Magic (cryptology)
Magic was the American name for information obtained from the decryption of Japanese codes such as the PURPLE encryption code during World War II . The US called decrypted PURPLE messages Magic to hide the fact that they could read PURPLE encrypted messages, analogous to the UK Ultra .
Japan had more than ten codes at the same time during World War II. Before the attack on Pearl Harbor , the following codes played a role:
- the PURPLE code of the Japanese Ministry of Foreign Affairs , for secret diplomatic correspondence,
- the Japanese Navy JN-25 code ,
- the weak Administrative Code (an old, little-used code for personnel matters).
prehistory
In the early 1930s, Japan purchased a commercial version of the German Enigma - rotor machine and modified them to their safety continues to improve. The result was one of the most secure cryptography machines in the world. The machine was given the code name RED by the US government: the preliminary stage of the PURPLE machine. It was used by the Japanese Navy and also passed on to the Ministry of Foreign Affairs, which used it for communication between Japan and its embassies and consulates worldwide.
Code break
After considerable effort, the US Army Signals Intelligence Service (SIS) managed to break the code in 1936 using a statistical analysis technique invented by William Friedman .
However, the code breach did not help the Americans for long: in early 1939, the Japanese Foreign Ministry introduced a new machine called the PURPLE. Nobody, not even the USA, knew whether this significantly more advanced machine could even be cracked. Japan used PURPLE to communicate with its key messages. The diplomatic message that signaled the break in communication between Japan and the USA and thus indirectly announced the war was also encrypted with PURPLE. PURPLE was also used to provide information on the state of German troops from Europe to Japan.
After months of arduous research, the USA succeeded in building a replica of the PURPLE in August 1940. But the keys and some additional information were still missing. Both were won a little later.
However, very few machines were issued and fewer people were provided with decoded information than would have been technically possible: They wanted to prevent Japan from finding out about the code break and simply changing it. The Japanese government received several reports from agents that the code had been broken. However, they were ignored in the belief in their own technical superiority.
literature
- Edward J. Drea: MacArthur's ULTRA: Codebreaking and the War against Japan, 1942-1945. University Press of Kansas, 1992. ISBN 0-7006-0504-5 .
- Ronald Lewin: The American Magic: Codes, Ciphers, and the Defeat of Japan. Penguin, 1984. ISBN 0-14-006471-0 .