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News | Dec. 19, 2022

World’s Oldest True Cipher Device, the “Jefferson Cipher,” on Display at the National Cryptologic Museum

The National Cryptologic Museum operates as the National Security Agency's principal gateway to the public, holding within its collection a treasure trove of cryptologic equipment. Its mission is to educate visitors in person and online about the role of cryptology in shaping history, from the ancient world to the present. In this occasional series, we highlight some of the rarest and most interesting artifacts found in its collection. Enjoy!
FORT MEADE, Md. – Thomas Jefferson, third president of the United States, had a deep interest in cryptology. He exchanged encrypted letters with friends, and he proposed a mathematics-based cryptologic system for U.S. government use (although it was never adopted).

Jefferson corresponded frequently with Robert Patterson, a professor of mathematics at the University of Pennsylvania and fellow member of the American Philosophical Society.

In December 1801, Patterson sent Jefferson a letter explaining a new cipher of his own design, one that he considered "flawless." Patterson included a sample message.

There is no evidence that Jefferson - or anybody else - solved Patterson's cipher. Until 2007.

Dr. Lawren Smithline, a mathematician at the Princeton, New Jersey Center for Communications Research, a think tank associated with NSA, examined the cipher and wrote a computer program to turn his theories into cryptanalysis.

Patterson disdained single substitution ciphers because of their vulnerability to frequency analysis, so he used lines of letters in a grid, 40 lines of 60 letters each. His security depended on rearranging the order of lines and adding a certain number of random letters, or nulls.

Dr. Smithline, after analysis of the one surviving message, believes the system could have been solved in Patterson's day, although the cryptanalytic process would have been slow and tedious. To solve the test message that Patterson sent Jefferson in 1801, Dr. Smithline devised a computer program that analyzed digraphs, eliminating combinations that were impermissible in English, and concentrated on those that were more common. This analysis determined the key with line order and number of random letters in the Patterson message and enabled its solution.

Patterson's message: "In Congress, July Fourth, one thousand seven hundred and seventy six. A declaration by the Representatives of the United States of America in Congress assembled. When in the course of human events…" - well, you know it.

Dr. Smithline explained, "Patterson played this little joke on Thomas Jefferson, and nobody knew it until now."

After Jefferson’s death, historians cataloging his papers found drawings of a cipher device like the one pictured. The device itself was discovered in an antique shop in West Virginia, near where Jefferson once owned land.

This early cipher machine, whether Jefferson's or not, is on display in the National Cryptologic Museum. Come visit and examine the device up close!