+"""Enciphering and deciphering using the [Column transposition cipher](https://en.wikipedia.org/wiki/Bifid_cipher).
+Also attempts to break messages that use a column transpositon cipher.
+
+A grid is layed out, with one column for each distinct letter in the keyword.
+The grid is filled by the plaintext, one letter per cell, either in rows or
+columns. The columns are rearranged so the keyword's letters are in alphabetical
+order, then the ciphertext is read from the rearranged grid, either in rows
+or columns.
+
+The Scytale cipher is a column cipher with an identity transposition, where the
+message is written in rows and read in columns.
+
+Messages that do not fill the grid are padded with fillvalue. Note that
+`szyfrow.support.utilities.pad` allows a callable, so that the message can be
+padded by random letters, for instance by calling
+`szyfrow.support.language_models.random_english_letter`.
+"""
+
import math
import multiprocessing
from itertools import chain
from szyfrow.support.utilities import *
from szyfrow.support.language_models import *
-# 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
-
-
-# transpositions = collections.defaultdict(list)
-# for word in keywords:
-# transpositions[transpositions_of(word)] += [word]
-
-
-# def pad(message_len, group_len, fillvalue):
-# """Return the padding needed to extend a message to a multiple of group_len
-# in length.
-
-# fillvalue can be a function or a literal value. If a function, it is called
-# once for each padded character. Use this will fillvalue=random_english_letter
-# to pad a message with random letters.
-# """
-# padding_length = group_len - message_len % group_len
-# if padding_length == group_len: padding_length = 0
-# padding = ''
-# for i 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):
"""Deciphers using the column transposition cipher.
Message is padded to allow all rows to be the same length.
+ Note that `fillcolumnwise` and `emptycolumnwise` refer to how the message
+ is enciphered. To decipher a message, the operations are performed as an
+ inverse-empty, then inverse-transposition, then inverse-fill.
+
>>> column_transposition_decipher('hellothere', 'abcde', fillcolumnwise=True, emptycolumnwise=True)
'hellothere'
>>> column_transposition_decipher('hlohreltee', 'abcde', fillcolumnwise=True, emptycolumnwise=False)
return cat(chain(*untransposed))
def scytale_encipher(message, rows, fillvalue=' '):
- """Enciphers using the scytale transposition cipher.
+ """Enciphers using the scytale transposition cipher. `rows` is the
+ circumference of the rod. The message is fitted inot columns so that
+ all rows are used.
+
Message is padded with spaces to allow all rows to be the same length.
+ For ease of implementation, the cipher is performed on the transpose
+ of the grid
+
>>> scytale_encipher('thequickbrownfox', 3)
'tcnhkfeboqrxuo iw '
>>> scytale_encipher('thequickbrownfox', 4)
fillcolumnwise=True, emptycolumnwise=False)
-def column_transposition_break_mp(message, translist=transpositions,
+def column_transposition_break(message, translist=None,
fitness=Pbigrams, chunksize=500):
"""Breaks a column transposition cipher using a dictionary and
n-gram frequency analysis
+ If `translist` is not specified, use
+ [`szyfrow.support.langauge_models.transpositions`](support/language_models.html#szyfrow.support.language_models.transpositions).
+
>>> len(keywords)
20
- >>> column_transposition_break_mp(column_transposition_encipher(sanitise( \
+ >>> 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 \
(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), False, False), -709.4646722...)
- >>> column_transposition_break_mp(column_transposition_encipher(sanitise( \
+ >>> 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 \
fitness=Ptrigrams) # doctest: +ELLIPSIS
(((2, 0, 5, 3, 1, 4, 6), False, False), -997.0129085...)
"""
+ if translist is None:
+ translist = transpositions
+
with multiprocessing.Pool() as pool:
helper_args = [(message, trans, fillcolumnwise, emptycolumnwise,
fitness)
breaks = pool.starmap(column_transposition_break_worker,
helper_args, chunksize)
return max(breaks, key=lambda k: k[1])
-column_transposition_break = column_transposition_break_mp
def column_transposition_break_worker(message, transposition,
fillcolumnwise, emptycolumnwise, fitness):
return (transposition, fillcolumnwise, emptycolumnwise), fit
-def scytale_break_mp(message, max_key_length=20,
+def scytale_break(message, max_key_length=20,
fitness=Pbigrams, chunksize=500):
"""Breaks a scytale cipher using a range of lengths and
n-gram frequency analysis
- >>> scytale_break_mp(scytale_encipher(sanitise( \
+ >>> scytale_break(scytale_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 \
rightful property of some one or other of their daughters."), \
5)) # doctest: +ELLIPSIS
(5, -709.4646722...)
- >>> scytale_break_mp(scytale_encipher(sanitise( \
+ >>> scytale_break(scytale_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 \
helper_args, chunksize)
best = max(breaks, key=lambda k: k[1])
return math.trunc(len(message) / len(best[0][0])), best[1]
-scytale_break = scytale_break_mp
if __name__ == "__main__":
import doctest
\ No newline at end of file
projects / szyfrow.git / blobdiff