On Thu, Aug 10, 2017 at 10:24 PM, Bill Frantz wrote:

I found an interesting book in a Sydney, Australia airport book stall:

Code Breakers Inside the shadow world of signals intelligence in Australia's two Bletchley Parks Craig Collie First published in 2017 by: Allen & Unwin 83 Alexander Street Crows Nest, NSW 2065 Australia ISBN 978 1 74331 210 0

This book describes the signals intelligence efforts in Australia during WWII. It goes into detail about the politics, personalities, code breaking, and traffic analysis used in some of the epic battles in the south Pacific. It describes the early use of IBM tabulating equipment in code breaking. It gives enough detail about the structure of the Japanese codes so the reader can appreciate the effort needed to break them and re-break them after they were changed.

A brief description of the typical code structure: First the messages was converted to numbers using a code book which took words or phrases as input. Then "additive tables" were used like a one time pad to scramble the output of the code book for transmission. Since the additive tables were reused many times, there were obvious security issues, although these issues don't seem to have been the major way the codes were actually broken.

Traffic analysis based on the strength and direction of radio signals allowed prediction of air attacks without being able to read the messages, although since the airplane codes were designed for easy use in the air, they were relatively easy to break.

The book is also a fun read. Recommended.

Cheers - Bill

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