From: Neil Smith <neil.git@njae.me.uk>
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()