Wheel Cipher

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. When he became America's minister to France (1784-1789), however, the adoption of codes was necessary. Codes were an essential part of his correspondence because European postmasters opened and read all letters passing through their command.

Reproduction of Jefferson's Wheel Cipher created by Ronald Kirby.

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.

Reproduction of Jefferson's Wheel Cipher (created by Ronald Kirby) disassembled

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, D.C.

- Ann M. Lucas, 9/95; revisions by Chad Wollerton, 12/03 and 4/05

Further Sources

Discussion

says

Fans of Dan Brown will delight in reading about Thomas Jefferson's wheel cipher.

says

In his 1996 book on the history of cryptology, The Codebreakers, David Kahn wrote "Jefferson's wheel cypher was far and away the most advanced [cipher] of its day." This online version was created by graduate students in Prof. David Evans's cryptology class at UVA. While it's a little difficult to figure out at first, it's a pretty cool rendition of the original, which -- as those who've played with the large reproduction in our Griffen Discovery Room have found -- was not the easiest device to manipulate. In fact, Jefferson himself seems to have not promoted the wheel cipher's use primarily because there were other ciphers, such as the one developed Vigenere, that were simpler to use and still quite difficult to break.

says

Thomas Jefferson Invention #2—the wheel cipher for encrypting and decrypting messages. Try this yourself and challenge your friends.

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