AI-assisted reading proposed for Napoleonic cipher

Carter Church says he used OpenAI’s GPT6 Astra to produce a proposed decipherment of a coded letter addressed to French general Auguste de Marmont, a message that had remained unread for more than two centuries. Church, an AI engineer at cybersecurity company SentinelOne, said the work of transcribing and analyzing the cipher took about six hours. The reconstruction has not been confirmed by recovery of the original key, which is lost, and remains a proposed reading rather than an established plaintext. The letter’s coded section contains about 1,300 units made up of numbers, letters and invented signs. Church’s account, as reported, says GPT6 Astra helped transcribe the marks and test possible French readings against patterns in the text and earlier cryptographic work. A partial table reportedly supplied 33 known symbol values; the remaining signs required further analysis. The method included simulated annealing, a process for testing candidate solutions, alongside linguistic comparisons. In Church’s proposed reading, the message sets out the locations and strengths of French and allied forces, as well as Austrian deployments, on the eve of war between France and Austria.