AI engineer says GPT-6 Astra deciphered 1809 coded letter to General Marmont

Carter Church, an engineer at the cybersecurity firm SentinelOne, says he used OpenAI's GPT-6 Astra model to decipher a coded letter sent in 1809 to the French general Auguste de Marmont, which had gone unread for 217 years. 1 2 The letter was written by Napoleon's stepson Eugène, the Viceroy of Italy, on the emperor's orders. The Daily Mail says Napoleon asked Eugène on 16 March 1809 to send it to Marmont, whose troops were in Dalmatia, cut off by Austrian territory from every other French army. 1 2 The Daily Mail says the first line is in French and the next 24 lines are two-digit numbers, stray letters and invented symbols. GB News describes a 1,300-character note whose symbols stood for both individual letters and archaic words. Both say the key was lost. 2 1

Church said on X that Astra completed the whole multi-modal workflow in six hours from a single image and goal. In a blog post he said it cut the 1,202 by 1,836 plate into rows, read the signs and decided which of 175 hand-drawn marks were the same sign written twice before breaking the cipher. 2 GB News adds that the system started from earlier cryptographers' identification of 33 characters, then used a method called "simulated annealing" to test word candidates against Marmont's known writings. 1 The decoded text sets out the positions and strengths of French and allied forces, including Bavarian, Polish, Saxon and French corps, and tells Marmont that "Austria will be attacked at once on every side. She is consequently hastening toward her ruin." It also tells him not to be intimidated by "a few troops or a gathering of rabble" when the order to march comes. 2 1

GB News says the intelligence "proved vital", with Marmont's forces fighting their way out of Croatia to join Napoleon at the Battle of Wagram, after which Marmont was made a Marshal. The Daily Mail does not make this claim. 1 Church said the cipher itself is not difficult and cryptographers could have cracked it given time and energy. He said the hard part was the multi-disciplinary work of transcribing, cataloguing and translating, and that outsiders will increasingly shorten the backlog of niche unsolved problems. GB News instead stresses that no cryptographer had ever completed the task, though it was theoretically achievable by hand. 2 1 GB News says Church had no prior codebreaking experience and was inspired by another developer, Carter Leffen, who used the same tool to crack an unsolved 1941 Enigma message in about 10 hours. It also notes researchers' warnings that such capabilities could be used to identify anonymous internet users. 1

Both reports rely on Church's own account. Neither cites an independent historian or cryptographer verifying the transcription. 2 1