#include <stdio.h>
#include <stdlib.h>
#include "rsa.h"
#include "prng.h"

/*
 * We will generate the public and private RSA key
 */
void generateKeys(unsigned long *e, unsigned long *d, unsigned long *n){
    unsigned long p = prng();
    unsigned long q = prng();
    unsigned long phi = 0;

    // Check if p and q are different
    if (p == q)
      q ^= q << 2;

    // Check if p and q are prime numbers
    if (isPrimeNumber(p) != 0)
        prime_number_finder(&p);

    if (isPrimeNumber(q) != 0)
        prime_number_finder(&q);

    // Calculate n
    *n = p * q;
    
    // We're going to calcule the Euler's totient
    phi = (p - 1)*(q - 1);

    /* We will calculate e for the public key */
    generatePublicKey(phi, e);

    /* We will calcuate d for the private key */
    generatePrivateKey(d, phi, e);
}
/*
 * This function will identify all the divider of the variable a
 * with the Euclidean algorithm
 */
static int gcd(unsigned long a, unsigned long b){
  if (b == 0)
        return a;
    return gcd(b, a%b);
}
/*
 * This function will check if te variable e is a prime number
 * is not, we increment the value to 1 and continue until is a prime number
 */
static void prime_number_finder(unsigned long *p){
    while(isPrimeNumber(*p) != 0)
        *p += 1;
}
/*
 * Check if the number specified is a prime number
 */
static int isPrimeNumber(unsigned long x){ 
    for (int i = 2; i < x; i++){
        if (x % i == 0)
            return 1;
    }
    return 0;
}
/*
 * Generate the public key and need to be coprime with phi(n)
 */
static unsigned long generatePublicKey(unsigned long phi, unsigned long *e){
    // Generate e
    *e = prng();

    while ((gcd(phi, *e)) != 1)
        *e += 1;
    
    return *e;
}
/*
 * We generate tne private key with the modular inverse of phi(n)
 */
static unsigned long generatePrivateKey(unsigned long *d, unsigned long phi, unsigned long *e){
    for (int i = 0; i <= phi; i++){
        if ((i * (*e)) % phi == 1){
            *d = i; 
            break;
        }
    }

    return *d;
}