Computer Security and Cryptography

1.5 THOMAS JEFFERSON AND THE M-94

The M-94, (Fig. 1.6) was adopted by the U.S. Army after World War I; the same device, now designated as the CSP-488, was adopted by the Navy. This encryption device was invented by Alberti in the fifteenth century; subsequently, Thomas Jefferson invented his Wheel Cipher, using the same idea. A good idea is not readily abandoned and the wheel cipher continued to be reinvented, in 1901 by the French Major Etienne Bazeries and in 1914 by Colonel Parker Hitt, who was a member of the Army Signal Service and the author of the Manual for the Solution of Military Ciphers (1915).

Figure 1.6 The Thomas Jefferson/M-94 Wheel Cipher (Courtesy, NSA).

The M-94 had 25 wheels numbered 1, 2, …, 25; a different permutation of the letters A, B, …, Z is written around the circumference of each wheel. To encipher, the order of the wheels on the spindle is determined by sorting a repeated key word alphabetically. For example, the key CHINESEFOOD is repeated to obtain 25 characters, which are numbered in sorted order. In the following array, the first row lists the wheel identifiers (numbers), the last row specifies the wheel positions on the spindle:

Wheel no. 1 is placed on the leftmost position of the spindle, wheel no. 12 next, wheel no. 23 next and finally wheel no. ...