Codes, ciphers and secret writing for code-breakers ages 7 to 11

EnglishTwenty-five letters, hidden in plain sight.

School of Cipher: codes, ciphers and secret writing for kids

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Twenty-six ciphers, each with its own page: the animation, where it came from, puzzles, and sheets to print.

Zig-zag the letters down the rails, then read each rail on its own. Nothing is swapped for anything else.

Write the message into a grid, then collect the letters along a secret path: a plow path, a spiral, or straight up the columns.

Key Word Columns

A key word numbers the columns, and the columns come out in that order. Change the key word and the whole cipher changes.

Slide the whole alphabet along by a secret number. Julius Caesar used this one, and it takes a code-breaker about a minute.

The shift changes with every letter, so the same letter rarely looks the same twice. Much harder to break than a plain shift.

Key Word Alphabet

Build a scrambled alphabet out of a key word. Nothing to carry, nothing to lose, and you can rebuild it from memory.

Every letter becomes the shape of the pen it lives in. The page stops looking like writing at all.

Polybius Squares

Turn every letter into two numbers: which row, then which column. A message made of nothing but digits.

Lewis Carroll's Table

A square of 26 alphabets. The key word picks a different one for every letter, which is why it held for centuries.

Letters travel in pairs, so counting single letters tells a code-breaker almost nothing. It lasted into two world wars.

The alphabet backwards, so A becomes Z. No key at all, and scribes were using it thousands of years ago.

Every letter becomes five units of two kinds, which can then be hidden inside an ordinary sentence.

Route with Nulls

A grid where some letters are nonsense on purpose, so even the right path gives a code-breaker noise.

Numbers pointing at words in a book you both own. Nothing to break, because the key is on your shelf.

A fresh random shift for every letter, used once and destroyed. Unbreakable, and almost unusable.

Simple Substitution

Any letter for any letter, with no pattern at all. The strongest one-letter cipher there is, and the hardest to remember.

Shift by one more letter every time. No key word, and no letter ever looks the same twice.

On or off, eight times over, and that is a letter. Everything you have ever typed is this underneath.

The Polybius square sent by knocking on a wall. Nothing to write, and it goes straight through.

A square and a transposition stacked together, with five letters chosen because they sound nothing alike in morse.

Four grids at once, and pairs of letters read across them. Playfair without the awkward X.

Cut every letter into two numbers, mix the numbers with the neighbours, then put them back together.

Homophonic Substitution

Common letters get several symbols each, so counting them tells a code-breaker nothing.

One agreed word standing for a whole sentence. Nothing is scrambled, and there is nothing to break.

Half cipher, half codebook. Important words vanish entirely, and the rest is enciphered letter by letter.

More to read, print and do

The whole site on paper, free to print and photocopy. Fifty one pages of worksheets, templates and answers.

Nonsense on the BBC, poem codes on silk, and a captured agent's missing mistake.

Where to compete

Cipher clubs, free competitions and museums, in the United States and elsewhere.

Codes at the movies

Enigma, a decoder pin, the beacons of Gondor, and what films get wrong.