Encryption In The 1790s | Hackaday
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For as long as humans have had writing, there’s been a need to send secret messages. It is easy to think that Enigma machines and their immediate predecessors are old tech, but they are much more recent than ancient systems used by the Greeks and Romans. Even Thomas Jefferson, one of the founding fathers of the United States, was interested in encryption and is often said to have invented the Jefferson Disk machine for encryption. The truth is, the device is probably older than Jefferson, but he certainly thought about using it for secret communications.
Simple but Effective
Thomas Jefferson was, apparently, a fan of secret messages<br>" data-large-file="https://hackaday.com/wp-content/uploads/2026/07/Official_Presidential_portrait_of_Thomas_Jefferson_by_Rembrandt_Peale_1800.jpeg?w=524" class="size-medium wp-image-1127481" src="https://hackaday.com/wp-content/uploads/2026/07/Official_Presidential_portrait_of_Thomas_Jefferson_by_Rembrandt_Peale_1800.jpeg?w=335" alt="" width="335" height="400" srcset="https://hackaday.com/wp-content/uploads/2026/07/Official_Presidential_portrait_of_Thomas_Jefferson_by_Rembrandt_Peale_1800.jpeg 2512w, https://hackaday.com/wp-content/uploads/2026/07/Official_Presidential_portrait_of_Thomas_Jefferson_by_Rembrandt_Peale_1800.jpeg?resize=210,250 210w, https://hackaday.com/wp-content/uploads/2026/07/Official_Presidential_portrait_of_Thomas_Jefferson_by_Rembrandt_Peale_1800.jpeg?resize=335,400 335w, https://hackaday.com/wp-content/uploads/2026/07/Official_Presidential_portrait_of_Thomas_Jefferson_by_Rembrandt_Peale_1800.jpeg?resize=524,625 524w, https://hackaday.com/wp-content/uploads/2026/07/Official_Presidential_portrait_of_Thomas_Jefferson_by_Rembrandt_Peale_1800.jpeg?resize=1288,1536 1288w, https://hackaday.com/wp-content/uploads/2026/07/Official_Presidential_portrait_of_Thomas_Jefferson_by_Rembrandt_Peale_1800.jpeg?resize=1717,2048 1717w" sizes="(max-width: 335px) 100vw, 335px" />Thomas Jefferson was, apparently, a fan of secret messages<br>The idea is simple. We make a series of disks. Each disk has a number on it and, around the edge, all the letters of the alphabet. The placement of each wheel with the same number is the same, but, overall, the arrangement is random. That is, all disks marked #5 might start with XCBYG, but all disks marked with #10 could start with FAYQL. You take one set of disks, and I keep the other set.
When we want to send secret messages, we agree to arrange our disks on an axle in the same order. Jefferson used a 36-disk system, so we might agree to go left to right with the odd numbers first and then the even numbers, or any other setup that we could agree on.
Encryption
Once the wheels are in place, encryption is simple. There’s a bar across the device, and you line up your message using a wheel for each letter: ENEMYCOMESBYSEA, for example. Then you look at any different row, which will now read something crazy like: FSRSSXQCGAEEFOR (plus the random letters on the rest of the disks). That’s the message you send.
Decryption
Upon receipt, you spell out the same message on the disks with the wheels in the agreed order. Once you have FSRSSXQCGAEEFOR lined up, you look at the other rows. It is a good chance that all of them will be gibberish except one. That’s the decoded message.
Of course, you could agree to shift a certain number of rows if you wanted to be sure. The order of the wheels amounts to a key, and while Jefferson wasn’t sure how secure this is, modern analysis says it is actually pretty good. If you don’t have the wheels and you don’t know the order of the wheels, it is actually excellent. If you have the wheels but don’t know the order, it is still very difficult to try all the permutations, especially without a computer.
History
The National Cryptologic Museum has this partial device which may or may not have been Jefferson’s<br>" data-large-file="https://hackaday.com/wp-content/uploads/2026/07/nsa-disk.jpg?w=764" class="size-medium wp-image-1127482" src="https://hackaday.com/wp-content/uploads/2026/07/nsa-disk.jpg?w=400" alt="" width="400" height="314" srcset="https://hackaday.com/wp-content/uploads/2026/07/nsa-disk.jpg 764w, https://hackaday.com/wp-content/uploads/2026/07/nsa-disk.jpg?resize=250,196 250w, https://hackaday.com/wp-content/uploads/2026/07/nsa-disk.jpg?resize=400,314 400w" sizes="(max-width: 400px) 100vw, 400px" />The National Cryptologic Museum has this partial device, which may or may not have been Jefferson’s<br>The Swede Fredrik Gripenstierna used a similar machine with 57 disks, but it had a slightly different purpose and operating principle. Jefferson described his device in the 1790s, and while he never claimed to invent it, the story has caught on that he did. Sometimes these are called Bazeries cylinders, as Etienne Bazeries had a 20-disk device in 1891, apparently independently invented.
It doesn’t appear that Jefferson or anyone else actually built the...