How did the U.S. break the Japanese diplomatic code in WWII?

Question

How did the intercepts affect the US policy specifically with regard to the peace talks that took place in Washington DC in November of 1941, just weeks before Pearl Harbor? What is the nature of the talks from both the Japanese and the US points of view?

Answer 1

I don't know if you need a short or long answer, but here are some options. If you want to know the details of how the US broke the codes, check out the book "The Emperor's Codes: The Breaking of Japan's Secret Ciphers". A website on Codebreaking gives kind of a technical discussion on how they did it, http://www.vectorsite.net/ttcode_07.html. Or, you can read a quick and dirty summary over at Wikipedia, http://en.wikipedia.org/wiki/PURPLE or http://en.wikipedia.org/wiki/Magic_%28cryptography%29

Answer 2

The diplomatic code was broken by mathematicians and engineers, as cyphers at the time were designed to change constantly -- that is, you couldn't solve them while chewing on a pencil. You had to reconstruct the machine that made them.

Nowadays we use one-time cyphers, which in theory at least are unbreakable.

Though we had the Japanese diplomatic code down cold -- we never fullly understood their military ones -- there was nothing sent till December 6 that might have alerted us to their intentions, as they were keeping their own diplomats in the dark till the last possible moment.

Answer 3

During WWII, the Japanese used a very early model of Egnima that they had gotten from Germany. After the British had broken this, they gave the information to the US who used it break the Japanese codes.