BN_rand
BN_rand(r, size * 8, 0, 0);
BN_rand(rnd, BN_num_bits(range), 1, 0);
int BN_rand(BIGNUM */*rnd*/, int /*bits*/, int /*top*/, int /*bottom*/);
BN_rand(a, Rand(), 0, 0);
BN_rand(b, Rand(), 0, 0);
BN_rand(largebase, power, 1, 1);