rotor
This module implements a rotor-based encryption algorithm, contributed by
Lance Ellinghouse. The design is derived from the Enigma device, a machine
used during World War II to encipher messages. A rotor is simply a
permutation. For example, if the character `A' is the origin of the rotor,
then a given rotor might map `A' to `L', `B' to `Z', `C' to `G', and so on.
To encrypt, we choose several different rotors, and set the origins of the
rotors to known positions; their initial position is the ciphering key. To
encipher a character, we permute the original character by the first rotor,
and then apply the second rotor's permutation to the result. We continue
until we've applied all the rotors; the resulting character is our
ciphertext. We then change the origin of the final rotor by one position,
from `A' to `B'; if the final rotor has made a complete revolution, then we
rotate the next-to-last rotor by one position, and apply the same procedure
recursively. In other words, after enciphering one character, we advance
the rotors in the same fashion as a car's odometer. Decoding works in the
same way, except we reverse the permutations and apply them in the opposite
order.
Enigmacipher
The available functions in this module are:
Rotor objects have the following methods:
An example usage:
>>> import rotor
>>> rt = rotor.newrotor('key', 12)
>>> rt.encrypt('bar')
'\2534\363'
>>> rt.encryptmore('bar')
'\357\375$'
>>> rt.encrypt('bar')
'\2534\363'
>>> rt.decrypt('\2534\363')
'bar'
>>> rt.decryptmore('\357\375$')
'bar'
>>> rt.decrypt('\357\375$')
'l(\315'
>>> del rt
The module's code is not an exact simulation of the original Enigma device;
it implements the rotor encryption scheme differently from the original. The
most important difference is that in the original Enigma, there were only 5
or 6 different rotors in existence, and they were applied twice to each
character; the cipher key was the order in which they were placed in the
machine. The Python rotor module uses the supplied key to initialize a
random number generator; the rotor permutations and their initial positions
are then randomly generated. The original device only enciphered the
letters of the alphabet, while this module can handle any 8-bit binary data;
it also produces binary output. This module can also operate with an
arbitrary number of rotors.
The original Enigma cipher was broken in 1944.