AI developer Carter Church from SentinelOne used the GPT-6 Astra model to decrypt a 217-year-old letter addressed to Marshal Auguste de Marmont. The document contains military intelligence regarding French and Austrian troop positions prior to the 1809 invasion.
The encrypted message consists of 24 lines of symbols. It was first published in a French military history journal in 1969 by J. Vilcoq but remained unsolved in historical cipher catalogs for decades. The model processed the scanned image in approximately six hours.
To decode the text, the AI integrated a partial key from historian Daniel Tant and utilized a simulated annealing algorithm to assign values to 155 unique characters. The decrypted content successfully completed a fragmented sentence found in Napoleon's 1865 memoirs.
Satoshi Tomokiyo, administrator of the Cryptiana historical resource, verified the findings and updated the cipher status to solved. Despite the breakthrough, the researcher noted that five characters still have alternative interpretations.
