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 modular_division_table = [[0]*26 for _ in range(26)]
  13 for a in range(26):
  14     for b in range(26):
  15         c = (a * b) % 26
  16         modular_division_table[b][c] = a
  17
  18
  19 def every_nth(text, n, fillvalue=''):
  20     """Returns n strings, each of which consists of every nth character,
  21     starting with the 0th, 1st, 2nd, ... (n-1)th character
  22
  23     >>> every_nth(string.ascii_lowercase, 5)
  24     ['afkpuz', 'bglqv', 'chmrw', 'dinsx', 'ejoty']
  25     >>> every_nth(string.ascii_lowercase, 1)
  26     ['abcdefghijklmnopqrstuvwxyz']
  27     >>> every_nth(string.ascii_lowercase, 26) # doctest: +NORMALIZE_WHITESPACE
  28     ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
  29      'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z']
  30     >>> every_nth(string.ascii_lowercase, 5, fillvalue='!')
  31     ['afkpuz', 'bglqv!', 'chmrw!', 'dinsx!', 'ejoty!']
  32     """
  33     split_text = chunks(text, n, fillvalue)
  34     return [''.join(l) for l in zip_longest(*split_text, fillvalue=fillvalue)]
  35
  36 def combine_every_nth(split_text):
  37     """Reforms a text split into every_nth strings
  38
  39     >>> combine_every_nth(every_nth(string.ascii_lowercase, 5))
  40     'abcdefghijklmnopqrstuvwxyz'
  41     >>> combine_every_nth(every_nth(string.ascii_lowercase, 1))
  42     'abcdefghijklmnopqrstuvwxyz'
  43     >>> combine_every_nth(every_nth(string.ascii_lowercase, 26))
  44     'abcdefghijklmnopqrstuvwxyz'
  45     """
  46     return ''.join([''.join(l)
  47                     for l in zip_longest(*split_text, fillvalue='')])
  48
  49 def chunks(text, n, fillvalue=None):
  50     """Split a text into chunks of n characters
  51
  52     >>> chunks('abcdefghi', 3)
  53     ['abc', 'def', 'ghi']
  54     >>> chunks('abcdefghi', 4)
  55     ['abcd', 'efgh', 'i']
  56     >>> chunks('abcdefghi', 4, fillvalue='!')
  57     ['abcd', 'efgh', 'i!!!']
  58     """
  59     if fillvalue:
  60         padding = fillvalue[0] * (n - len(text) % n)
  61     else:
  62         padding = ''
  63     return [(text+padding)[i:i+n] for i in range(0, len(text), n)]
  64
  65 def deduplicate(text):
  66     """If a string contains duplicate letters, remove all but the first. Retain
  67     the order of the letters.
  68
  69     >>> deduplicate('cat')
  70     ['c', 'a', 't']
  71     >>> deduplicate('happy')
  72     ['h', 'a', 'p', 'y']
  73     >>> deduplicate('cattca')
  74     ['c', 'a', 't']
  75     """
  76     return list(collections.OrderedDict.fromkeys(text))
  77
  78
  79 def caesar_encipher_letter(accented_letter, shift):
  80     """Encipher a letter, given a shift amount
  81
  82     >>> caesar_encipher_letter('a', 1)
  83     'b'
  84     >>> caesar_encipher_letter('a', 2)
  85     'c'
  86     >>> caesar_encipher_letter('b', 2)
  87     'd'
  88     >>> caesar_encipher_letter('x', 2)
  89     'z'
  90     >>> caesar_encipher_letter('y', 2)
  91     'a'
  92     >>> caesar_encipher_letter('z', 2)
  93     'b'
  94     >>> caesar_encipher_letter('z', -1)
  95     'y'
  96     >>> caesar_encipher_letter('a', -1)
  97     'z'
  98     >>> caesar_encipher_letter('A', 1)
  99     'B'
 100     >>> caesar_encipher_letter('é', 1)
 101     'f'
 102     """
 103     letter = unaccent(accented_letter)
 104     if letter in string.ascii_letters:
 105         if letter in string.ascii_uppercase:
 106             alphabet_start = ord('A')
 107         else:
 108             alphabet_start = ord('a')
 109         return chr(((ord(letter) - alphabet_start + shift) % 26) +
 110                    alphabet_start)
 111     else:
 112         return letter
 113
 114 def caesar_decipher_letter(letter, shift):
 115     """Decipher a letter, given a shift amount
 116
 117     >>> caesar_decipher_letter('b', 1)
 118     'a'
 119     >>> caesar_decipher_letter('b', 2)
 120     'z'
 121     """
 122     return caesar_encipher_letter(letter, -shift)
 123
 124 def caesar_encipher(message, shift):
 125     """Encipher a message with the Caesar cipher of given shift
 126
 127     >>> caesar_encipher('abc', 1)
 128     'bcd'
 129     >>> caesar_encipher('abc', 2)
 130     'cde'
 131     >>> caesar_encipher('abcxyz', 2)
 132     'cdezab'
 133     >>> caesar_encipher('ab cx yz', 2)
 134     'cd ez ab'
 135     >>> caesar_encipher('Héllo World!', 2)
 136     'Jgnnq Yqtnf!'
 137     """
 138     enciphered = [caesar_encipher_letter(l, shift) for l in message]
 139     return ''.join(enciphered)
 140
 141 def caesar_decipher(message, shift):
 142     """Decipher a message with the Caesar cipher of given shift
 143
 144     >>> caesar_decipher('bcd', 1)
 145     'abc'
 146     >>> caesar_decipher('cde', 2)
 147     'abc'
 148     >>> caesar_decipher('cd ez ab', 2)
 149     'ab cx yz'
 150     >>> caesar_decipher('Jgnnq Yqtnf!', 2)
 151     'Hello World!'
 152     """
 153     return caesar_encipher(message, -shift)
 154
 155 def affine_encipher_letter(accented_letter, multiplier=1, adder=0,
 156                            one_based=True):
 157     """Encipher a letter, given a multiplier and adder
 158     >>> ''.join([affine_encipher_letter(l, 3, 5, True) \
 159             for l in string.ascii_uppercase])
 160     'HKNQTWZCFILORUXADGJMPSVYBE'
 161     >>> ''.join([affine_encipher_letter(l, 3, 5, False) \
 162             for l in string.ascii_uppercase])
 163     'FILORUXADGJMPSVYBEHKNQTWZC'
 164     """
 165     letter = unaccent(accented_letter)
 166     if letter in string.ascii_letters:
 167         if letter in string.ascii_uppercase:
 168             alphabet_start = ord('A')
 169         else:
 170             alphabet_start = ord('a')
 171         letter_number = ord(letter) - alphabet_start
 172         if one_based: letter_number += 1
 173         cipher_number = (letter_number * multiplier + adder) % 26
 174         if one_based: cipher_number -= 1
 175         return chr(cipher_number % 26 + alphabet_start)
 176     else:
 177         return letter
 178
 179 def affine_decipher_letter(letter, multiplier=1, adder=0, one_based=True):
 180     """Encipher a letter, given a multiplier and adder
 181
 182     >>> ''.join([affine_decipher_letter(l, 3, 5, True) \
 183             for l in 'HKNQTWZCFILORUXADGJMPSVYBE'])
 184     'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
 185     >>> ''.join([affine_decipher_letter(l, 3, 5, False) \
 186             for l in 'FILORUXADGJMPSVYBEHKNQTWZC'])
 187     'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
 188     """
 189     if letter in string.ascii_letters:
 190         if letter in string.ascii_uppercase:
 191             alphabet_start = ord('A')
 192         else:
 193             alphabet_start = ord('a')
 194         cipher_number = ord(letter) - alphabet_start
 195         if one_based: cipher_number += 1
 196         plaintext_number = (
 197             modular_division_table[multiplier]
 198                                   [(cipher_number - adder) % 26]
 199                             )
 200         if one_based: plaintext_number -= 1
 201         return chr(plaintext_number % 26 + alphabet_start)
 202     else:
 203         return letter
 204
 205 def affine_encipher(message, multiplier=1, adder=0, one_based=True):
 206     """Encipher a message
 207
 208     >>> affine_encipher('hours passed during which jerico tried every ' \
 209            'trick he could think of', 15, 22, True)
 210     'lmyfu bkuusd dyfaxw claol psfaom jfasd snsfg jfaoe ls omytd jlaxe mh'
 211     """
 212     enciphered = [affine_encipher_letter(l, multiplier, adder, one_based)
 213                   for l in message]
 214     return ''.join(enciphered)
 215
 216 def affine_decipher(message, multiplier=1, adder=0, one_based=True):
 217     """Decipher a message
 218
 219     >>> affine_decipher('lmyfu bkuusd dyfaxw claol psfaom jfasd snsfg ' \
 220            'jfaoe ls omytd jlaxe mh', 15, 22, True)
 221     'hours passed during which jerico tried every trick he could think of'
 222     """
 223     enciphered = [affine_decipher_letter(l, multiplier, adder, one_based)
 224                   for l in message]
 225     return ''.join(enciphered)
 226
 227
 228 class KeywordWrapAlphabet(Enum):
 229     """Ways of wrapping the alphabet for keyword-based substitution ciphers."""
 230     from_a = 1
 231     from_last = 2
 232     from_largest = 3
 233
 234
 235 def keyword_cipher_alphabet_of(keyword,
 236         wrap_alphabet=KeywordWrapAlphabet.from_a):
 237     """Find the cipher alphabet given a keyword.
 238     wrap_alphabet controls how the rest of the alphabet is added
 239     after the keyword.
 240
 241     >>> keyword_cipher_alphabet_of('bayes')
 242     'bayescdfghijklmnopqrtuvwxz'
 243     >>> keyword_cipher_alphabet_of('bayes', KeywordWrapAlphabet.from_a)
 244     'bayescdfghijklmnopqrtuvwxz'
 245     >>> keyword_cipher_alphabet_of('bayes', KeywordWrapAlphabet.from_last)
 246     'bayestuvwxzcdfghijklmnopqr'
 247     >>> keyword_cipher_alphabet_of('bayes', KeywordWrapAlphabet.from_largest)
 248     'bayeszcdfghijklmnopqrtuvwx'
 249     """
 250     if wrap_alphabet == KeywordWrapAlphabet.from_a:
 251         cipher_alphabet = ''.join(deduplicate(sanitise(keyword) +
 252                                               string.ascii_lowercase))
 253     else:
 254         if wrap_alphabet == KeywordWrapAlphabet.from_last:
 255             last_keyword_letter = deduplicate(sanitise(keyword))[-1]
 256         else:
 257             last_keyword_letter = sorted(sanitise(keyword))[-1]
 258         last_keyword_position = string.ascii_lowercase.find(
 259             last_keyword_letter) + 1
 260         cipher_alphabet = ''.join(
 261             deduplicate(sanitise(keyword) +
 262                         string.ascii_lowercase[last_keyword_position:] +
 263                         string.ascii_lowercase))
 264     return cipher_alphabet
 265
 266
 267 def keyword_encipher(message, keyword,
 268                      wrap_alphabet=KeywordWrapAlphabet.from_a):
 269     """Enciphers a message with a keyword substitution cipher.
 270     wrap_alphabet controls how the rest of the alphabet is added
 271     after the keyword.
 272     0 : from 'a'
 273     1 : from the last letter in the sanitised keyword
 274     2 : from the largest letter in the sanitised keyword
 275
 276     >>> keyword_encipher('test message', 'bayes')
 277     'rsqr ksqqbds'
 278     >>> keyword_encipher('test message', 'bayes', KeywordWrapAlphabet.from_a)
 279     'rsqr ksqqbds'
 280     >>> keyword_encipher('test message', 'bayes', KeywordWrapAlphabet.from_last)
 281     'lskl dskkbus'
 282     >>> keyword_encipher('test message', 'bayes', KeywordWrapAlphabet.from_largest)
 283     'qspq jsppbcs'
 284     """
 285     cipher_alphabet = keyword_cipher_alphabet_of(keyword, wrap_alphabet)
 286     cipher_translation = ''.maketrans(string.ascii_lowercase, cipher_alphabet)
 287     return unaccent(message).lower().translate(cipher_translation)
 288
 289 def keyword_decipher(message, keyword,
 290                      wrap_alphabet=KeywordWrapAlphabet.from_a):
 291     """Deciphers a message with a keyword substitution cipher.
 292     wrap_alphabet controls how the rest of the alphabet is added
 293     after the keyword.
 294     0 : from 'a'
 295     1 : from the last letter in the sanitised keyword
 296     2 : from the largest letter in the sanitised keyword
 297
 298     >>> keyword_decipher('rsqr ksqqbds', 'bayes')
 299     'test message'
 300     >>> keyword_decipher('rsqr ksqqbds', 'bayes', KeywordWrapAlphabet.from_a)
 301     'test message'
 302     >>> keyword_decipher('lskl dskkbus', 'bayes', KeywordWrapAlphabet.from_last)
 303     'test message'
 304     >>> keyword_decipher('qspq jsppbcs', 'bayes', KeywordWrapAlphabet.from_largest)
 305     'test message'
 306     """
 307     cipher_alphabet = keyword_cipher_alphabet_of(keyword, wrap_alphabet)
 308     cipher_translation = ''.maketrans(cipher_alphabet, string.ascii_lowercase)
 309     return message.lower().translate(cipher_translation)
 310
 311
 312 def vigenere_encipher(message, keyword):
 313     """Vigenere encipher
 314
 315     >>> vigenere_encipher('hello', 'abc')
 316     'hfnlp'
 317     """
 318     shifts = [ord(l) - ord('a') for l in sanitise(keyword)]
 319     pairs = zip(message, cycle(shifts))
 320     return ''.join([caesar_encipher_letter(l, k) for l, k in pairs])
 321
 322 def vigenere_decipher(message, keyword):
 323     """Vigenere decipher
 324
 325     >>> vigenere_decipher('hfnlp', 'abc')
 326     'hello'
 327     """
 328     shifts = [ord(l) - ord('a') for l in sanitise(keyword)]
 329     pairs = zip(message, cycle(shifts))
 330     return ''.join([caesar_decipher_letter(l, k) for l, k in pairs])
 331
 332 beaufort_encipher = vigenere_decipher
 333 beaufort_decipher = vigenere_encipher
 334
 335
 336 if __name__ == "__main__":
 337     import doctest
 338     doctest.testmod()