Quagmire ciphers
The four Quagmire ciphers are Vigenère variants that use keyword-mixed alphabets. Quagmire I keys the plaintext alphabet, II keys the ciphertext alphabet, III keys both with the same keyword, and IV uses two different keywords. The indicator letter fixes how the key letters align with the plaintext alphabet. Kryptos K1 and K2 are Quagmire III with the keyword KRYPTOS.
Break Quagmire without the keywords
The solver tries nearly ten thousand English words as the alphabet keyword first, in all three single-keyword variants (I, II, and III) — with the alphabet fixed, each key position is a simple shift, so even short ciphertexts break in seconds when the keyword is a dictionary word. If no keyword fits, it falls back to the statistical attack: break the text as a general polyalphabetic cipher, check whether one shared mixed alphabet explains every key position — the mark of Quagmire III — and rewrite that alphabet into its keyword form, naming the period key. The fallback needs roughly two hundred letters per key position and can take a minute or two; everything runs in your browser. Quagmire IV comes out as the general polyalphabetic decryption, as on thepolyalphabetic solver page.
About the Quagmire ciphers
The four Quagmires are the American Cryptogram Association's names for periodic ciphers that combine a Vigenère-style repeating key with keyword-mixed alphabets. A keyword like KRYPTOS produces the alphabet KRYPTOSABCDEFGHIJLMNQUVWXZ; the variants differ in whether the plaintext side, the ciphertext side, or both use such an alphabet. The indicator letter records where the key letters line up, so the same keywords always produce the same cipher.
The best-known Quagmire in the world sits in a courtyard at CIA headquarters: the first two sections of the Kryptos sculpture are Quagmire III with alphabets keyed by KRYPTOS and keys PALIMPSEST and ABSCISSA. TheKryptos page tells the full story and decrypts K1 and K2 in this tool with one click.