Tuesday, November 15, 2011

Cryptologic cooperation between Germany and Japan - The State Department's Strip cipher

Cryptologic cooperation between Germany and Japan during WWII is a subject that hasn’t received much attention mostly due to lack of information. According to David Kahn’s‘’The codebreakers ‘’ and Ken Kotani  ‘’Japanese Intelligence in WWII’’ the Japanese managed to break into the US consulate in Kobe in late 1937 and take photos of the strips used in the State Department’s M-138 cipher as well as the instructions for using them.

As I’ve mentioned before the M-138 strip cipher was the State Department’s high level code.

This material (O-1 strip ) was given to the Germans in 1941 and it allowed OKW/Chi and Pers Z to read messages but with a time lag of months.

In early 1943 the Germans and the Finns managed independently to break into the new strips used at the time between European embassies and Washington. The Finns shared this information with the Japanese and offered to cooperate.

However there is no sign that the Germans shared their success with the Japanese at this time.

In summer 1944 the Japanese military attaché in Budapest ,Colonel Tahei Hayashi, reported to Tokyo that the Germans  for their own reasons had  agreed to share their results on US codes with Japan. In a following message he mentioned the codes given to him.

The Allies learned of this by decoding the relevant messages but with a time lag of roughly four months.

Here are the decodes :

Notice that the strip Washington-Berne  was not given even though both Huettenhain ( chief cryptanalyst of OKW/Chi )  and Pers Z personnel mention it in Ticom reports as being read.Could it have something to do with the  OSS messages passing through?

Source for the decodes : HW 40/132 ''Decrypts relating to enemy exploitation of US State Department cyphers, with related correspondence''

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