|
bgneal@4
|
1 Introducing Py-Enigma
|
|
bgneal@4
|
2 #####################
|
|
bgneal@4
|
3
|
|
bgneal@4
|
4 :date: 2012-06-06 18:45
|
|
bgneal@4
|
5 :tags: Python, Py-Enigma, Enigma
|
|
bgneal@4
|
6 :slug: introducing-py-enigma
|
|
bgneal@4
|
7 :author: Brian Neal
|
|
bgneal@4
|
8
|
|
bgneal@4
|
9 Py-Enigma
|
|
bgneal@4
|
10 ---------
|
|
bgneal@4
|
11
|
|
bgneal@4
|
12 For some strange reason, I don't even remember why or how, I found myself
|
|
bgneal@4
|
13 browsing the `Wikipedia page for the Enigma Machine
|
|
bgneal@4
|
14 <http://en.wikipedia.org/wiki/Enigma_machine>`_. I quickly became fascinated and
|
|
bgneal@4
|
15 started surfing around some more. I found several Enigma machine simulators,
|
|
bgneal@4
|
16 some of them even online. It suddenly occured to me that it would be a fun
|
|
bgneal@4
|
17 project to try and write my own in Python_. I wanted to challenge myself to see
|
|
bgneal@4
|
18 if I could figure it all without help, so I vowed not to look at anyone else's
|
|
bgneal@4
|
19 source code.
|
|
bgneal@4
|
20
|
|
bgneal@4
|
21 In order to write an Enigma simulator, you need a really good technical
|
|
bgneal@4
|
22 explanation of how it worked, along with numerous details like how the rotors
|
|
bgneal@4
|
23 were wired. Fortunately I very quickly found Dirk Rijmenants' incredible `Cipher
|
|
bgneal@4
|
24 Machines and Cryptology website`_. In particular, his `Technical Details of the
|
|
bgneal@4
|
25 Enigma Machine`_ page was exactly what I was looking for, a real gold mine of
|
|
bgneal@4
|
26 information.
|
|
bgneal@4
|
27
|
|
bgneal@4
|
28 I had a long Memorial Day weekend, so I spent many hours in front of the
|
|
bgneal@4
|
29 computer, consuming every word of Dirk's explanations and trying to sort it all
|
|
bgneal@4
|
30 out in my head. And so a very fun marathon hacking session began. In the end I
|
|
bgneal@4
|
31 got it figured out, and you cannot believe how excited I was when I was able to
|
|
bgneal@4
|
32 decode actual Enigma messages from World War II!
|
|
bgneal@4
|
33
|
|
bgneal@4
|
34 And so `Py-Enigma <https://bitbucket.org/bgneal/enigma>`_ was born! Py-Enigma is
|
|
bgneal@4
|
35 a historically accurate simulation library for war-time Enigma machines, written
|
|
bgneal@4
|
36 in Python 3. I also included a simple command-line application for doing
|
|
bgneal@4
|
37 scripting or quick commad-line experiments.
|
|
bgneal@4
|
38
|
|
bgneal@4
|
39 Lessons learned
|
|
bgneal@4
|
40 ---------------
|
|
bgneal@4
|
41
|
|
bgneal@4
|
42 Since I didn't really know what I was doing at first, I wrote little classes for
|
|
bgneal@4
|
43 each of the components and unit tested them. I'm really glad I did this because
|
|
bgneal@4
|
44 not only did it find bugs, it also made me think harder about the problem and
|
|
bgneal@4
|
45 made me realize I didn't understand everything. When you make a mistake in
|
|
bgneal@4
|
46 cryptography, very often the answer you get is gibberish and there is no way to
|
|
bgneal@4
|
47 tell how close you are to the right answer. This was almost the case here, and I
|
|
bgneal@4
|
48 think I stumbled upon an Enigma weakness that the allied codebreakers must have
|
|
bgneal@4
|
49 seen also. I had a bug in my rotor stepping algorithm, and I got the right
|
|
bgneal@4
|
50 answer up until the point where the right rotor stepped the middle rotor, then
|
|
bgneal@4
|
51 the output went all garbage. Once I noticed this, I was able to focus on the
|
|
bgneal@4
|
52 stepping algorithm and find the bug. I'm sure the allied codebreakers must have
|
|
bgneal@4
|
53 experienced the same thing when they were guessing what rotors were being used
|
|
bgneal@4
|
54 for the message they were cracking.
|
|
bgneal@4
|
55
|
|
bgneal@4
|
56 I also decided to use this little project to really learn Sphinx_. I had dabbled
|
|
bgneal@4
|
57 around in it before when I contributed some documentation patches to Django_. I
|
|
bgneal@4
|
58 think writing the documentation took almost as long as my research and coding,
|
|
bgneal@4
|
59 but with Sphinx at least it was fun! It is a very useful and powerful package. I
|
|
bgneal@4
|
60 also checked out the awesome `readthedocs.org <http://readthedocs.org>`_ and
|
|
bgneal@4
|
61 quickly got my documentation `hosted there
|
|
bgneal@4
|
62 <http://py-enigma.readthedocs.org/>`_. What a fantastic service! Now whenever I
|
|
bgneal@4
|
63 push changes to bitbucket my docs are automatically built on readthedocs!
|
|
bgneal@4
|
64
|
|
bgneal@4
|
65 This was also my second project that I put up on PyPI. I'm a little bit more
|
|
bgneal@4
|
66 comfortable with the packaging process, but it is still a bit bewildering given
|
|
bgneal@4
|
67 all the choices.
|
|
bgneal@4
|
68
|
|
bgneal@4
|
69 Conclusion
|
|
bgneal@4
|
70 ----------
|
|
bgneal@4
|
71
|
|
bgneal@4
|
72 I hope folks who are interested in history, cryptography, World War II, and
|
|
bgneal@4
|
73 Python find Py-Enigma useful and fun! You can get the code from either the
|
|
bgneal@4
|
74 `Py-Enigma Bitbucket page`_ or from PyPI_. And a big thank-you to Dirk
|
|
bgneal@4
|
75 Rijmenants! Without his hard work and detailed explanation, Py-Enigma would
|
|
bgneal@4
|
76 have been considerably more difficult.
|
|
bgneal@4
|
77
|
|
bgneal@4
|
78 .. _Python: http://www.python.org
|
|
bgneal@4
|
79 .. _Cipher Machines and Cryptology website: http://users.telenet.be/d.rijmenants/index.htm
|
|
bgneal@4
|
80 .. _Technical Details of the Enigma Machine: http://users.telenet.be/d.rijmenants/en/enigmatech.htm
|
|
bgneal@4
|
81 .. _Sphinx: http://sphinx.pocoo.org/
|
|
bgneal@4
|
82 .. _Django: http://www.djangoproject.com/
|
|
bgneal@4
|
83 .. _Py-Enigma Bitbucket page: https://bitbucket.org/bgneal/enigma
|
|
bgneal@4
|
84 .. _PyPI: http://pypi.python.org/pypi/py-enigma/
|
