cipher.py

   1 """A set of ciphers with implementations for both enciphering and deciphering
   2 them. See cipherbreak for automatic breaking of these ciphers
   3 """
   4
   5 import string
   6 # import collections
   7 # from enum import Enum
   8 # from itertools import zip_longest, cycle, chain
   9
  10 from language_models import unaccent, sanitise
  11
  12
  13 def caesar_encipher_letter(accented_letter, shift):
  14     """Encipher a letter, given a shift amount
  15
  16     >>> caesar_encipher_letter('a', 1)
  17     'b'
  18     >>> caesar_encipher_letter('a', 2)
  19     'c'
  20     >>> caesar_encipher_letter('b', 2)
  21     'd'
  22     >>> caesar_encipher_letter('x', 2)
  23     'z'
  24     >>> caesar_encipher_letter('y', 2)
  25     'a'
  26     >>> caesar_encipher_letter('z', 2)
  27     'b'
  28     >>> caesar_encipher_letter('z', -1)
  29     'y'
  30     >>> caesar_encipher_letter('a', -1)
  31     'z'
  32     >>> caesar_encipher_letter('A', 1)
  33     'B'
  34     >>> caesar_encipher_letter('é', 1)
  35     'f'
  36     """
  37     letter = unaccent(accented_letter)
  38     if letter in string.ascii_letters:
  39         if letter in string.ascii_uppercase:
  40             alphabet_start = ord('A')
  41         else:
  42             alphabet_start = ord('a')
  43         return chr(((ord(letter) - alphabet_start + shift) % 26) +
  44                    alphabet_start)
  45     else:
  46         return letter
  47
  48 def caesar_decipher_letter(letter, shift):
  49     """Decipher a letter, given a shift amount
  50
  51     >>> caesar_decipher_letter('b', 1)
  52     'a'
  53     >>> caesar_decipher_letter('b', 2)
  54     'z'
  55     """
  56     return caesar_encipher_letter(letter, -shift)
  57
  58 def caesar_encipher(message, shift):
  59     """Encipher a message with the Caesar cipher of given shift
  60
  61     >>> caesar_encipher('abc', 1)
  62     'bcd'
  63     >>> caesar_encipher('abc', 2)
  64     'cde'
  65     >>> caesar_encipher('abcxyz', 2)
  66     'cdezab'
  67     >>> caesar_encipher('ab cx yz', 2)
  68     'cd ez ab'
  69     >>> caesar_encipher('Héllo World!', 2)
  70     'Jgnnq Yqtnf!'
  71     """
  72     enciphered = [caesar_encipher_letter(l, shift) for l in message]
  73     return ''.join(enciphered)
  74
  75 def caesar_decipher(message, shift):
  76     """Decipher a message with the Caesar cipher of given shift
  77
  78     >>> caesar_decipher('bcd', 1)
  79     'abc'
  80     >>> caesar_decipher('cde', 2)
  81     'abc'
  82     >>> caesar_decipher('cd ez ab', 2)
  83     'ab cx yz'
  84     >>> caesar_decipher('Jgnnq Yqtnf!', 2)
  85     'Hello World!'
  86     """
  87     return caesar_encipher(message, -shift)
  88
  89
  90 if __name__ == "__main__":
  91     import doctest
  92     doctest.testmod()