import collections
import norms
import logging
-from itertools import zip_longest, cycle
+from itertools import zip_longest, cycle, permutations
from segment import segment, Pwords
from multiprocessing import Pool
+from math import log10
+
+import matplotlib.pyplot as plt
from cipher import *
letter_frequencies = frequencies
+def bigram_likelihood(bigram, bf, lf):
+ return bf[bigram] / (lf[bigram[0]] * lf[bigram[1]])
+
def caesar_break(message,
metric=norms.euclidean_distance,
sanitise(scytale_decipher(message, best_key))[:50]))
return best_key, best_fit
-def column_transposition_break(message,
- translist=transpositions,
- metric=norms.euclidean_distance,
- target_counts=normalised_english_bigram_counts,
- message_frequency_scaling=norms.normalise):
- """Breaks a column transposition cipher using a dictionary and
- n-gram frequency analysis
-
- >>> column_transposition_break(column_transposition_encipher(sanitise( \
- "It is a truth universally acknowledged, that a single man in \
- possession of a good fortune, must be in want of a wife. However \
- little known the feelings or views of such a man may be on his \
- first entering a neighbourhood, this truth is so well fixed in the \
- minds of the surrounding families, that he is considered the \
- rightful property of some one or other of their daughters."), \
- 'encipher'), \
- translist={(2, 0, 5, 3, 1, 4, 6): ['encipher'], \
- (5, 0, 6, 1, 3, 4, 2): ['fourteen'], \
- (6, 1, 0, 4, 5, 3, 2): ['keyword']}) # doctest: +ELLIPSIS
- ((2, 0, 5, 3, 1, 4, 6), 0.0628106372...)
- >>> column_transposition_break(column_transposition_encipher(sanitise( \
- "It is a truth universally acknowledged, that a single man in \
- possession of a good fortune, must be in want of a wife. However \
- little known the feelings or views of such a man may be on his \
- first entering a neighbourhood, this truth is so well fixed in the \
- minds of the surrounding families, that he is considered the \
- rightful property of some one or other of their daughters."), \
- 'encipher'), \
- translist={(2, 0, 5, 3, 1, 4, 6): ['encipher'], \
- (5, 0, 6, 1, 3, 4, 2): ['fourteen'], \
- (6, 1, 0, 4, 5, 3, 2): ['keyword']}, \
- target_counts=normalised_english_trigram_counts) # doctest: +ELLIPSIS
- ((2, 0, 5, 3, 1, 4, 6), 0.0592259560...)
- """
- best_transposition = ''
- best_fit = float("inf")
- ngram_length = len(next(iter(target_counts.keys())))
- for transposition in translist.keys():
- if len(message) % len(transposition) == 0:
- plaintext = column_transposition_decipher(message, transposition)
- counts = message_frequency_scaling(frequencies(
- ngrams(sanitise(plaintext), ngram_length)))
- fit = metric(target_counts, counts)
- logger.debug('Column transposition break attempt using key {0} '
- 'gives fit of {1} and decrypt starting: {2}'.format(
- translist[transposition][0], fit,
- sanitise(plaintext)[:50]))
- if fit < best_fit:
- best_fit = fit
- best_transposition = transposition
- logger.info('Column transposition break best fit with key {0} gives fit '
- 'of {1} and decrypt starting: {2}'.format(
- translist[best_transposition][0],
- best_fit, sanitise(
- column_transposition_decipher(message,
- best_transposition))[:50]))
- return best_transposition, best_fit
-
def column_transposition_break_mp(message,
translist=transpositions,
translist={(2, 0, 5, 3, 1, 4, 6): ['encipher'], \
(5, 0, 6, 1, 3, 4, 2): ['fourteen'], \
(6, 1, 0, 4, 5, 3, 2): ['keyword']}) # doctest: +ELLIPSIS
- ((2, 0, 5, 3, 1, 4, 6), 0.0628106372...)
+ (((2, 0, 5, 3, 1, 4, 6), False), 0.0628106372...)
>>> column_transposition_break_mp(column_transposition_encipher(sanitise( \
"It is a truth universally acknowledged, that a single man in \
possession of a good fortune, must be in want of a wife. However \
(5, 0, 6, 1, 3, 4, 2): ['fourteen'], \
(6, 1, 0, 4, 5, 3, 2): ['keyword']}, \
target_counts=normalised_english_trigram_counts) # doctest: +ELLIPSIS
- ((2, 0, 5, 3, 1, 4, 6), 0.0592259560...)
+ (((2, 0, 5, 3, 1, 4, 6), False), 0.0592259560...)
"""
ngram_length = len(next(iter(target_counts.keys())))
with Pool() as pool:
- helper_args = [(message, trans, metric, target_counts, ngram_length,
+ helper_args = [(message, trans, columnwise, metric, target_counts, ngram_length,
message_frequency_scaling)
- for trans in translist.keys()]
+ for trans in translist.keys() for columnwise in [True, False]]
# Gotcha: the helper function here needs to be defined at the top level
# (limitation of Pool.starmap)
breaks = pool.starmap(column_transposition_break_worker, helper_args, chunksize)
return min(breaks, key=lambda k: k[1])
+column_transposition_break = column_transposition_break_mp
-def column_transposition_break_worker(message, transposition, metric, target_counts,
+def column_transposition_break_worker(message, transposition, columnwise, metric, target_counts,
ngram_length, message_frequency_scaling):
- plaintext = column_transposition_decipher(message, transposition)
+ plaintext = column_transposition_decipher(message, transposition, columnwise=columnwise)
counts = message_frequency_scaling(frequencies(
ngrams(sanitise(plaintext), ngram_length)))
fit = metric(target_counts, counts)
'gives fit of {1} and decrypt starting: {2}'.format(
transposition, fit,
sanitise(plaintext)[:50]))
- return transposition, fit
+ return (transposition, columnwise), fit
+
+
+def transposition_break_exhaustive(message):
+ best_transposition = ''
+ best_pw = -float('inf')
+ for keylength in range(1, 21):
+ if len(message) % keylength == 0:
+ for transposition in permutations(range(keylength)):
+ for columnwise in [True, False]:
+ plaintext = column_transposition_decipher(message,
+ transposition, columnwise=columnwise)
+ # pw = Pwords(segment(plaintext))
+ pw = sum([log10(bigram_likelihood(b,
+ normalised_english_bigram_counts,
+ normalised_english_counts))
+ for b in ngrams(plaintext, 2)])
+ logger.debug('Column transposition break attempt using key {0} {1} '
+ 'gives fit of {2} and decrypt starting: {3}'.format(
+ transposition, columnwise, pw,
+ sanitise(plaintext)[:50]))
+ if pw > best_pw:
+ best_transposition = transposition
+ best_columnwise = columnwise
+ best_pw = pw
+ return (best_transposition, best_columnwise), best_pw
+
def vigenere_keyword_break(message,
wordlist=keywords,
vigenere_decipher(message, best_key))[:50]))
return best_key, best_fit
+def beaufort_frequency_break(message,
+ metric=norms.euclidean_distance,
+ target_counts=normalised_english_counts,
+ message_frequency_scaling=norms.normalise):
+ """Breaks a Beaufort cipher with frequency analysis
+
+ >>> vigenere_frequency_break(vigenere_encipher(sanitise("It is time to " \
+ "run. She is ready and so am I. I stole Daniel's pocketbook this " \
+ "afternoon when he left his jacket hanging on the easel in the " \
+ "attic."), 'florence')) # doctest: +ELLIPSIS
+ ('florence', 0.077657073...)
+ """
+ best_fit = float("inf")
+ best_key = ''
+ sanitised_message = sanitise(message)
+ for trial_length in range(1, 20):
+ splits = every_nth(sanitised_message, trial_length)
+ key = ''.join([chr(caesar_break(s, target_counts=target_counts)[0] + ord('a')) for s in splits])
+ plaintext = beaufort_decipher(sanitised_message, key)
+ counts = message_frequency_scaling(frequencies(plaintext))
+ fit = metric(target_counts, counts)
+ logger.debug('Beaufort key length of {0} ({1}) gives fit of {2}'.
+ format(trial_length, key, fit))
+ if fit < best_fit:
+ best_fit = fit
+ best_key = key
+ logger.info('Beaufort break best fit with key {0} gives fit '
+ 'of {1} and decrypt starting: {2}'.format(best_key,
+ best_fit, sanitise(
+ beaufort_decipher(message, best_key))[:50]))
+ return best_key, best_fit
+
+
+
+def plot_frequency_histogram(freqs, sort_key=None):
+ x = range(len(freqs.keys()))
+ y = [freqs[l] for l in sorted(freqs.keys(), key=sort_key)]
+ f = plt.figure()
+ ax = f.add_axes([0.1, 0.1, 0.9, 0.9])
+ ax.bar(x, y, align='center')
+ ax.set_xticks(x)
+ ax.set_xticklabels(sorted(freqs.keys(), key=sort_key))
+ f.show()
if __name__ == "__main__":
projects / cipher-tools.git / blobdiff