X-Git-Url: https://git.njae.me.uk/?a=blobdiff_plain;f=cipher%2Fpolybius.py;fp=cipher%2Fpolybius.py;h=79aeb386a5f2920893a83a2f2cef8594a9439080;hb=311b300d197536622980f7a837294d8245e326b4;hp=0000000000000000000000000000000000000000;hpb=d7224fba67d9f99c01bd78ef669c96189686e4c2;p=cipher-tools.git diff --git a/cipher/polybius.py b/cipher/polybius.py new file mode 100644 index 0000000..79aeb38 --- /dev/null +++ b/cipher/polybius.py @@ -0,0 +1,185 @@ +from utilities import * +from language_models import * +import multiprocessing + +from keyword_cipher import KeywordWrapAlphabet + +from logger import logger + +def polybius_grid(keyword, column_order, row_order, letters_to_merge=None, + wrap_alphabet=KeywordWrapAlphabet.from_a): + """Grid for a Polybius cipher, using a keyword to rearrange the + alphabet. + + + >>> polybius_grid('a', 'abcde', 'abcde')['x'] == ('e', 'c') + True + >>> polybius_grid('elephant', 'abcde', 'abcde')['e'] == ('a', 'a') + True + >>> polybius_grid('elephant', 'abcde', 'abcde')['b'] == ('b', 'c') + True + """ + alphabet = keyword_cipher_alphabet_of(keyword, wrap_alphabet=wrap_alphabet) + if letters_to_merge is None: + letters_to_merge = {'j': 'i'} + grid = {l: k + for k, l in zip([(c, r) for c in column_order for r in row_order], + [l for l in alphabet if l not in letters_to_merge])} + for l in letters_to_merge: + grid[l] = grid[letters_to_merge[l]] + return grid + +def polybius_reverse_grid(keyword, column_order, row_order, letters_to_merge=None, + wrap_alphabet=KeywordWrapAlphabet.from_a): + """Grid for decrypting using a Polybius cipher, using a keyword to + rearrange the alphabet. + + >>> polybius_reverse_grid('a', 'abcde', 'abcde')['e', 'c'] == 'x' + True + >>> polybius_reverse_grid('elephant', 'abcde', 'abcde')['a', 'a'] == 'e' + True + >>> polybius_reverse_grid('elephant', 'abcde', 'abcde')['b', 'c'] == 'b' + True + """ + alphabet = keyword_cipher_alphabet_of(keyword, wrap_alphabet=wrap_alphabet) + if letters_to_merge is None: + letters_to_merge = {'j': 'i'} + grid = {k: l + for k, l in zip([(c, r) for c in column_order for r in row_order], + [l for l in alphabet if l not in letters_to_merge])} + return grid + + +def polybius_flatten(pair, column_first): + """Convert a series of pairs into a single list of characters""" + if column_first: + return str(pair[1]) + str(pair[0]) + else: + return str(pair[0]) + str(pair[1]) + +def polybius_encipher(message, keyword, column_order, row_order, + column_first=False, + letters_to_merge=None, wrap_alphabet=KeywordWrapAlphabet.from_a): + """Encipher a message with Polybius cipher, using a keyword to rearrange + the alphabet + + + >>> polybius_encipher('this is a test message for the ' \ + 'polybius decipherment', 'elephant', \ + [1, 2, 3, 4, 5], [1, 2, 3, 4, 5], \ + wrap_alphabet=KeywordWrapAlphabet.from_last) + '2214445544551522115522511155551543114252542214111352123234442355411135441314115451112122' + >>> polybius_encipher('this is a test message for the ' \ + 'polybius decipherment', 'elephant', 'abcde', 'abcde', \ + column_first=False) + 'bbadccddccddaebbaaddbbceaaddddaecbaacadadcbbadaaacdaabedbcccdeddbeaabdccacadaadcceaababb' + >>> polybius_encipher('this is a test message for the ' \ + 'polybius decipherment', 'elephant', 'abcde', 'abcde', \ + column_first=True) + 'bbdaccddccddeabbaaddbbecaaddddeabcaaacadcdbbdaaacaadbadecbccedddebaadbcccadaaacdecaaabbb' + """ + grid = polybius_grid(keyword, column_order, row_order, letters_to_merge, wrap_alphabet) + return cat(polybius_flatten(grid[l], column_first) + for l in message + if l in grid) + + +def polybius_decipher(message, keyword, column_order, row_order, + column_first=False, + letters_to_merge=None, wrap_alphabet=KeywordWrapAlphabet.from_a): + """Decipher a message with a Polybius cipher, using a keyword to rearrange + the alphabet + + >>> polybius_decipher('bbdaccddccddeabbaaddbbecaaddddeabcaaacadcdbbdaaaca'\ + 'adbadecbccedddebaadbcccadaaacdecaaabbb', 'elephant', 'abcde', 'abcde', \ + column_first=False) + 'toisisvtestxessvbephktoefhnugiysweqifoekxelt' + + >>> polybius_decipher('bbdaccddccddeabbaaddbbecaaddddeabcaaacadcdbbdaaaca'\ + 'adbadecbccedddebaadbcccadaaacdecaaabbb', 'elephant', 'abcde', 'abcde', \ + column_first=True) + 'thisisatestmessageforthepolybiusdecipherment' + """ + grid = polybius_reverse_grid(keyword, column_order, row_order, letters_to_merge, wrap_alphabet) + column_index_type = type(column_order[0]) + row_index_type = type(row_order[0]) + if column_first: + pairs = [(column_index_type(p[1]), row_index_type(p[0])) for p in chunks(message, 2)] + else: + pairs = [(row_index_type(p[0]), column_index_type(p[1])) for p in chunks(message, 2)] + return cat(grid[p] for p in pairs if p in grid) + + +def polybius_break_mp(message, column_labels, row_labels, + letters_to_merge=None, + wordlist=keywords, fitness=Pletters, + number_of_solutions=1, chunksize=500): + """Breaks a Polybius substitution cipher using a dictionary and + frequency analysis + + >>> polybius_break_mp(polybius_encipher('this is a test message for the ' \ + 'polybius decipherment', 'elephant', 'abcde', 'abcde'), \ + 'abcde', 'abcde', \ + wordlist=['cat', 'elephant', 'kangaroo']) # doctest: +ELLIPSIS, +NORMALIZE_WHITESPACE + (('elephant', , 'abcde', 'abcde', False), \ + -54.53880...) + >>> polybius_break_mp(polybius_encipher('this is a test message for the ' \ + 'polybius decipherment', 'elephant', 'abcde', 'abcde', column_first=True), \ + 'abcde', 'abcde', \ + wordlist=['cat', 'elephant', 'kangaroo']) # doctest: +ELLIPSIS, +NORMALIZE_WHITESPACE + (('elephant', , 'abcde', 'abcde', True), \ + -54.53880...) + >>> polybius_break_mp(polybius_encipher('this is a test message for the ' \ + 'polybius decipherment', 'elephant', 'abcde', 'abcde', column_first=False), \ + 'abcde', 'abcde', \ + wordlist=['cat', 'elephant', 'kangaroo']) # doctest: +ELLIPSIS, +NORMALIZE_WHITESPACE + (('elephant', , 'abcde', 'abcde', False), \ + -54.53880...) + >>> polybius_break_mp(polybius_encipher('this is a test message for the ' \ + 'polybius decipherment', 'elephant', 'abcde', 'pqrst', column_first=True), \ + 'abcde', 'pqrst', \ + wordlist=['cat', 'elephant', 'kangaroo']) # doctest: +ELLIPSIS, +NORMALIZE_WHITESPACE + (('elephant', , 'abcde', 'pqrst', True), \ + -54.53880...) + """ + if letters_to_merge is None: + letters_to_merge = {'j': 'i'} + with multiprocessing.Pool() as pool: + helper_args = [(message, word, wrap, + column_labels, row_labels, column_first, + letters_to_merge, + fitness) + for word in wordlist + for wrap in KeywordWrapAlphabet + for column_first in [False, True]] + # Gotcha: the helper function here needs to be defined at the top level + # (limitation of Pool.starmap) + breaks = pool.starmap(polybius_break_worker, helper_args, chunksize) + if number_of_solutions == 1: + return max(breaks, key=lambda k: k[1]) + else: + return sorted(breaks, key=lambda k: k[1], reverse=True)[:number_of_solutions] + +def polybius_break_worker(message, keyword, wrap_alphabet, + column_order, row_order, column_first, + letters_to_merge, + fitness): + plaintext = polybius_decipher(message, keyword, + column_order, row_order, + column_first=column_first, + letters_to_merge=letters_to_merge, + wrap_alphabet=wrap_alphabet) + if plaintext: + fit = fitness(plaintext) + else: + fit = float('-inf') + logger.debug('Polybius break attempt using key {0} (wrap={1}, merging {2}), ' + 'columns as {3}, rows as {4} (column_first={5}) ' + 'gives fit of {6} and decrypt starting: ' + '{7}'.format(keyword, wrap_alphabet, letters_to_merge, + column_order, row_order, column_first, + fit, sanitise(plaintext)[:50])) + return (keyword, wrap_alphabet, column_order, row_order, column_first), fit + +if __name__ == "__main__": + import doctest \ No newline at end of file