Fable 5.1 cracked a 373-year-old cipher in 44 minutes

Fable 5.1 solved a cipher that outlasted cryptographers for 373 years, according to Vals AI.

Sir Thomas Urquhart published the two-line Cyphral Distich in 1653. Cryptographer Klaus Schmeh ranks it 28th on his list of 50 unsolved encrypted messages, a list built on centuries of failed frequency analysis and substitution attempts.

Fable took 176,000 tokens and 44 minutes, without any human interjections. The two lines, 32 numbers apiece, sit right after Urquhart's 32 Proquiritations. Each number points to a word position inside the matching proquiration, and the first letters of those words spell the plaintext.

The win was structural, not cryptographic. Centuries of codebreakers treated the distich as its own puzzle and never checked what sat on the page next to it, a numbered set of orations printed right above the code.

A model rereads the whole document instead of just the marked passage. A career cryptographer, ten reads in, stops seeing the page around the puzzle. The distich didn't need better math. It needed someone, or something, to look one page up.