The Newshound

AI cracks Napoleon's 217-year-old secret military cipher in just six hours from a single scanned image

From the Newshound archive · first published 2 October 2026 · last updated 3 October 2026.

Napoleon Bonaparte, whose stepson Eugène wrote the enciphered 1809 dispatch, had its cipher key lost so completely that GPT-6 Astra needed six hours and 1,300 characters to reconstruct the message.
Napoleon Bonaparte, whose stepson Eugène wrote the enciphered 1809 dispatch, had its cipher key lost so completely that GPT-6 Astra needed six hours and 1,300 characters to reconstruct the message.

Carter Church, an AI engineer at cybersecurity firm SentinelOne, has deciphered a coded 1809 letter from Napoleon's stepson Eugène to General Auguste de Marmont — a cipher no cryptographer had cracked in over two centuries. Church used OpenAI's GPT-6 Astra, which transcribed 1,300 hand-drawn symbols, independently located a partial code table compiled by a historian, and cracked the remainder using a simulated-annealing solver. The letter turned out to be a pre-war military briefing detailing French and allied troop positions across Europe, urging Marmont not to be rattled by his isolated position in Dalmatia.

Church had never attempted to decode a cipher before, inspired by watching AI crack a 1941 German army Enigma message.

The decoded letter also fills a gap in Napoleon's own 1865 memoir, completing a sentence that broke off mid-word: Marmont mustn't be deterred by 'a gathering of rabble.'

The letter overstates available troops by 60,000 and wrongly claims 'the Russians are marching on Austria' — raising, one historian says, 'curious questions about Napoleon's mindset.'

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