#include <unistd.h>
#include <errno.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <time.h>
#include <windows.h>
#include <stdio.h>
#include <stdlib.h>
#include <winsock.h>


int repeatsquare( int x, int e, int n);
bool RelativelyPrime (int a, int b);


int main(){
	unsigned char chararray[80];
	unsigned char encrypted[80];
	unsigned char normalarray[80];
	char temp[80];
	int length;
	printf("Please Enter A Word : ");
	//scanf("%s",chararray);
	fgets(temp,80,stdin);
//	strcpy(chararray, (unsigned char) temp);
	//strcpy(chararray, temp);
	for(int i=0; i<strlen(temp); i++){
		chararray[i] = (unsigned char)temp[i];
		printf("-> %c", chararray[i]);
	}

	length = sizeof(chararray);
	int primenumbers[15] = {11,13,17,19,23,29,31,37,41,43};
	int q,p,n,z,e,d;
	while(true){
		srand(time(NULL));
		q = primenumbers[(rand()%15)];
		p = primenumbers[(rand()%15)];
		z = (p-1)*(q-1);
		n = q*p;
		e = n-1;
		if(n == 0){
			continue;
		}
		//printf("p=%d,q=%d n=%d\n",p,q,n);
		if((n)>255){
			continue;
		}
		while(!RelativelyPrime(e,z)){

			e = rand()%n;
			if(n==(e-1)){
				continue;
			}
		}

		if ((RelativelyPrime(e,z)) && (n <= 255)){
			printf("break\n");
			break;
		}
	}

	int i = 0;
	while(true){
		if((((e*i)-1)% z) == 0){
			d = i;
			break;
		}else{
			i++;
		}
	}

	printf("p=%d q=%d n=%d z=%d, e=%d d=%d\n",p,q,n,z,e,d);

	for(i=0;i<length;i++){
		encrypted[i]=repeatsquare(chararray[i],e,n);
		//printf("%d\n",encrypted[i]);
	}
	printf("TITLE : %s\n",encrypted);
	for(i=0;i<length;i++){
		normalarray[i]=repeatsquare(encrypted[i],d,n);
		//printf("%d\n",normalarray[i]);
	}
	printf("TITLE 2 : %s\n",normalarray);

}

int repeatsquare( int x, int e, int n) {
	int y=1;//initialize y to 1, very important
	while (e > 0) {
		if (( e % 2 ) == 0) {
			x = (x*x) % n;
			e = e/2;
		}
		else {
			y = (x*y) % n;
			e = e-1;
		}
	}
	return y; //the result is stored in y
}

bool RelativelyPrime (int a, int b) { // Assumes a, b > 0
	for ( ; ; ) {
		if (!(a %= b)) return b == 1 ;
		if (!(b %= a)) return a == 1 ;
	}
}