From: Neil Smith Date: Mon, 14 Jul 2014 18:40:17 +0000 (+0100) Subject: Breaking keyword ciphers X-Git-Url: https://git.njae.me.uk/?a=commitdiff_plain;h=e514a90b030632244bb10636ed0fe54cffb56f19;p=cipher-training.git Breaking keyword ciphers --- diff --git a/cipher.py b/cipher.py index 5a7781b..bde9ea1 100644 --- a/cipher.py +++ b/cipher.py @@ -16,82 +16,6 @@ for a in range(26): modular_division_table[b][c] = a -def every_nth(text, n, fillvalue=''): - """Returns n strings, each of which consists of every nth character, - starting with the 0th, 1st, 2nd, ... (n-1)th character - - >>> every_nth(string.ascii_lowercase, 5) - ['afkpuz', 'bglqv', 'chmrw', 'dinsx', 'ejoty'] - >>> every_nth(string.ascii_lowercase, 1) - ['abcdefghijklmnopqrstuvwxyz'] - >>> every_nth(string.ascii_lowercase, 26) # doctest: +NORMALIZE_WHITESPACE - ['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', - 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z'] - >>> every_nth(string.ascii_lowercase, 5, fillvalue='!') - ['afkpuz', 'bglqv!', 'chmrw!', 'dinsx!', 'ejoty!'] - """ - split_text = chunks(text, n, fillvalue) - return [''.join(l) for l in zip_longest(*split_text, fillvalue=fillvalue)] - -def combine_every_nth(split_text): - """Reforms a text split into every_nth strings - - >>> combine_every_nth(every_nth(string.ascii_lowercase, 5)) - 'abcdefghijklmnopqrstuvwxyz' - >>> combine_every_nth(every_nth(string.ascii_lowercase, 1)) - 'abcdefghijklmnopqrstuvwxyz' - >>> combine_every_nth(every_nth(string.ascii_lowercase, 26)) - 'abcdefghijklmnopqrstuvwxyz' - """ - return ''.join([''.join(l) - for l in zip_longest(*split_text, fillvalue='')]) - -def chunks(text, n, fillvalue=None): - """Split a text into chunks of n characters - - >>> chunks('abcdefghi', 3) - ['abc', 'def', 'ghi'] - >>> chunks('abcdefghi', 4) - ['abcd', 'efgh', 'i'] - >>> chunks('abcdefghi', 4, fillvalue='!') - ['abcd', 'efgh', 'i!!!'] - """ - if fillvalue: - padding = fillvalue[0] * (n - len(text) % n) - else: - padding = '' - return [(text+padding)[i:i+n] for i in range(0, len(text), n)] - -def transpose(items, transposition): - """Moves items around according to the given transposition - - >>> transpose(['a', 'b', 'c', 'd'], (0,1,2,3)) - ['a', 'b', 'c', 'd'] - >>> transpose(['a', 'b', 'c', 'd'], (3,1,2,0)) - ['d', 'b', 'c', 'a'] - >>> transpose([10,11,12,13,14,15], (3,2,4,1,5,0)) - [13, 12, 14, 11, 15, 10] - """ - transposed = [''] * len(transposition) - for p, t in enumerate(transposition): - transposed[p] = items[t] - return transposed - -def untranspose(items, transposition): - """Undoes a transpose - - >>> untranspose(['a', 'b', 'c', 'd'], [0,1,2,3]) - ['a', 'b', 'c', 'd'] - >>> untranspose(['d', 'b', 'c', 'a'], [3,1,2,0]) - ['a', 'b', 'c', 'd'] - >>> untranspose([13, 12, 14, 11, 15, 10], [3,2,4,1,5,0]) - [10, 11, 12, 13, 14, 15] - """ - transposed = [''] * len(transposition) - for p, t in enumerate(transposition): - transposed[t] = items[p] - return transposed - def deduplicate(text): """If a string contains duplicate letters, remove all but the first. Retain the order of the letters. @@ -363,175 +287,6 @@ beaufort_encipher = vigenere_decipher beaufort_decipher = vigenere_encipher -def transpositions_of(keyword): - """Finds the transpostions given by a keyword. For instance, the keyword - 'clever' rearranges to 'celrv', so the first column (0) stays first, the - second column (1) moves to third, the third column (2) moves to second, - and so on. - - If passed a tuple, assume it's already a transposition and just return it. - - >>> transpositions_of('clever') - (0, 2, 1, 4, 3) - >>> transpositions_of('fred') - (3, 2, 0, 1) - >>> transpositions_of((3, 2, 0, 1)) - (3, 2, 0, 1) - """ - if isinstance(keyword, tuple): - return keyword - else: - key = deduplicate(keyword) - transpositions = tuple(key.index(l) for l in sorted(key)) - return transpositions - -def pad(message_len, group_len, fillvalue): - """Returns the padding required to extend a message of message_len to an - even multiple of group_len, by adding repreated copies of fillvalue. - fillvalue can either be a character or a function that returns a character. - - >>> pad(10, 4, '!') - '!!' - >>> pad(8, 4, '!') - '' - >>> pad(16, 4, '!') - '' - >>> pad(10, 4, lambda: '*') - '**' - """ - padding_length = group_len - message_len % group_len - if padding_length == group_len: padding_length = 0 - padding = '' - for _ in range(padding_length): - if callable(fillvalue): - padding += fillvalue() - else: - padding += fillvalue - return padding - -def column_transposition_encipher(message, keyword, fillvalue=' ', - fillcolumnwise=False, - emptycolumnwise=False): - """Enciphers using the column transposition cipher. - Message is padded to allow all rows to be the same length. - - >>> column_transposition_encipher('hellothere', 'abcdef', fillcolumnwise=True) - 'hlohr eltee ' - >>> column_transposition_encipher('hellothere', 'abcdef', fillcolumnwise=True, emptycolumnwise=True) - 'hellothere ' - >>> column_transposition_encipher('hellothere', 'abcdef') - 'hellothere ' - >>> column_transposition_encipher('hellothere', 'abcde') - 'hellothere' - >>> column_transposition_encipher('hellothere', 'abcde', fillcolumnwise=True, emptycolumnwise=True) - 'hellothere' - >>> column_transposition_encipher('hellothere', 'abcde', fillcolumnwise=True, emptycolumnwise=False) - 'hlohreltee' - >>> column_transposition_encipher('hellothere', 'abcde', fillcolumnwise=False, emptycolumnwise=True) - 'htehlelroe' - >>> column_transposition_encipher('hellothere', 'abcde', fillcolumnwise=False, emptycolumnwise=False) - 'hellothere' - >>> column_transposition_encipher('hellothere', 'clever', fillcolumnwise=True, emptycolumnwise=True) - 'heotllrehe' - >>> column_transposition_encipher('hellothere', 'clever', fillcolumnwise=True, emptycolumnwise=False) - 'holrhetlee' - >>> column_transposition_encipher('hellothere', 'clever', fillcolumnwise=False, emptycolumnwise=True) - 'htleehoelr' - >>> column_transposition_encipher('hellothere', 'clever', fillcolumnwise=False, emptycolumnwise=False) - 'hleolteher' - >>> column_transposition_encipher('hellothere', 'cleverly') - 'hleolthre e ' - >>> column_transposition_encipher('hellothere', 'cleverly', fillvalue='!') - 'hleolthre!e!' - >>> column_transposition_encipher('hellothere', 'cleverly', fillvalue=lambda: '*') - 'hleolthre*e*' - """ - transpositions = transpositions_of(keyword) - message += pad(len(message), len(transpositions), fillvalue) - if fillcolumnwise: - rows = every_nth(message, len(message) // len(transpositions)) - else: - rows = chunks(message, len(transpositions)) - transposed = [transpose(r, transpositions) for r in rows] - if emptycolumnwise: - return combine_every_nth(transposed) - else: - return ''.join(chain(*transposed)) - -def column_transposition_decipher(message, keyword, fillvalue=' ', - fillcolumnwise=False, - emptycolumnwise=False): - """Deciphers using the column transposition cipher. - Message is padded to allow all rows to be the same length. - - >>> column_transposition_decipher('hellothere', 'abcde', fillcolumnwise=True, emptycolumnwise=True) - 'hellothere' - >>> column_transposition_decipher('hlohreltee', 'abcde', fillcolumnwise=True, emptycolumnwise=False) - 'hellothere' - >>> column_transposition_decipher('htehlelroe', 'abcde', fillcolumnwise=False, emptycolumnwise=True) - 'hellothere' - >>> column_transposition_decipher('hellothere', 'abcde', fillcolumnwise=False, emptycolumnwise=False) - 'hellothere' - >>> column_transposition_decipher('heotllrehe', 'clever', fillcolumnwise=True, emptycolumnwise=True) - 'hellothere' - >>> column_transposition_decipher('holrhetlee', 'clever', fillcolumnwise=True, emptycolumnwise=False) - 'hellothere' - >>> column_transposition_decipher('htleehoelr', 'clever', fillcolumnwise=False, emptycolumnwise=True) - 'hellothere' - >>> column_transposition_decipher('hleolteher', 'clever', fillcolumnwise=False, emptycolumnwise=False) - 'hellothere' - """ - transpositions = transpositions_of(keyword) - message += pad(len(message), len(transpositions), '*') - if emptycolumnwise: - rows = every_nth(message, len(message) // len(transpositions)) - else: - rows = chunks(message, len(transpositions)) - untransposed = [untranspose(r, transpositions) for r in rows] - if fillcolumnwise: - return combine_every_nth(untransposed) - else: - return ''.join(chain(*untransposed)) - -def scytale_encipher(message, rows, fillvalue=' '): - """Enciphers using the scytale transposition cipher. - Message is padded with spaces to allow all rows to be the same length. - - >>> scytale_encipher('thequickbrownfox', 3) - 'tcnhkfeboqrxuo iw ' - >>> scytale_encipher('thequickbrownfox', 4) - 'tubnhirfecooqkwx' - >>> scytale_encipher('thequickbrownfox', 5) - 'tubn hirf ecoo qkwx ' - >>> scytale_encipher('thequickbrownfox', 6) - 'tqcrnxhukof eibwo ' - >>> scytale_encipher('thequickbrownfox', 7) - 'tqcrnx hukof eibwo ' - """ - transpositions = [i for i in range(rows)] - return column_transposition_encipher(message, transpositions, - fillvalue=fillvalue, fillcolumnwise=True, emptycolumnwise=False) - -def scytale_decipher(message, rows): - """Deciphers using the scytale transposition cipher. - Assumes the message is padded so that all rows are the same length. - - >>> scytale_decipher('tcnhkfeboqrxuo iw ', 3) - 'thequickbrownfox ' - >>> scytale_decipher('tubnhirfecooqkwx', 4) - 'thequickbrownfox' - >>> scytale_decipher('tubn hirf ecoo qkwx ', 5) - 'thequickbrownfox ' - >>> scytale_decipher('tqcrnxhukof eibwo ', 6) - 'thequickbrownfox ' - >>> scytale_decipher('tqcrnx hukof eibwo ', 7) - 'thequickbrownfox ' - """ - transpositions = [i for i in range(rows)] - return column_transposition_decipher(message, transpositions, - fillcolumnwise=True, emptycolumnwise=False) - - if __name__ == "__main__": import doctest doctest.testmod()