A coded letter carrying a message from Napoleon Bonaparte to one of his senior generals has been cracked by AI after 217 years.
The contents of the letter, sent by Eugène, Napoleon’s stepson, on the emperor’s instructions, had remained a mystery since it was sent to Auguste de Marmont in 1809.
However, Carter Church, an AI engineer at cybersecurity company SentinelOne, said this week he had used OpenAI’s GPT-6 Astra system to decrypt and transcribe the message for the first time.
The letter contained details of French and Austrian troop movements on the eve of war between France and the Habsburg Empire.
The note contained 1,300 characters, some of which represented letters and other old words. The cipher to decrypt the message has been lost, meaning the letter’s contents have been unknown for more than two centuries.
GPT-6 Astra – an advanced version of the AI system that powers ChatGPT – spent six hours transcribing the characters and mapping them against work from cryptographers that had solved 33 of the characters.
It then decoded the message using a technique known as “simulated annealing”, a process of trial and error in which multiple candidate words are tried to see whether they fit, and compared them to Marmont’s existing writing.
While the process could have been done by hand, it would have been a laborious process that no cryptographer to date has accomplished.
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