[Cryptography] Pearl Harbor

[Steven M. Bellovin]

You may want to look at page number 37 of https://www.nsa.gov/portals/75/documents/news-features/declassified-documents/friedman-documents/pearl-harbor/FOLDER_494/41782679082173.pdf — it's a declassified document from the Friedman Collection, released by the NSA about 10 years ago. Another document from the Friedman collection, which I can't find at the moment, noted that in May 1941 the US actually wargamed a Japanese carrier-based attack on Pearl Harbor—but forgot about it. Add to that a non-trivial amount of anti-Japanese racism, and you had the makings of a disaster.

From everything I've read, the US had known for quite some time that war was coming, with the tip-off that war was imminent just before Pearl Harbor, but they didn't know just where Japan would strike—attacks much closer to home and to the south were seen as far more likely. Japan had excellent operational security and didn't leak anything. (I once asked an expert why the crack of the Purple machine, used for Japanese diplomatic communications, didn't give any clues—the Allies learned a lot from communications between Tokyo and Berlin (https://en.wikipedia.org/wiki/Hiroshi_%C5%8Cshima). The answer, I was told, was that the Japanese ambassador had been a general in the Japanese Army, whereas the strike on Pearl Harbor was a Navy operation, and interservice rivalry meant that he and the Army were never told.)

        --Steve Bellovin, https://www.cs.columbia.edu/~smb