incanus / enigma

Some Python fun in the spirit of the German wartime Enigma machine. See the bottom if you have no idea what this is.

>>> from enigma import *
>>>
>>> e=Enigma() # can optionally set a three-element array of a-z
>>>            # rotor mappings and/or starting letters
>>>            # defaults are 3x `abcdefghijklmnopqrstuvwxyz`
>>>
>>> e.setTo('r','x','g')
>>>
>>> e.run('here is a test')
V       SYH
V       TZI
F       UAJ
P       VBK

I       WCL
V       XDM

K       YEN

O       ZFO
A       AGP
J       BHQ
F       CIR
>>>
>>> e.currentSetting()
'CIR'
>>>
>>> e.setTo('r','x','g') # to decrypt, use the same starting letters (and
>>>                      # implicitly here since we are using the same
>>>                      # instance, the same rotors)
>>>
>>> e.run('vvfp iv k oajf')
H       SYH
E       TZI
R       UAJ
E       VBK

I       WCL
S       XDM

A       YEN

T       ZFO
E       AGP
S       BHQ
T       CIR

Notes

• Default rotor mapping is abcdefghijklmnopqrstuvwxyz, which just passes the same letters out as in for each rotor. A mapping of bcdefghijklmnopqrstuvwxyza would pass b for a, c for b, ... on up to a for z.
• The "rightmost" rotor (rotor 3) rotates one position before each letter coding, but in a true rotor, it would rotate the rotor to its left at some interval, much like an odometer, and then that rotor would rotate the one to its left.
• There is no plug board (Steckerbrett). Sue me.

Uh, what?

The bare minimum you need to know to understand what the Enigma machine did:

• The machine had three rotors, each with the 26 letters of the alphabet along their edges. A letter would map to a certain other letter due to the wiring inside. An operator might select from five or more different rotors for the three positions.
• The three rotors would be set to initial rotation position, say L, D, and P.
• Pressing a letter on the keyboard would light up a different letter on the output, representing the encrypted version.
• Even pressing the same letter again would yield a different letter the next time, since the mechanics of the machine are advancing the rotors in a predefined, mechanical manner on each letter. A typical Enigma machine would have 158,962,555,217,826,360,000 combinations of settings.
• To decrypt a message on another machine, use the same three rotors, in order, and the same three initial positions. Pressing each letter of the encrypted message would this time yield the decrypted version. Genius, right?
• Now try to break the code, and then also watch The Imitation Game (again, possibly).