buttcrack. Cipher Wiki

URL encoding

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

URL encoding — Percent escapes: %20 for a space.

Bytes as %XX hex escapes.

A worked example§

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

MEET ME BY THE OLD CLOCK TOWER AT DAWN

No key — the transformation is fixed.

produces the ciphertext

MEET%20ME%20BY%20THE%20OLD%20CLOCK%20TOWER%20AT%20DAWN

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§

Decode it.

History and context§

RFC 3986. It appears in puzzles because URL-encoded text still reads as English once the escapes are dropped, which fools naive detectors.

See also§

Base64 · Base32 · Hex / base16 · Base58 · ASCII85 / base85 · Binary ASCII

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

Frequently asked questions§

How is the URL encoding broken?

Decode it.

What key does the URL encoding use?

none. There are 1 possible keys.

How much ciphertext do I need?

At least 3 characters for this solver to attempt it; short messages can be readable and still not be proof.

Can I break a URL encoding 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: Encodings | 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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What this browser solver can—and cannot—do

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.

It does not: prove a decryption, cover every classical cipher, or break modern encryption such as AES or RSA. Its ranking model is tuned for English, so a high score is a lead to verify with the method, key, and source context—not a guarantee.

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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