While serving as George Washington's secretary of state (1790-1793), Thomas Jefferson devised an ingenious and secure method to encode and decode messages: the wheel cipher. During the American Revolution, Jefferson had relied primarily on messengers to hand-carry sensitive letters, but codes became an essential part of his correspondence when he was America's minister to France (1784-1789) since European postmasters opened and read all letters passing through their command.
Jefferson's wheel cipher consisted of twenty-six cylindrical wooden pieces, each threaded onto an iron spindle. The letters of the alphabet were inscribed on the edge of each wheel in a random order. Turning these wheels, words could be scrambled and unscrambled.
As an example, the sender of the message shown in the picture, "COOL JEFFERSON WHEEL CIPHER," spells the message out and then looks to any other line of text -- possibly the one directly above, which on this version of the cipher begins with the letter "N." The sender then copies the rest of the letters from that line into the correspondence to spell out "NKYG NSUS NXML CQYO TYUH HFTD".
The recipient of the coded message would spell out these random-seeming letters on his own identical cipher and then begin looking for the one line that made sense. In this case, the line below.
Although Jefferson apparently abandoned use of the wheel after 1802, it was "re-invented" twice: first by a French government official around 1890, and then just prior to World War I by an officer in the United States Army. Designated as M-94, the latter version was used by the Army and other military services from 1922 to the beginning of World War II.
The cipher shown is a reproduction made according to Jefferson's instructions, with the exception that it has only 24 wheels instead of 26. The model is presently in use at Monticello's Education Department. Another model, created by scholar Silvio Bedini, is in the collection at the National Museum of American History in Washington, DC.
- ↑ This article is based on Ann M. Lucas, Monticello Research Report, September 1995; Revisions by Chad Wollerton, December 2003 and April 2005.
- Copy of The wheel cypher in Jefferson's hand at the Library of Congress American Memory site.
- Online Wheel Cipher, which graphically recreates the original and sends enciphered emails