bn_add_dig(prv->p, prv->p, 1);
bn_add_dig(prv->q, prv->q, 1);
bn_mul(pub->n, prv->p, prv->q);
bn_copy(prv->n, pub->n);
/* Select random y such that y^{(p-1)(q-1)}/block \neq 1 mod N. */
do {
bn_rand(pub->y, BN_POS, bits);
bn_mxp(r, pub->y, t, pub->n);
} while (bn_cmp_dig(r, 1) == CMP_EQ);
bn_copy(prv->y, pub->y);
}
CATCH_ANY {
result = STS_ERR;
}
FINALLY {
bn_free(t);
bn_free(r);
}
return result;
}
void bn_gen_prime_stron(bn_t a, int bits) {
dig_t i, j;
int found, k;
bn_t r, s, t;
bn_null(r);
bn_null(s);
bn_null(t);
TRY {
bn_new(r);
bn_new(s);
bn_new(t);
do {
do {
/* Generate two large primes r and s. */
bn_rand(s, BN_POS, bits / 2 - BN_DIGIT / 2);
bn_rand(t, BN_POS, bits / 2 - BN_DIGIT / 2);
} while (!bn_is_prime(s) || !bn_is_prime(t));
found = 1;
bn_rand(a, BN_POS, bits / 2 - bn_bits(t) - 1);
i = a->dp[0];
bn_dbl(t, t);
do {
/* Find first prime r = 2 * i * t + 1. */
bn_mul_dig(r, t, i);
bn_add_dig(r, r, 1);
i++;
if (bn_bits(r) > bits / 2 - 1) {
found = 0;
break;
}
} while (!bn_is_prime(r));
if (found == 0) {
continue;
}
/* Compute t = 2 * (s^(r-2) mod r) * s - 1. */
bn_sub_dig(t, r, 2);
#if BN_MOD != PMERS
bn_mxp(t, s, t, r);
#else
bn_exp(t, s, t, r);
#endif
bn_mul(t, t, s);
bn_dbl(t, t);
bn_sub_dig(t, t, 1);
k = bits - bn_bits(r);
k -= bn_bits(s);
bn_rand(a, BN_POS, k);
j = a->dp[0];
do {
/* Find first prime a = t + 2 * j * r * s. */
bn_mul(a, r, s);
bn_mul_dig(a, a, j);
bn_dbl(a, a);
bn_add(a, a, t);
j++;
if (bn_bits(a) > bits) {
found = 0;
break;
}
} while (!bn_is_prime(a));
} while (found == 0 && bn_bits(a) != bits);
}
CATCH_ANY {
THROW(ERR_CAUGHT);
}
FINALLY {
bn_free(r);
bn_free(s);
bn_free(t);
}
}
