Purple (machine)
Purple (German literally: violet , lilac, purple , spelling also: PURPLE ) was the American code name for an encryption machine that was constructed by the Japanese before the Second World War and used for the diplomatic service. The Japanese name was "Latin letter typewriter type 97" ( Japanese 九七 式 欧文 印字 機 , kyū-nana-shiki ōbun injiki ), where the number 97 stood for the Japanese year 2597 corresponding to the western year 1937. The Purple method was deciphered by the American side by a group around the mathematician William Friedman .
Technology and function
Like the German Enigma , the Purple machine consisted of an input unit, an output unit and the actual cryptographically effective key mechanism. For encryption, Japanese communication was transcribed into Latin script ( Rōmaji ) using the Hepburn system . If required, the machine could also encrypt Western texts verbatim for transmission. Punctuation marks and digits had to be converted into letters using a table before encryption.
Unlike comparable Western machines, Purple used an electric typewriter as input and output unit. Due to its size, the machine was only transportable to a limited extent and was used stationary.
The actual key unit, computationally largely equivalent to a 3-roller Enigma, was located between the two typewriters. The contacts between the key unit and the typewriter could be removed for transport and changed to set additional keys.
Instead of rotors, Purple used selector switches arranged one behind the other, like those used in telephone exchanges . The basic element was an electromechanical switch with a six-pole input and an arm that could be switched to 25 different output positions. The arm was moved by an electromagnet and shifted one position at a time until the last position was reached, from which it returned to the starting position by means of a spring.
In each switching position, the multiple contacts on the arm and output closed, one contact for each encryptable letter, and formed the electrical circuit required for encryption.
The wiring that made up the actual key alphabets lay rigidly between the selector switches. In contrast to the rotor principle, it was not interchangeable.
The circuit ran for the encryption and decryption of 20 consonants by three selector switches in series, wherein in each case four switches were connected in parallel (a battery of twelve switches) for the six vowels of the contact was only separated by a single current selector.
Purple is similar in structure, design and size to the Japanese CORAL and JADE encryption machines, which also used selector switches, albeit in larger numbers. The third known Japanese key machine of the RED type, on the other hand, used half-rotors, while the JN-25 method used at the same time relied on code books. The less common - Enigma-like - Japanese machine San-shiki Kaejiki (allied alias "Green") used four rotors with vertical axes. A German Enigma model specially designed for the communications of the two war allies Germany and Japan was the Enigma-T (also called “Tirpitz” by the Germans and “Tirupitsu” by the Japanese, allied alias “Opal”).
history
After the first break into Japanese code systems around 1940, Purple was broken by the United States Coast Guard Unit 387 under the direction of the American cryptanalyst Elizebeth Friedman (picture) . Later it was due to the important contributions of Leo Rosen able to recreate the machine and radio messages within Action MAGIC decipher . As MAGIC Code were intercepted on the US side and deciphered information referred to by the Purple procedure encrypted were. The idea was to cover up the fact that Purple had been cracked . Both the replica and the original used telephone dialer. Purple and other Japanese methods were seen as unbroken by the Japanese and were used throughout the war.
In December 1941 a radio message encrypted with Purple was overheard and deciphered. The 14-part text contained the breakdown of diplomatic relations and was ultimately the declaration of war before the attack on Pearl Harbor . Delays in the evaluation and forwarding of the information prevented a timely warning - the message reached the naval base after the attack by means of a regular civilian telegram.
It should be noted that British and American efforts to decipher Japanese codes and read radio communications continued. Knowledge of the Japanese JN-25 code book and the determination of the Midway Islands as a Japanese target by a group under the cryptologist Joseph Rochefort were ultimately decisive for the outcome of the Battle of Midway in 1942 . The same can be said for the battle in the Coral Sea (the Japanese target was Australian positions in Papua New Guinea). Deciphered travel plans later enabled the targeted downing of the aircraft of Japanese commander Admiral Yamamoto Isoroku , who had helped plan the attack on Pearl Harbor.
The only known authentic remains (top picture) of a purple machine were found in the ruins of the Japanese embassy in Berlin and are now in the publicly accessible museum of the National Security Agency (NSA). The coded Japanese descriptions of German military technology and the fortifications, for example in France, had been read beforehand.
literature
- Klaus Schmeh : Code breakers versus code makers. The fascinating story of encryption. 2nd edition, W3L-Verlag, Herdecke et al. 2008, ISBN 978-3-937137-89-6 .
