#include "rsa.h"

uint32_t get_random_bytes(int fd) {
	uint32_t ret;
	if (read(fd, &ret, sizeof(uint32_t)) == -1) {
		exit(1);
	}
	return ret;
}

// nn pow e mod mm
uint32_t pow_mod(uint32_t nn, uint32_t e, uint32_t mm) {
	uint64_t x = nn;
	uint64_t m = mm;
	uint64_t y = 1;

	while (e > 1) {
		if (e % 2) {
			y *= x;
			e -= 1;
			y = y % m;
		}
		x *= x;
		e /= 2;
		x = x % m;
	}
	return (uint32_t)(x * y % m);
}

bool is_prime(uint32_t n, uint32_t k_max, int fd) {
	uint32_t a = get_random_bytes(fd);
	uint32_t d = n - 1;
	uint32_t s = 0;

	while ((d & 1) == 0) {
		s++;
		d = d >> 1;
	}

	for (uint32_t k = 0; k < k_max; k++) {
		while (a < 2 || a > (n - 2)) {
			a = get_random_bytes(fd);
		}
		uint32_t x = pow_mod(a, d, n);
		uint32_t y;
		for (uint32_t i = 0; i < s; i++) {
			y = pow_mod(x, 2, n);
			if (y == 1 && x != 1 && x != n - 1)
				return false;
			x = y;
		}
		if (y != 1) {
			return false;
		}
	}
	return true;
}

uint32_t generate_prime_fd(int fd) {
	uint32_t n = get_random_bytes(fd);
	n |= 1 << 31;
	n |= 1;

	while (n % 65537 == 0 || !is_prime(n, 128, fd)) {
		n = get_random_bytes(fd);
		n |= 1 << 31;
		n |= 1;
	}
	return n;
}

uint32_t generate_prime() {
	int fd = open("/dev/urandom", O_RDONLY);
	uint32_t n = generate_prime_fd(fd);
	close(fd);
	return n;
}