Carter Church · AI Cipher Decryption

The Letter to Marmont

A write-up, published 18 September, of using GPT-6 Astra to decipher a 1,300-symbol homophonic cipher letter to General Marmont that had been listed as an unsolved historical cipher. Working from one low-resolution plate in a 1969 French army journal, the model spent about six hours transcribing the hand-drawn signs, telling pen variants apart and recovering the key by simulated annealing against French letter statistics. The post rebuilds the full 155-sign cipher table, gives French and English translations, redates the letter from 1807 to March 1809 and publishes verification scripts. According to the post, Satoshi Tomokiyo's Cryptiana catalogue now lists the cipher as solved. A personal blog rather than an institutional publication.