Computer Security and Cryptography

7.6 “CLIMB MOUNT ITAKA” – WAR!

The following was included in a cable sent November 19, 1941, from the Japanese Foreign Ministry to all Japanese foreign diplomatic posts:

…Consequently, we will include in the middle and atthe end of our Japanese language news programs beamed to all points one or another or all of the followingcode phrases:

1. HIGASHI NO KAZE AME (East Wind Rain) meaning relations with America are not according to expectations.
2. KITANOKAZE KUMORI (North Wind Cloudy) meaning relations with Soviet Union are not according to expectations.
3. NISHO NO KAZE HARE (West Wind Clear) meaning relations with England are not according to expectations.

When you hear any or all of these phrases repeated twice in the newscasts, destroy your codes and confidential papers.

A new Japanese machine ciphermachine (Fig. 7.4) went into service in March 1939 [Rowlett and Kahn, 1998], designated by the Japanese as 97-shiki O-bun In-ji-ki (Alphabetical Typewriter ’97), the number 97 signaling the year 2597 of its creation in the Japanese calendar [Kahn, 1967]. It was also referred to as Angooki taipu B (Cryptographic system, type B) and PURPLE by the United States intelligence community.

PURPLE replaced the Type Number ’91 [Farago, 1967], also referred to as Angooki taipu A (Cryptographic system, type A) and RED. Alphabetical Typewriter ’97 was developed by naval Captain Risaburo Ito, who had also helped design the Red code machine. Ito was familiar with Yardley's success in cryptanalyzing ...