PURPLE

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Fragment of an actual Purple machine from the Japanese embassy in Berlin, obtained by the United States at the end of World War II.

In the history of cryptography, 97-shiki oobun Inji-ki (九七式欧文印字機) ("System 97 Printing Machine for European Characters") or Angooki B-gata (暗号機B型) ("Type B Cipher Machine"), codenamed PURPLE by the United States, was a diplomatic cryptographic machine used by the Japanese Foreign Office just before and during World War II. The machine was an electromechanical stepping-switch device.

The information gained from decryptions was eventually code-named Magic within the US government.

The codename "PURPLE" referred to binders used by US cryptanalysts for material produced by various systems; there had been a RED machine used by the Japanese Foreign Office, and purple was the next available color. The Japanese also used CORAL and JADE stepping-switch systems. PURPLE was a successor to, and improvement on, both the RED machine and what the Americans called the "M machine" (used in some embassies and consulates by attachés). PURPLE and RED were designed by Japanese Navy Captain Risaburo Ito^[1]. The chief designer of PURPLE was Kazuo Tanabe.^{[citation needed]}

[edit] Weaknesses

In operation, the enciphering machine accepted typewritten input (in Latin letters) and produced ciphertext output, and vice versa when deciphering messages. The result was a potentially excellent cryptosystem. In fact, operational errors, chiefly in key choice, made the system less secure than it could have been; in that way the PURPLE code shared the fate of the German Enigma machine. The Japanese believed it to be effectively unbreakable throughout, and somewhat after, the war. It was broken by a team from the US Army Signals Intelligence Service, then directed by William Friedman. The team was led by Frank Rowlett.

The United States obtained portions of a PURPLE machine from the Japanese Embassy in Germany following Germany's defeat in 1945 (see image above) and discovered that the Japanese had used precisely the same "stepping switch" in its construction that Leo Rosen of SIS had chosen when building a "duplicate" (or Purple analog machine) in Washington in 1939 and 1940. The "stepping switch" was a common type of unit used in high-tech telephone-company exchanges in countries like the United States, Canada, the UK, and Japan that had good dial-telephone systems in their large cities. These fast switches were at the heart of the systems.

Apparently, all of the other PURPLE machines at Japanese embassies and consulates around the world (e.g. in Axis countries, Washington, London, Moscow, and in neutral countries) and in Japan itself, were destroyed and ground into sand by Japanese. It is certain that the American occupation troops in Japan in 1945-52 searched for any remaining units.

The PURPLE machine itself was first used by Japan in June 1938, but US and British cryptologists had broken some of its messages well before the attack on Pearl Harbor. US cryptologists decrypted and translated the 14-part Japanese diplomatic message breaking off relations (ominously) with the United States at 1 p.m. Washington time on 7 December 1941 before the Japanese Embassy in Washington could do so. Difficulties at the Embassy were a major reason the diplomatic "note" was delivered late.

[edit] Other Factors

During WW-II, the Japanese ambassador in Berlin, who was a military man, avidly studied German military developments and deployments and reported on them at length back to Tokyo via PURPLE-enciphered messages sent via radio. A good example of this was that he reported on the emplacement of the Atlantic Wall fortifications that the German Wehrmacht was building along the coasts of France and Belgium. Thus, unaware to himself, he was reporting to the Allies all about German military preparations against the forthcoming D-Day invasion of Western Europe. All that time, the Americans and the British were reading every report that the Japanese ambassador was sending in PURPLE to Tokyo.

The decrypted PURPLE traffic, and Japanese messages generally, was the subject of acrimonious hearings in Congress post-WW-II in connection with an attempt to decide who, if anyone, had allowed the disaster at Pearl Harbor to happen and who therefore should be blamed. It was during those hearings that the Japanese learned, for the first time, that the PURPLE cypher machine had indeed been broken.

[edit] Further reading

An account of the WW-II cryptographic struggle is Battle of Wits, by S. Budiansky, which is not too overwhelmingly long or technical. Combined Fleet Decoded by J. Prados has, in somewhat dispersed form, a complementary and fuller account of Japanese cryptography specifically, much of it from sources on the Japanese side. Both are recent enough to reflect much of the release of information that had been kept secret since the war.

[edit] References

• Freeman, Wes., Geoff Sullivan, and Frode Weierud, "PURPLE Revealed: Simulation and Computer-Aided Cryptanalysis of Angooki Taipu B", Cryptologia 27(1), January 2003. pp 1–43.
• Ronald W. Clark, "The Man Who Broke Purple: the Life of Colonel William F. Friedman, Who Deciphered the Japanese Code in World War II", September 1977, Little Brown & Co, ISBN 0-316-14595-5.
• Frank Rowlett, "The Story of Magic, Memoirs of an American Cryptologic Pioneer", 1998, Aegean Park Press, ISBN 0-89412-273-8. First-hand account of the breaking of Purple.

1. ^ Robert J. Hanyok, "Before Enigma: Jan Kowalewski and the Early Days of the Polish Cipher Bureau (1919–22)", Appendix B in Władysław Kozaczuk and Jerzy Straszak, Enigma — How the Poles Broke the Nazi Code, 2004, ISBN 0-7818-0941-X, p. 93

[edit] External links

• The PURPLE Machine — information and a simulator (for Windows)
• PURPLE, CORAL, and JADE