Caesar Cipher Decryption Script

caesar_cipher_decrypt.py

"""
Code to crack Google Security Key Challenge #3
Accompanying blog post: http://www.jasondsouza.org/post/caesar-cipher-decryption/
@author: Jason Dsouza
"""

from string import punctuation

ALPHABET = "abcdefghijklmnopqrstuvwxyz"
KEY_SPACE = len(ALPHABET)

def create_caesar_cipher(N):
  # we use the mod operator here to perform the wrap-around mentioned above
  cipher = {ALPHABET[i]: ALPHABET[(i+N) % KEY_SPACE] for i, _ in enumerate(ALPHABET)}	
  return cipher

def decrypt(cipher, ciphertext):
  # remember we need to ignore letter case and punctuation
  decrypted = [letter if letter in punctuation + " " else cipher[letter] for letter in ciphertext.lower()]
  return "".join(decrypted)

if __name__ == "__main__":
  cipher_text = "Wuhdw brxu sdvvzrug olnh brxu wrrwkeuxvk. Grq'w ohw dqbergb hovh xvh lw, dqg jhw d qhz rqh hyhub vla prqwkv. Foliirug Vwroo"
	
  for n in range(KEY_SPACE):
    cipher = create_caesar_cipher(n)
    plaintext = decrypt(cipher, cipher_text)
    print("{}:\t{}".format(n, plaintext))