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