[Cryptography] How crypto killed Admiral Yamamoto

Ray Dillinger bear at sonic.net
Sun Apr 18 06:38:12 EDT 2021


On 4/17/21 10:19 PM, Dave Horsfall wrote:
> On this day in 1943, Admiral Yamamoto (the architect of the Pearl
> Harbor attack) was shot down by a squadron of P-38 Lightnings that
> just "happened" to be loitering in the area at their extreme range
> where he was known to be (the Japanese had a thing about punctuality).
>
> I think that it was "Purple" that was broken?  In any case, there was
> some debate about whether to shoot him down (thereby revealing that
> their crypto had been broken) or let him go (thereby keeping the
> secret); well, we know what happened next...
>

IIRC it was "JN-25" - a 'dictionary code' or 'nomenclator' of some tens
of thousands of tokens which was then enciphered for transmission - that
was the broken system implicated in Yamamoto's demise.  "Purple" was a
diplomatic channel; Admiral Yamamoto's itinerary was communicated via
naval channels.

JN-25 was notoriously difficult to break; because it operated at the
level of words and phrases rather than individual letters, it required
deep knowledge of the Japanese language and how it was used specifically
in naval communications to even build the frequency tables needed to
attack it. 

The Japanese are believed to have underestimated the availability of
American cryptographers familiar with the Japanese language.  But we
were then as we still are today, 'A Nation Of Immigrants'.   However
badly we may have treated Japanese-Americans during the war, recruiting
and training cryptographers familiar with that language was not a
show-stopping problem.

Bear




More information about the cryptography mailing list