Image Courtesy of the National Cryptologic Museum
Japan's PURPLE
Encryption:
The Japanese were most efficient at destroying their cryptographic machines during World War II. To this date, not even one complete machine has been discovered. However, with pure genius and ingenuity, cryptographers from the United States were able to crack the PURPLE, as it was called.
In 1940, the British, Polish, and French were working hard on cracking the German Enigma (and for the most part, succeeding). Meanwhile, the US Signals Intelligence Service (SIS) worked on Japan’s code machine. What made cracking the PURPLE more difficult than the enigma was that it used a revolutionary concept in machine cryptography.
In fact, PURPLE used telephone stepping switches instead of rotors in its encryption scheme. A stepping switch was used in those days to route telephone calls from source to destination. By utilizing this, the encrypted letters did not follow patterns that codebreakers were accustomed to with traditional rotor machines.
So, William Friedman, a renowned cryptographer, was curious about what could make these patterns? Eventually, he and his team were able to put together a version of the PURPLE machine almost exactly the same as the Japanese version. However, Friedman did so without ever seeing a picture or blueprint of the machine; he only saw messages encrypted with it!
So, knowing how the machine worked, the United States was able to build a machine to crack the code of PURPLE. It figured out the code used to encrypt messages, thus allowing for plaintext viewing by the user. As a result of Friedman’s work, allied lives were saved, and battles were won, helping to bring the war to a close as quickly as possible.
The following picture is the only part of a real Japanese PURPLE machine to have ever been recovered by anyone. Everything else was destroyed.
This image, however, is a simulated PURPLE machine that Freedman and his team was able to put together without ever seeing a real PURPLE. It works almost exactly like the original!
