X-Git-Url: https://git.njae.me.uk/?a=blobdiff_plain;f=railfence.py;fp=railfence.py;h=0000000000000000000000000000000000000000;hb=311b300d197536622980f7a837294d8245e326b4;hp=78154aaff905f994b211f4041cd48838e6239ed6;hpb=d7224fba67d9f99c01bd78ef669c96189686e4c2;p=cipher-tools.git diff --git a/railfence.py b/railfence.py deleted file mode 100644 index 78154aa..0000000 --- a/railfence.py +++ /dev/null @@ -1,178 +0,0 @@ -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])