Mirabeau's Undecoded Letter (1787)

In addition to the Spanish decryption of a French cipher mentioned yesterday, Desenclos and Clinet (2025) presents their own decryption of a letter of Francis I to Christophe Richer, mbassador to Denmark (21 January 1547). The feat was achieved in February 2025 by Ioana Ionescu under the supervision of Paul Zimmermann and was completed and verified by Camille Desenclos with the key found in the archives (BnF NAF 8431, f.182). By comparing the ciphertext and plaintext, it can be seen that the cipher has homophones, double letters, nulls, and symbols for short words or titles ("que", "je", "faict", "et", "le roy de Danemarck", "Escossois", "le roy d'Angleterre", etc.).

They also present an undecoded letter of Mirabeau (the last image of the article). They give a date of 12 April 1787, but the cleartext seems to be "X. en reponse au n^o 3. le 12 aout". Anyway, if this is 1787, it is shortly after he came back in January 1587 from a stay in the Prussian court, where he had been sent on a mission by the Foreign Minister Vergennes. (His trip is recorded in Histoire secrete de la cour de Berlin (Internet Archive; translation: The Secret History oof the Court of Berlin (Internet Archive).)

The ciphertext is transcribed below:

549 1450 623 506 71 611 1296 61 57 1146 713 884 1017 878 556 655 846 703 991 984 791 806 1023 511 723 482 814 467 1090 1030 687 705 1151 426 934 1059 1002 99 1231 882 738 1199 1071

Mirabeau is said to have devised, during imprisonment when young, a cipher for representing a letter with two figures (LANAKI), but it would have been for personal use.

The short specimen above seems to be a full-fledged diplomatic code and has a number as high as 1450, which is higher than the size of typical French codes at the time (see my blogpost). It is wondered whether the code really had about 1500 entries (rather than using high numbers as nulls). If the above is all we've got, cryptanalysis would be impossible. But code numbers from the following page are faintly visible. If more pages (actually, it has to be many more pages) are available, it may be an interesting challenge for codebreakers.

Spanich Decryption of Claude Blatier's letter (1582)

One of many interesting pieces described in Desenclos and Clinet (2025) mentioned the other day is the Spanish decryption of a letter of Claude Blatier in Tournai to Henry III (23 October 1582). The arrangement of the decrypted key with borders is very similar to that in the decryption of the Duke of Anjou's cipher I quoted from BNE in "French ciphers during the Reigns of Charles IX and Henry III". Probably Blatier's cipher was also decrypted by the same Spanish codebreaker, Luis de la Cerda.

My article mentions a short ciphertext of a Claude Blatier du Belloy, a French agent in the Low Countries, with what seems to be the plaintext in the margin. I was hoping to establish the mapping between the cipher symbols and the plaintext, but the Spanish key does not seem to match. So this short specimen remains a riddle. (Some letters of S^r Blatier in the Low Countries (1584) in BnF fr.16127 (f.196 ff.) do not include cipher.)

Ciphers in the Archives of French Foreign Ministry

Desenclos and Clinet (2025) I mentioned yesterday not only provides many images but also the authors take care to cite primary sources to support their statements. Especially, materials from the archives of the Foreign Ministry are new to me.

Among others, I was excited to see the image of the original cipher for the French plenipotentiaries for the Treaty of Ryswick in 1697. It is the same as the cipher used by them in a first talk in Ryswick in 1694, of which I posted a reconstruction in "French Ciphers during the Reign of Louis XIV". (It will be seen that the reconstruction on my page needs some correction: the inflectional endings "ais" and "ait" should be "ois" and "oit" according to the convention at the time.)

Conversely, I posted the original cipher between Henry IV and the Landgrave of Hesse-Cassel in "French Ciphers during the Reign of Henry IV of France" but the specimen from BnF fr.15920, f.162 (Gallica) was not in my list.

These are only two of the many materials included in this article. It is a treasure trove for students of French historical ciphers.

Earliest French Ciphers (1507, 1513, 1521)

Introduction of ciphers in France was later than in Italy or Spain.

While absence of extant ciphertext does not mean there was no cipher, the pursuit of the earliest specimen is not without merit. As of 2018, the oldest specimen was from 1526. In 2023, I thought specimens from ca.1520-1521 might be the oldest (blog post; identified as Antoine Duprat's reports (1521) in Camille Desenclos and George Lasry, "Cryptanalytic and historical challenges with unidentified encrypted documents from the early modern era" (HistoCrypt 2025), 2.2).

But I now see a specimen from 1513 had already been reported in Camille Desenclos (2021), "Le premier essor de la cryptographie en France (1510-1630)" (HAL). It is a letter in cipher from Louis de Solliès to Florimond Robertet, dated 8 July 1513 (BnF Dupuy 261, f.121).

And now, an even earlier instance is given in Camille Desenclos and Sarah Clinet (2025), "Diplomatie et gestion du secret" (Bibliothèque diplomatique numérique (BDN)). It is Robert de Gramont to Georges d'Amboise (ca. 1507) (BnF fr.2930, f.189 (catalogue info)).

Heavy-Null Cipher Challenge

Inspired by Henry of Navarre's cipher posted the other day, I created a challenge cryptogram.

It is a monoalphabetic substitution cipher and the plaintext is English. The catch is that it includes a large number of nulls. I know once nulls are removed, modern computers would solve it in an instant. But I suppose trying every possible combination of 26 significant symbol numbers is not computationally feasible.

If someone succeeds in solving this, please let me know how this can be broken.

79 41 80 68 50 26 82 76 61 80 92 66 13 18 52 56 17 46 71 25 64 79 98 74 18 93 18 51 26 81 67 75 35 37 71 73 46 74 52 29 52 26 16 95 85 65 30 14 31 24 26 35 82 78 66 37 95 28 85 69 25 39 26 36 15 51 52 35 64 41 19 41 69 50 82 14 28 31 32 26 85 78 95 65 55 40 64 46 27 44 90 11 27 64 26 37 37 26 47 35 37 55 41 92 61 38 36 15 13 59 73 41 99 80 69 46 83 79 35 39 24 91 44 26 68 59 79 37 69 73 93 79 68 49 82 49 87 18 94 36 45 59 90 16 66 66 83 33 28 26 44 49 18 26 18 68 29 35 73 81 85 33 90 16 28 95 69 26 91 97 35 91 57 43 56 20 30 23 58 52 26 44 73 80 66 55 10 37 55 44 89 55 83 92 32 22 91 91 44 40 13 79 16 79 29 98 62 99 87 27 17 24 28 53 63 58 35 46 82 55 48 25 85 74 45 52 18 68 96 11 16 15 45 42 44 74 35 19 44 39 47 37 68 35 56 66 73 55 22 42 80 34 84 25 90 44 14 32 89 13 98 92 37 46 68 49 43 24 15 34 35 39 65 44 47 66 71 64 26 40 35 76 99 96 96 92 53 25 26 37 46 15 69 15 40 92 35 46 11 26 31 86 94 75 84 85 84 52 31 66 92 55 77 49 26 87 79 82 74 37 70 19 69 55 34 83 23 73 93 28 44 29 34 91 90 28 90 87 35 56 87 40 49 81 67 15 34 46 25 93 64 63 34 33 46 51 87 26 25 67 49 48 96 61 59 64 66 80 66 73 23 64 52 91 93 26 31 62 11 97 28 44 34 45 56 46 20 65 27 67 34 32 37 83 22 46 68 14 52 40 49 10 43 38 18 35 66 43 70 26 34 46 60 32 36 68 90 76 68 80 38 82 96 22 94 11 67 41 96 55 67 67 61 37 48 71 47 71 10 55 92 27 24 18 67 40 24 92 93 66 28 87 23 23 26 58 94 94 83 84 15 65 61 49 65 27 98 45 46 99 30 92 14 80 98 52 18 67 47 82 31 66 41 22 85 48 25 55 81 17 27 42 82 41 50 71 26 44 15 13 60 30 71 46 51 81 26 30 26 34 44 37 47 26 25 22 53 75 66 90 69 26 34 91 36 42 49 84 34 55 35 46 84 36 36 55 68 90 44 73 13 98 25

(To insert the null symbols, I used a Perl script generated by AI. Of course, I verified that the above can be decrypted correctly. Randomness based on the rand() function may not be ideal but I believe it served the purpose. On the other hand, when I first asked AI to create a random sequence, it failed my expectation.)

Heavy Use of Nulls in Henry of Navarre's Cipher (1586)

More than half of the symbols are nulls in a letter (1586) from Henry of Navarre, later Henry IV of France. I have observed several French cipher letters employing many nulls, but this is by far the heaviest use of nulls.

I uploaded a new article, "Heavy Use of Nulls in Henry of Navarre's Cipher (1586)" to report this. 

 

Ciphering Errors of Elizabeth Stuart, Queen of Bohemia

Elizabeth Stuart, Queen of Bohemia, tried a polyalphabetic cipher in her correspondence with Thomas Roe, as described in "Ciphers in Early Stuart England before the Civil War". It switches Caesar substitution tables between words or word fragments. The key in Arabic figure placed before the word (fragment) indicates the shift in the Caesar cipher (counting from the plaintext itself). Thus, when the key is 4, "a" is enciphered as "d".

This cipher is called "Key 1 Roe" in Nadine Akkerman (ed.), The Correspondence of Elizabeth Stuart, Queen of Bohemia, Volume II (2011), p.1062, according to which only the keys 4, 5, 6, and 7 were used (obviously because larger shifts would make the counting too cumbersome).

Nadine Akkerman and Pete Langman (2024), Spycraft: Tricks and Tools of the Dangerous Trade from Elizabeth I to the Restoration provides specific examples (p.388, n.134). A typical ciphertext is:

I have had newes from K.[Arundell] 50.[Emperor] 6nfzn.[hath] 4kmyhq4.[giuen-] 4lmp.[him] 5mnw[hir] last 4dkwzhu[agswer]

("K" and "50" are nomenclature elements.) 

This short specimen includes two enciphering errors: "hir" should be "his" and "agswer" should be "answer". The first error is a simple counting error, while the latter error arose because counting was in the opposite direction. That is, for the plaintext letter N, the fourth letter afterward, Q, should be the ciphertext letter, instead of which the ciphertext actually includes K, the fourth letter forward.

Similar errors due to opposite shifting were made when "electorat" was enciphered as "4bobz5yswey" (p.387, n.132). Here, E is incorrectly enciphered as B (instead of H) and C is incorrectly rendered Z (instead of F).

Akkerman and Lagman considers this kind of errors suggests use of a cipher wheel. That is, this can be readily explained as "reading the plaintext on the inner wheel and the ciphertext on the outer, that is, the 'wrong' way around". (You can see this by switching the plaintext and ciphertext lines in the above image.)

I think, however, counting in the opposite direction is more likely. The fact that only four shifts (4, 5, 6, 7) were used seems to show that Elizabeth did not have a table or a wheel at hand when working on the cipher. She was counting for enciphering each letter.

Sittler's Commercial Codebook Used for Dutch Diplomatic Service

In the age of telegraphy, commercial codebooks were occasionally adopted by governments. Slater's codebook was used in the U.S. and Canada and Bolton's was used in Japan (see "Nonsecret Code: An Overview of Early Telegraph Codes").

Sittler's codebook in French was used by the Dutch for many years, as I learned in Jip Boer, "Only Gentlemen Read Each Other's Mail: Over 50 Years of Sittler Codebooks in the Dutch Diplomatic Service" (HistoCrypt 2026).

The earliest record of its use by the Dutch government is from 1878. Since the codebooks came in many versions, larger consulates as in Constantinople had to keep many books. (p.147) Even before the First World War, there were reports that the code was compromised. (For example, Bazeries demonstrated its breaking, as I described in "How to Break a Code (Not a Cipher)").

But only partial improvements were made such as "adding nulls, reversing the code when written down, using multiple sets of paginations or adding a certain number to specific groups of numbers based on a chosen lawbook or day of the year" (p.147).

The "nonchalance" about security risk was not due to incompetence but because they were not much concerned about their communications being read by foreign governments. Their aim was to avoid the prying eyes of subordinate officials and telegraph personnel regarded as less trustworthy. (p.147-150)

In July 1915, an additional security measure involving superencipherment (initially called cijferstammen (cipherstems)) was introduced for "secret" communication. (p.149, Figure 2) Later, an updated system cijferstaten (cipher tables) was introduced (p.150-151, Figure 3). In 1920, each page was given an additional page number written in black pencil unique to each book, besides regular page numbers in blue pencil. (p.151)

Early in the 1920s, a new mode of using the Sittler codebook, called "Babibo-code", was introduced, whereby, apparently, code numbers were transformed into letter bigrams (p.153).

It was only in 1931 that the Sittler codebook started to be phased out by new Dutch-language codebooks (p.153-154).

 

What Happened to Code when France was Occupied by Nazi Germany?

What happens to secret codes when a nation comes under control of another? I once mentioned Stephan (2022) about German Reunification in 1990. Now I learned about France under control of Nazi Germany in André Falut, "Encrypted official telegrams of the Vichy government" (HistoCrypt 2026).

A victory of Germany early in WWII led to an armistice in June 1940, whereby a major part of France was occupied by Germany. A French government in Vichy was allowed to govern the Zone libre south to the demarcation line.

In wireless telegraphy (télégraphie sans fil, "TSF"), the French officials were required to use encryption methods that the German authorities can decrypt. Telegrams sent via cable were not subject to this condition, unless they crossed the demarcation line (p.156).

In July, a copy of Code des Colonies (and later, keys used with the code) were handed over. When the German authorities could not decrypt a transmission, the French had to provide the decryption with an explanation on the encryption method. (p.157)

Occasionally, it was still desired to use an undisclosed code. At one time, a telegram from Rabat (Morocco) to Dakar (Senegal) was to be sent by the Casablanca-Dakar cable but an interruption made it ncessary to send it wirelessly. Since French stations were not allowed, it was sent via Berne and Ongar (England). (p.157) Some extant telegrams bear a note to make sure to send them via cable. (p.158)

The request from the French to allow undisclosed methods in diplomatic transmissions seems to have been granted by October 1940, but a similar request for Vichy officials in their trips to Paris seems to have been rejected in April 1941. (p.157)

The semblance of independence of the Vichy government came to an end in November 1942, when the Germans invaded the south following the Allie's invasion of French North Africa. After this, the number of Vichy officials receiving encrypted telegrams was significantly reduced. (p.159)

 

Issues with Recent "Solution" of Zodiac Z13

Of the Zodiac ciphers, Z13 (thirteen characters long) is considered too short for cryptanalysis. Late last year, however, Alex Baber not only came up with a solution but got endorsement from three ex-NSA officers. I read the experts' analysis, "Zodiac Z13 Decryption" (somehow, this page ends in an out-of-memory error on my PC), and liked their fairness in admitting the proposed reading may be "one of many possible solutions" and there may be many other possibilities for the substitution/permutation keys. From such an attitude, it is hard to understand how they can say the solution is "compelling". They appear to have been convinced because they found the proposed transposition can be derived by using a relevant name as a key. But such a key may also be one of many possibilities, as pointed out in David Oranchak's recent video.

Now I uploaded an article to discuss issues with the solution for Japanese readers, "ゾディアックZ13の「解読」は本物か".

 

A Pigpen Cipher of Philip II's Agent (1577)

Martin de Acuña, an agent for Philip II, used a pigpen cipher in his letters to Philip II. The following is my reconstruction from the letter dated 27 January 1577, written on his way to Constantinople. (One can see the letters of the alphabet are arranged alphabetically among the three tables.)

 I learned this in Blog el Salón de Cris. Its source is:

Javier Marcos (2013-2014), "Sombras de Martín de Acuña 2: La Misión secreta de Martín de Acuña en el invierno de 1577, narrada por el mismo durante el viaje" (Archivo de la Fontera)

The paper notes one undeciphered passages in a letter from Mondéjar to Antonio Pérez dated 17 January 1577, reporting his doubts about Acuña's mission. If the same pigpen cipher is used, it will be readily deciphered with the above.

 For contemporary Spanish ciphers, see "Spanish Ciphers during the Reign of Philip II".

A Match Wanted for Another Cipher to Emperor Charles V

I added a mention of a letter from Hugo de Moncada, Viceroy of Naples to Emperor Charles V, dated 6 October 1524 (BNE, see Carta 9) in "Scholarly Studies on Ciphers in the Reign of Emperor Charles V". The marginal note in later hand indicates "Decifrada en ...," but I have not been able to locate the decipherment. If someone finds the deciphered text or a matching cipher or solves this, please let me know. 

 

Undecoded Armstrong's Letter (1808) Sent to Madison by Mistake

Further to the call for help to decode a letter from John Armstrong (20 February 1808) for Madison Papers in a post last year, I made two updates in "An Outlier Code in Armstrong-Madison Correspondence (1808)" (marked "June 2026").

(1) The editors of Madison Papers found evidence suggesting that the letter was not intended for Madison. It is then no wonder that this could not be read with Madison's known ciphers or other State Department ciphers. I wonder whether Armstrong used any ciphers other than the known one with Madison, perhaps a private cipher with the ambassador in England or Spain that was not stored in the State Department office.

Even if the letter is not meant for Madison, the editorial team is still very interested in the content of the letter. If it can be solved in the next year or two, they could probably include it in their next volume of Madison Papers.

(2) This letter is interesting in that it consists of not only numerical codes but also what seems to be shorthand. In this regard, my original article only mentioned Taylor's shorthand did not match. Now I added names of other shorthands known at the time. (I thank Norbert Biermann for the info.) If the code is too tough, hopefully, the shorthand portion may provide a clue.

Yet More Ciphers from Emperor Charles V's Time

I noticed many ciphertexts from Emperor Charles V's time were recently uploaded in the DECODE database. I added a section for them in "Scholarly Studies on Ciphers in the Reign of Emperor Charles V". While most turned out to be the same as ones studied by scholars and/or by me, three were new to me:
- A simple cipher between Cardinal Cisneros and Diego Lopez de Ayala, his envoy (1516);
- A syllabic cipher between the Marquis of Mantua and Antonio Leyva (1529). Interestingly, on the same day the Marquis used this in a letter to Antonio de Leyva, he used another syllabic cipher from 1527 in a letter to the Emperor.
- Juan Manrique's letter to the Emperor (1555) is marked "Decrypted" in DECODE, but I have not been able to identify the matching plaintext. If anyone has some success, please let me know!

A French Diplomatic Code from 1748

It was only two months ago that I presented a French code based on materials from Alexandre Pillon. Now he provided me with a copy of a French foreign minister's letter (1748) he has along with his analysis. It is described in the new artice, "A French Diplomatic Code (1748)". 

 

Full Decipherment of Pedro de Ayala's Letter to Ferdinand and Isabella (1498)

Three historians have achieved complete transcription and decipherment (as well as full translation into English) of a partially enciphered letter from Pedro de Ayala to Ferdinand and Isabella dated 25 July 1498. (I thank George Lasry for bringing a report in French by Korben to my attention. Its source is Medievalists.net in English.)
The paper was published on 16 March 2026:
Adrian William Jaime, Valeria Tapia Cruz, Mairi Cowan (2026), "Tudor England and Stewart Scotland Through Spanish Eyes: A Complete Transcription and Translation of Pedro de Ayala's Letter of 1498 to King Ferdinand of Castile and Queen Isabella of Aragon", DOI: https://doi.org/10.1111/rest.70019 (an online version before inclusion in an issue of Journal of the Society for Renaissance Studies).
The original letter in the archives (PTR,LEG,52,166 f.857) is available at PARES.

The letter itself has been known to historians by a calendar by Bergenroth (Google, p.168) and also by Almazán's summary "currently archived together with the original manuscript". (Quotations are from the paper. See several paragraphs from n.74.)
Bergenroth deciphered passages in cipher and his key is in PRO31/11/11 in three versions ("Correspondence with Pedro de Ayala and Don Martin", "Cifra de Don Pedro de Ayala", "1498 Pedro de Ayala"; see "Bergenroth's Papers on Spanish Ciphers in PRO 31/11/11"). However, it has been pointed out that "his edition contains mistakes, and much of the English version printed in the Calendar of State Papers is more a paraphrase than a direct translation" and there have been works for a more accurate edition for parts of the letter. The authors' key "builds off the work of Luis A. Robles Macías ["Transcripción revisada del informe de Pedro de Ayala de 1498"], adding new symbols based upon how Almazán deciphers the letter in his summary." 

 

Extending the Key of Barbeu-Dubourg's Passage Cipher with Franklin

Barbeu-Dubourg is known for translating Benjamin Franklin's work into French.

In his letter written from 10 June to 2 July 1776, he sent Franklin a cipher. It was a passage cipher whereby each letter of a key text is assigned sequential numbers. A similar scheme had been used between Franklin and Charles William Frederick Dumas.

The letter is in PCC (Papers of Continental Congress), (roll number?) p.70 and printed in Papers of Benjamin Franklin, vol.22, p.453-470.

The short specimen allows partial reconstruction of the original key text.

Such Barbeu-Dubourg's passage cipher is described in Weber (1979), United States Diplomatic Codes and Ciphers 1775-1938 and my article, "Benjamin Franklin's Codes and Ciphers" (2009). Actually, more is known from:

Leighton, A.C., Matyas, S.M. (1985). The History of Book Ciphers. In: Blakley, G.R., Chaum, D. (eds) Advances in Cryptology. CRYPTO 1984. Lecture Notes in Computer Science, vol 196. Springer, Berlin, Heidelberg. https://doi.org/10.1007/3-540-39568-7_11 p.105.

The example given by Barbeu-Dubourg is:

3,2,Β,19,5,23,16,12,γι,44,53,δ,10,51,4,61,θ,36,17,6,24,71,1,λ,42,28,37,33,μ,82,54,11,9,8,47,59,88,13,69,ξι,31,92,π,72,34,56,73,σ,6,94,4,20,φ,40,100,68,48,ψω

(The Greek letters are word breaks.)

The latter half of the example is left without decipherment. This kind of cipher cannot be deciphered without finding out the key text, but Leighton succeeded in extending the key text with the assistance of Dr. Eric Gans, who thought of extending the plaintext "Ma femme et deux filles vous" with "embrassent de tout leur etre".

3 2 * 19 5 23 16 12 * 44 53 * 10 51 4 61 * 36 17 6 24 71 1 * 42 28 37 33 * 
m a    f e  m  m  e    e  t    d  e u  x    f  i l  l  e s    v  o  u  s   

82 54 11 9 8 47 59 88 13 69 * 31 92 * 72 34 56 73 * 6 94 4 20 * 40 100 68 48
 e  m  b r a  s  s  a  n  t    d  e    t  o  u  t   l  e u  r    e   t  r  e

It is remarkable that there are few repetitions. The mere two instances of consistent assignment 4=u and 6=l are hardly enough to justify the extension. But when these figures are sorted, a meaningful key text emerges.

(In the above image, highlighted cells are from the extension.)

It will be reasonable to read the beginning (SAMUEL_ARDBEN__MI_FR__ML__) as "Samuel Ward Benjamin Franklin" (M toward the last is an error for K). (Samuel Ward was a member of the Secret Committee of the Continental Congress (Rhode Island Historical Society, One Eternal Day (by Standfast)), of which Franklin was among the original members.)

The occurrence of these names hardly seem to be a coincidence and thus makes the extension plausible (at least for the part involved in these names).

It will be seen there are higher numbers yet unaccounted for. If someone can think of some plausible text to fill the gaps, I'd like to know, though it will be more difficult because known figures are sparse.

The following revisits Leighton's extension. Absence of highlight for "de tout" and "etre" indicates these may be altered without affecting the above discovery.

A British Book Cipher during the American Revolutionary War

During the American Revolutionary war, a book cipher was used between Frederick Haldimand, Governor in Quebec, and Sir Henry Clinton, Commander-in-Chief in New York. It is described in a new article, "Haldimand-Clinton Book Cipher (1778-1782)".

It appears that the book cipher was also applied in letters from Lord Germain. It is wondered whether ciphers had not been used in trans-Atlantic communication. British ciphers during the Revolutionary War are also outlined.

An Essay on Spanish Ciphers by 19th Century Archivist at Simancas

AGS (Archivo General de Simancas) Est. Leg. 1.1.1 is a collection of 238 ciphers from various times. Regrettably, these ciphers are not organized or properly labelled, as I hear.

The other day, I learned in Pich-Ponce (2024) (see here for citation) that Claudio Pérez y Gredilla compiled ciphers in AGS in "El Libro de cifras" (AGS D/203). According to Otto Vervaart's blog, it is an unpublished manuscript and deals with about 200 ciphers. (I guess AGS Est. Leg. 1.1.1 is its major scope.)

Perhaps Benavent (2025) refers to the same manuscript by "El estudio de la claves" written by Claudio Pérez y Gredilla, an official of the archives. She tells this essay was even favourably reviewed for publication by Antonio Rodríguez Villa in Boletín de la Real Academia de la Historia.

A list of Rodriguez Villa's papers at Biblioteca Virtual includes the review:

Rodríguez Villa, "Cifra diplomática", Boletín de la Real Academia de la Historia, tomo 24 (1894), p.108-109 (bibliography, text). (It shows that Claudio Pérez y Gredilla was head of AGS and the title given by Benavent is correct.)

Benavent says it is not certain whether Claudio Pérez y Gredilla's essay was ever printed. Given that it is at least not easily accessible now, I hope someone publishes its edition somewhere. (For example, Cryptologia accepts "From the Archives" pieces.)

Two More Ciphers of Emperor Charles V in 1527 Identified

When I called for a match for unsolved Charles V's ciphers in a collection of ciphers from 1521-1527, George Lasry immediately responded with solutions produced by his solver. I now added a section for these in an article for his achievements. As it turned out, I already posted his solution to one back in 2023 but I was not aware of it in writing the last blogpost. (The solutions still require attention of someone versed in Spanish.)

This adds two more ciphers to the collection of Charles V's ciphers from 1521-1527 in Kolosova (2017) I introduced here.

It is interesting that the Marquis of Gasto (Guasto, Vasto) used different ciphers in writing to the Emperor in September and November 1527.