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Quagmire III (keyed alphabet)

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

Quagmire III (keyed alphabet) — Vigenere arithmetic performed in a keyed alphabet's index space rather than A to Z, so the keyword and the alphabet are two separate secrets.

Vigenere over a keyed alphabet (KRYPTOS by default). Period from IC, columns by chi-squared in keyed space.

A worked example§

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

MEET ME BY THE OLD CLOCK TOWER AT DAWN

Key: key=PROVENANCE, alphabet=kryptos

produces the ciphertext

UFJKPTIUGZHSVSQDFYCIBXJWMWLKST

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§

Given the alphabet it is Vigenere in disguise. Not given it, the alphabet has to be searched too — and a solver that assumes A = 0 recovers nothing at all, because the per-column shift it finds is a shift of the wrong alphabet.

History and context§

The form used on the Kryptos sculpture at CIA headquarters, whose K1 and K2 panels use the keyed alphabet KRYPTOSABCDEFGHIJLMNQUVWXZ. This solver reproduces the published Paradigm Kryptos PK1 answer, keyword PROVENANCE, from ciphertext alone.

See also§

Vigenère · Beaufort · Variant Beaufort · Gronsfeld · Porta · Sum-clock (additive wheels)

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

Frequently asked questions§

How is the Quagmire III (keyed alphabet) broken?

Given the alphabet it is Vigenere in disguise. Not given it, the alphabet has to be searched too — and a solver that assumes A = 0 recovers nothing at all, because the per-column shift it finds is a shift of the wrong alphabet.

What key does the Quagmire III (keyed alphabet) use?

keyword + alphabet. The keyspace is unbounded in practice.

How much ciphertext do I need?

At least 40 characters for this solver to attempt it; short messages can be readable and still not be proof.

Can I break a Quagmire III (keyed alphabet) 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: Polyalphabetic ciphers | 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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