Claude Fable 5.1 has solved the Cyphral Distich, a cryptogram that remained unsolved for centuries despite appearing in historical cipher literature and being listed among cryptography researcher Klaus Schmeh’s Top 50 unsolved encrypted messages.
The cipher, published at the end of Urquhart’s Logopandecteision, consists of two lines of 32 numbers each. Historical attempts to decipher it employed standard cryptographic methods including frequency analysis, substitution, and homophonic substitution, but all failed. According to the source, these attempts were missing a crucial insight.
Fable 5.1 arrived at the solution after 44 minutes and 176,000 tokens of analysis. The model identified two key clues. First, the cipher appears immediately after Urquhart’s 32 Proquiritations, a section Urquhart emphasized by stating “there can no number like that of two and thirty … be pitched upon.” Second, the accompanying poem promises that readers will find in it “his own heart’s wishes, and the Author’s minde,” with the Proquiritations repeatedly concluding with phrases like “is the desire,” “wish,” or “hope of.”
The decryption rule was simple: for each number in a cipher line, locate the corresponding Proquiritation, use the number as a word index within that section, and take the first letter of that word. This revealed the plaintext: “O GOD UPHOLD KING CHARLS THE SECOND AND / MAKE HIM THE SUPREME RULER OF THIS LAND.”
The solution is self-verifying. Each line contains exactly 32 letters and forms a rhyming distich, consistent with the promised format. The content—a prayer for Charles II—aligns with Urquhart’s known Royalist politics.
Using the same methodology, Fable 5.1 also deciphered the Cyphral Octastich, a much larger cryptogram from Urquhart’s The Jewel (1652) containing 285 numbers. The book has exactly 284 numbered pages, and the k-th number keys to page k, with the word index pointing to text on that page. The decoded message forms an eight-line prayer in ottava rima meter, written in London in March 1652, with all but nine letters successfully recovered.
Key facts
- The Cyphral Distich remained unsolved for approximately 370 years, appearing in Notes and Queries in 1899 and listed among Top 50 unsolved ciphers
- Previous attempts used frequency analysis, substitution, and homophonic substitution methods
- The cipher key was not external but embedded in Urquhart’s text—each number indexed a word in the Proquiritations
- Fable 5.1 solved it in 44 minutes using 176,000 tokens
- The solution revealed a royalist prayer for King Charles II
- The AI also deciphered the larger Cyphral Octastich from The Jewel (1652)