Recently, my children have been studying the American Revolution. Last fall, I wrote them a chapter book about teenage Revolutionary War heroine Sybil Luddington, and inspired by this book, they've been a little obsessed with learning about Revolutionary War spies. (Incidentally, the Sybil Luddington book will be available to everyone in the coming months; it's a sequel to my free children's chapter book Day with the Dinosaurs - which you can snag here.)As part of our studies, we've been having lots of fun with invisible ink (made from a variety of household materials) and ciphers. We learned that Thomas Jefferson invented something called the Jefferson Disc Cipher (sometimes called a wheel cipher or Bazeries cylinder; you can see an image of it to the left). It worked so well, the American government continued to use it right on up to WWII! You can read more about the Jefferson Disc Cipher at Wikipedia and CipherMachines.com.
Online, I found a number of sites that suggested ways to make a disc cipher; one recommended collecting mayonnaise lids for the discs - but it would take us a long time to go through enough mayo to get the required number of lids. Another suggested ribbon spools, but I didn't have any on hand. And others suggested just using paper - but the directions were either non-existent or confusing. In the end, I made our own paper template, which you can download for free by clicking the link below.
Free Jefferson Disc Cipher Printable (.PDF)
My kids absolutely love this simple cipher! They've spent hours creating and deciphering messages with each other. Maybe they need a nice wooden one that will last; they sell them at Monticello, and at Amazon. We'll see.
How to Make a Simple Jefferson Wheel Cipher
You will need:
Printed "free Jefferson Disc Cipher Printable" (see above link)
An empty toilet paper tube (or empty paper towel tube)
Scissors
Tape
1. Cut out the columns of letters. There will be 7 strips. (If using a paper towel tube, you will need to print out more than one sheet of letters.)
2. Take one of the strips of paper and wrap it around the
outside of the tube. Tape the two ends of the paper together. The strip should
spin around the tube; do not tape the strip to the tube. Continue with the remaining strips of
paper.
3. To use the disc cipher, first decide what you want to say. Then find where the first letter of the
first word is on the first strip of paper. On a piece of blank paper, write
down the letter that's beneath it on
the disc cipher. Now find the second letter of the word on the second strip of
paper. Write down the letter beneath
it...and so on, until your message is complete. Use an underscore ( _ ) between
words. Now someone with the exact same cipher can decode your message!
Example of How to Use the Disc Cipher:
Let's say I want to send the following message: "Help me!"
First, I'd find the letter H on the first strip of paper. Since the letter under that is O, I'd write the letter O on a blank piece of paper.
Next, I'd find the letter E on the second strip of paper. Since the letter under it is L, I'd write the letter L on the paper.
I'd continue, moving to the next strip of paper each time I needed a new letter, until I no longer had letter strips on the right hand side of the tube. Then I'd move back to the first (left hand side) letter strip...until I'd written out my entire message. When I was done, my message would read:
OLSW _ TL
Now I'd hand the cipher wheel over to my fellow spy, along with my coded message.
To decipher the message, my friend would find the letter O on the first paper strip. The letter just above it is H, so he'd write H down on a piece of paper.
Now he'd look at the second strip of paper and find the letter L. The letter just below it is E, so he'd write that down...and so on until the message is deciphered.
My eldest is going to love this - thanks!
ReplyDeleteBeing in the old cryptographer for the US military I hope find these things extreme fun. Thanks for the post easy to make fun to play with
ReplyDeleteI used your Jefferson Cipher document for my summer math camp today. It was awesome, and I'm so grateful you created it and shared it with the internet. Thank you!
ReplyDeleteI have these three notes:
1) I didn't prepare in time to save up enough toilet paper tubes for every student at camp, so instead, I cut a piece of 1-1/2" PVC to 7" long for each student as a substitute. We wrapped 3/8" strips of felt around each end to keep our paper rings from slipping off. It worked beautifully.
2) This code is SO MUCH FUN! We did shift ciphers, morse code, tap code, pigpen ciphers, and even Sherlock Holmes's dancing men, but this was their favorite. It's fast and involves a little simple machine. Let me repeat my thanks.
3) Because there are 30 rows on each paper strip, some letters in each column have to repeat. That leads to differences, depending on which of the repeated letters you use for the code. For example, in the first column, the top "V" has "C" underneath, and the second "V" has "W" underneath. I was going to use your chart as a model and then try some experiments to size it so that each column has the letters of the alphabet in a different random order, but only one iteration of the alphabet to reduce confusion. I also think it might be a fun idea to introduce a space to each ring/disc in order to add some random work breaks to the encrypted text.
Again, thank you! I would never have felt empowered to do this cipher without your awesome idea!
I'm so glad you enjoyed it!
ReplyDelete