❯ An engineer uses GPT-6 Astra to break a Napoleonic-era cipher letter in six hours, and a 217-year-old puzzle is marked solved

An 1809 order read in six hoursCarter Church, an AI engineer at SentinelOne, used GPT-6 Astra to decipher, in about six hours starting from a single scanned image, a cipher letter written in March 1809 to French General Auguste de Marmont. CTech and Euronews reported the work, and he has published his transcription and scripts for others to verify.

155 signs, only 33 known beforeApart from one line of ordinary French, the letter consists of 24 rows of numbers, letters and invented symbols, about 1,300 cipher units and 155 distinct signs, of which researchers had previously identified only 33. It contains a military briefing ordered by Napoleon: the positions of French forces and Bavarian, Polish and other allied troops, written about two weeks before Austria attacked Bavaria in April.

How the model did itGPT-6 Astra first cut the scan into rows, read the handwritten signs and judged which were the same sign. It then used simulated annealing, a large-scale trial-and-error search, to match the remaining signs to letters and words, checking the output against French text by authors such as Dumas and Hugo. Church also reran the analysis with Napoleonic references excluded to confirm the model was not reciting. Satoshi Tomokiyo, who maintains the Cryptiana site of unsolved historical ciphers, has marked it solved.

A Vatican manuscript fell tooThis is not a one-off. A report in May said the Borg cipher, a 408-page manuscript in the Vatican library that had gone unread for more than 400 years, was solved with AI in 29 minutes by the Descrypt project, whose team includes Stockholm University professor Beáta Megyesi. It turned out to be a collection of old medical recipes. By contrast, a three-page cipher letter from Holy Roman Emperor Charles V had taken six months to break by hand. The project’s AI still relies on expert corrections to improve.

▪ SIGNALGeneral-purpose models have turned breaking old ciphers from a craft of a few specialists into something any patient person can attempt, so what history will run short of is verifiers, not solvers.