buttcrack. Cipher Wiki

Polybius square

From the Buttcrack Cipher Wiki — the free field guide to classical ciphers

Polybius square — A five-by-five grid turns each letter into a pair of coordinates, with I and J sharing a cell.

5x5 coordinate grid (I/J merged). Both digit pairs and tap-code style separators are accepted.

A worked example§

Encrypting a sample with the cipher itself, at build time:

MEET ME BY THE OLD CLOCK TOWER AT DAWN

Key: MONARCHY

produces the ciphertext

11 31 31 45 11 31 24 23 45 22 31 12 41 25 21 41 12 21 35 45 12 53 31 15 14 45 25 14 53 13

This example is generated by running the cipher when the page is built, and the round trip is checked, so it always matches what the solver does.

How it is broken§

Unkeyed, it is a decode. Keyed, it is a substitution cipher wearing coordinates, and falls to the same statistics.

History and context§

Polybius described the square in the second century BC as a way to signal letters with two groups of torches — telegraphy two millennia early. Every fractionating cipher since is built on it.

See also§

Morse code · Bacon cipher · Bacon (letter case) · A1Z26 (numbered alphabet) · Tap code · NATO phonetic alphabet

Browse every cipher in the Codes and alphabets family, read the history of codebreaking, or return to the wiki main page.

Frequently asked questions§

How is the Polybius square broken?

Unkeyed, it is a decode. Keyed, it is a substitution cipher wearing coordinates, and falls to the same statistics.

What key does the Polybius square use?

keyword (optional). There are 2 possible keys.

How much ciphertext do I need?

At least 6 characters for this solver to attempt it; short messages can be readable and still not be proof.

Can I break a Polybius square on this page?

Not with the browser build, which targets the common puzzle families. The desktop version searches it: see the Windows app page.

Categories: Codes and alphabets | Full-version ciphers | Cipher wiki
The facts in this article are generated from buttcrack's cipher registry when the site is built, so they describe the implementation you can run on this page. Registry-generated content is checked against the code; the history is editorial.

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It tries: Caesar, Atbash, ROT13, affine, Trithemius, rail fence, single-byte XOR, periodic Vigenère-family ciphers, autokey, selected encoding layers (such as Base64, hex, binary, decimal ASCII, Morse, and reverse), and—only with 60+ A–Z letters—statistical substitution.

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Short text, non-English plaintext, non-Latin or symbol alphabets, missing keys, and unsupported formats can all leave no high-confidence answer. When that happens, the result includes input-specific observations and suggested next checks; those observations are not a claim to know the exact cause.

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