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A young woman holding a worksheet stands behind a homemade cipher wheel.
Renee with her finished activities during Family Mystery Day. (Photo courtesy of Renee Madrigal.)

Ciphers and Secret Codes: No Security Clearance Needed!

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This post was written by Renee Madrigal, a graduate student at Johns Hopkins University and fall 2023 Library of Congress Internship (LOCI) program participant at the Library of Congress.

In October of 2023 the Library of Congress held a Can You Solve It? Family Mystery Day, which included cipher and secret code activities I developed during my Library of Congress Internship (LOCI). While looking into the Library’s collection, I began to imagine how we might use codes in our everyday life, even if most of us aren’t protecting classified government secrets. Codes are like puzzles, and code-making and code-breaking can be a rewarding experience for all ages. This blog will explore how people used ciphers throughout history. In addition, throughout the blog there are activities for you and the children in your life to have fun with ciphers today.

A cipher is a message written in secret code, usually requiring a key to decipher it. One of the most famous messaging systems with a very well-known key is Morse Code, developed by Samuel F. B. Morse and Alfred Vail in 1838. Each letter of the English alphabet is represented by a series of dots and dashes, as seen in the image below.

A diagram of a telegraph machine above a Morse code alphabet
Morse apparatus and alphabet, 1877. (General Collections, Library of Congress)

Morse and Vail developed the electromagnetic telegraph and sent the first telegraphic message, “What hath God wrought?” on May 24, 1844. Morse sent the message from the US Supreme Court room in the US Capitol in Washington, D.C. to Vail in Baltimore, Maryland. Invite your child to imagine they had the chance to send the world’s first telegraphic message. What would their message be?

Morse code and the telegraphic instrument continued to evolve, eventually becoming commonplace in military and civilian lives.

A black and white photo of a woman sitting at a table with a telegraph machine. In front of her is a sign with the Morse code alphabet.
Mezzo-soprano opera singer Ada Jones tapping out Morse Code. Ca. 1915 – 1920. (Bain News Service photograph collection, Prints & Photographs Division, Library of Congress)

If you want to practice Morse code, you can try sending a message using light or sound—especially since you probably don’t have a telegraph machine at home. Use the Morse alphabet above to create dots with a quick flash of light or a short blip of sound. Dashes should last a bit longer. Lastly, don’t forget to take a pause in between words.

While Morse Code was intended to be deciphered easily, there are plenty of codes specifically designed to protect confidential information. One example is the unbreakable Navajo code developed during World War II. The Navajo Code Talkers created a method of encoding and decoding Navajo and English words to transmit sensitive messages over the open air waves. Another example was designed by Thomas Jefferson, who was a major proponent of using ciphers in his personal letters. Jefferson designed a cipher wheel using 36 individual rungs which could be scrambled and re-aligned to protect and reveal messages.

A close up of a cipher wheel.
A modern recreation of Jefferson’s cipher wheel design. (Photo courtesy of Renee Madrigal.)

With Jefferson’s cipher wheel one could send a seemingly random sequence of letters and numbers in the mail. If the person who received the correspondence had a key, they would then be able to use their own cipher wheel to match the key’s sequence and find the hidden message on the wheel.

For the October event, I created a table-top version of a Jefferson cipher wheel—which you can build at home! To begin, find a material you can use as the individual rungs of the wheel. I used rolls of duct tape. Then find straight, sturdy lines to hold the rungs up, like taut string or wooden dowels.

Many wheels of colorful duct tape on a desk, some on a dowl suspended between two bookends.
The start of the cipher wheel project. (Photo courtesy of Renee Madrigal.)

Next, write your message across the rungs, one letter per rung. While your message is legible, choose a different line of letters and numbers to be your key. My key is RZ8ㅎC.

Two sets of tape suspended on dowels between book ends. The tape rolls have numbers and symbols on them, some of which spell out solve.
My key and message are visible in this photograph of the cypher wheel fully assembled and set. (Photo courtesy of Renee Madrigal.)

Once you have your key and your message, fill in the left-over space with random letters and numbers.

Many rolls of tape on a table, with letters drawn on them.
Filling in the left-over space on each rung. (Photo courtesy of Renee Madrigal.)

Lastly, scramble the rungs to encode your secret message. When you want to decode it, just match the rungs to your key and reveal the hidden words. Find a friend and challenge them to decoding your message.

Two sets of rolls of tape suspended on dowels across bookends. Each tape roll has symbols and letters written on it.
Finished cipher wheel with secret message hidden. (Photo courtesy of Renee Madrigal.)

Ciphers haven’t always been just for government leaders, militaries, or even adults! Before television, families could gather around the radio to hear the news, short stories, radio plays, and more. Some radio programs even included secret messages for children to decipher. For example, while listening to Little Orphan Annie Secret Society radio programs in the 1940s, children listened for the code and then used their own decoder ring to reveal the secret messages.

Black and white newspaper advertisement for Orphan Annie's 1942 Safety Guard.
Advertisement for Orphan Annie’s decoder ring. Evening Star, January 25, 1942, Page 5.

Child-friendly puzzles were also published in newspapers, like this 1910 San Francisco Call article featuring ciphers and code-breaking techniques. Check out this checkerboard cipher key in the picture below, from this article.  Each double-digit number represents one letter of the English alphabet. Start on the left side of the square with the first digit, then the top for the second digit. Where the two numbers intersect is the secret letter. Example: 54=Y. Using this technique, reveal this secret message: 32 15 15 44 • 44 34 33 24 22 23 44 • 11 44 • 44 52 15 31 51 15. Scroll to the very bottom of this blog post for the answer!

Chart with numbers and letters.
Key to a 1910 checkerboard cipher. The San Francisco Call. July 17, 1910, Page 11.

Encourage your children to use the checkerboard cipher above to encode more messages for their friends to figure out. If they’re feeling really creative, they can try their hand at making their own cipher keys.

Whether you have a future spy, a puzzle buster, or simply a bored child at home, introduce them to ciphers and encourage them to think about how protecting messages and decoding puzzles might be useful in their own lives. Maybe they want to protect a private diary, send notes to friends, or communicate in secret across the schoolyard. However they choose to play, children can experience the thrill of cracking a secret code with some help from the Library of Congress’s collections.

Checkerboard cipher answer: MEET TONIGHT AT TWELVE

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