972Unsolved Historical Ciphers
Ж ɪ ≈ ɾ ρ N L Ж 8 ρ ʃ ɸ L ρ Π ʃ ɸ ϙ
m a l i s s i m o · s a t i s f a t o
ɪ ʃ Ȥ = a · ω P ∞ = e · 8 ϙ = o

Venice → Anne de Montmorency · homophonic substitution · 1529–1530

Guido Rangone to Anne de Montmorency, December 1529 and January 1530

Guido Rangone
fromGuido Rangone
Anne de Montmorency
toAnne de Montmorency

BnF Français 3070 f. 81 (DECODE R4249, catalogue item 181) and its sibling Français 3082 f. 42, with the eighteenth-century copies in Clairambault 331 and 330. Two short cipher passages in Italian letters, about fifty invented signs standing for Italian letters, several for each vowel; the key was recovered from the ciphertext alone.

Daniel Bourdeau · posted · updated

Method: key recovered from ciphertext-only · Extent: partial (88% of the cipher)

Summary. The catalogue card was DECODE R4249, a letter of “Guido Ramgone” from Venice, 10 January 1530, with seven lines of cipher and no decipherment. Tomokiyo had listed its Clairambault copy and a copy of a second Rangone letter (24 December 1529), in the same cipher, as having no decipherment; no key or decipherment was found on Lasry’s key list or in print. The Clairambault headings give the old Béthune volume numbers, and that led to the original of the second letter, Français 3082 f. 42, which DECODE does not have. The two passages together are 264 signs of 54 kinds. No key survives and none of the keys known for Italians in French service in these years uses these signs. So the key was recovered from the ciphertext alone: simulated annealing against a sixteenth-century Italian letter model, 40 long runs, until one reached the score of real Italian and produced “malissimo satisfato di lui”, “il signore Cesare” and “il Fregoso”. Hand corrections from the words and a check of every sign’s weight finished the key: 232 of 264 signs (88%) give sense. Both passages are about Cesare Fregoso, who had just married Rangone’s sister and whom Venice made governor of Verona that January, the “grande oferte” of the January letter. Four short runs of signs that occur only once stay open, because there is no more ciphertext.

01 The letters

Count Guido Rangone (1485–1539), a condottiere from Modena in French service, spent the winter of 1529–30 in Venice after the defeat at Landriano. He wrote to the Grand Master, Anne de Montmorency, in Italian, mostly in clear: news of the Peace of Bologna, the Duke of Urbino, the Turkish envoy, the Swiss and Grisons going home. Twice he switched to cipher.

Neither copy has a decipherment. Four other Rangone letters from Venice in 1529–30 (Français 3012 no. 44, 3013 no. 19, 3034 no. 18, 2980 no. 44) were checked and are in clear. The ciphered letter of Joachin de Vaux from Ferrara, March 1529, in Français 3012 uses a different sign set.

The cipher lines of Rangone's letter of 10 January 1530
Français 3070 f. 81r: the seven cipher lines of 10 January 1530, with the clear words “vida V. Ex. che tratti sono questi” in line 5. Image: Bibliothèque nationale de France, fr. 3070 f. 81r, via Gallica and DECODE R4249.

02 The cipher

A homophonic simple substitution without word division. Vowels have two to eight signs each (e: ω, P, ∞ and two stars; a: ɪ, ʃ, Ȥ; o: 8 and ϙ), consonants one to three (n: K, ᏕᏏ, ㅌ; l: ≈, ξ, ✡). One sign is a null: it stands inside the name Fre·goso. No code signs for names were found. This is the ordinary Italian design of the 1520s, with more homophones than the ciphers of Visconti or Bizozola from the same campaigns. The key is in rangone1530/key.json.

Three pairs of look-alike signs turned out to be different signs and had to be separated: a capital Θ (t) against the narrow θ (i), a “∋” with a leading dash (u) against the plain one (i), and two blotted stars.

03 The letter of 24 December 1529

The cipher lines of the letter of 24 December 1529
Français 3082 f. 42r: the cipher begins after “sua bona voluntade” (“il Fre·goso”) and resumes after “li giorni passati con spada et cappa”. Image: Bibliothèque nationale de France, fr. 3082 f. 42r, via Gallica (btv1b9060318p, view 65).

Clear text in roman, the decipherment in bold; [?] marks signs not deciphered.

… ancora che la recuperi per questa altra via, haura visto sua bona voluntade il Fregoso li giorni passati con spada et cappa tolse fare la cosa de [?]en; mai più [v]olse r[? ? ?]a le cose ben disposte in casa, e harà il f[?] da rovi[n]are; e ho una pratica di lei [che] mi dispiacerà. Qui ancora si trovarà l’Orator del Turco …

“… will have seen his good will. Fregoso, these past days, ‘with sword and cloak’, took it on himself to do the business of [?]; never again did he want [?] the things well arranged in the house, and he will have the [?] to ruin [?]; and I have a negotiation concerning her [or: Your Excellency] which will displease me.”

Fregoso had commanded Ravenna and Cervia for Venice since September 1528, the towns the clear sentence before the cipher is about. Con spada et cappa means in person and without ceremony. The word after “la cosa de” has one sign not deciphered. Fregoso’s old enterprise against Genoa would give de Gen[ova], cut short, and de ben fits as well.

04 The letter of 10 January 1530

Io vi scrissi ultimamente Ill.mo S.re uno certo caso acaduto mi et non li dissi più oltra per alhora; adesso lo dirò più brevemente che io potrò. Mons.r ’l fa instantia a [? ?] de venire al servicio loro, [? ?] le mie … malissimo satisfato di lui; ha mandato a dirlo al signore Cesare e farli grande oferte. Vida V. Ex. che tratti sono questi, essendo seguito la [?]icon[p]uorano a[t]tenderui. Hora lassamo andare questi mei particulari …

“My Lord, he urges [me?] to come into their service … is very ill satisfied with him; he has sent to tell it to Signor Cesare and to make him great offers. See, Your Excellency, what treatment this is, it having followed [?] …”

In January 1530 the Venetian Senate appointed Cesare Fregoso military governor of Verona with 2,500 ducats a year (Dizionario Biografico degli Italiani, “Fregoso, Cesare”). He had married Rangone’s sister Costanza that autumn. The cipher is Rangone’s complaint that the Republic was courting his brother-in-law while it treated him badly, the “certo caso” of his previous letter. In October 1530 the French in turn dismissed Rangone over his protests at a cut in his pension.

05 How the key was recovered

  1. Both originals and both copies were transcribed sign by sign (cipher.txt): 264 signs, flat top frequencies, so homophonic.
  2. Simulated annealing of the sign-to-letter map against the it-cinquecento five-gram model, with a letter-frequency penalty. Short runs gave pseudo-Italian and no two runs agreed. The clear text of the same letter scores −1.72 per five-gram, the runs −2.3. The search had failed; the model was adequate.
  3. An incremental annealer, 40 restarts of two million moves each. One restart reached −1.97 and gave real words and the name Fregoso. Every perturbed restart from that key went back to it.
  4. A sensitivity table: 35 signs are fixed by the text with margins of 6 to 85 log units; the others occur once or twice.
  5. Corrections from the words: б = h (ha mandato, e harà, ho una), the tailed sign = f (oferte), D = b (ben disposte), the null, and the three split pairs.
  6. Word-aware scoring of the remaining signs, singly and in pairs, under a spaced language model. No value won by more than noise, so they stay open.

06 What remains open

These are blocked by length: the two passages are all the known text in this cipher.

07 Sources

Transcription, key, solvers and notes: rangone1530/.