python: Chaocipher (source: https://bitbucket.org/carver/chaocipher/src/tip/chaocipher.py)

chaocipher.py

"""
This provides a simple implementation of the 'Chaocipher' encryption
algorithm described at:
http://www.ciphermysteries.com/2010/07/03/the-chaocipher-revealed

Example usage:
import chaocipher
sender = chaocipher.Wheels(CtWheel='QYNBOWTGIRJFEPKLSDMAVZCUXH', PtWheel='JGUACNQLTDHKSOPZFYMXWRVEBI')
receiver = chaocipher.Wheels(CtWheel='QYNBOWTGIRJFEPKLSDMAVZCUXH', PtWheel='JGUACNQLTDHKSOPZFYMXWRVEBI')
cyphertext = sender.encipher("Green eggs and spam")
print "Cyphertext: " + cyphertext
print "Deciphered: " + receiver.decipher(cyphertext)
"""

from string import uppercase #All uppercase letters

class Wheels(object):
    def __init__(self, CtWheel='HXUCZVAMDSLKPEFJRIGTWOBNYQ', PtWheel = 'PTLNBQDEOYSFAVZKGJRIHWXUMC'):
        #ciphertext alphabet
        self.ct = CtWheel[:26].upper()
        #plaintext alphabet
        self.pt = PtWheel[:26].upper()
        #Check we have all the letters in each
        for l in uppercase:
            if not l in CtWheel:
                raise ValueError, "Missing letter(s) in cyphertext wheel"
            if not l in PtWheel:
                raise ValueError, "Missing letter(s) in plaintext wheel"

    def _encipherNext(self, next):
        loc = self.pt.index(next)
        enciphered = self.ct[loc]
        self._permute(loc)
        return enciphered

    def _decipherNext(self, next):
        loc = self.ct.index(next)
        deciphered = self.pt[loc]
        self._permute(loc)
        return deciphered

    def _permute(self, loc):
        self.ct = self._permuteLeft(self.ct, loc)
        self.pt = self._permuteRight(self.pt, loc)

    def _permuteLeft(self, wheel, lastCipherPos):
        #rotate so last used letter is at front
        rotated = wheel[lastCipherPos:] + wheel[:lastCipherPos]
        #swap 2nd char to 14th position (1 indexed)
        return rotated[0] + rotated[2:14] + rotated[1] + rotated[14:]

    def _permuteRight(self, wheel, lastCipherPos):
        #rotate so last used letter is at rear
        rotated = wheel[lastCipherPos+1:] + wheel[:lastCipherPos+1]
        #swap 3rd char to 14th position (1 indexed)
        return rotated[0:2] + rotated[3:14] + rotated[2] + rotated[14:]

    def encipher(self, text):
        """Encipher some text. This changes the state of the object, so you need
        a separate set of Wheels to decipher it."""
        text = text.upper()
        enciphered = ''
        for letter in text:
            if letter in uppercase:
                enciphered += self._encipherNext(letter)
            else:
                enciphered += letter #Handle spaces and punctuation
        return enciphered
    
    def decipher(self, encrypted):
        """Decipher encrypted text. This changes the state of the Wheels."""
        text = encrypted.upper()
        deciphered = ''
        for letter in text:
            if letter in uppercase:
                deciphered += self._decipherNext(letter)
            else:
                deciphered += letter #Handle spaces and punctuation
        return deciphered
    
if __name__ == '__main__':
    text = 'WELLDONEISBETTERTHANWELLSAID'
    sender = Wheels()
    receiver = Wheels() # Separate instances to keep the initial state the same.
    enciphered = sender.encipher(text)
    print 'enciphered %s to %s' % (text, enciphered)
    print 'deciphered %s to %s' % (enciphered, receiver.decipher(enciphered))