buttcrack. Cipher Wiki

ROT47

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

ROT47 — Caesar arithmetic over the 94 printable ASCII characters instead of 26 letters, so digits and punctuation rotate too.

Rotates printable ASCII (0x21-0x7e) by 47 places. Preserves case and digits.

A worked example§

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

MEET ME BY THE OLD CLOCK TOWER AT DAWN

Key: 47

produces the ciphertext

|tt% |t q* %wt ~{s r{~rz %~(t# p% sp(}

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§

Ninety-four keys. The catch is that a reading can be mostly punctuation and still look plausible to a letters-only scorer, which is why this solver checks letter density before believing one.

History and context§

A programmer's joke that outlived the joke, now standard in CTF puzzles where the payload is ASCII rather than prose.

See also§

Caesar (ROT-N) · ROT13 · Atbash · Affine · Reverse

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

Frequently asked questions§

How is the ROT47 broken?

Ninety-four keys. The catch is that a reading can be mostly punctuation and still look plausible to a letters-only scorer, which is why this solver checks letter density before believing one.

What key does the ROT47 use?

shift 0-93. There are 94 possible keys.

How much ciphertext do I need?

At least 4 characters for this solver to attempt it; short messages can be readable and still not be proof.

Can I break a ROT47 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: Shift and reciprocal 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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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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