Deciphering a 1593 cipher letter with GPT-6 Sol and Astra
The author recounts the process: GPT-6.1 Sol deciphered about 80% of the Frachetta letter before stalling, GPT-6 Astra completed the translation, and a custom app helped resolve symbols Astra struggled with.
A few technical notes on the ciphers and the deciphering process: - The key to the ciphers was already known (see below), but using it to translate the letters was complicated for a number of reasons. First, each symbol in the cipher corresponds to one of *two* letters (for example, the same symbol could be used for "A" or "N"). Desportes did not always leave spaces between words, which made the deciphering process particularly challenging. Second, Desportes wrote the letters in a hurry, and some of the symbols were not easy to interpret. Third, French spellings of a number of words have changed since 1593 (as you will be able to see when viewing the French versions of the letters). Fourth, a number of symbols (e.g., the signs for the Pope, "Navarre" (i.e., Henry IV) and words like "and") had to be inferred from context or taken from other deciphered letters. - Probably around 80% of the Frachetta letter was deciphered by GPT-6.1 Sol before it hit a wall. I then used GPT-6 Astra to complete the translation. There were a few symbols that Astra had trouble deciphering, and I had it make a custom app for me to help it decipher these symbols. In the end, the deciphering process wound up being a collaborative effort between me and the model! That said, GPT-6.1 Sol and GPT-6 Astra deciphered >95% of the symbols without any help from me. - The letters are listed as previously undeciphered here: https://github.com/dbourdeau/cyphersolver/blob/main/targets/sega1593/NOTES.md
I have used GPT-6 Astra to decipher two Catholic League letters from 1593, written by Thibault Desportes, the secretary to the Duke of Mayenne. To my knowledge, these letters have never been deciphered before. Desportes wrote these letters to Pope Clement VIII's nephew Pietro Aldobrandini (who was responsible for French affairs in Rome) and to Mayenne's agent in Rome, Girolamo Frachetta, just as Mayenne's war against the Protestant French king Henry IV was beginning to unravel. The letters were written 3 days before Henry converted to Catholicism in a bid to be recognized as the rightful ruler of France by the Pope and the French nobility. (You may have heard the expression "Paris is well worthy of a Mass", which Henry allegedly offered as the reason for his conversion.) In these letters, Desportes accuses the Pope of favoring Spanish interests over those of France and explains why a truce between the Catholic League (headed by Mayenne) and Henry IV would become inevitable following Henry IV's conversion. Some really interesting details: - Desportes names the exact price that Henry IV accepted to convert to Catholicism: 500,000 écus. - Just two months after these letters were written, Frachetta betrayed Mayenne by handing over Desportes' correspondence to the Spanish ambassador. These letters may explain why he did it: Desportes writes to Frachetta that Mayenne is unable to pay for Frachetta's services allegedly because funds for this payment had to come from a third party (a prelate) and "this is no time to take anything" from these funds. - The letter to Frachetta reads like a piece of detective fiction, with elaborate code words used for names of various parties in Rome involved in an anti-Spanish conspiracy ("our friend at the college", "the man of La Chesne", "our uncle"). You can view the ciphers, their translations to French, and the translation from French to English (with significant historical notes included) at: https://prinzai.com/desportes-1593/
