From: Neil Smith Date: Mon, 14 Jul 2014 19:07:18 +0000 (+0100) Subject: Keyword ciphers X-Git-Url: https://git.njae.me.uk/?a=commitdiff_plain;h=adc4d25f65ea851bc53341dc8cf463469f48d603;p=cipher-training.git Keyword ciphers --- diff --git a/cipherbreak.py b/cipherbreak.py index f4c9c03..c239400 100644 --- a/cipherbreak.py +++ b/cipherbreak.py @@ -128,65 +128,6 @@ def affine_break(message, fitness=Pletters): best_adder, best_one_based)[:50])) return (best_multiplier, best_adder, best_one_based), best_fit -def keyword_break(message, wordlist=keywords, fitness=Pletters): - """Breaks a keyword substitution cipher using a dictionary and - frequency analysis. - - >>> keyword_break(keyword_encipher('this is a test message for the ' \ - 'keyword decipherment', 'elephant', KeywordWrapAlphabet.from_last), \ - wordlist=['cat', 'elephant', 'kangaroo']) # doctest: +ELLIPSIS - (('elephant', ), -52.834575011...) - """ - best_keyword = '' - best_wrap_alphabet = True - best_fit = float("-inf") - for wrap_alphabet in KeywordWrapAlphabet: - for keyword in wordlist: - plaintext = keyword_decipher(message, keyword, wrap_alphabet) - fit = fitness(plaintext) - logger.debug('Keyword break attempt using key {0} (wrap={1}) ' - 'gives fit of {2} and decrypt starting: {3}'.format( - keyword, wrap_alphabet, fit, - sanitise(plaintext)[:50])) - if fit > best_fit: - best_fit = fit - best_keyword = keyword - best_wrap_alphabet = wrap_alphabet - logger.info('Keyword break best fit with key {0} (wrap={1}) gives fit of ' - '{2} and decrypt starting: {3}'.format(best_keyword, - best_wrap_alphabet, best_fit, sanitise( - keyword_decipher(message, best_keyword, - best_wrap_alphabet))[:50])) - return (best_keyword, best_wrap_alphabet), best_fit - -def keyword_break_mp(message, wordlist=keywords, fitness=Pletters, - chunksize=500): - """Breaks a keyword substitution cipher using a dictionary and - frequency analysis - - >>> keyword_break_mp(keyword_encipher('this is a test message for the ' \ - 'keyword decipherment', 'elephant', KeywordWrapAlphabet.from_last), \ - wordlist=['cat', 'elephant', 'kangaroo']) # doctest: +ELLIPSIS - (('elephant', ), -52.834575011...) - """ - with Pool() as pool: - helper_args = [(message, word, wrap, fitness) - for word in wordlist - for wrap in KeywordWrapAlphabet] - # Gotcha: the helper function here needs to be defined at the top level - # (limitation of Pool.starmap) - breaks = pool.starmap(keyword_break_worker, helper_args, chunksize) - return max(breaks, key=lambda k: k[1]) - -def keyword_break_worker(message, keyword, wrap_alphabet, fitness): - plaintext = keyword_decipher(message, keyword, wrap_alphabet) - fit = fitness(plaintext) - logger.debug('Keyword break attempt using key {0} (wrap={1}) gives fit of ' - '{2} and decrypt starting: {3}'.format(keyword, - wrap_alphabet, fit, sanitise(plaintext)[:50])) - return (keyword, wrap_alphabet), fit - - def plot_frequency_histogram(freqs, sort_key=None): x = range(len(freqs.keys()))