[ARC5] FW: How the U.S. Cracked Japan's 'Purple Encryption Machine' at the Dawn of World War II

[Richard Knoppow]

     I am very interested in this discussion. There seems to be so much 
conflicting opinion about the events leading to the Japanese attack. One 
must carefully discriminate between the propaganda of the time, 
established fact, later political propaganda from the usual conspiracy 
mongers, &etc.
     Since I was born just before Pearl Harbor WW-2 history has always 
been of great interest to me.

On 12/6/2016 1:29 PM, Jim Haynes wrote:
> A good book on a lot of the Pacific action is "Joe Rochefort's War : the
> odyssey of the codebreaker who outwitted Yamamoto at Midway" by Eliot
> Carlson, Naval Institute Press, 2011.
>
> As I understand it JN-25 was a book code, meaning that for each word or
> phrase in plain text there were one or more numbers transmitted as the
> encrypted text.  A complementary book translated from numbers back to
> words and phrases.
>
> What made it all the more difficult was that a second book called additive
> tables contained a list of random numbers that were added, without carry,
> to the numbers in the code book before transmission, and subtracted
> from the received numbers before decoding.  So the communicators had to
> have copies of the code book, plus the book of additives and information
> about where in the latter to start using the additives.  In one sense a
> code-book code is pretty archaic, but for a language like Japanese with
> thousands of characters it is about the only way to go.  I believe JN-25
> was only partially broken throughout the inter-war and war period.
>
> Purple, on the other hand, is a mechanical cipher.  It makes use of a
> Japanese rendering called Roma-Ji.  In this case there are syllables
> spelled with Roman letters and the spoken Japanese is rendered into
> those syllables, which then can be transmitted by any system such as
> Morse or teleprinter code that can handle the Roman alphabet.  In the'
> purple machine the consonants and vowels are encrypted by separate parts
> of the mechanism.  Purple was used for the diplomatic service, partly
> because it allowed transmission through commercial telegraph systems.
> Machines equivalent to the purple machine were made by U.S. code breakers
> and could pretty thoroughly decode the messages once the keying scheme
> was worked out.
>
> I have seen some articles by Navy officers highly critical of Washington
> for sending purple machines to England while denying one to Pearl Harbor.
> But this criticism ignores the fact that Pearl Harbor was told to work
> on Japanese naval codes, while the diplomatic stuff was being handled in
> Washington.  If Pearl Harbor had had a purple machine, and if they had
> intercepted the Japanese messages, it would have given Pearl the warning
> of war beginning some hours before the message decrypted in Washington
> had been turned into a warning to Pearl.  But that's about the only time
> a purple machine at Pearl would have had any effect on the Pacific war;
> and it's a big IF whether Pearl was intercepting the diplomatic traffic
> anyway.
>
> Another reason, and I'll cut those Navy officers some slack because they
> probably didn't know, not having a need to know.  The Japanese ambassador
> to Berlin sent Tokyo voluminous reports of his observations and
> conversations with high Nazi officials, including Hitler himself.
> These could be intercepted and decrypted in England and provided vital
> information to the prosecution of the war in Europe.
>
>
> ______________________________________________________________
> ARC5 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/arc5
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:ARC5 at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL