Wednesday, April 11, 2012

Did the Forchungsamt solve the Japanese ‘Purple’ cipher machine?

The Japanese Foreign ministry used cipher machines for its confidential traffic from the 1930’s. The reason they were so concerned about the security of their communications was the disclosure by Herbert Yardley that the Japanese codes were ‘read’ by the United States government. Yardley was in a position to know as he headed the ‘Black Chamber’ which decoded these messages. His book came out in 1931 and led the Japanese to upgrade their cipher security.

In the early ‘30’s they used the ‘Red’ cipher machine and from 1939 ‘Purple’. Solving these machines became a priority for the codebreakers of the Major Powers of that time but not all were successful. ‘Red’ was reconstructed by British, German, American and probably Soviet cryptanalysts. However the ‘Purple’ machine was only solved by the Americans and the Russians.

According to more recent reports the Germans might have also solved ‘Purple’. I have gone over the available evidence here.

Recently I had another look at my files and noticed an interesting connection.

From TICOM I-22 ‘Interrogation of German Cryptographers of Pers Z S Department of the Auswaertiges Amt’, p7

46. Dr. Kunze was then asked about the Japanese machine traffic discussed at a previous meeting (see para. 19) and whether a machine had been constructed to decode it. He replied no, that they had been able to achieve the desired result with paper models.

Paragraph 19 referred to the Japanese ‘Red’ cipher machine. This was used prior to ‘Purple’. The Germans were able to solve it in September 1938 and read all the back traffic up to 1936. However in February 1939 the ‘Purple’ machine replaced the ‘Red’. ‘Purple’ was much harder to solve.

So why am I posting this report?

There is an interesting mention of papers strips used to solve a Japanese cipher machine in a Forschungsamt interrogation report.

From TICOM I-54 ‘Second interrogation of five members of the RLM/Forschungsamt’, p2-3


….When asked if they had broken any other machine systems he replied that they had broken a Japanese system in ‘41-’42 which was thought to be a machine system though their solution was not mechanical but employed simply paper strips.

Paetzel was head of the cipher research department of the Forschungsamt.

So did the Forschungsamt succeed in solving the Japanese Purple cipher machine? After all that was the machine used in that time period…

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