GPT-6 Astra Helps Decode a 217-Year-Old Napoleonic Cipher

Summary

GPT-6 Astra helped American AI engineer Carter Church decode an encrypted military briefing from 1809 in about six hours of model execution. The message originated at the headquarters of Eugène de Beauharnais and was sent to General Auguste de Marmont under Napoleon’s orders; it had remained unsolved on the historical cryptography site Cryptiana. Working from a low-resolution scan, Astra transcribed roughly 1,300 cipher units, analyzed 155 symbols, used previously identified mappings and plain-text clues, wrote a simulated-annealing solver, and evaluated candidate French text against 19th-century language corpora. The system also recognized that 29 symbols represented whole words rather than individual letters. The resulting plaintext describes troop strengths and positions involving Bavarian, Polish, Saxon and French forces, and broadly matches Napoleon’s March 16 orders to Eugène. Church’s historical dating places the briefing in late March 1809, shortly before Austria attacked. Cryptiana’s maintainer reviewed the solution, marked the entry solved and corrected its date, while Church published the transcription, cipher tables and reproduction programs. Five symbols remain ambiguous, but Church says they do not change the message’s meaning. The article notes important qualifications: the six-hour figure excludes later human work preparing and checking the materials; no new cryptographic principle was introduced; and one claim about Russian forces was apparently deliberate disinformation. The case is presented as evidence that AI can connect archival retrieval, image recognition, linguistic analysis, programming and verification into one workflow, while related AI-assisted Enigma and ADFGVX cases have received different levels of independent confirmation.