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1 Announcing my Purple simulator
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2 ##############################
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3
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4 :date: 2014-02-20 19:59
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5 :tags: Python, m209, Enigma, Purple, simulator
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6 :slug: announcing-my-purple-simulator
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7 :author: Brian Neal
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8 :Summary: I recently created a simulation of the Japanese PURPLE cipher machine
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9 in Python.
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10
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11 After working on a `M-209 simulator`_ last summer and an `Enigma simulator`_ the
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12 year before, I got the World War 2 era cipher machine bug again. It all started
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13 by reading about the `Japanese PURPLE machine`_ at Frode Weierud's excellent
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14 CryptoCellar_ website. I read with great interest a paper available at that
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15 site titled *PURPLE Revealed: Simulation and Computer-aided Cryptanalysis of
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16 Angooki Taipu B* by Wes Freeman, Geof Sullivan, and Frode Weierud. This paper
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17 is a fascinating read, with detailed descriptions of how the machine worked,
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18 the complicated keying system employed by the Japanese, and information on
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19 using a technique known as *hill-climbing* to mount a ciphertext only attack on
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20 a messages. Highly recommended!
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21
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22 After reading the paper I knew I had to try to write a simulator for the PUPRLE
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23 machine in Python_. Writing these simulators is great fun. You have to
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24 understand how the machine works, get a bunch of tiny details correct, have
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25 a bit of patience, and do a lot of detective work and debugging. Once you have
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26 them built, they aren't all that complicated when coded on a modern computer.
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27 But you get an amazing appreciation for these machines as originally
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28 implemented as electro-mechanical devices. The PURPLE machine, for example,
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29 required almost 2,000 wired connections! It is even more amazing when you know
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30 the U.S. code breakers built replicas without even seeing an original Japanese
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31 machine. When the war ended, only a few parts of one Japanese machine were ever
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32 recovered!
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33
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34 I had a lot of fun writing this and playing with it. I hope someone else finds
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35 it interesting or educational. Please contact me and let me know if you use it
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36 for anything. Please see these links for documentation, the code, and licensing
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37 details:
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38
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39 * `Purple simulator on PyPI`_
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40 * `Purple simulator on Bitbucket`_
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41
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42 Once again, many thanks to Frode Weierud, Geoff Sullivan, and Wes Sullivan for
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43 the very interesting paper. I'm also grateful to Messrs. Weierud and Sullivan
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44 who provided me with valuable plaintext, advice and encouragement while
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45 I worked on this project.
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46
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47 I also recommend the book *Battle of Wits: The Complete Story of Codebreaking
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48 in World War II* by Stephen Budiansky, which details the efforts and the people
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49 behind the cracking of the PURPLE cipher.
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50
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51 .. _M-209 simulator: https://m209.readthedocs.org/en/latest/
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52 .. _Enigma simulator: http://py-enigma.readthedocs.org/en/latest/
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53 .. _Japanese PURPLE machine: http://cryptocellar.web.cern.ch/cryptocellar/simula/purple/
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54 .. _CryptoCellar: http://cryptocellar.web.cern.ch/cryptocellar/
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55 .. _Python: http://www.python.org/
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56 .. _Purple simulator on PyPI: https://pypi.python.org/pypi/purple
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57 .. _Purple simulator on Bitbucket: https://bitbucket.org/bgneal/purple/
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