+++ /dev/null
-from utilities import *
-from language_models import *
-from enum import Enum
-from itertools import starmap
-from itertools import zip_longest
-
-from logger import logger
-
-def railfence_encipher(message, height, fillvalue=''):
- """Railfence cipher.
- Works by splitting the text into sections, then reading across them to
- generate the rows in the cipher. The rows are then combined to form the
- ciphertext.
-
- Example: the plaintext "hellotherefriends", with a height of four, written
- out in the railfence as
- h h i
- etere*
- lorfns
- l e d
- (with the * showing the one character to finish the last section).
- Each 'section' is two columns, but unfolded. In the example, the first
- section is 'hellot'.
-
- >>> railfence_encipher('hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers', 2, fillvalue='!')
- 'hlohraateerishsslnpeefetotsigaleccpeselteevsmhatetiiaogicotxfretnrifneihr!'
- >>> railfence_encipher('hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers', 3, fillvalue='!')
- 'horaersslpeeosglcpselteevsmhatetiiaogicotxfretnrifneihr!!lhateihsnefttiaece!'
- >>> railfence_encipher('hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers', 5, fillvalue='!')
- 'hresleogcseeemhetaocofrnrner!!lhateihsnefttiaece!!ltvsatiigitxetifih!!oarspeslp!'
- >>> railfence_encipher('hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers', 10, fillvalue='!')
- 'hepisehagitnr!!lernesge!!lmtocerh!!otiletap!!tseaorii!!hassfolc!!evtitffe!!rahsetec!!eixn!'
- >>> railfence_encipher('hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers', 3)
- 'horaersslpeeosglcpselteevsmhatetiiaogicotxfretnrifneihrlhateihsnefttiaece'
- >>> railfence_encipher('hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers', 5)
- 'hresleogcseeemhetaocofrnrnerlhateihsnefttiaeceltvsatiigitxetifihoarspeslp'
- >>> railfence_encipher('hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers', 7)
- 'haspolsevsetgifrifrlatihnettaeelemtiocxernhorersleesgcptehaiaottneihesfic'
- """
- sections = chunks(message, (height - 1) * 2, fillvalue=fillvalue)
- n_sections = len(sections)
- # Add the top row
- rows = [cat([s[0] for s in sections])]
- # process the middle rows of the grid
- for r in range(1, height-1):
- rows += [cat([s[r:r+1] + s[height*2-r-2:height*2-r-1] for s in sections])]
- # process the bottom row
- rows += [cat([s[height - 1:height] for s in sections])]
- # rows += [wcat([s[height - 1] for s in sections])]
- return cat(rows)
-
-def railfence_decipher(message, height, fillvalue=''):
- """Railfence decipher.
- Works by reconstructing the grid used to generate the ciphertext, then
- unfolding the sections so the text can be concatenated together.
-
- Example: given the ciphertext 'hhieterelorfnsled' and a height of 4, first
- work out that the second row has a character missing, find the rows of the
- grid, then split the section into its two columns.
-
- 'hhieterelorfnsled' is split into
- h h i
- etere
- lorfns
- l e d
- (spaces added for clarity), which is stored in 'rows'. This is then split
- into 'down_rows' and 'up_rows':
-
- down_rows:
- hhi
- eee
- lrn
- led
-
- up_rows:
- tr
- ofs
-
- These are then zipped together (after the up_rows are reversed) to recover
- the plaintext.
-
- Most of the procedure is about finding the correct lengths for each row then
- splitting the ciphertext into those rows.
-
- >>> railfence_decipher('hlohraateerishsslnpeefetotsigaleccpeselteevsmhatetiiaogicotxfretnrifneihr!', 2).strip('!')
- 'hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers'
- >>> railfence_decipher('horaersslpeeosglcpselteevsmhatetiiaogicotxfretnrifneihr!!lhateihsnefttiaece!', 3).strip('!')
- 'hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers'
- >>> railfence_decipher('hresleogcseeemhetaocofrnrner!!lhateihsnefttiaece!!ltvsatiigitxetifih!!oarspeslp!', 5).strip('!')
- 'hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers'
- >>> railfence_decipher('hepisehagitnr!!lernesge!!lmtocerh!!otiletap!!tseaorii!!hassfolc!!evtitffe!!rahsetec!!eixn!', 10).strip('!')
- 'hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers'
- >>> railfence_decipher('horaersslpeeosglcpselteevsmhatetiiaogicotxfretnrifneihrlhateihsnefttiaece', 3)
- 'hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers'
- >>> railfence_decipher('hresleogcseeemhetaocofrnrnerlhateihsnefttiaeceltvsatiigitxetifihoarspeslp', 5)
- 'hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers'
- >>> railfence_decipher('haspolsevsetgifrifrlatihnettaeelemtiocxernhorersleesgcptehaiaottneihesfic', 7)
- 'hellothereavastmeheartiesthisisalongpieceoftextfortestingrailfenceciphers'
- """
- # find the number and size of the sections, including how many characters
- # are missing for a full grid
- n_sections = math.ceil(len(message) / ((height - 1) * 2))
- padding_to_add = n_sections * (height - 1) * 2 - len(message)
- # row_lengths are for the both up rows and down rows
- row_lengths = [n_sections] * (height - 1) * 2
- for i in range((height - 1) * 2 - 1, (height - 1) * 2 - (padding_to_add + 1), -1):
- row_lengths[i] -= 1
- # folded_rows are the combined row lengths in the middle of the railfence
- folded_row_lengths = [row_lengths[0]]
- for i in range(1, height-1):
- folded_row_lengths += [row_lengths[i] + row_lengths[-i]]
- folded_row_lengths += [row_lengths[height - 1]]
- # find the rows that form the railfence grid
- rows = []
- row_start = 0
- for i in folded_row_lengths:
- rows += [message[row_start:row_start + i]]
- row_start += i
- # split the rows into the 'down_rows' (those that form the first column of
- # a section) and the 'up_rows' (those that ofrm the second column of a
- # section).
- down_rows = [rows[0]]
- up_rows = []
- for i in range(1, height-1):
- down_rows += [cat([c for n, c in enumerate(rows[i]) if n % 2 == 0])]
- up_rows += [cat([c for n, c in enumerate(rows[i]) if n % 2 == 1])]
- down_rows += [rows[-1]]
- up_rows.reverse()
- return cat(c for r in zip_longest(*(down_rows + up_rows), fillvalue='') for c in r)
-
-
-def railfence_break(message, max_key_length=20,
- fitness=Pletters, chunksize=500):
- """Breaks a railfence cipher using a matrix of given rank and letter frequencies
-
-
- """
-
- sanitised_message = sanitise(message)
- results = starmap(worker, [(sanitised_message, i, fitness)
- for i in range(2, max_key_length+1)])
- return max(results, key=lambda k: k[1])
-
-
-def railfence_break(message, max_key_length=20,
- fitness=Pbigrams, chunksize=500):
- """Breaks a railfence cipher using a range of lengths and
- n-gram frequency analysis
-
- >>> railfence_break(railfence_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 \
- first entering a neighbourhood, this truth is so well fixed in \
- the minds of the surrounding families, that he is considered the \
- rightful property of some one or other of their daughters."), \
- 7)) # doctest: +ELLIPSIS
- (7, -709.46467226...)
- >>> railfence_break(railfence_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 \
- first entering a neighbourhood, this truth is so well fixed in \
- the minds of the surrounding families, that he is considered the \
- rightful property of some one or other of their daughters."), \
- 7), \
- fitness=Ptrigrams) # doctest: +ELLIPSIS
- (7, -997.0129085...)
- """
- def worker(message, height, fitness):
- plaintext = railfence_decipher(message, height)
- fit = fitness(plaintext)
- return height, fit
-
- sanitised_message = sanitise(message)
- results = starmap(worker, [(sanitised_message, i, fitness)
- for i in range(2, max_key_length+1)])
- return max(results, key=lambda k: k[1])
projects / cipher-tools.git / blobdiff