6cce72543224f02468e8a7609b674d158d238127
[cipher-training.git] / cipher.py
1 import string
2 import collections
3 import math
4 from enum import Enum
5 from itertools import zip_longest, cycle, chain
6 from language_models import *
7
8
9 modular_division_table = [[0]*26 for _ in range(26)]
10 for a in range(26):
11 for b in range(26):
12 c = (a * b) % 26
13 modular_division_table[b][c] = a
14
15
16 def every_nth(text, n, fillvalue=''):
17 """Returns n strings, each of which consists of every nth character,
18 starting with the 0th, 1st, 2nd, ... (n-1)th character
19
20 >>> every_nth(string.ascii_lowercase, 5)
21 ['afkpuz', 'bglqv', 'chmrw', 'dinsx', 'ejoty']
22 >>> every_nth(string.ascii_lowercase, 1)
23 ['abcdefghijklmnopqrstuvwxyz']
24 >>> every_nth(string.ascii_lowercase, 26) # doctest: +NORMALIZE_WHITESPACE
25 ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
26 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z']
27 >>> every_nth(string.ascii_lowercase, 5, fillvalue='!')
28 ['afkpuz', 'bglqv!', 'chmrw!', 'dinsx!', 'ejoty!']
29 """
30 split_text = chunks(text, n, fillvalue)
31 return [''.join(l) for l in zip_longest(*split_text, fillvalue=fillvalue)]
32
33 def combine_every_nth(split_text):
34 """Reforms a text split into every_nth strings
35
36 >>> combine_every_nth(every_nth(string.ascii_lowercase, 5))
37 'abcdefghijklmnopqrstuvwxyz'
38 >>> combine_every_nth(every_nth(string.ascii_lowercase, 1))
39 'abcdefghijklmnopqrstuvwxyz'
40 >>> combine_every_nth(every_nth(string.ascii_lowercase, 26))
41 'abcdefghijklmnopqrstuvwxyz'
42 """
43 return ''.join([''.join(l)
44 for l in zip_longest(*split_text, fillvalue='')])
45
46 def chunks(text, n, fillvalue=None):
47 """Split a text into chunks of n characters
48
49 >>> chunks('abcdefghi', 3)
50 ['abc', 'def', 'ghi']
51 >>> chunks('abcdefghi', 4)
52 ['abcd', 'efgh', 'i']
53 >>> chunks('abcdefghi', 4, fillvalue='!')
54 ['abcd', 'efgh', 'i!!!']
55 """
56 if fillvalue:
57 padding = fillvalue[0] * (n - len(text) % n)
58 else:
59 padding = ''
60 return [(text+padding)[i:i+n] for i in range(0, len(text), n)]
61
62 def transpose(items, transposition):
63 """Moves items around according to the given transposition
64
65 >>> transpose(['a', 'b', 'c', 'd'], (0,1,2,3))
66 ['a', 'b', 'c', 'd']
67 >>> transpose(['a', 'b', 'c', 'd'], (3,1,2,0))
68 ['d', 'b', 'c', 'a']
69 >>> transpose([10,11,12,13,14,15], (3,2,4,1,5,0))
70 [13, 12, 14, 11, 15, 10]
71 """
72 transposed = [''] * len(transposition)
73 for p, t in enumerate(transposition):
74 transposed[p] = items[t]
75 return transposed
76
77 def untranspose(items, transposition):
78 """Undoes a transpose
79
80 >>> untranspose(['a', 'b', 'c', 'd'], [0,1,2,3])
81 ['a', 'b', 'c', 'd']
82 >>> untranspose(['d', 'b', 'c', 'a'], [3,1,2,0])
83 ['a', 'b', 'c', 'd']
84 >>> untranspose([13, 12, 14, 11, 15, 10], [3,2,4,1,5,0])
85 [10, 11, 12, 13, 14, 15]
86 """
87 transposed = [''] * len(transposition)
88 for p, t in enumerate(transposition):
89 transposed[t] = items[p]
90 return transposed
91
92 def deduplicate(text):
93 return list(collections.OrderedDict.fromkeys(text))
94
95
96 def caesar_encipher_letter(accented_letter, shift):
97 """Encipher a letter, given a shift amount
98
99 >>> caesar_encipher_letter('a', 1)
100 'b'
101 >>> caesar_encipher_letter('a', 2)
102 'c'
103 >>> caesar_encipher_letter('b', 2)
104 'd'
105 >>> caesar_encipher_letter('x', 2)
106 'z'
107 >>> caesar_encipher_letter('y', 2)
108 'a'
109 >>> caesar_encipher_letter('z', 2)
110 'b'
111 >>> caesar_encipher_letter('z', -1)
112 'y'
113 >>> caesar_encipher_letter('a', -1)
114 'z'
115 >>> caesar_encipher_letter('A', 1)
116 'B'
117 >>> caesar_encipher_letter('é', 1)
118 'f'
119 """
120 letter = unaccent(accented_letter)
121 if letter in string.ascii_letters:
122 if letter in string.ascii_uppercase:
123 alphabet_start = ord('A')
124 else:
125 alphabet_start = ord('a')
126 return chr(((ord(letter) - alphabet_start + shift) % 26) +
127 alphabet_start)
128 else:
129 return letter
130
131 def caesar_decipher_letter(letter, shift):
132 """Decipher a letter, given a shift amount
133
134 >>> caesar_decipher_letter('b', 1)
135 'a'
136 >>> caesar_decipher_letter('b', 2)
137 'z'
138 """
139 return caesar_encipher_letter(letter, -shift)
140
141 def caesar_encipher(message, shift):
142 """Encipher a message with the Caesar cipher of given shift
143
144 >>> caesar_encipher('abc', 1)
145 'bcd'
146 >>> caesar_encipher('abc', 2)
147 'cde'
148 >>> caesar_encipher('abcxyz', 2)
149 'cdezab'
150 >>> caesar_encipher('ab cx yz', 2)
151 'cd ez ab'
152 >>> caesar_encipher('Héllo World!', 2)
153 'Jgnnq Yqtnf!'
154 """
155 enciphered = [caesar_encipher_letter(l, shift) for l in message]
156 return ''.join(enciphered)
157
158 def caesar_decipher(message, shift):
159 """Decipher a message with the Caesar cipher of given shift
160
161 >>> caesar_decipher('bcd', 1)
162 'abc'
163 >>> caesar_decipher('cde', 2)
164 'abc'
165 >>> caesar_decipher('cd ez ab', 2)
166 'ab cx yz'
167 >>> caesar_decipher('Jgnnq Yqtnf!', 2)
168 'Hello World!'
169 """
170 return caesar_encipher(message, -shift)
171
172 def affine_encipher_letter(accented_letter, multiplier=1, adder=0, one_based=True):
173 """Encipher a letter, given a multiplier and adder
174
175 >>> ''.join([affine_encipher_letter(l, 3, 5, True) \
176 for l in string.ascii_uppercase])
177 'HKNQTWZCFILORUXADGJMPSVYBE'
178 >>> ''.join([affine_encipher_letter(l, 3, 5, False) \
179 for l in string.ascii_uppercase])
180 'FILORUXADGJMPSVYBEHKNQTWZC'
181 """
182 letter = unaccent(accented_letter)
183 if letter in string.ascii_letters:
184 if letter in string.ascii_uppercase:
185 alphabet_start = ord('A')
186 else:
187 alphabet_start = ord('a')
188 letter_number = ord(letter) - alphabet_start
189 if one_based: letter_number += 1
190 cipher_number = (letter_number * multiplier + adder) % 26
191 if one_based: cipher_number -= 1
192 return chr(cipher_number % 26 + alphabet_start)
193 else:
194 return letter
195
196 def affine_decipher_letter(letter, multiplier=1, adder=0, one_based=True):
197 """Encipher a letter, given a multiplier and adder
198
199 >>> ''.join([affine_decipher_letter(l, 3, 5, True) \
200 for l in 'HKNQTWZCFILORUXADGJMPSVYBE'])
201 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
202 >>> ''.join([affine_decipher_letter(l, 3, 5, False) \
203 for l in 'FILORUXADGJMPSVYBEHKNQTWZC'])
204 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
205 """
206 if letter in string.ascii_letters:
207 if letter in string.ascii_uppercase:
208 alphabet_start = ord('A')
209 else:
210 alphabet_start = ord('a')
211 cipher_number = ord(letter) - alphabet_start
212 if one_based: cipher_number += 1
213 plaintext_number = (
214 modular_division_table[multiplier]
215 [(cipher_number - adder) % 26])
216 if one_based: plaintext_number -= 1
217 return chr(plaintext_number % 26 + alphabet_start)
218 else:
219 return letter
220
221 def affine_encipher(message, multiplier=1, adder=0, one_based=True):
222 """Encipher a message
223
224 >>> affine_encipher('hours passed during which jerico tried every ' \
225 'trick he could think of', 15, 22, True)
226 'lmyfu bkuusd dyfaxw claol psfaom jfasd snsfg jfaoe ls omytd jlaxe mh'
227 """
228 enciphered = [affine_encipher_letter(l, multiplier, adder, one_based)
229 for l in message]
230 return ''.join(enciphered)
231
232 def affine_decipher(message, multiplier=1, adder=0, one_based=True):
233 """Decipher a message
234
235 >>> affine_decipher('lmyfu bkuusd dyfaxw claol psfaom jfasd snsfg ' \
236 'jfaoe ls omytd jlaxe mh', 15, 22, True)
237 'hours passed during which jerico tried every trick he could think of'
238 """
239 enciphered = [affine_decipher_letter(l, multiplier, adder, one_based)
240 for l in message]
241 return ''.join(enciphered)
242
243
244 class KeywordWrapAlphabet(Enum):
245 from_a = 1
246 from_last = 2
247 from_largest = 3
248
249
250 def keyword_cipher_alphabet_of(keyword, wrap_alphabet=KeywordWrapAlphabet.from_a):
251 """Find the cipher alphabet given a keyword.
252 wrap_alphabet controls how the rest of the alphabet is added
253 after the keyword.
254
255 >>> keyword_cipher_alphabet_of('bayes')
256 'bayescdfghijklmnopqrtuvwxz'
257 >>> keyword_cipher_alphabet_of('bayes', KeywordWrapAlphabet.from_a)
258 'bayescdfghijklmnopqrtuvwxz'
259 >>> keyword_cipher_alphabet_of('bayes', KeywordWrapAlphabet.from_last)
260 'bayestuvwxzcdfghijklmnopqr'
261 >>> keyword_cipher_alphabet_of('bayes', KeywordWrapAlphabet.from_largest)
262 'bayeszcdfghijklmnopqrtuvwx'
263 """
264 if wrap_alphabet == KeywordWrapAlphabet.from_a:
265 cipher_alphabet = ''.join(deduplicate(sanitise(keyword) +
266 string.ascii_lowercase))
267 else:
268 if wrap_alphabet == KeywordWrapAlphabet.from_last:
269 last_keyword_letter = deduplicate(sanitise(keyword))[-1]
270 else:
271 last_keyword_letter = sorted(sanitise(keyword))[-1]
272 last_keyword_position = string.ascii_lowercase.find(
273 last_keyword_letter) + 1
274 cipher_alphabet = ''.join(
275 deduplicate(sanitise(keyword) +
276 string.ascii_lowercase[last_keyword_position:] +
277 string.ascii_lowercase))
278 return cipher_alphabet
279
280
281 def keyword_encipher(message, keyword, wrap_alphabet=KeywordWrapAlphabet.from_a):
282 """Enciphers a message with a keyword substitution cipher.
283 wrap_alphabet controls how the rest of the alphabet is added
284 after the keyword.
285 0 : from 'a'
286 1 : from the last letter in the sanitised keyword
287 2 : from the largest letter in the sanitised keyword
288
289 >>> keyword_encipher('test message', 'bayes')
290 'rsqr ksqqbds'
291 >>> keyword_encipher('test message', 'bayes', KeywordWrapAlphabet.from_a)
292 'rsqr ksqqbds'
293 >>> keyword_encipher('test message', 'bayes', KeywordWrapAlphabet.from_last)
294 'lskl dskkbus'
295 >>> keyword_encipher('test message', 'bayes', KeywordWrapAlphabet.from_largest)
296 'qspq jsppbcs'
297 """
298 cipher_alphabet = keyword_cipher_alphabet_of(keyword, wrap_alphabet)
299 cipher_translation = ''.maketrans(string.ascii_lowercase, cipher_alphabet)
300 return unaccent(message).lower().translate(cipher_translation)
301
302 def keyword_decipher(message, keyword, wrap_alphabet=KeywordWrapAlphabet.from_a):
303 """Deciphers a message with a keyword substitution cipher.
304 wrap_alphabet controls how the rest of the alphabet is added
305 after the keyword.
306 0 : from 'a'
307 1 : from the last letter in the sanitised keyword
308 2 : from the largest letter in the sanitised keyword
309
310 >>> keyword_decipher('rsqr ksqqbds', 'bayes')
311 'test message'
312 >>> keyword_decipher('rsqr ksqqbds', 'bayes', KeywordWrapAlphabet.from_a)
313 'test message'
314 >>> keyword_decipher('lskl dskkbus', 'bayes', KeywordWrapAlphabet.from_last)
315 'test message'
316 >>> keyword_decipher('qspq jsppbcs', 'bayes', KeywordWrapAlphabet.from_largest)
317 'test message'
318 """
319 cipher_alphabet = keyword_cipher_alphabet_of(keyword, wrap_alphabet)
320 cipher_translation = ''.maketrans(cipher_alphabet, string.ascii_lowercase)
321 return message.lower().translate(cipher_translation)
322
323
324 def vigenere_encipher(message, keyword):
325 """Vigenere encipher
326
327 >>> vigenere_encipher('hello', 'abc')
328 'hfnlp'
329 """
330 shifts = [ord(l) - ord('a') for l in sanitise(keyword)]
331 pairs = zip(message, cycle(shifts))
332 return ''.join([caesar_encipher_letter(l, k) for l, k in pairs])
333
334 def vigenere_decipher(message, keyword):
335 """Vigenere decipher
336
337 >>> vigenere_decipher('hfnlp', 'abc')
338 'hello'
339 """
340 shifts = [ord(l) - ord('a') for l in sanitise(keyword)]
341 pairs = zip(message, cycle(shifts))
342 return ''.join([caesar_decipher_letter(l, k) for l, k in pairs])
343
344 beaufort_encipher=vigenere_decipher
345 beaufort_decipher=vigenere_encipher
346
347
348 def transpositions_of(keyword):
349 """Finds the transpostions given by a keyword. For instance, the keyword
350 'clever' rearranges to 'celrv', so the first column (0) stays first, the
351 second column (1) moves to third, the third column (2) moves to second,
352 and so on.
353
354 If passed a tuple, assume it's already a transposition and just return it.
355
356 >>> transpositions_of('clever')
357 (0, 2, 1, 4, 3)
358 >>> transpositions_of('fred')
359 (3, 2, 0, 1)
360 >>> transpositions_of((3, 2, 0, 1))
361 (3, 2, 0, 1)
362 """
363 if isinstance(keyword, tuple):
364 return keyword
365 else:
366 key = deduplicate(keyword)
367 transpositions = tuple(key.index(l) for l in sorted(key))
368 return transpositions
369
370 def pad(message_len, group_len, fillvalue):
371 padding_length = group_len - message_len % group_len
372 if padding_length == group_len: padding_length = 0
373 padding = ''
374 for i in range(padding_length):
375 if callable(fillvalue):
376 padding += fillvalue()
377 else:
378 padding += fillvalue
379 return padding
380
381 def column_transposition_encipher(message, keyword, fillvalue=' ',
382 fillcolumnwise=False,
383 emptycolumnwise=False):
384 """Enciphers using the column transposition cipher.
385 Message is padded to allow all rows to be the same length.
386
387 >>> column_transposition_encipher('hellothere', 'abcdef', fillcolumnwise=True)
388 'hlohr eltee '
389 >>> column_transposition_encipher('hellothere', 'abcdef', fillcolumnwise=True, emptycolumnwise=True)
390 'hellothere '
391 >>> column_transposition_encipher('hellothere', 'abcdef')
392 'hellothere '
393 >>> column_transposition_encipher('hellothere', 'abcde')
394 'hellothere'
395 >>> column_transposition_encipher('hellothere', 'abcde', fillcolumnwise=True, emptycolumnwise=True)
396 'hellothere'
397 >>> column_transposition_encipher('hellothere', 'abcde', fillcolumnwise=True, emptycolumnwise=False)
398 'hlohreltee'
399 >>> column_transposition_encipher('hellothere', 'abcde', fillcolumnwise=False, emptycolumnwise=True)
400 'htehlelroe'
401 >>> column_transposition_encipher('hellothere', 'abcde', fillcolumnwise=False, emptycolumnwise=False)
402 'hellothere'
403 >>> column_transposition_encipher('hellothere', 'clever', fillcolumnwise=True, emptycolumnwise=True)
404 'heotllrehe'
405 >>> column_transposition_encipher('hellothere', 'clever', fillcolumnwise=True, emptycolumnwise=False)
406 'holrhetlee'
407 >>> column_transposition_encipher('hellothere', 'clever', fillcolumnwise=False, emptycolumnwise=True)
408 'htleehoelr'
409 >>> column_transposition_encipher('hellothere', 'clever', fillcolumnwise=False, emptycolumnwise=False)
410 'hleolteher'
411 >>> column_transposition_encipher('hellothere', 'cleverly')
412 'hleolthre e '
413 >>> column_transposition_encipher('hellothere', 'cleverly', fillvalue='!')
414 'hleolthre!e!'
415 >>> column_transposition_encipher('hellothere', 'cleverly', fillvalue=lambda: '*')
416 'hleolthre*e*'
417 """
418 transpositions = transpositions_of(keyword)
419 message += pad(len(message), len(transpositions), fillvalue)
420 if fillcolumnwise:
421 rows = every_nth(message, len(message) // len(transpositions))
422 else:
423 rows = chunks(message, len(transpositions))
424 transposed = [transpose(r, transpositions) for r in rows]
425 if emptycolumnwise:
426 return combine_every_nth(transposed)
427 else:
428 return ''.join(chain(*transposed))
429
430 def column_transposition_decipher(message, keyword, fillvalue=' ',
431 fillcolumnwise=False,
432 emptycolumnwise=False):
433 """Deciphers using the column transposition cipher.
434 Message is padded to allow all rows to be the same length.
435
436 >>> column_transposition_decipher('hellothere', 'abcde', fillcolumnwise=True, emptycolumnwise=True)
437 'hellothere'
438 >>> column_transposition_decipher('hlohreltee', 'abcde', fillcolumnwise=True, emptycolumnwise=False)
439 'hellothere'
440 >>> column_transposition_decipher('htehlelroe', 'abcde', fillcolumnwise=False, emptycolumnwise=True)
441 'hellothere'
442 >>> column_transposition_decipher('hellothere', 'abcde', fillcolumnwise=False, emptycolumnwise=False)
443 'hellothere'
444 >>> column_transposition_decipher('heotllrehe', 'clever', fillcolumnwise=True, emptycolumnwise=True)
445 'hellothere'
446 >>> column_transposition_decipher('holrhetlee', 'clever', fillcolumnwise=True, emptycolumnwise=False)
447 'hellothere'
448 >>> column_transposition_decipher('htleehoelr', 'clever', fillcolumnwise=False, emptycolumnwise=True)
449 'hellothere'
450 >>> column_transposition_decipher('hleolteher', 'clever', fillcolumnwise=False, emptycolumnwise=False)
451 'hellothere'
452 """
453 transpositions = transpositions_of(keyword)
454 message += pad(len(message), len(transpositions), fillvalue)
455 if emptycolumnwise:
456 rows = every_nth(message, len(message) // len(transpositions))
457 else:
458 rows = chunks(message, len(transpositions))
459 untransposed = [untranspose(r, transpositions) for r in rows]
460 if fillcolumnwise:
461 return combine_every_nth(untransposed)
462 else:
463 return ''.join(chain(*untransposed))
464
465 def scytale_encipher(message, rows, fillvalue=' '):
466 """Enciphers using the scytale transposition cipher.
467 Message is padded with spaces to allow all rows to be the same length.
468
469 >>> scytale_encipher('thequickbrownfox', 3)
470 'tcnhkfeboqrxuo iw '
471 >>> scytale_encipher('thequickbrownfox', 4)
472 'tubnhirfecooqkwx'
473 >>> scytale_encipher('thequickbrownfox', 5)
474 'tubn hirf ecoo qkwx '
475 >>> scytale_encipher('thequickbrownfox', 6)
476 'tqcrnxhukof eibwo '
477 >>> scytale_encipher('thequickbrownfox', 7)
478 'tqcrnx hukof eibwo '
479 """
480 # transpositions = [i for i in range(math.ceil(len(message) / rows))]
481 # return column_transposition_encipher(message, transpositions,
482 # fillvalue=fillvalue, fillcolumnwise=False, emptycolumnwise=True)
483 transpositions = [i for i in range(rows)]
484 return column_transposition_encipher(message, transpositions,
485 fillvalue=fillvalue, fillcolumnwise=True, emptycolumnwise=False)
486
487 def scytale_decipher(message, rows):
488 """Deciphers using the scytale transposition cipher.
489 Assumes the message is padded so that all rows are the same length.
490
491 >>> scytale_decipher('tcnhkfeboqrxuo iw ', 3)
492 'thequickbrownfox '
493 >>> scytale_decipher('tubnhirfecooqkwx', 4)
494 'thequickbrownfox'
495 >>> scytale_decipher('tubn hirf ecoo qkwx ', 5)
496 'thequickbrownfox '
497 >>> scytale_decipher('tqcrnxhukof eibwo ', 6)
498 'thequickbrownfox '
499 >>> scytale_decipher('tqcrnx hukof eibwo ', 7)
500 'thequickbrownfox '
501 """
502 # transpositions = [i for i in range(math.ceil(len(message) / rows))]
503 # return column_transposition_decipher(message, transpositions,
504 # fillcolumnwise=False, emptycolumnwise=True)
505 transpositions = [i for i in range(rows)]
506 return column_transposition_decipher(message, transpositions,
507 fillcolumnwise=True, emptycolumnwise=False)
508
509
510 def railfence_encipher(message, height, fillvalue=''):
511 """Railfence cipher.
512 Works by splitting the text into sections, then reading across them to
513 generate the rows in the cipher. The rows are then combined to form the
514 ciphertext.
515
516 Example: the plaintext "hellotherefriends", with a height of four, written
517 out in the railfence as
518 h h i
519 etere*
520 lorfns
521 l e d
522 (with the * showing the one character to finish the last section).
523 Each 'section' is two columns, but unfolded. In the example, the first
524 section is 'hellot'.
525
526 >>> railfence_encipher('hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers', 2, fillvalue='!')
527 'hlohraateerishsslnpeefetotsigaleccpeselteevsmhatetiiaogicotxfretnrifneihr!'
528 >>> railfence_encipher('hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers', 3, fillvalue='!')
529 'horaersslpeeosglcpselteevsmhatetiiaogicotxfretnrifneihr!!lhateihsnefttiaece!'
530 >>> railfence_encipher('hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers', 5, fillvalue='!')
531 'hresleogcseeemhetaocofrnrner!!lhateihsnefttiaece!!ltvsatiigitxetifih!!oarspeslp!'
532 >>> railfence_encipher('hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers', 10, fillvalue='!')
533 'hepisehagitnr!!lernesge!!lmtocerh!!otiletap!!tseaorii!!hassfolc!!evtitffe!!rahsetec!!eixn!'
534 >>> railfence_encipher('hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers', 3)
535 'horaersslpeeosglcpselteevsmhatetiiaogicotxfretnrifneihrlhateihsnefttiaece'
536 >>> railfence_encipher('hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers', 5)
537 'hresleogcseeemhetaocofrnrnerlhateihsnefttiaeceltvsatiigitxetifihoarspeslp'
538 >>> railfence_encipher('hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers', 7)
539 'haspolsevsetgifrifrlatihnettaeelemtiocxernhorersleesgcptehaiaottneihesfic'
540 """
541 sections = chunks(message, (height - 1) * 2, fillvalue=fillvalue)
542 n_sections = len(sections)
543 # Add the top row
544 rows = [''.join([s[0] for s in sections])]
545 # process the middle rows of the grid
546 for r in range(1, height-1):
547 rows += [''.join([s[r:r+1] + s[height*2-r-2:height*2-r-1] for s in sections])]
548 # process the bottom row
549 rows += [''.join([s[height - 1:height] for s in sections])]
550 # rows += [' '.join([s[height - 1] for s in sections])]
551 return ''.join(rows)
552
553 def railfence_decipher(message, height, fillvalue=''):
554 """Railfence decipher.
555 Works by reconstructing the grid used to generate the ciphertext, then
556 unfolding the sections so the text can be concatenated together.
557
558 Example: given the ciphertext 'hhieterelorfnsled' and a height of 4, first
559 work out that the second row has a character missing, find the rows of the
560 grid, then split the section into its two columns.
561
562 'hhieterelorfnsled' is split into
563 h h i
564 etere
565 lorfns
566 l e d
567 (spaces added for clarity), which is stored in 'rows'. This is then split
568 into 'down_rows' and 'up_rows':
569
570 down_rows:
571 hhi
572 eee
573 lrn
574 led
575
576 up_rows:
577 tr
578 ofs
579
580 These are then zipped together (after the up_rows are reversed) to recover
581 the plaintext.
582
583 Most of the procedure is about finding the correct lengths for each row then
584 splitting the ciphertext into those rows.
585
586 >>> railfence_decipher('hlohraateerishsslnpeefetotsigaleccpeselteevsmhatetiiaogicotxfretnrifneihr!', 2).strip('!')
587 'hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers'
588 >>> railfence_decipher('horaersslpeeosglcpselteevsmhatetiiaogicotxfretnrifneihr!!lhateihsnefttiaece!', 3).strip('!')
589 'hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers'
590 >>> railfence_decipher('hresleogcseeemhetaocofrnrner!!lhateihsnefttiaece!!ltvsatiigitxetifih!!oarspeslp!', 5).strip('!')
591 'hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers'
592 >>> railfence_decipher('hepisehagitnr!!lernesge!!lmtocerh!!otiletap!!tseaorii!!hassfolc!!evtitffe!!rahsetec!!eixn!', 10).strip('!')
593 'hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers'
594 >>> railfence_decipher('horaersslpeeosglcpselteevsmhatetiiaogicotxfretnrifneihrlhateihsnefttiaece', 3)
595 'hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers'
596 >>> railfence_decipher('hresleogcseeemhetaocofrnrnerlhateihsnefttiaeceltvsatiigitxetifihoarspeslp', 5)
597 'hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers'
598 >>> railfence_decipher('haspolsevsetgifrifrlatihnettaeelemtiocxernhorersleesgcptehaiaottneihesfic', 7)
599 'hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers'
600 """
601 # find the number and size of the sections, including how many characters
602 # are missing for a full grid
603 n_sections = math.ceil(len(message) / ((height - 1) * 2))
604 padding_to_add = n_sections * (height - 1) * 2 - len(message)
605 # row_lengths are for the both up rows and down rows
606 row_lengths = [n_sections] * (height - 1) * 2
607 for i in range((height - 1) * 2 - 1, (height - 1) * 2 - (padding_to_add + 1), -1):
608 row_lengths[i] -= 1
609 # folded_rows are the combined row lengths in the middle of the railfence
610 folded_row_lengths = [row_lengths[0]]
611 for i in range(1, height-1):
612 folded_row_lengths += [row_lengths[i] + row_lengths[-i]]
613 folded_row_lengths += [row_lengths[height - 1]]
614 # find the rows that form the railfence grid
615 rows = []
616 row_start = 0
617 for i in folded_row_lengths:
618 rows += [message[row_start:row_start + i]]
619 row_start += i
620 # split the rows into the 'down_rows' (those that form the first column of
621 # a section) and the 'up_rows' (those that ofrm the second column of a
622 # section).
623 down_rows = [rows[0]]
624 up_rows = []
625 for i in range(1, height-1):
626 down_rows += [''.join([c for n, c in enumerate(rows[i]) if n % 2 == 0])]
627 up_rows += [''.join([c for n, c in enumerate(rows[i]) if n % 2 == 1])]
628 down_rows += [rows[-1]]
629 up_rows.reverse()
630 return ''.join(c for r in zip_longest(*(down_rows + up_rows), fillvalue='') for c in r)
631
632
633 class PocketEnigma(object):
634 """A pocket enigma machine
635 The wheel is internally represented as a 26-element list self.wheel_map,
636 where wheel_map[i] == j shows that the position i places on from the arrow
637 maps to the position j places on.
638 """
639 def __init__(self, wheel=1, position='a'):
640 """initialise the pocket enigma, including which wheel to use and the
641 starting position of the wheel.
642
643 The wheel is either 1 or 2 (the predefined wheels) or a list of letter
644 pairs.
645
646 The position is the letter pointed to by the arrow on the wheel.
647
648 >>> pe.wheel_map
649 [25, 4, 23, 10, 1, 7, 9, 5, 12, 6, 3, 17, 8, 14, 13, 21, 19, 11, 20, 16, 18, 15, 24, 2, 22, 0]
650 >>> pe.position
651 0
652 """
653 self.wheel1 = [('a', 'z'), ('b', 'e'), ('c', 'x'), ('d', 'k'),
654 ('f', 'h'), ('g', 'j'), ('i', 'm'), ('l', 'r'), ('n', 'o'),
655 ('p', 'v'), ('q', 't'), ('s', 'u'), ('w', 'y')]
656 self.wheel2 = [('a', 'c'), ('b', 'd'), ('e', 'w'), ('f', 'i'),
657 ('g', 'p'), ('h', 'm'), ('j', 'k'), ('l', 'n'), ('o', 'q'),
658 ('r', 'z'), ('s', 'u'), ('t', 'v'), ('x', 'y')]
659 if wheel == 1:
660 self.make_wheel_map(self.wheel1)
661 elif wheel == 2:
662 self.make_wheel_map(self.wheel2)
663 else:
664 self.validate_wheel_spec(wheel)
665 self.make_wheel_map(wheel)
666 if position in string.ascii_lowercase:
667 self.position = ord(position) - ord('a')
668 else:
669 self.position = position
670
671 def make_wheel_map(self, wheel_spec):
672 """Expands a wheel specification from a list of letter-letter pairs
673 into a full wheel_map.
674
675 >>> pe.make_wheel_map(pe.wheel2)
676 [2, 3, 0, 1, 22, 8, 15, 12, 5, 10, 9, 13, 7, 11, 16, 6, 14, 25, 20, 21, 18, 19, 4, 24, 23, 17]
677 """
678 self.validate_wheel_spec(wheel_spec)
679 self.wheel_map = [0] * 26
680 for p in wheel_spec:
681 self.wheel_map[ord(p[0]) - ord('a')] = ord(p[1]) - ord('a')
682 self.wheel_map[ord(p[1]) - ord('a')] = ord(p[0]) - ord('a')
683 return self.wheel_map
684
685 def validate_wheel_spec(self, wheel_spec):
686 """Validates that a wheel specificaiton will turn into a valid wheel
687 map.
688
689 >>> pe.validate_wheel_spec([])
690 Traceback (most recent call last):
691 ...
692 ValueError: Wheel specification has 0 pairs, requires 13
693 >>> pe.validate_wheel_spec([('a', 'b', 'c')]*13)
694 Traceback (most recent call last):
695 ...
696 ValueError: Not all mappings in wheel specificationhave two elements
697 >>> pe.validate_wheel_spec([('a', 'b')]*13)
698 Traceback (most recent call last):
699 ...
700 ValueError: Wheel specification does not contain 26 letters
701 """
702 if len(wheel_spec) != 13:
703 raise ValueError("Wheel specification has {} pairs, requires 13".
704 format(len(wheel_spec)))
705 for p in wheel_spec:
706 if len(p) != 2:
707 raise ValueError("Not all mappings in wheel specification"
708 "have two elements")
709 if len(set([p[0] for p in wheel_spec] +
710 [p[1] for p in wheel_spec])) != 26:
711 raise ValueError("Wheel specification does not contain 26 letters")
712
713 def encipher_letter(self, letter):
714 """Enciphers a single letter, by advancing the wheel before looking up
715 the letter on the wheel.
716
717 >>> pe.set_position('f')
718 5
719 >>> pe.encipher_letter('k')
720 'h'
721 """
722 self.advance()
723 return self.lookup(letter)
724 decipher_letter = encipher_letter
725
726 def lookup(self, letter):
727 """Look up what a letter enciphers to, without turning the wheel.
728
729 >>> pe.set_position('f')
730 5
731 >>> ''.join([pe.lookup(l) for l in string.ascii_lowercase])
732 'udhbfejcpgmokrliwntsayqzvx'
733 >>> pe.lookup('A')
734 ''
735 """
736 if letter in string.ascii_lowercase:
737 return chr(
738 (self.wheel_map[(ord(letter) - ord('a') - self.position) % 26] +
739 self.position) % 26 +
740 ord('a'))
741 else:
742 return ''
743
744 def advance(self):
745 """Advances the wheel one position.
746
747 >>> pe.set_position('f')
748 5
749 >>> pe.advance()
750 6
751 """
752 self.position = (self.position + 1) % 26
753 return self.position
754
755 def encipher(self, message, starting_position=None):
756 """Enciphers a whole message.
757
758 >>> pe.set_position('f')
759 5
760 >>> pe.encipher('helloworld')
761 'kjsglcjoqc'
762 >>> pe.set_position('f')
763 5
764 >>> pe.encipher('kjsglcjoqc')
765 'helloworld'
766 >>> pe.encipher('helloworld', starting_position = 'x')
767 'egrekthnnf'
768 """
769 if starting_position:
770 self.set_position(starting_position)
771 transformed = ''
772 for l in message:
773 transformed += self.encipher_letter(l)
774 return transformed
775 decipher = encipher
776
777 def set_position(self, position):
778 """Sets the position of the wheel, by specifying the letter the arrow
779 points to.
780
781 >>> pe.set_position('a')
782 0
783 >>> pe.set_position('m')
784 12
785 >>> pe.set_position('z')
786 25
787 """
788 self.position = ord(position) - ord('a')
789 return self.position
790
791
792 if __name__ == "__main__":
793 import doctest
794 doctest.testmod(extraglobs={'pe': PocketEnigma(1, 'a')})