+def vigenere_keyword_break(message,
+ wordlist=keywords,
+ metric=norms.euclidean_distance,
+ target_counts=normalised_english_counts,
+ message_frequency_scaling=norms.normalise):
+ """Breaks a vigenere cipher using a dictionary and
+ frequency analysis
+
+ >>> vigenere_keyword_break(keyword_encipher('this is a test message for the ' \
+ 'keyword decipherment', 'elephant', 1), \
+ wordlist=['cat', 'elephant', 'kangaroo']) # doctest: +ELLIPSIS
+ ('elephant', 0.7166585201707...)
+ """
+ best_keyword = ''
+ best_fit = float("inf")
+ for keyword in wordlist:
+ plaintext = vigenere_decipher(message, keyword)
+ counts = message_frequency_scaling(letter_frequencies(plaintext))
+ fit = metric(target_counts, counts)
+ logger.debug('Vigenere break attempt using key {0} '
+ 'gives fit of {1} and decrypt starting: {2}'.format(
+ keyword, fit,
+ sanitise(plaintext)[:50]))
+ if fit < best_fit:
+ best_fit = fit
+ best_keyword = keyword
+ logger.info('Vigenere break best fit with key {0} gives fit '
+ 'of {1} and decrypt starting: {2}'.format(best_keyword,
+ best_fit, sanitise(
+ vigenere_decipher(message, best_keyword))[:50]))
+ return best_keyword, best_fit
+
+def vigenere_keyword_break_mp(message,
+ wordlist=keywords,
+ metric=norms.euclidean_distance,
+ target_counts=normalised_english_counts,
+ message_frequency_scaling=norms.normalise,
+ chunksize=500):
+ """Breaks a vigenere cipher using a dictionary and
+ frequency analysis
+
+ >>> vigenere_keyword_break_mp(keyword_encipher('this is a test message for the ' \
+ 'keyword decipherment', 'elephant', 1), \
+ wordlist=['cat', 'elephant', 'kangaroo']) # doctest: +ELLIPSIS
+ ('elephant', 0.7166585201707...)
+ """
+ with Pool() as pool:
+ helper_args = [(message, word, metric, target_counts,
+ message_frequency_scaling)
+ for word in wordlist]
+ # Gotcha: the helper function here needs to be defined at the top level
+ # (limitation of Pool.starmap)
+ breaks = pool.starmap(vigenere_keyword_break_worker, helper_args, chunksize)
+ return min(breaks, key=lambda k: k[1])
+
+def vigenere_keyword_break_worker(message, keyword, metric, target_counts,
+ message_frequency_scaling):
+ plaintext = vigenere_decipher(message, keyword)
+ counts = message_frequency_scaling(letter_frequencies(plaintext))
+ fit = metric(target_counts, counts)
+ logger.debug('Vigenere keyword break attempt using key {0} gives fit of '
+ '{1} and decrypt starting: {2}'.format(keyword,
+ fit, sanitise(plaintext)[:50]))
+ return keyword, fit
+