[Cryptography] Re: Pearl Harbor and Crypto (was Re: ISIS has ‘help desk’ to ai d would-be terrorists with encryption)

[Arnold Reinhold]

On Saturday 21 Nov 2015 Perry E. Metzger wrote:

> On Fri, 20 Nov 2015 08:47:55 -0800 Henry Baker <hbaker1 at pipeline.com <mailto:hbaker1 at pipeline.com>>
> wrote:
> > Apparently, even though the US had completely broken the Japanese
> > codes, the Navy still lost track of the Japanese fleet *due to
> > total radio silence* (this problem wasn't completely fixed until
> > spy satellites were deployed), so Pearl Harbor was a "complete"
> > surprise (except that radar picked up the incoming planes, but
> > apparently no one was willing to believe that new-fangled radar
> > technology).
> 
> The actual events were a bit more complicated. A better explanation is
> given in the opening section of "The Codebreakers" by Kahn. (The
> chapter is entitled "One Day of Magic", "MAGIC" having been the
> codename for the decrypted Japanese intercepts.)

The “Codebreakers” chapter is an essential read for anyone interested in cryptography, but doesn’t materially change the conclusion. The US was generally aware that conflict was immanent and sent a message to all its bases in the Pacific in late November 1941 saying war could break out at any time.  The US did intercept and decode diplomatic traffic between Japan and its consulate in Honolulu requesting very detailed information on which warships were in the harbor and where each was located. This alarmed some lower level intelligence officers who finally got a message off to Pearl Harbor at the last minute, but it did not arrive in time due to communication screw-ups. 

The bottom line is that the Japanese fleet’s strict adherence to radio silence (orders for the attack were delivered by hand before the fleet left Japan) succeeded in preserving surprise. By contrast, the attack on Midway required radio traffic for coordination of an already dispersed fleet. The target identity was super-encrypted using a map code that took considerable ingenuity to break convincingly. That intelligence plus a fair amount of luck resulted in a devastating defeat for the Japanese Navy, from which they never recovered, and is widely considered the turning point in the Pacific war. Kahn’s chapter on Midway is also worth reading.

The lesson here is that even with strong encryption, electronic communication provides a wealth of opportunities for intelligence gathering. Good communication security requires a great deal of discipline, with even the best trained operatives making mistakes that can be exploited. The last thing we should want is for terrorists to learn to completely avoid electronic communication. 

Arnold Reinhold


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