01 The letter
| Shelfmark | BnF Français 3758 · Louis XIII, 30 juin 1635 |
|---|---|
| Sender | Louis XIII |
| Recipient | Châtillon and Brézé |
| Date | 30 June 1635 |
| Language | French |
| Report status | 10/10 pages transcribed; 6/6 cipher pages deciphered in part |
| Ciphertext | 967 elements, 722 identified (74.7%). |
02 The key
53 mapped signs: 40 letter signs, 13 in nomenclature.
03 The decipherment
f117r
Quand vous m’escriprez quelque chose d’importance souvenez vous que ce soit en chiffre. Car sy la despesche du xviiᵉ fust tombée entre les mains des Ennemis, ilz eussent appris [?] et en eussent tiré ?duantage.
Translation. When you write something important to me, remember to put it in cipher. For if the dispatch of the seventeenth had fallen into the enemies’ hands, they would have learned [?] and gained an [?] advantage from it.
04 Plaintext and other sources
Where a decipherment or clear copy already existed, as George Lasry gives it:
- Plaintext in another folio of the same volume
- Actual historical plaintext copies appear in blank/facing-page areas: PDF128 right lower and PDF129 left for f115r; PDF131 left (f116v) copies selected f117r passages, including the Orange/route instructions and the warning about an intercepted dispatch.
05 Our check
This result is George Lasry’s. This project did not re-solve the cipher: it checked one sample against the Gallica image and recorded what it found.
- Batch B. Image checked: none (no Gallica link; fr. 3758 ark not resolvable offline, gallica.bnf.fr behind Cloudflare)
- Folio matches the report: unclear; cipher present: yes
- What we checked: his f117r crop: clear "quand vous mescriprez quelque chose dImportance souvenez vous que ce soit en chiffre" then 48(car) XX(y) 96(la) 61.. 54 du xvii(e) ... = "car sy la despesche du xviie" fits his codes at the start; rest not decodable from crop, many key values marked ?
- Verdict: partly confirmed (method key recovered based on adjacent plaintext, extent partial). The check is a sample, not a re-solution.
- Notes: 74.7% identified; key values heavily queried. Same volume as chatillon1635 (fr. 3758). Clear copies of some passages on facing pages.
06 Notes and corrections
Fr. 3758 is also part of targets/rohan1636.
07 Sources
- George Lasry, with ChatGPT Astra 6 and Anthropic Opus 5.5, BnF cipher research, 10 October 2026 (sent to Daniel Bourdeau on 13 October 2026 for publication here), p. 103; his other items are listed on his contributor card.
- The working folder:
targets/louis1635/(his entry as extracted from the report, our spot-check,profile.json).