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