THE CRYPTOLOGY OF MULTIPLEX SYSTEMS

Abstract

Multiplex systems are a family of cryptosystems whose origin can be traced to Thomas Jefferson. They were not used extensively, however, until the period just prior to World War II. The characteristic feature of a multiplex system is that it permits the encipherer to select the ciphertext from among 25 alternatives, reducing the likelihood that the same block of plaintext will result in identical blocks of ciphertext. This paper traces the history of multiplex systems and examines both their cryptographic and their cryptanalytic aspects. The computer simulation of one system, U.S. Army Signal Corps Cipher Device, Type M-94, is described.