OTP - Encryt / Decrypt example

otp.py

import sys
import string
import random

# return a key of the size
# of the PT
def generate_key(length):
    r = lambda: \
        string.ascii_letters[int(random.random() * len(string.ascii_letters))]
    key = b''
    for k in range(length):
        key += bytes(r().encode())
    return key

def encrypt(msg: bytes):
    length = len(msg)
    key = generate_key(length)
    i = 0
    c = b''
    while i < length:
        c += bytes(chr(key[i] ^ msg[i]).encode())
        i += 1
    return c, key

def decrypt(c: bytes, key: bytes):
    i = 0
    m = b''
    while i < len(key):
        m += bytes(chr(key[i] ^ c[i]).encode())
        i += 1
    return m

if __name__ == "__main__":

    if len(sys.argv) < 2:
        print("usage: python otp.py <message>")
        exit(0)

    msg = sys.argv[1]
    c, k = encrypt(bytes(msg.encode()))
    print(decrypt(c, k))