#include <iostream>
#include <string>
#include <stdlib.h>
#include <cstring>
#include <fstream>

using namespace std;

void encrypt(const string &key, ifstream &from, ofstream &to) {
	int key_size = key.size();
	char *key_cstr;

	key_cstr = (char*) malloc(key_size*sizeof(char));
	strcpy(key_cstr, key.c_str());

	char ch;
	int i=0;
	while (from.get(ch)) {
		int tex_c =(int) ch;
		int key_c =(int) key[i%key_size];
		to.put((char) tex_c^key_c);
		i++;
	}
	free(key_cstr);
}

void error(const char* p1, const char* p2="") {
	cerr<<p1<<" "<<p2<<endl;
	exit(1);
}

int main(int argc, char* argv[]) {

	if (argc!=4) error("./ex key fromfile tofile");

	string key;
	key.assign(argv[1]);

	ifstream from(argv[2]);
	ofstream to(argv[3]);
	if (!from) error("cannot open file", argv[2]);

	encrypt(key, from, to);


	return 1;
}