A favorable and a confidential opportunity offering by Mr. Dupont de Nemours, who is revisiting his native country gives me an opportunity of sending you a cipher to be used between us, which will give you some trouble to understand, but, once understood, is the easiest to use, the most indecipherable, and varied by a new key with the greatest facility of any one I have ever known.
Thomas Jefferson to Robert Livingstone
April 18, 1802
The success of the recent film, The Imitation Game, reminds me of Thomas Jefferson's efforts to encrypt his official and personal correspondence. Jefferson was a Renaissance man, America's Leonardo Da Vinci, and there was almost no subject to which he did not turn his genius in the course of a long and amazingly productive life.
Jefferson was an exceedingly private man, sometimes a secretive one. He was well aware that the fledgling U.S. Postal System was inefficient and seldom secure. It was not uncommon for postmasters to open the mail that passed through their offices, especially letters written by political figures or famous men and women. Jefferson rightly understood that his Federalist enemies would very gladly open his correspondence, read it out loud to those gathered in the nation's post offices, and take hand written extracts from his correspondence to use against him in the political arena.
Jefferson experimented with several cyphers. His famous "Cypher Wheel" was developed sometime between 1790-1800. His Enlightenment friend Dr. Robert Patterson, a mathematician at the University of Pennsylvania, and vice president of the American Philosophical Society, may have had a hand in the project. The Cypher Wheel was a set of 26 cylindrical disks, each with all of the letters of the alphabet etched randomly on its circumference. Each wooden disk had a small hole at its center, and they were assembled on a stiff wire and bound at either end. Jefferson would turn the wheels to spell out the words he had in mind to encrypt, and then choose another random line of letters to reproduce on the page of his letter. The recipient, with an identical set of disks, would align his device to reproduce the encrypted gibberish on the baseline, and then turn the cypher wheel until an intelligible line of English words appeared.
According to historian David Kahn, "Jefferson's wheel cypher was far and away the most advanced devised in its day. It seems to have come out of the blue rather than as a result of mature reflection upon cryptology." Kahn's second sentence almost certainly fails to do Jefferson justice. Jefferson had a genius for this sort of creative thinking. He puzzled over systems, ways of ordering (and disordering) knowledge, and what he called "gimcracks" all of his life. He had a rage for order that enabled him to see into the heart of machines and taxonomical systems, and to discover possible improvements.
Jefferson seems to have abandoned the cypher wheel in 1802. The device was forgotten, therefore, and not rediscovered among his papers in the Library of Congress until 1922.
Meanwhile, Jefferson's system was discovered independently, twice, by other individuals. In 1817 a man named Colonel Decius Wadsworth created a similar cypher wheel His cylinders were made of brass. He added the numerical digits 2 through 8 to the system. Wadsworth was probably assisted in this invention by his friend Eli Whitney, the inventor of the cotton gin and a pioneer in the use of interchangeable parts.
A second re-invention occurred just before World War I. The device, known as M-94, was used by American military personnel from 1922 until just before World War II.
Jefferson's Cypher Wheel bears no resemblance to the Enigma Machine devised by German engineer Arthur Scherbius at the end of World War I.
Jefferson also developed a two-dimensional encryption device, though it was not an original creation. It was based on the European Vigenere cypher. It was a 28-column alphanumerical grid. Jefferson made that version available to Meriwether Lewis when he ascended the Missouri River in 1804. Jefferson believed that Lewis may need to send messages of a sensitive geopolitical nature to Washington, D.C., and the president did not wish such communiques to fall into the hands of America's rivals for the West, Britain, France, or Spain. In his letter of instructions to Lewis, Jefferson showed his protege how to encrypt the sentence, "I am at the head of the Missouri. All is well, and the Indians so far friendly." This quintessentially optimistic and Jeffersonian sentence would be encrypted as "jsfjwawpmfsxxiawprjjlxxzpwqxweudusdmf&gmlibexpxu&izxpsecr."
Lewis never employed encryption in the course of his transcontinental journey.
A children's version of Jefferson's Cypher Wheel is available in some bookstores and online.
Read Jefferson’s letter to Robert Livingstone on April 18, 1802.
The Code Breakers: The First Comprehensive History of Secret Communication from Ancient Times to the Threshold of Outer Space
by David Kahn
Thomas Jefferson: Statesman of Science
by Silvio A. Bedini
Jefferson's Shadow: The Story of His Science
by Keith Stewart Thomson