From: Neil Smith Date: Mon, 14 Jul 2014 18:00:41 +0000 (+0100) Subject: Breaking transpositon ciphers X-Git-Url: https://git.njae.me.uk/?a=commitdiff_plain;h=ae4400046f558cbea84662a0159d13bfa9cbb569;p=cipher-training.git Breaking transpositon ciphers --- diff --git a/cipher.py b/cipher.py index 3783d57..5a7781b 100644 --- a/cipher.py +++ b/cipher.py @@ -532,165 +532,6 @@ def scytale_decipher(message, rows): fillcolumnwise=True, emptycolumnwise=False) -class PocketEnigma(object): - """A pocket enigma machine - The wheel is internally represented as a 26-element list self.wheel_map, - where wheel_map[i] == j shows that the position i places on from the arrow - maps to the position j places on. - """ - def __init__(self, wheel=1, position='a'): - """initialise the pocket enigma, including which wheel to use and the - starting position of the wheel. - - The wheel is either 1 or 2 (the predefined wheels) or a list of letter - pairs. - - The position is the letter pointed to by the arrow on the wheel. - - >>> pe.wheel_map - [25, 4, 23, 10, 1, 7, 9, 5, 12, 6, 3, 17, 8, 14, 13, 21, 19, 11, 20, 16, 18, 15, 24, 2, 22, 0] - >>> pe.position - 0 - """ - self.wheel1 = [('a', 'z'), ('b', 'e'), ('c', 'x'), ('d', 'k'), - ('f', 'h'), ('g', 'j'), ('i', 'm'), ('l', 'r'), ('n', 'o'), - ('p', 'v'), ('q', 't'), ('s', 'u'), ('w', 'y')] - self.wheel2 = [('a', 'c'), ('b', 'd'), ('e', 'w'), ('f', 'i'), - ('g', 'p'), ('h', 'm'), ('j', 'k'), ('l', 'n'), ('o', 'q'), - ('r', 'z'), ('s', 'u'), ('t', 'v'), ('x', 'y')] - if wheel == 1: - self.make_wheel_map(self.wheel1) - elif wheel == 2: - self.make_wheel_map(self.wheel2) - else: - self.validate_wheel_spec(wheel) - self.make_wheel_map(wheel) - if position in string.ascii_lowercase: - self.position = ord(position) - ord('a') - else: - self.position = position - - def make_wheel_map(self, wheel_spec): - """Expands a wheel specification from a list of letter-letter pairs - into a full wheel_map. - - >>> pe.make_wheel_map(pe.wheel2) - [2, 3, 0, 1, 22, 8, 15, 12, 5, 10, 9, 13, 7, 11, 16, 6, 14, 25, 20, 21, 18, 19, 4, 24, 23, 17] - """ - self.validate_wheel_spec(wheel_spec) - self.wheel_map = [0] * 26 - for p in wheel_spec: - self.wheel_map[ord(p[0]) - ord('a')] = ord(p[1]) - ord('a') - self.wheel_map[ord(p[1]) - ord('a')] = ord(p[0]) - ord('a') - return self.wheel_map - - def validate_wheel_spec(self, wheel_spec): - """Validates that a wheel specificaiton will turn into a valid wheel - map. - - >>> pe.validate_wheel_spec([]) - Traceback (most recent call last): - ... - ValueError: Wheel specification has 0 pairs, requires 13 - >>> pe.validate_wheel_spec([('a', 'b', 'c')]*13) - Traceback (most recent call last): - ... - ValueError: Not all mappings in wheel specificationhave two elements - >>> pe.validate_wheel_spec([('a', 'b')]*13) - Traceback (most recent call last): - ... - ValueError: Wheel specification does not contain 26 letters - """ - if len(wheel_spec) != 13: - raise ValueError("Wheel specification has {} pairs, requires" - " 13".format(len(wheel_spec))) - for p in wheel_spec: - if len(p) != 2: - raise ValueError("Not all mappings in wheel specification" - "have two elements") - if len(set([p[0] for p in wheel_spec] + - [p[1] for p in wheel_spec])) != 26: - raise ValueError("Wheel specification does not contain 26 letters") - - def encipher_letter(self, letter): - """Enciphers a single letter, by advancing the wheel before looking up - the letter on the wheel. - - >>> pe.set_position('f') - 5 - >>> pe.encipher_letter('k') - 'h' - """ - self.advance() - return self.lookup(letter) - decipher_letter = encipher_letter - - def lookup(self, letter): - """Look up what a letter enciphers to, without turning the wheel. - - >>> pe.set_position('f') - 5 - >>> ''.join([pe.lookup(l) for l in string.ascii_lowercase]) - 'udhbfejcpgmokrliwntsayqzvx' - >>> pe.lookup('A') - '' - """ - if letter in string.ascii_lowercase: - return chr( - (self.wheel_map[(ord(letter) - ord('a') - self.position) % 26] + - self.position) % 26 + - ord('a')) - else: - return '' - - def advance(self): - """Advances the wheel one position. - - >>> pe.set_position('f') - 5 - >>> pe.advance() - 6 - """ - self.position = (self.position + 1) % 26 - return self.position - - def encipher(self, message, starting_position=None): - """Enciphers a whole message. - - >>> pe.set_position('f') - 5 - >>> pe.encipher('helloworld') - 'kjsglcjoqc' - >>> pe.set_position('f') - 5 - >>> pe.encipher('kjsglcjoqc') - 'helloworld' - >>> pe.encipher('helloworld', starting_position = 'x') - 'egrekthnnf' - """ - if starting_position: - self.set_position(starting_position) - transformed = '' - for l in message: - transformed += self.encipher_letter(l) - return transformed - decipher = encipher - - def set_position(self, position): - """Sets the position of the wheel, by specifying the letter the arrow - points to. - - >>> pe.set_position('a') - 0 - >>> pe.set_position('m') - 12 - >>> pe.set_position('z') - 25 - """ - self.position = ord(position) - ord('a') - return self.position - - if __name__ == "__main__": import doctest - doctest.testmod(extraglobs={'pe': PocketEnigma(1, 'a')}) + doctest.testmod()