44 ϝ 4 ʤ ⧺ ℓ ʒ ‡ π ӻ ⊥ φ k 6 Ƶ 80 ∫∫ 33 Ƒ d ξ s
y a n s m u e · i a u o i s d c s e i o u r n · 315 = the Béarnais

Burgos → France · homophonic letter cipher with nulls and code groups · 1592 · read, gaps marked

A. Pelissier to Pierre Jeannin, Burgos, 13 September 1592

BnF Français 3982 no. 22, ff. 46r–50r · nine pages, 377 cipher runs, about 18,400 signs · listed by Tomokiyo as “mostly in cipher, only partially deciphered” · the League’s agent at Philip II’s court, four months before the Estates of 1593

Tomokiyo’s key for Pelissier’s cipher fits. It was calibrated sign by sign on 1,764 signs of Pelissier’s October letters aligned with their clear decipherment, and the whole letter was then re-read with the split sign classes: 94 % of the ciphered words now read (90 % firmly), and every gap is listed

Daniel Bourdeau · solved

Summary. Pelissier was the Catholic League’s agent in Spain, and this is his long report of September 1592 to Pierre Jeannin, the duc de Mayenne’s councillor. The clear-text passages had been legible all along. The ciphered ones, most of the letter, carry the negotiation itself, and the letter survives with only a few scattered interlinear glosses by a contemporary decipherer. Satoshi Tomokiyo reconstructed Pelissier’s key from two later letters in the same volume that have a clean decipherment (nos. 45 and 46, 27 October 1592), but he did not read no. 22. His key reads it. What the cipher says: Philip grants Pelissier 500 ducats to stay and wait for news. Pelissier argues against holding the Estates now and for two armies in the field, one to push Henri IV back from the Seine to the Loire, the other to free Paris and Rouen, at about 300,000 écus a month. He reports what people in France were saying for recognising Navarre, and the suspicion that Philip wanted France kept divided. He warns that Mayenne’s authority is being undermined, and he is still waiting on the 50,000 écus the Idiáquez keep promising. A first reading got about half to two-thirds of the cipher. The residue was not in the key but in look-alike signs merged in transcription, so the key was then calibrated on Pelissier’s own October letters, 1,764 signs aligned with their clear decipherment, and every page re-read with the split sign classes. 94 % of the ciphered words now read, 90 % firmly; the 256 remaining gaps are single hard signs, holes in the paper and a few names, and they are marked as unread rather than guessed. Two new code groups are identified from context: 310, probably the Duke of Savoy, and 441, probably France.

01 The letter

BnF fr. 3982 is one of the Mémoires de la Ligue volumes (fr. 3974–3995), which gather League correspondence, much of it ciphered, from the 1580s and 1590s. No. 22 runs from f. 46r to f. 50r with the address on f. 50v: nine close-written pages, about fifty lines each, dated “A Burgos le xiij septembre 1592”, signed “Vre bien humble et obeissant serviteur Pelissier”, and marked Tripta (the third copy sent). Clear French and cipher alternate within the same lines, and the cipher is written with a small repertory of letter-like signs, figures and marks.

Head of BnF fr. 3982 f. 46r: five lines of clear French, then rows of cipher signs with small interlinear glosses
f. 46r: “Monsieur J’entreprins mon voyage de la court si a contre temps que arrivant a Valladolid ou le Roy avoit sejourné deulx moys…”, and then the first cipher. The small writing between the cipher rows is the contemporary decipherer’s. His glosses are few and scattered, and they are the letter’s whole “partial decipherment”.

02 The key

Tomokiyo’s League page reconstructs the cipher Pelissier used in nos. 45 and 46 (Madrid, 27 October 1592) from their clean decipherment on f. 115. It is a homophonic alphabet with one to seven signs per letter. Some signs are two-digit numbers (24, 26, 28, 30, 33, 36, 44, 56, 60, 80). There is a sign for et, signs for the doubled letters rr, ss and uu, and six nulls. His table is not reproduced here; it is on his page. No. 22 is six weeks older and on the same key, with two additions:

The decipherer’s glosses check the key wherever they are legible. They agree on de, auisa, meschans, roy, les tirer, Noyon, a la main qu, n’auoit, en atendant, quar la bataille, mais le retour, de crainte, langaiges, Valentia, a gens matez des and (qu’ay)ant pleu a Dieu, among others. One gloss disagrees in an instructive way. Over “nos forces” the glosser wrote os a orc: he applied the table’s ϝ = a literally where the sense needs f. The hand that deciphered this letter in 1592 was working from the same table, and it slipped on the same sign.

Calibration. Tomokiyo’s table gives each sign a letter; it does not say how to tell apart signs that look alike on a fast page, and that is where the first reading stalled. The two letters he built the key from were therefore aligned with their clear text on f. 115, sign by sign: 835 signs of no. 45 (f. 111r) and 929 of no. 46 (ff. 113r–v). That settles the look-alikes with known plaintext:

The October letters and no. 22 were written by the same hand six weeks apart, and the page readers found a few further habits in no. 22 alone: an alpha-shaped sign and a barred 5 for g, a small box-shaped ∐ for e, the tall double long-s for rr, and a looped ℓ that stands for u or e by context. The whole guide, with exemplar crops of every form, is pelissier1592/GLYPHS.md and cal/atlas/.

Five lines of f. 46v: cipher runs broken by clear French such as 'a l'arrivee du roy en ce dict lieu de Burgos'
f. 46v. Clear text (“a l’arrivee du Roy en ce dict lieu de Burgos Je retornay treuver le seigneur Don Joan, lequel m’ayant donné une heure particulliere”) runs straight into cipher. The cipher opens “i’exposay pour fondement de mon discours qu’il n’est rien plus requis en un estat que la conservation de la reputation”.

03 What it says

Deciphered words are in the reading as written, with the letter’s spelling. The page summaries below are in English. The full text, page by page, with gaps marked, is in pelissier1592/READING.md.

04 How it was read

  1. Transcription by sign. Each page was cut into third-width bands at 1.5× from the full-resolution Gallica scan. Every sign was written as a token (a name for its shape) and every clear passage in full. Seven parallel agents did ff. 47r–50r; ff. 46r–46v were done here and served as the worked example.
  2. A beam decoder, not a solver. Each token carries the letter the key gives it, plus cheap alternatives where two signs look alike. A beam search over a conditional quadgram model of period French picks the reading, and word breaks come out of the model.
  3. Second pass. For every row that did not decode to French, the signs were re-read at 2.5× and genuine misreadings were corrected on every page. A change was made only when the sign was visibly different on the leaf, never just because French would then appear. Each page’s reading lists the glosses and whether they agree.
  4. Calibration and third pass. The key’s own source letters were aligned with their clear text (section 02), the look-alike families were split into separate tokens, and every row of all nine pages was re-read against the scans with them. Unread words fell from 413 to 256 and doubtful ones from 278 to 158.

What went wrong, usefully. Twice, once per page and once over the whole letter, the sign-to-letter map was hill-climbed against the language model from the key as a start. Both times it drifted to the degenerate “every frequent sign is e” attractor, which a noisy transcription always rewards. The key was right. The errors were in the tokens, which had merged signs the key keeps apart:

That diagnosis was right, and the calibration in section 02 is the remedy: most of these splits are now tokens in their own right, confirmed on known plaintext.

05 What remains open

Everything is in the repository under pelissier1592/: the account in NOTES.md, the reading in READING.md and reading_46r.mdreading_50r.md, the token transcriptions t46r.txtt50r.txt, the decoder beam.py with cands.txt, the sign vocabulary in TOKENS.md, the calibrated guide in GLYPHS.md, and the alignments of nos. 45 and 46 with their exemplar crops in cal/.

06 Sources