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Polybius square

Each letter becomes two digits, its row and its column in a 5 by 5 square. I and J share a square.

Leave it empty for the classic square, or give a keyword to scramble it.

Result

The link opens a page that reads it. Without the key, your friend has to crack it. The message travels after the # in the link, which a browser never sends to our server.

Polybius square chart

Every letter, A to Z.

Where it comes from

The Greek historian Polybius described signaling letters with torches over two thousand years ago: one hand of torches for the row, the other for the column. The same square is the heart of tap code, and I and J share a cell.

A message worth knowing: Light the torches. Polybius's square was built to be signaled with torches from hill to hill.

Learn it by heart

This is the cipher desk from Covert Mail, our free app for learning codes. The app teaches Polybius square a few characters at a time, plans practice around the ones you miss, and keeps an archive of famous real messages to unlock. It is coming soon to the App Store and Google Play.

Coming soon to the App Store and Google Play

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