Secret codes for kids

The best way in is to let kids crack a short message first, then hand them the key and let them write one back. Writing back is the part they remember. Each code below has a free translator on this site for checking answers, and four of them have a sheet to print.

Six codes, easiest first

1. Caesar shift

Every letter moves the same number of places along the alphabet, wrapping from Z back to A. Julius Caesar used a shift of three, so A became D and B became E. A paper cipher wheel makes it quick: turn the inner wheel to the shift and read straight across.

Example: HELLO with a shift of 3 is KHOOR.

Print the Caesar cipher wheel (you need a brad to pin it) or use the Caesar cipher translator.

2. Pigpen cipher

Letters become shapes cut from two tic-tac-toe grids and two Xs. Each letter is drawn as the lines around its box, and the letters in the second grid and second X get a dot. It looks like a real secret alphabet, which is most of the fun.

Example: A sits in the top-left box of the first grid, so it is written ⌟. E sits in the middle, so it is a full square.

Print the pigpen cipher key, which has every letter drawn out, or see the chart on the pigpen cipher page.

3. Morse code

Each letter is a pattern of short and long signals: dots and dashes on paper, or beeps, flashes and taps. Kids can send it with a flashlight across a dark yard or tap it on a wall, and that is what makes it stick.

Example: HELLO is .... . .-.. .-.. ---.

Print the Morse code chart, or let the Morse code translator play a message out loud and flash it. Older kids who want to read it by ear can try the Morse code trainer.

4. Keyword cipher

Write a secret word at the start of the alphabet, leave out any letter it repeats, then write the rest of the alphabet after it, skipping letters already used. Line that up under the normal A to Z and you have the key. Without the word, the key is hard to guess.

Example: with the keyword SPY, the key starts S P Y A B C, and HELLO becomes EBIIL.

Write the key out on the secret code worksheet, or use the keyword cipher translator.

5. Vigenère cipher, for older kids

A Caesar shift that changes with every letter. Each letter of a keyword says how far to shift: with KEY, the first letter moves 10, the second 4, the third 24, and then the pattern repeats. For three hundred years it was called the cipher nobody could break.

Example: HELLO with the keyword KEY is RIJVS.

Try it on the Vigenère cipher page.

6. Make up your own

After a few codes, kids want one of their own. Any rule works as long as the reader gets the key: numbers for letters, a scrambled alphabet, little drawings. They fill in the A to Z key on the secret code worksheet and write the message in the boxes underneath.

Example: with A=1, B=2 and so on, HELLO is 8 5 12 12 15.

A scrambled alphabet with no key is a fair challenge for another team, and the cryptogram solver helps them crack it.

Run a code hunt

A code hunt is a treasure hunt where every clue is in code, and each one decodes to the hiding place of the next. Plan on 30 to 45 minutes of play for five clues. Setting up is mostly printing and hiding five slips of paper.

What you need

• The four free printables: the Morse code chart, the pigpen key, the Caesar cipher wheel and the secret code worksheet. One set per team.
• A brad for each cipher wheel, scissors and pencils.
• Five slips of paper or envelopes, some tape, and a small prize.

The clues

These use hiding places most homes have. Swap in your own by typing them into the translators linked above.

1. Hand each team the Morse chart and this: ..- -. -.. . .-. / - .... . / -- .- - (UNDER THE MAT)
2. Under the mat: the word BOOKSHELF, drawn in pigpen from the key. (BOOKSHELF)
3. On the bookshelf: XQGHU BRXU SLOORZ and a note that says "shift 3". (UNDER YOUR PILLOW)
4. Under the pillow: PBEFKA REB YTORSFK and the keyword SPY. (BEHIND THE CURTAIN)
5. Behind the curtain: the prize, and a blank secret code worksheet so the team can write a code for you to crack.

Tips

• Teams of two or three work well. One decodes, one checks the key, one runs to the next spot.
• For younger kids, stop after the Caesar clue and put the prize under the pillow.
• For a big group, run two chains in a different order, so one team can't just follow another.

In a classroom or a troop meeting

The same clues work as stations around a room, with a team at each and a signal to rotate. Codes fit a lot of lessons. Caesar's cipher comes down to us from the Roman historian Suetonius, Freemasons used pigpen in the 1700s, and Morse code is a way into how the telegraph worked. Older students can crack a scrambled alphabet by counting which letters come up most, a first look at letter frequency.

The sheets are free to print and copy for a class or a meeting. For learning Morse by ear, there's a separate guide on how to learn Morse code.

Keep going on a phone

Covert Mail, our app, teaches these codes a few characters at a time, with famous real messages to unlock along the way. It is free on the App Store.

 Download on the App Store▶ Coming soon to Google Play