The Rise of the Machines: 1918–1941

The volume of cipher traffic that was made possible by radio showed the need for vastly increased security, speed, and accuracy in both enciphering and deciphering messages. The use of mechanical and electromechanical machines to do the encipherment was a logical outgrowth of this need. The first electromechanical rotorRotor cipher machines began to appear right after World War I, and the next three decades saw their steady improvement in both complexity and speed. The Enigma, the Typex and the M-134C/SIGABA were the epitome of these machines and the efforts to create and cryptanalyze them led us into the computer age. This chapter examines the history of cipher machines in the first part of the twentieth century and looks in some detail at the cryptographic construction of the Enigma and the Japanese Purple machinePurple machine.