Jefferson’s Cipher – Pic of the Week

This is a guest post by Kaitlyn Norris, an intern with the Law Library Office of External Relations.

Thomas Jefferson was a Founding Father of the United States of America, the primary author of the Declaration of Independence, and held positions as secretary of state, vice president, and—from 1801-1809—third president of the United States. Not only was Jefferson a Founding Father, he was also an avid inventor of multiple ciphers used to encrypt confidential information. One of his best-known inventions was the Jefferson Wheel cipher—a manual polyalphabetic substitution cipher system. This cipher was a wooden wheel assembled by 36 disks strung together on a metal axle, with each disk containing every letter of the alphabet in random order, so the recipient reads the encoded message horizontally.

Since the Revolutionary War, where Jefferson relied on hand-carried mail, operatives and public officials used complex ciphers to protect sensitive information. Jefferson invented this cipher during his time as America’s minister to France in 1784-1789, because he needed a way to get his messages securely past European postmasters who opened the mail. Since this cipher was so elaborate, Americans even utilized it at the start of World War II to spread sensitive information before other intelligence communications protocols were developed. This cipher became a building block to U.S. intelligence due to its intricacy. Also, the limited availability of decoders with the correct lettering guaranteed security of the exchanged messages.

When Jefferson was President, he used many other codes and ciphers, including a nomenclator, which was 1700 words and syllables ordered by numbers, but arranged randomly. Jefferson’s cipher has been mistaken as a Vigenere cipher; however, they are not the same type of code due to differences in the way messages are encrypted and decrypted. In addition, Jefferson gave Meriwether Lewis a square table cipher in 1803, which was to be used to inform Jefferson of Lewis and William Clark’s expedition to find the Northwest Passage.

In order to decode this cipher, one person encoding the cipher holds one wheel, and the person decoding the message holds the other wheel. Other than the decoding wheels, the only necessary component is an encoded message. An encoded message appears as jumbled letters and would be meaningless to one who did not have the instructions for the cipher.

For users to encrypt a message, they would place their message by moving the disks to the letters that would spell out their message. For example, for this photo we chose to encode the words “LAWLIBRARY” as seen at left, starting at the second disk, we placed the letters in a line. We can encrypt this message by finding another line of letters while the decoder still has our message placed correctly. For this example, we chose our encrypted message to be the letters two lines down from our message, which reads, “OIDYGOGLDAK.” We could then pass “OIDYGOGLDAK” along to anyone who has a wheel cipher so that they are able to decrypt our message. The person decoding the message will place it in the wheel and once finished inputting every letter in a horizontal line, will see a message appear in another location on the wheel. This is the decoded message.

Due to the success of this cipher, Jefferson is credited for laying the foundations of cryptography in the U.S. His trailblazing would be used for intelligence work in centuries to come.