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