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author Brian Neal <bgneal@gmail.com>
date Thu, 30 Jan 2014 21:45:03 -0600
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1 Introducing m209
2 ################
3
4 :date: 2013-08-01 20:05
5 :tags: Python, m209, Enigma
6 :slug: introducing-m209
7 :author: Brian Neal
8
9 I'm very pleased to announce yet another M-209_ simulator written in Python,
10 creatively called m209_. Last summer I worked on Enigma_ simulators in both
11 `Python <http://py-enigma.readthedocs.org/en/latest/>`_ and `C++
12 <https://bitbucket.org/bgneal/cpp-enigma>`_, and I thought it would be fun to
13 try another World War II-era crypto device. m209_ is a Python 3 library and
14 command-line utility for encrypting and decrypting text by simulating the
15 operation of an actual M-209_ device.
16
17 One fun part about doing something like this is researching the original
18 device. It seems like there are more resources online about the M-209_ than the
19 Enigma_. I even found an actual 1940's War Department training film on YouTube
20 that explains how to operate the M-209_, including the procedure for encrypting
21 and decrypting messages! I want to thank `Mark J. Blair`_ for his very
22 informative pages on the M-209_ which were very helpful to me. Check out the
23 `m209 references section <https://m209.readthedocs.org/en/latest/#references>`_
24 for these and other useful links.
25
26 The M-209_ isn't as complex as the Enigma_. That isn't meant to knock it. The
27 M-209_, while cryptographically not as secure as the Enigma_, is a remarkable
28 piece of mechanical engineering. It is much more portable and easier to
29 operate compared to the Enigma_. It has user-friendly features like printing to
30 paper tape and a letter counter for backing up when mistakes are made.
31 According to Wikipedia, about 140,000 of these machines were produced. They
32 even come up on eBay a few times a year, and seem to go for between $1000
33 - $2000 USD. Maybe someday I can score an actual unit!
34
35 Coding the actual simulator wasn't all that hard. I spent much more time on
36 the unit tests, documentation, and creating an application to generate key
37 lists. Writing the documentation gave me some good practice with Sphinx_, an
38 awesome Python based documentation tool that uses the `reStructured Text`_
39 markup language.
40
41 Writing the key list generator was actually the hardest part. The procedure for
42 creating key lists is spelled out in a M-209 manual from 1944 (which exists
43 online as a series of photos). The procedure is kind of loosely specified, and
44 a lot is left up to the soldier creating the key list. I came up with an
45 ad-hoc, heuristic-based algorithm that works most of the time. If it got stuck
46 it simply started over, and retried up to a certain number of attempts.
47
48 While researching the procedure, I noticed what appears to be a typo in the
49 data tables in the manual that are used when developing a key list. On top of
50 that I found several sets of initial numbers that I could not generate a key
51 list from. In other words, using these starting numbers, my algorithm could not
52 generate M-209 settings that satisfied the exit criteria for the procedure in
53 the manual. After a while, I just removed those troublesome initial conditions
54 as possible inputs. It would be interesting to return to this some day and
55 write a program to search the solution space exhaustively to see if there
56 really was a solution for these numbers. It could just be that my
57 trial-and-error algorithm could not find a solution, even after tens of
58 thousands of attempts. However this doesn't seem likely. I wonder if these
59 initial settings caused lots of head scratching for the poor officer trying to
60 create a key list.
61
62 In any event, if you are into this kind of thing, I hope you check out m209_.
63 Doing a project like this is a lot of fun. I enjoy doing the research, creating
64 the code, and working on the test suite. I also get some practice with Python
65 packaging and writing documentation with Sphinx.
66
67 Future enhancements include adding the ability to read Mark Blair's key lists
68 that he created for his C++ simulator. This would make it easier for our two
69 simulators to interoperate.
70
71 Links:
72
73 * `m209 documentation <http://m209.readthedocs.org>`_
74 * `m209 on PyPi <https://pypi.python.org/pypi/m209>`_
75 * `m209 source code repository on Bitbucket <https://bitbucket.org/bgneal/m209/>`_
76
77 .. _M-209: http://en.wikipedia.org/wiki/M-209
78 .. _m209: http://m209.readthedocs.org/
79 .. _Enigma: https://en.wikipedia.org/wiki/Enigma_machine
80 .. _Mark J. Blair: http://www.nf6x.net/groups/m209group/
81 .. _Sphinx: http://sphinx-doc.org/index.html
82 .. _reStructured Text: http://docutils.sf.net/rst.html