Type B Cipher Machine

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The "System 97 Typewriter for European Characters" (九七式欧文印字機 kyūnana-shiki ōbun injiki) or "Type B Cipher Machine", codenamed Purple by the United States, was an encryption machine used by the Japanese Foreign Office from February 1939 to the end of World War II. It replaced the Type A Red machine encrypt the most sensitive diplomatic traffic. The Purple was an electromechanical device that used stepping-switches, rather than rotors as other contemporary devices. All messages were written in the 26-letter English alphabet, which was commonly used for telegraphy. Any Japanese text had to be transliterated or coded. The 26-letters were separated using a plug board into two groups, of six and twenty letters respectively. The letters in the sixes group were scrambled using a 6 × 25 substitution table, while letters in the twenties group were more thoroughly scrambled using three successive 20 × 25 substitution tables. The Japanese also used stepping-switches in other systems, codenamed Coral and Jade, that did not divide their alphabets. The sixes and twenties division was familiar to U.S. Army Signals Intelligence Service (SIS) cryptographers from their work on the Type A cipher, and it allowed them to make early progress on the sixes portion of messages. The twenties cipher proved much more difficult, but a breakthrough in September 1940 allowed the Army cryptographers to construct an analogous machine that duplicated the behavior of the Japanese machines, even though no one in the U.S. had any technical description of the originals. American forces referred to information gained from decryptions as Magic.