#!/usr/bin/env python

def xor(data, key):
    keylen = len(key)
    return bytearray((
        (data[i] ^ key[i % keylen]) for i in range(0,len(data))
    ))
    

if __name__ == "__main__":
    data = bytearray(open('topsecret.txt', 'rb').read())
    key = b'key'
    res = xor(data, key)
    print(res.decode())