A 2,500-year mission through spies, codebreakers, and the codes that changed history. Then you crack a secret code yourself.
A message is only useful if the right person can read it and the wrong person can't. For thousands of years, people have invented sneaky ways to hide and scramble messages. Making secret codes is called cryptography, from the Greek word kryptos, meaning hidden. Breaking those codes makes you a codebreaker.
According to the Greek historian Herodotus, a man needed to get a message past enemy soldiers. He shaved a messenger's head, tattooed the message on his scalp, and waited for his hair to grow back. Talk about the world's slowest text message!
Spartan generals wrapped a strip of leather around a wooden stick and wrote across it. Unwrapped, the strip looked like random letters. The only way to read it was to wrap it around another stick of the exact same size. The stick was the key.
Julius Caesar moved every letter forward three spots in the alphabet. A became D, B became E, and so on. CAT becomes FDW. It's called the Caesar cipher, and puzzle books still use it today.
Scholar Al-Kindi noticed that some letters appear far more often than others. In English, E is the most common. If a coded message has tons of H's, the H probably stands for E. Codebreakers still use this idea.
Mary, Queen of Scots, sent coded letters hidden inside a beer barrel, thinking they were safe. Queen Elizabeth's spymaster, Sir Francis Walsingham, had them read, and codebreaker Thomas Phelippes cracked the code. Code makers and codebreakers have been in a race ever since.
General George Washington ran a secret spy network called the Culper Ring. They used invisible ink and a code book where numbers stood for people, places, and words. Washington himself was number 711. Legend says spy Anna Strong signaled with a black petticoat on her clothesline. Nobody knows if it's true, but it's one of the coolest spy stories ever told.
The Zimmermann Note was a secret German telegram written in code. British codebreakers in a hidden office called Room 40 cracked it. When it was revealed, it helped push the United States into the war.
Bonus intel: spy pigeons carried tiny cameras in the early 1900s.Germany's Enigma machine had about 159 quintillion possible settings. British codebreakers at Bletchley Park, including Alan Turing and many women, cracked it in secret, and many couldn't tell their own families. Meanwhile, Navajo Code Talkers sent messages in the Navajo language that the enemy never cracked.
In 1945, Soviet children gave the American ambassador in Moscow a carved wooden Great Seal of the United States. Hidden inside was a listening device with no batteries and no wires. It was powered by radio waves beamed from outside the building, and it wasn't discovered until 1952.
Here's a message written with Caesar's code. Every letter was shifted forward three spots, so to decode it, move each letter backward three spots.
That's right: LAB, as in Kids Learning Lab. Congratulations, agent. You're officially a codebreaker.
Real spies used invisible ink, and you can make your own with things from your kitchen.
Squeeze lemon juice into a small bowl and add a few drops of water.
Dip a cotton swab in the mix and write a secret message on white paper.
Let it dry completely. Your message is now invisible.
Ask a grown-up to gently warm the paper with a low-heat iron. Your message appears in brown.
Why it works: lemon juice turns brown when it gets warm, and it weakens the paper a little where you wrote, so your message darkens before the rest of the page does.
A message on a leather strip only makes sense around a stick of the exact same size.
That's 159 followed by 18 zeros, the number of possible Enigma settings.
Navajo Code Talkers could send a message in about 20 seconds. A code machine needed around half an hour.
Websites with a lock icon scramble your data into code. Some codes would take the fastest computers billions of years to crack.
Five questions. Prove you were paying attention.
Stuck on a code or curious about a case? Ask the Handler anything from this episode.
The Handler is an AI and can make mistakes. Double-check with a grown-up.
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