Cipher Decoders

Paste the code, set the key, and watch a classical cipher come apart one step at a time.

These pages undo classical ciphers, the pen-and-paper kind from puzzle hunts, escape rooms and history lessons. Each decodes and encodes one cipher with its working on show, so a wrong key fails where you can see it.

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A book cipher swaps words for numbers that point into a text both sides own. A Vernam cipher adds a key one letter at a time, a trifid sends each letter through three squares, and a Jefferson cipher stacks lettered wheels. A scytale and a columnar transposition keep every letter and shuffle the order. The Caesar wheel prints on one sheet for a classroom. Under each tool is the table its cipher runs on. Keep real secrets out of all of them: most fall to a pencil and some patience, and a one-time pad only holds while its key is random, as long as the message, never reused and kept secret.

Ciphers that replace letters or words 4

The message is swapped for numbers or for other letters. Trifid is filed here although it also shuffles, because the swap comes first.

Ciphers that rearrange the letters 2

Every letter of the message is still there, only in the wrong order. Counting the letters is the first clue.

To print and cut out 1

Paper tools for a table or a classroom, with no screen needed once they are printed.

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