"""
Implement repeating-key XOR

Here is the opening stanza of an important work of the English language:

Burning 'em, if you ain't quick and nimble
I go crazy when I hear a cymbal

Encrypt it, under the key "ICE", using repeating-key XOR.

In repeating-key XOR, you'll sequentially apply each byte of the key; the first byte
of plaintext will be XOR'd against I, the next C, the next E, then I again for the 4th
byte, and so on.

It should come out to:

0b3637272a2b2e63622c2e69692a23693a2a3c6324202d623d63343c2a26226324272765272
a282b2f20430a652e2c652a3124333a653e2b2027630c692b20283165286326302e27282f

Encrypt a bunch of stuff using your repeating-key XOR function. Encrypt your mail.
Encrypt your password file. Your .sig file. Get a feel for it. I promise, we aren't
wasting your time with this.
"""

import itertools
import sys


def repeating_xor(plaintext):
    pt_bytes = bytes(plaintext, "utf-8")
    key_bytes = bytes("ICE", "utf-8")

    encoded_phrase = bytes(
        [p ^ k for p, k in zip(pt_bytes, itertools.cycle(key_bytes))]
    )
    return encoded_phrase.hex()


if __name__ == "__main__":
    print(repeating_xor(sys.argv[1]))
