6 from itertools
import zip_longest
, repeat
7 from segment
import segment
8 from multiprocessing
import Pool
13 # c5a = open('2012/5a.ciphertext', 'r').read()
14 # timeit.timeit('keyword_break(c5a)', setup='gc.enable() ; from __main__ import c5a ; from cipher import keyword_break', number=1)
15 # timeit.repeat('keyword_break_mp(c5a, chunksize=500)', setup='gc.enable() ; from __main__ import c5a ; from cipher import keyword_break_mp', repeat=5, number=1
17 logger
= logging
.getLogger(__name__
)
18 logger
.addHandler(logging
.FileHandler('cipher.log'))
19 logger
.setLevel(logging
.WARNING
)
20 #logger.setLevel(logging.INFO)
21 #logger.setLevel(logging.DEBUG)
23 english_counts
= collections
.defaultdict(int)
24 with
open('count_1l.txt', 'r') as f
:
26 (letter
, count
) = line
.split("\t")
27 english_counts
[letter
] = int(count
)
28 normalised_english_counts
= norms
.normalise(english_counts
)
30 english_bigram_counts
= collections
.defaultdict(int)
31 with
open('count_2l.txt', 'r') as f
:
33 (bigram
, count
) = line
.split("\t")
34 english_bigram_counts
[bigram
] = int(count
)
35 normalised_english_bigram_counts
= norms
.normalise(english_bigram_counts
)
37 english_trigram_counts
= collections
.defaultdict(int)
38 with
open('count_3l.txt', 'r') as f
:
40 (trigram
, count
) = line
.split("\t")
41 english_trigram_counts
[trigram
] = int(count
)
42 normalised_english_trigram_counts
= norms
.normalise(english_trigram_counts
)
45 with
open('words.txt', 'r') as f
:
46 keywords
= [line
.rstrip() for line
in f
]
48 modular_division_table
= [[0]*26 for x
in range(26)]
52 modular_division_table
[b
][c
] = a
55 """Remove all non-alphabetic characters from a text
56 >>> letters('The Quick')
58 >>> letters('The Quick BROWN fox jumped! over... the (9lazy) DOG')
59 'TheQuickBROWNfoxjumpedoverthelazyDOG'
61 return ''.join([c
for c
in text
if c
in string
.ascii_letters
])
64 """Remove all non-alphabetic characters and convert the text to lowercase
66 >>> sanitise('The Quick')
68 >>> sanitise('The Quick BROWN fox jumped! over... the (9lazy) DOG')
69 'thequickbrownfoxjumpedoverthelazydog'
71 # sanitised = [c.lower() for c in text if c in string.ascii_letters]
72 # return ''.join(sanitised)
73 return letters(text
).lower()
76 """Returns all n-grams of a text
78 >>> ngrams(sanitise('the quick brown fox'), 2) # doctest: +NORMALIZE_WHITESPACE
79 ['th', 'he', 'eq', 'qu', 'ui', 'ic', 'ck', 'kb', 'br', 'ro', 'ow', 'wn',
81 >>> ngrams(sanitise('the quick brown fox'), 4) # doctest: +NORMALIZE_WHITESPACE
82 ['theq', 'hequ', 'equi', 'quic', 'uick', 'ickb', 'ckbr', 'kbro', 'brow',
83 'rown', 'ownf', 'wnfo', 'nfox']
85 return [text
[i
:i
+n
] for i
in range(len(text
)-n
+1)]
87 def every_nth(text
, n
, fillvalue
=''):
88 """Returns n strings, each of which consists of every nth character,
89 starting with the 0th, 1st, 2nd, ... (n-1)th character
91 >>> every_nth(string.ascii_lowercase, 5)
92 ['afkpuz', 'bglqv', 'chmrw', 'dinsx', 'ejoty']
93 >>> every_nth(string.ascii_lowercase, 1)
94 ['abcdefghijklmnopqrstuvwxyz']
95 >>> every_nth(string.ascii_lowercase, 26) # doctest: +NORMALIZE_WHITESPACE
96 ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n',
97 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z']
98 >>> every_nth(string.ascii_lowercase, 5, fillvalue='!')
99 ['afkpuz', 'bglqv!', 'chmrw!', 'dinsx!', 'ejoty!']
101 split_text
= [text
[i
:i
+n
] for i
in range(0, len(text
), n
)]
102 return [''.join(l
) for l
in zip_longest(*split_text
, fillvalue
=fillvalue
)]
104 def combine_every_nth(split_text
):
105 """Reforms a text split into every_nth strings
107 >>> combine_every_nth(every_nth(string.ascii_lowercase, 5))
108 'abcdefghijklmnopqrstuvwxyz'
109 >>> combine_every_nth(every_nth(string.ascii_lowercase, 1))
110 'abcdefghijklmnopqrstuvwxyz'
111 >>> combine_every_nth(every_nth(string.ascii_lowercase, 26))
112 'abcdefghijklmnopqrstuvwxyz'
114 return ''.join([''.join(l
)
115 for l
in zip_longest(*split_text
, fillvalue
='')])
117 def transpose(items
, transposition
):
118 """Moves items around according to the given transposition
120 >>> transpose(['a', 'b', 'c', 'd'], [0,1,2,3])
122 >>> transpose(['a', 'b', 'c', 'd'], [3,1,2,0])
124 >>> transpose([10,11,12,13,14,15], [3,2,4,1,5,0])
125 [13, 12, 14, 11, 15, 10]
127 transposed
= list(repeat('', len(transposition
)))
128 for p
, t
in enumerate(transposition
):
129 transposed
[p
] = items
[t
]
132 def untranspose(items
, transposition
):
133 """Undoes a transpose
135 >>> untranspose(['a', 'b', 'c', 'd'], [0,1,2,3])
137 >>> untranspose(['d', 'b', 'c', 'a'], [3,1,2,0])
139 >>> untranspose([13, 12, 14, 11, 15, 10], [3,2,4,1,5,0])
140 [10, 11, 12, 13, 14, 15]
142 transposed
= list(repeat('', len(transposition
)))
143 for p
, t
in enumerate(transposition
):
144 transposed
[t
] = items
[p
]
148 def frequencies(text
):
149 """Count the number of occurrences of each character in text
151 >>> sorted(frequencies('abcdefabc').items())
152 [('a', 2), ('b', 2), ('c', 2), ('d', 1), ('e', 1), ('f', 1)]
153 >>> sorted(frequencies('the quick brown fox jumped over the lazy ' \
154 'dog').items()) # doctest: +NORMALIZE_WHITESPACE
155 [(' ', 8), ('a', 1), ('b', 1), ('c', 1), ('d', 2), ('e', 4), ('f', 1),
156 ('g', 1), ('h', 2), ('i', 1), ('j', 1), ('k', 1), ('l', 1), ('m', 1),
157 ('n', 1), ('o', 4), ('p', 1), ('q', 1), ('r', 2), ('t', 2), ('u', 2),
158 ('v', 1), ('w', 1), ('x', 1), ('y', 1), ('z', 1)]
159 >>> sorted(frequencies('The Quick BROWN fox jumped! over... the ' \
160 '(9lazy) DOG').items()) # doctest: +NORMALIZE_WHITESPACE
161 [(' ', 8), ('!', 1), ('(', 1), (')', 1), ('.', 3), ('9', 1), ('B', 1),
162 ('D', 1), ('G', 1), ('N', 1), ('O', 2), ('Q', 1), ('R', 1), ('T', 1),
163 ('W', 1), ('a', 1), ('c', 1), ('d', 1), ('e', 4), ('f', 1), ('h', 2),
164 ('i', 1), ('j', 1), ('k', 1), ('l', 1), ('m', 1), ('o', 2), ('p', 1),
165 ('r', 1), ('t', 1), ('u', 2), ('v', 1), ('x', 1), ('y', 1), ('z', 1)]
166 >>> sorted(frequencies(sanitise('The Quick BROWN fox jumped! over... ' \
167 'the (9lazy) DOG')).items()) # doctest: +NORMALIZE_WHITESPACE
168 [('a', 1), ('b', 1), ('c', 1), ('d', 2), ('e', 4), ('f', 1), ('g', 1),
169 ('h', 2), ('i', 1), ('j', 1), ('k', 1), ('l', 1), ('m', 1), ('n', 1),
170 ('o', 4), ('p', 1), ('q', 1), ('r', 2), ('t', 2), ('u', 2), ('v', 1),
171 ('w', 1), ('x', 1), ('y', 1), ('z', 1)]
172 >>> frequencies('abcdefabcdef')['x']
175 #counts = collections.defaultdict(int)
179 return collections
.Counter(c
for c
in text
)
180 letter_frequencies
= frequencies
182 def deduplicate(text
):
183 return list(collections
.OrderedDict
.fromkeys(text
))
187 def caesar_encipher_letter(letter
, shift
):
188 """Encipher a letter, given a shift amount
190 >>> caesar_encipher_letter('a', 1)
192 >>> caesar_encipher_letter('a', 2)
194 >>> caesar_encipher_letter('b', 2)
196 >>> caesar_encipher_letter('x', 2)
198 >>> caesar_encipher_letter('y', 2)
200 >>> caesar_encipher_letter('z', 2)
202 >>> caesar_encipher_letter('z', -1)
204 >>> caesar_encipher_letter('a', -1)
207 if letter
in string
.ascii_letters
:
208 if letter
in string
.ascii_uppercase
:
209 alphabet_start
= ord('A')
211 alphabet_start
= ord('a')
212 return chr(((ord(letter
) - alphabet_start
+ shift
) % 26) +
217 def caesar_decipher_letter(letter
, shift
):
218 """Decipher a letter, given a shift amount
220 >>> caesar_decipher_letter('b', 1)
222 >>> caesar_decipher_letter('b', 2)
225 return caesar_encipher_letter(letter
, -shift
)
227 def caesar_encipher(message
, shift
):
228 """Encipher a message with the Caesar cipher of given shift
230 >>> caesar_encipher('abc', 1)
232 >>> caesar_encipher('abc', 2)
234 >>> caesar_encipher('abcxyz', 2)
236 >>> caesar_encipher('ab cx yz', 2)
239 enciphered
= [caesar_encipher_letter(l
, shift
) for l
in message
]
240 return ''.join(enciphered
)
242 def caesar_decipher(message
, shift
):
243 """Encipher a message with the Caesar cipher of given shift
245 >>> caesar_decipher('bcd', 1)
247 >>> caesar_decipher('cde', 2)
249 >>> caesar_decipher('cd ez ab', 2)
252 return caesar_encipher(message
, -shift
)
254 def affine_encipher_letter(letter
, multiplier
=1, adder
=0, one_based
=True):
255 """Encipher a letter, given a multiplier and adder
257 >>> ''.join([affine_encipher_letter(l, 3, 5, True) \
258 for l in string.ascii_uppercase])
259 'HKNQTWZCFILORUXADGJMPSVYBE'
260 >>> ''.join([affine_encipher_letter(l, 3, 5, False) \
261 for l in string.ascii_uppercase])
262 'FILORUXADGJMPSVYBEHKNQTWZC'
264 if letter
in string
.ascii_letters
:
265 if letter
in string
.ascii_uppercase
:
266 alphabet_start
= ord('A')
268 alphabet_start
= ord('a')
269 letter_number
= ord(letter
) - alphabet_start
270 if one_based
: letter_number
+= 1
271 cipher_number
= (letter_number
* multiplier
+ adder
) % 26
272 if one_based
: cipher_number
-= 1
273 return chr(cipher_number
% 26 + alphabet_start
)
277 def affine_decipher_letter(letter
, multiplier
=1, adder
=0, one_based
=True):
278 """Encipher a letter, given a multiplier and adder
280 >>> ''.join([affine_decipher_letter(l, 3, 5, True) \
281 for l in 'HKNQTWZCFILORUXADGJMPSVYBE'])
282 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
283 >>> ''.join([affine_decipher_letter(l, 3, 5, False) \
284 for l in 'FILORUXADGJMPSVYBEHKNQTWZC'])
285 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
287 if letter
in string
.ascii_letters
:
288 if letter
in string
.ascii_uppercase
:
289 alphabet_start
= ord('A')
291 alphabet_start
= ord('a')
292 cipher_number
= ord(letter
) - alphabet_start
293 if one_based
: cipher_number
+= 1
294 plaintext_number
= ( modular_division_table
[multiplier
]
295 [(cipher_number
- adder
) % 26] )
296 if one_based
: plaintext_number
-= 1
297 return chr(plaintext_number
% 26 + alphabet_start
)
301 def affine_encipher(message
, multiplier
=1, adder
=0, one_based
=True):
302 """Encipher a message
304 >>> affine_encipher('hours passed during which jerico tried every ' \
305 'trick he could think of', 15, 22, True)
306 'lmyfu bkuusd dyfaxw claol psfaom jfasd snsfg jfaoe ls omytd jlaxe mh'
308 enciphered
= [affine_encipher_letter(l
, multiplier
, adder
, one_based
)
310 return ''.join(enciphered
)
312 def affine_decipher(message
, multiplier
=1, adder
=0, one_based
=True):
313 """Decipher a message
315 >>> affine_decipher('lmyfu bkuusd dyfaxw claol psfaom jfasd snsfg ' \
316 'jfaoe ls omytd jlaxe mh', 15, 22, True)
317 'hours passed during which jerico tried every trick he could think of'
319 enciphered
= [affine_decipher_letter(l
, multiplier
, adder
, one_based
)
321 return ''.join(enciphered
)
324 def keyword_cipher_alphabet_of(keyword
, wrap_alphabet
=0):
325 """Find the cipher alphabet given a keyword.
326 wrap_alphabet controls how the rest of the alphabet is added
329 1 : from the last letter in the sanitised keyword
330 2 : from the largest letter in the sanitised keyword
332 >>> keyword_cipher_alphabet_of('bayes')
333 'bayescdfghijklmnopqrtuvwxz'
334 >>> keyword_cipher_alphabet_of('bayes', 0)
335 'bayescdfghijklmnopqrtuvwxz'
336 >>> keyword_cipher_alphabet_of('bayes', 1)
337 'bayestuvwxzcdfghijklmnopqr'
338 >>> keyword_cipher_alphabet_of('bayes', 2)
339 'bayeszcdfghijklmnopqrtuvwx'
341 if wrap_alphabet
== 0:
342 cipher_alphabet
= ''.join(deduplicate(sanitise(keyword
) +
343 string
.ascii_lowercase
))
345 if wrap_alphabet
== 1:
346 last_keyword_letter
= deduplicate(sanitise(keyword
))[-1]
348 last_keyword_letter
= sorted(sanitise(keyword
))[-1]
349 last_keyword_position
= string
.ascii_lowercase
.find(
350 last_keyword_letter
) + 1
351 cipher_alphabet
= ''.join(
352 deduplicate(sanitise(keyword
) +
353 string
.ascii_lowercase
[last_keyword_position
:] +
354 string
.ascii_lowercase
))
355 return cipher_alphabet
358 def keyword_encipher(message
, keyword
, wrap_alphabet
=0):
359 """Enciphers a message with a keyword substitution cipher.
360 wrap_alphabet controls how the rest of the alphabet is added
363 1 : from the last letter in the sanitised keyword
364 2 : from the largest letter in the sanitised keyword
366 >>> keyword_encipher('test message', 'bayes')
368 >>> keyword_encipher('test message', 'bayes', 0)
370 >>> keyword_encipher('test message', 'bayes', 1)
372 >>> keyword_encipher('test message', 'bayes', 2)
375 cipher_alphabet
= keyword_cipher_alphabet_of(keyword
, wrap_alphabet
)
376 cipher_translation
= ''.maketrans(string
.ascii_lowercase
, cipher_alphabet
)
377 return message
.lower().translate(cipher_translation
)
379 def keyword_decipher(message
, keyword
, wrap_alphabet
=0):
380 """Deciphers a message with a keyword substitution cipher.
381 wrap_alphabet controls how the rest of the alphabet is added
384 1 : from the last letter in the sanitised keyword
385 2 : from the largest letter in the sanitised keyword
387 >>> keyword_decipher('rsqr ksqqbds', 'bayes')
389 >>> keyword_decipher('rsqr ksqqbds', 'bayes', 0)
391 >>> keyword_decipher('lskl dskkbus', 'bayes', 1)
393 >>> keyword_decipher('qspq jsppbcs', 'bayes', 2)
396 cipher_alphabet
= keyword_cipher_alphabet_of(keyword
, wrap_alphabet
)
397 cipher_translation
= ''.maketrans(cipher_alphabet
, string
.ascii_lowercase
)
398 return message
.lower().translate(cipher_translation
)
400 def scytale_encipher(message
, rows
):
401 """Enciphers using the scytale transposition cipher.
402 Message is padded with spaces to allow all rows to be the same length.
404 >>> scytale_encipher('thequickbrownfox', 3)
406 >>> scytale_encipher('thequickbrownfox', 4)
408 >>> scytale_encipher('thequickbrownfox', 5)
409 'tubn hirf ecoo qkwx '
410 >>> scytale_encipher('thequickbrownfox', 6)
412 >>> scytale_encipher('thequickbrownfox', 7)
413 'tqcrnx hukof eibwo '
415 if len(message
) % rows
!= 0:
416 message
+= ' '*(rows
- len(message
) % rows
)
417 row_length
= round(len(message
) / rows
)
418 slices
= [message
[i
:i
+row_length
]
419 for i
in range(0, len(message
), row_length
)]
420 return ''.join([''.join(r
) for r
in zip_longest(*slices
, fillvalue
='')])
422 def scytale_decipher(message
, rows
):
423 """Deciphers using the scytale transposition cipher.
424 Assumes the message is padded so that all rows are the same length.
426 >>> scytale_decipher('tcnhkfeboqrxuo iw ', 3)
428 >>> scytale_decipher('tubnhirfecooqkwx', 4)
430 >>> scytale_decipher('tubn hirf ecoo qkwx ', 5)
432 >>> scytale_decipher('tqcrnxhukof eibwo ', 6)
434 >>> scytale_decipher('tqcrnx hukof eibwo ', 7)
437 cols
= round(len(message
) / rows
)
438 columns
= [message
[i
:i
+rows
] for i
in range(0, cols
* rows
, rows
)]
439 return ''.join([''.join(c
) for c
in zip_longest(*columns
, fillvalue
='')])
442 def transpositions_of(keyword
):
443 """Finds the transpostions given by a keyword. For instance, the keyword
444 'clever' rearranges to 'celrv', so the first column (0) stays first, the
445 second column (1) moves to third, the third column (2) moves to second,
448 >>> transpositions_of('clever')
451 key
= deduplicate(keyword
)
452 transpositions
= [key
.index(l
) for l
in sorted(key
)]
453 return transpositions
455 def column_transposition_encipher(message
, keyword
, fillvalue
=' '):
456 """Enciphers using the column transposition cipher.
457 Message is padded to allow all rows to be the same length.
459 >>> column_transposition_encipher('hellothere', 'clever')
461 >>> column_transposition_encipher('hellothere', 'cleverly', fillvalue='!')
464 return column_transposition_worker(message
, keyword
, encipher
=True,
467 def column_transposition_decipher(message
, keyword
, fillvalue
=' '):
468 """Deciphers using the column transposition cipher.
469 Message is padded to allow all rows to be the same length.
471 >>> column_transposition_decipher('hleolteher', 'clever')
473 >>> column_transposition_decipher('hleolthre!e!', 'cleverly', fillvalue='?')
476 return column_transposition_worker(message
, keyword
, encipher
=False,
479 def column_transposition_worker(message
, keyword
,
480 encipher
=True, fillvalue
=' '):
481 """Does the actual work of the column transposition cipher.
482 Message is padded with spaces to allow all rows to be the same length.
484 >>> column_transposition_worker('hellothere', 'clever')
486 >>> column_transposition_worker('hellothere', 'clever', encipher=True)
488 >>> column_transposition_worker('hleolteher', 'clever', encipher=False)
491 transpositions
= transpositions_of(keyword
)
492 columns
= every_nth(message
, len(transpositions
), fillvalue
=fillvalue
)
494 transposed_columns
= transpose(columns
, transpositions
)
496 transposed_columns
= untranspose(columns
, transpositions
)
497 return combine_every_nth(transposed_columns
)
501 def caesar_break(message
,
502 metric
=norms
.euclidean_distance
,
503 target_counts
=normalised_english_counts
,
504 message_frequency_scaling
=norms
.normalise
):
505 """Breaks a Caesar cipher using frequency analysis
507 >>> caesar_break('ibxcsyorsaqcheyklxivoexlevmrimwxsfiqevvmihrsasrxliwyrh' \
508 'ecjsppsamrkwleppfmergefifvmhixscsymjcsyqeoixlm') # doctest: +ELLIPSIS
509 (4, 0.31863952890183...)
510 >>> caesar_break('wxwmaxdgheetgwuxztgptedbgznitgwwhpguxyhkxbmhvvtlbhgtee' \
511 'raxlmhiixweblmxgxwmhmaxybkbgztgwztsxwbgmxgmert') # doctest: +ELLIPSIS
512 (19, 0.42152901235832...)
513 >>> caesar_break('yltbbqnqnzvguvaxurorgenafsbezqvagbnornfgsbevpnaabjurer' \
514 'svaquvzyvxrnznazlybequrvfohgriraabjtbaruraprur') # doctest: +ELLIPSIS
515 (13, 0.316029208075451...)
517 sanitised_message
= sanitise(message
)
519 best_fit
= float("inf")
520 for shift
in range(26):
521 plaintext
= caesar_decipher(sanitised_message
, shift
)
522 counts
= message_frequency_scaling(letter_frequencies(plaintext
))
523 fit
= metric(target_counts
, counts
)
524 logger
.debug('Caesar break attempt using key {0} gives fit of {1} '
525 'and decrypt starting: {2}'.format(shift
, fit
, plaintext
[:50]))
529 logger
.info('Caesar break best fit: key {0} gives fit of {1} and '
530 'decrypt starting: {2}'.format(best_shift
, best_fit
,
531 caesar_decipher(sanitised_message
, best_shift
)[:50]))
532 return best_shift
, best_fit
534 def affine_break(message
,
535 metric
=norms
.euclidean_distance
,
536 target_counts
=normalised_english_counts
,
537 message_frequency_scaling
=norms
.normalise
):
538 """Breaks an affine cipher using frequency analysis
540 >>> affine_break('lmyfu bkuusd dyfaxw claol psfaom jfasd snsfg jfaoe ls ' \
541 'omytd jlaxe mh jm bfmibj umis hfsul axubafkjamx. ls kffkxwsd jls ' \
542 'ofgbjmwfkiu olfmxmtmwaokttg jlsx ls kffkxwsd jlsi zg tsxwjl. jlsx ' \
543 'ls umfjsd jlsi zg hfsqysxog. ls dmmdtsd mx jls bats mh bkbsf. ls ' \
544 'bfmctsd kfmyxd jls lyj, mztanamyu xmc jm clm cku tmmeaxw kj lai kxd ' \
545 'clm ckuxj.') # doctest: +ELLIPSIS
546 ((15, 22, True), 0.23570361818655...)
548 sanitised_message
= sanitise(message
)
551 best_one_based
= True
552 best_fit
= float("inf")
553 for one_based
in [True, False]:
554 for multiplier
in range(1, 26, 2):
555 for adder
in range(26):
556 plaintext
= affine_decipher(sanitised_message
,
557 multiplier
, adder
, one_based
)
558 counts
= message_frequency_scaling(letter_frequencies(plaintext
))
559 fit
= metric(target_counts
, counts
)
560 logger
.debug('Affine break attempt using key {0}x+{1} ({2}) '
561 'gives fit of {3} and decrypt starting: {4}'.
562 format(multiplier
, adder
, one_based
, fit
,
566 best_multiplier
= multiplier
568 best_one_based
= one_based
569 logger
.info('Affine break best fit with key {0}x+{1} ({2}) gives fit of {3} '
570 'and decrypt starting: {4}'.format(
571 best_multiplier
, best_adder
, best_one_based
, best_fit
,
572 affine_decipher(sanitised_message
, best_multiplier
,
573 best_adder
, best_one_based
)[:50]))
574 return (best_multiplier
, best_adder
, best_one_based
), best_fit
576 def keyword_break(message
,
578 metric
=norms
.euclidean_distance
,
579 target_counts
=normalised_english_counts
,
580 message_frequency_scaling
=norms
.normalise
):
581 """Breaks a keyword substitution cipher using a dictionary and
584 >>> keyword_break(keyword_encipher('this is a test message for the ' \
585 'keyword decipherment', 'elephant', 1), \
586 wordlist=['cat', 'elephant', 'kangaroo']) # doctest: +ELLIPSIS
587 (('elephant', 1), 0.41643991598441...)
590 best_wrap_alphabet
= True
591 best_fit
= float("inf")
592 for wrap_alphabet
in range(3):
593 for keyword
in wordlist
:
594 plaintext
= keyword_decipher(message
, keyword
, wrap_alphabet
)
595 counts
= message_frequency_scaling(letter_frequencies(plaintext
))
596 fit
= metric(target_counts
, counts
)
597 logger
.debug('Keyword break attempt using key {0} (wrap={1}) '
598 'gives fit of {2} and decrypt starting: {3}'.format(
599 keyword
, wrap_alphabet
, fit
,
600 sanitise(plaintext
)[:50]))
603 best_keyword
= keyword
604 best_wrap_alphabet
= wrap_alphabet
605 logger
.info('Keyword break best fit with key {0} (wrap={1}) gives fit of '
606 '{2} and decrypt starting: {3}'.format(best_keyword
,
607 best_wrap_alphabet
, best_fit
, sanitise(
608 keyword_decipher(message
, best_keyword
,
609 best_wrap_alphabet
))[:50]))
610 return (best_keyword
, best_wrap_alphabet
), best_fit
612 def keyword_break_mp(message
,
614 metric
=norms
.euclidean_distance
,
615 target_counts
=normalised_english_counts
,
616 message_frequency_scaling
=norms
.normalise
,
618 """Breaks a keyword substitution cipher using a dictionary and
621 >>> keyword_break_mp(keyword_encipher('this is a test message for the ' \
622 'keyword decipherment', 'elephant', 1), \
623 wordlist=['cat', 'elephant', 'kangaroo']) # doctest: +ELLIPSIS
624 (('elephant', 1), 0.41643991598441...)
627 helper_args
= [(message
, word
, wrap
, metric
, target_counts
,
628 message_frequency_scaling
)
629 for word
in wordlist
for wrap
in range(3)]
630 # Gotcha: the helper function here needs to be defined at the top level
631 # (limitation of Pool.starmap)
632 breaks
= pool
.starmap(keyword_break_one
, helper_args
, chunksize
)
633 return min(breaks
, key
=lambda k
: k
[1])
635 def keyword_break_one(message
, keyword
, wrap_alphabet
, metric
, target_counts
,
636 message_frequency_scaling
):
637 plaintext
= keyword_decipher(message
, keyword
, wrap_alphabet
)
638 counts
= message_frequency_scaling(letter_frequencies(plaintext
))
639 fit
= metric(target_counts
, counts
)
640 logger
.debug('Keyword break attempt using key {0} (wrap={1}) gives fit of '
641 '{2} and decrypt starting: {3}'.format(keyword
,
642 wrap_alphabet
, fit
, sanitise(plaintext
)[:50]))
643 return (keyword
, wrap_alphabet
), fit
645 def scytale_break(message
,
646 metric
=norms
.euclidean_distance
,
647 target_counts
=normalised_english_bigram_counts
,
648 message_frequency_scaling
=norms
.normalise
):
649 """Breaks a Scytale cipher
651 >>> scytale_break('tfeulchtrtteehwahsdehneoifeayfsondmwpltmaoalhikotoere' \
652 'dcweatehiplwxsnhooacgorrcrcraotohsgullasenylrendaianeplscdriioto' \
653 'aek') # doctest: +ELLIPSIS
654 (6, 0.83453041115025...)
657 best_fit
= float("inf")
658 ngram_length
= len(next(iter(target_counts
.keys())))
659 for key
in range(1, 20):
660 if len(message
) % key
== 0:
661 plaintext
= scytale_decipher(message
, key
)
662 counts
= message_frequency_scaling(frequencies(
663 ngrams(sanitise(plaintext
), ngram_length
)))
664 fit
= metric(target_counts
, counts
)
665 logger
.debug('Scytale break attempt using key {0} gives fit of '
666 '{1} and decrypt starting: {2}'.format(key
,
667 fit
, sanitise(plaintext
)[:50]))
671 logger
.info('Scytale break best fit with key {0} gives fit of {1} and '
672 'decrypt starting: {2}'.format(best_key
, best_fit
,
673 sanitise(scytale_decipher(message
, best_key
))[:50]))
674 return best_key
, best_fit
676 def column_transposition_break(message
,
678 metric
=norms
.euclidean_distance
,
679 target_counts
=normalised_english_bigram_counts
,
680 message_frequency_scaling
=norms
.normalise
):
681 """Breaks a column transposition cipher using a dictionary and
682 n-gram frequency analysis
684 >>> column_transposition_break(column_transposition_encipher(sanitise( \
685 "Turing's homosexuality resulted in a criminal prosecution in 1952, \
686 when homosexual acts were still illegal in the United Kingdom. "), \
688 wordlist=['encipher', 'keyword', 'fourteen']) # doctest: +ELLIPSIS
689 ('encipher', 0.898128626285...)
690 >>> column_transposition_break(column_transposition_encipher(sanitise( \
691 "Turing's homosexuality resulted in a criminal prosecution in 1952, " \
692 "when homosexual acts were still illegal in the United Kingdom."), \
694 wordlist=['encipher', 'keyword', 'fourteen'], \
695 target_counts=normalised_english_trigram_counts) # doctest: +ELLIPSIS
696 ('encipher', 1.1958792913127...)
699 best_fit
= float("inf")
700 ngram_length
= len(next(iter(target_counts
.keys())))
701 for keyword
in wordlist
:
702 if len(message
) % len(deduplicate(keyword
)) == 0:
703 plaintext
= column_transposition_decipher(message
, keyword
)
704 counts
= message_frequency_scaling(frequencies(
705 ngrams(sanitise(plaintext
), ngram_length
)))
706 fit
= metric(target_counts
, counts
)
707 logger
.debug('Column transposition break attempt using key {0} '
708 'gives fit of {1} and decrypt starting: {2}'.format(
710 sanitise(plaintext
)[:50]))
713 best_keyword
= keyword
714 logger
.info('Column transposition break best fit with key {0} gives fit '
715 'of {1} and decrypt starting: {2}'.format(best_keyword
,
717 column_transposition_decipher(message
,
718 best_keyword
))[:50]))
719 return best_keyword
, best_fit
722 def column_transposition_break_mp(message
,
724 metric
=norms
.euclidean_distance
,
725 target_counts
=normalised_english_bigram_counts
,
726 message_frequency_scaling
=norms
.normalise
,
728 """Breaks a column transposition cipher using a dictionary and
729 n-gram frequency analysis
731 >>> column_transposition_break_mp(column_transposition_encipher(sanitise( \
732 "Turing's homosexuality resulted in a criminal prosecution in 1952, \
733 when homosexual acts were still illegal in the United Kingdom. "), \
735 wordlist=['encipher', 'keyword', 'fourteen']) # doctest: +ELLIPSIS
736 ('encipher', 0.898128626285...)
737 >>> column_transposition_break_mp(column_transposition_encipher(sanitise( \
738 "Turing's homosexuality resulted in a criminal prosecution in 1952, " \
739 "when homosexual acts were still illegal in the United Kingdom."), \
741 wordlist=['encipher', 'keyword', 'fourteen'], \
742 target_counts=normalised_english_trigram_counts) # doctest: +ELLIPSIS
743 ('encipher', 1.1958792913127...)
745 ngram_length
= len(next(iter(target_counts
.keys())))
747 helper_args
= [(message
, word
, metric
, target_counts
, ngram_length
,
748 message_frequency_scaling
)
749 for word
in wordlist
]
750 # Gotcha: the helper function here needs to be defined at the top level
751 # (limitation of Pool.starmap)
752 breaks
= pool
.starmap(column_transposition_break_worker
, helper_args
, chunksize
)
753 return min(breaks
, key
=lambda k
: k
[1])
755 def column_transposition_break_worker(message
, keyword
, metric
, target_counts
,
756 ngram_length
, message_frequency_scaling
):
757 plaintext
= column_transposition_decipher(message
, keyword
)
758 counts
= message_frequency_scaling(frequencies(
759 ngrams(sanitise(plaintext
), ngram_length
)))
760 fit
= metric(target_counts
, counts
)
761 logger
.debug('Column transposition break attempt using key {0} '
762 'gives fit of {1} and decrypt starting: {2}'.format(
764 sanitise(plaintext
)[:50]))
769 if __name__
== "__main__":