xor.py

import unittest
from itertools import cycle
from binascii import hexlify
from os import urandom

# returns a random hex string of length l
# urandom returns 2 bits for every length unit hence the 'l/2'
uniqid = lambda l: hexlify(urandom(round(l/2))).decode()

# '^' = xor (exclusive or): is true when bit a != bit b e.g. 0b10 ^ 0b01 = 0b11
xor = lambda s, k: "".join(chr(ord(x) ^ ord(y)) for x,y in zip(s, cycle(k)))

class TestXOR(unittest.TestCase):
    def setUp(self):
        self.string = "This needs to be encrypted"
        self.key = uniqid(16)

    def test_decryption(self):
        """ Test that the decrypted string == the original string"""
        encrypted = xor(self.string, self.key)
        self.assertEqual(self.string, xor(encrypted, self.key))

if __name__ == '__main__':
    unittest.main()