The Universal Computer

Alan Turing’s War

between input letter and the letter’s encrypted version from letter to letter.

In the military version security was enhanced by an additional plugboard.

Each day there would be a different initial setting of the machine which

had to be the same for the sender and the recipient.

A group of Polish mathematicians had done an amazing job of deci-

phering German Enigma messages before the war began, but when the

Germans added a layer of complexity to the machines, they were stymied,

and passed their work onto the British. The cryptanalysts at Bletchley

Park were mostly people who liked to work on puzzles, and at times they

were deeply engrossed ...