#include "stdio.h"

int power_modulo_fast(int a, int b, int m)
{
int i;
int result = 1;
int x = a % m;

for (i=1; i<=b; i<<=1)
{
  x %= m;

    if ((b&i) != 0)
      {
    result *= x;
    result %= m;
      }

   x *= x;
}

  return result;
}

int decrypt_encrypt(int num, int Decrypt, int Encrypt, int PQ) {
    printf("Decrypt op for %d\n", num);
    int ctxt = power_modulo_fast(num, Encrypt, PQ);
    printf("cipher num %d\n", ctxt);
    int ctxt2 = power_modulo_fast(ctxt, Decrypt, PQ);
    printf("decrypt num %d\n", ctxt2);
    return 0;
}

int main() {
    int Decrypt = 157;
    int Encrypt = 17;
    int P = 47;
    int Q = 59;
    int PQ = P*Q;

    printf("Modulo %d\n", PQ);
    decrypt_encrypt(920, Decrypt, Encrypt, PQ);
    decrypt_encrypt(100, Decrypt, Encrypt, PQ);
    decrypt_encrypt(1000, Decrypt, Encrypt, PQ);
}