AI engineer Carter Church, an employee at SentinelOne, utilized the OpenAI GPT-6 Astra model to decrypt a military letter written by Napoleon Bonaparte in 1809. The document, which had remained unreadable for 217 years due to a lost codebook, was successfully deciphered in approximately 6 hours.
The letter, dated March 16, 1809, was addressed to Eugène de Beauharnais, the Viceroy of Italy, and intended for General Auguste de Marmont. It consists of one line of plain French followed by 24 lines of encrypted text containing 1,300 units and 155 distinct symbols, including letters and custom characters.
The AI model processed the scanned image by segmenting the document and identifying symbols. It employed simulated annealing algorithms and compared the text against historical French literature, including works by Alexandre Dumas and Victor Hugo, to validate potential letter and word combinations.
The decrypted content details French and allied military deployments in Bavaria, Poland, Saxony, and Italy, as well as movements of Russian forces. The information provides insights into Napoleon's strategic plans and the positioning of General Marmont, who was stationed in Dalmatia at the time.
To ensure accuracy, Church re-ran the analysis without historical references to Napoleon or Marmont, yielding identical results. The decryption has been officially recognized by Satoshi Tomokiyo, the maintainer of the historical cryptography database Cryptiana, which now lists the letter as solved.
