Among the things that Meriwether Lewis took west with him on his expedition to the Pacific Ocean was a special cipher designed by President Thomas Jefferson for encoding messages. The cipher consisted of a table of 26 rows and 26 columns of sequentially arranged letters, plus an example keyword (Jefferson actually provided Lewis with two examples, one with the keyword “artichokes” and another with the keyword “antipodes”). Upon receipt of the coded message, presuming the recipient knew the agreed-upon keyword, he could use the cipher table to decode the message. In one example, Jefferson showed Lewis how to encode the optimistic message, “I am at the head of the Missouri. All well and the Indians so far friendly.”
Although there is no evidence that Lewis ever used the cipher to code a message to Jefferson, clearly the president was concerned about the possibility of Lewis’s correspondence from the field being intercepted by agents of European powers who opposed American expansion to the West. Simple but ingenious, this cipher was one manifestation of Thomas Jefferson’s interest in cryptography, defined as “the practice and study of techniques for secure communication in the presence of adversaries.” As in so many of his scientific pursuits, the president’s thinking in this area was decades ahead of his time.
As Silvio Bedini writes in his fascinating monograph Jefferson and Science, Jefferson first became interested in the security of the government’s official communications while serving as George Washington’s Secretary of State in the early 1790’s. With war threatening between England and France, and delicate negotiations ongoing with Spain over American trade and navigation on the Mississippi River, Jefferson knew that plain text letters to his overseas representatives could easily be intercepted and read by prying eyes, blowing his diplomatic efforts out of the water. It was at that time that he began experimenting with different ways to put messages into secret code.
Jefferson first devised a system of 26 paper strips, each containing a scrambled version of the alphabet, which he could arrange and rearrange in different ways to form a flexible cipher system. More than one correspondent could use the system, with each person having an individually assigned keyword for coding and decoding messages. However, with 26 moving parts to keep track of, the system proved too cumbersome and impractical for most of his correspondents.
Undaunted, Jefferson came up with the idea of having a wheel-style cipher, that could more easily be used in the field. He took as his inspiration the cipher padlock, typically used to secure diplomatic dispatch boxes. Like our modern combination lock, the cipher lock unlocked when lettered disks were arranged to spell a certain keyword.
Jefferson took the 26 strips of paper and had the scrambled alphabets punched onto a wooden cylinder, which was then segmented into disks and mounted on a spindle. It is known that Jefferson had two of these devices made while he was Secretary of State. He apparently tested the device with Robert Patterson, a professor of mathematics, chemistry and natural philosophy and a member of the American Philosophical Society. The two exchanged a series of coded messages, but the wheel cipher was never put into diplomatic service. At some point, for some reason, Jefferson set the wheel cipher aside and forgot about it. The two wheel ciphers used by Jefferson and Patterson have been lost, though a detailed description of how to make it was saved among Jefferson’s papers.
It was another hundred years before the science of cryptography caught up with Jefferson’s mind. In 1890, Commandant Etienne Bazeries, chief of the cryptographic bureau of the French Ministry of Foreign Affairs, invented a “cylindrical cryptograph” that was almost identical to Jefferson’s design. During World War I, a U.S. infantry captain named Parker Hitt refined Bazeries’ design, using a methodology very similar to Jefferson’s. After extensive testing by Assistant Commandant Joseph Mauborgne of the Army Signal Corps, the device was approved for military use in 1918. It was not until 1922 that the device was actually manufactured for military use, becoming known as “Cipher Device M-94 of the U.S. Army.”
Ironically, that same year, Jefferson’s original description of the device was discovered among his papers in the Library of Congress, astonishing the military community. Army cryptographers were stunned that President Jefferson had already envisioned a device that had taken them 100 years to develop, and that his description had been available to the public all this time.
Jefferson would have been pleased to know that Cipher Device M-94 proved to be a robust security device, especially practical for tactical communications from the field. It saw two decades of military service before finally being phased out during World War II.
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