Japan’s Enigma Machine
Baron Hiroshi Oshima, a Japanese General and Ambassador to Nazi Germany prior to the Second World War, was able to purchase an Enigma Machine with the approval of Hitler. The objective was for Japan to replicate and possibly improve the German encryption device. The Japanese soon created a similar machine, which the Americans, on learning of its existence, code-named ‘Red’.
This was the machine the Japanese Navy used from 1931 to 1936 when the American code-breakers cracked it.
Having learnt of the security breach the Japanese went about creating a new system based on a 97 Alphabetical Typewriter. This device was better known by its US code-name, ‘Purple’.
The Purple Machine comprised two typewriters as well as an electrical rotor system with a twenty-five character alphabetic switchboard. Similar to the Enigma Machine, the first typewriter was the method by which the plain text, or unencrypted message, could be manually typed. The typewriter was built to be compatible with English, and Roman, adding a level of mystery through language choice.
The major difference between the Enigma Machine, which presented the text in the form of blinking lights, and the Purple Machine was that Purple used a second electric typewriter, which would type the cypher text, or encrypted message, onto a piece of paper. This was a major improvement on the Enigma Machine.
The Purple Machine in addition to its encryption capabilities also used a secret key that was changed on a daily basis. This meant that even if a Purple Machine were stolen, it would be useless without the key of the day.
Additionally, as the key changed every day, code-breakers would not be able to find patterns in messages sent over several days. The daily key would be inputted into the device by the arrangement of the switchboard and rotors. The switchboard contained twenty-five connections, which could be arranged in six pairs of connections, yielding over 70,000,000,000,000 possible arrangements, which would determine the method of encryption. This would make Purple extremely difficult to crack. Add to that the daily key.
Eventually, Lt Francis A. Raven, a member of the team, discovered a pattern being used by the Japanese in their daily keys. He noticed that each month was broken into three ten-day segments in which a pattern was discerned. The Purple cypher was effectively broken and Japanese secrets were exposed.
The cracking of the Purple Machine’s code remained a closely kept secret - not even the British or its allies were aware of the American breakthrough. They were able to track Japanese naval troop movement as well as other military communications.
Therefore why didn’t the US know of the Japanese plan to attack Pearl Harbour? Or did they?