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.

Can You Find a Match from a List of Ciphers of Charles V?

Three ciphers used in letters to/from Charles V remain unsolved ("Unsolved Historical Ciphers"):

- Letter from Emperor Charles V (1521?): BnF Clair. 322, f.105v (Gallica)

- A Report to Charles V (1527?): BnF fr.3022, f.16 (Gallica)

- Marquis of Gasto to Charles V (1527). ff.26-28, 39, 40-43 (Gallica)

When I came to know 17 ciphers reconstructed by Olga Kolosova from letters to Charles V in 1521-1527 ("Scholarly Studies on Ciphers in the Reign of Emperor Charles V"), I was thrilled because the scope exactly matched these unsolved ciphers. But I couldn't find a mathing cipher among her reconstructions. It may well have been that the three ciphers are simply not among the 17 reconstructions, but I have to admit my search was not thorough. I simply looked for a couple of symbols in each cipher (e.g., "3" with an additional stroke below in BnF fr.3022, f.16; "s", "3", "v" with two additional lines in BnF fr.3022, f.26). Although this worked for Mary-Grange Cipher (1571) (see here), there's some chance that I simply overlooked this time. If someone finds a match, please let me know.

NB. BnF fr.3022 also includes other ciphers:
f.12 (no.5) Perez to Charles V, Rome, 24 September 1527 (the same cipher as in BnF Clair.326): George Lasry solved this. I also found it matched a cipher I reconstructed. The cipher corresponds to one of Kolosova's reconstructions (Ko.1).
f.16-f.17 (no.6) Report to Charles V, unsolved (see above).
f.20 (loose sheet) The same cipher as f.12.
f.26-28 (no.10) Marquese del Gasto to Charles V, Ysola, 27 September 1527, unsolved (see above).
f.39 Belong to the following?
f.40 Marquese del Gasto to Charles V, Rome, 6 November 1527, unsolved (see above).
f.44 Memoire in Italian, Madrid, 11 April 1528, unsolved (see here). The symbols with superscript figures look like those in Lu.6 (used by Andrea Doria and Charles V in 1537) reconstructed by Luo (2021) but the range of figures does not match at all.
f.48 Jargon in Italian (ibid.)
f.50 "Aditione del zifra" (ibid.)

Recent Studies on Ciphers in the Reign of Emperor Charles V

When working on some recent posts, I noticed there has been active research about ciphers in the time of Emperor Charles V in the past few years. I outlined them in a new article, "Scholarly Studies on Ciphers in the Reign of Emperor Charles V" with some observations from cryptographer's perspective.

Most of the many ciphers reconstructed by scholars from archival materials are not covered in my article, "Ciphers during the Reign of Emperor Charles V", while my article also has some not covered by their work. In a few cases where we work on the same cipher, independent reconstructions will supplement each other.

A Code of Count of Maurepas, Secretary of State of the Navy (1733)

I uploaded "A Code of Count of Maurepas, Secretary of State of the Navy (1733)", which is based on letters and reconstruction provided by Alexandre Pillon. He is a collector of ciphers and has kindly provided me with a lot of materials about ciphers of Louis XIV, delegates for peace negotiations, Torcy/Gualterio, and Georg Adam Starhemberg. 

 

A Power from Prince Philip Arrived in Cipher (1554)

Simon Renard mentioned yesterday was a familiar figure to me as the "bad guy" in Jane Grey's story I read as a child (Ainsworth's The Tower of London adapted for junior readers) or in a 1986 film "Lady Jane".

I mentioned some episodes related to him from CSP in "Ciphers during the Reign of Emperor Charles V". At one time, Renard was puzzled because he received a power from Prince Philip but it was in cipher.

While writing these letters I received a packet from his Highness dated November 12th. The courier was delayed 40 days at the port of Plaisance. I have no news of the other three who passed this way. His Highness's letters confer upon me full power to promise whatever is necessary for the marriage, but as they are in cipher, I do not see how I can use them. I will inform the Queen, however, the better to confirm her in her resolve.
(Renard to Charles V, 18 January 1554) (CSP Spain)

The Spanish ambassadors in England had been negotiating for the marriage with authorities from the Emperor, but the English required a power signed by Prince Philip himself because they wanted to be assured that the Prince would not repudiate the agreement to restrict his power in England.

I suppose the problem here was not about cryptography but that the original power in clear (rather than decipherment) should be presented to the English government.

Soon after this, the Emperor in Brussels signed the agreement and required the Prince in Spain to ratify it and return it with powers for the contraction of the marriage (CSP Spain).

Three Ciphers Used in Correspondence between Granvelle and Simon Renard

Antoine Perrenot de Granvelle, a trusted secretary of state of Emperor Charles V, and Simon Renard, ambassador to England, used three ciphers, according to Eva Pich-Ponce (2023a), "Les messages secrets d'Antoine Perrenot de Granvelle à Simon Renard : la question du mariage de Marie Tudor", Thélème 38(2) (DOI: https://doi.org/10.5209/thel.90555 ), a study of volumes of "Collection Granvelle" in the Besançon Municipal Library (esp. ms. 73). (Their letters per se are familiar to historians (e.g., CSP Spain). They are in French because both were from Burgundian families.)

The first cipher is the one used by Jean de Saint-Mauris as early as 1544, reported separately in Eva Pich-Ponce (2023b), "La cifra secreta de Carlos V y la subida al trono de María Tudor", C&eacyte;dille (DOI: ttps://doi.org/10.25145/j.cedille.2023.24.22 ). This particular cipher attracted attention by a discovery by Pierrot, Gaudry, Zimmermann, and Desenclos in 2022 and had also been reported in my article, "Ciphers during the Reign of Emperor Charles V".

It was used in more than 100 letters until 1554 by the Emperor, Saint Mauris, Simon Renard, the Bishop of Arras (Granvelle), Mary of Austria, the Bishop of Luxeuil, Francisco de los Cobos, and Ferdinand (brother of the Emperor). In particular, the Emperor used this in 1553 in his letters to ambassadors in England about the succession (Jane Grey, "Nine Days Queen", was on the throne in July 1553) and the marriage of Mary Tudor with his son Philip. Between Granvelle and Renard, this cipher was used from December 1553 to May 1554.

The second cipher was only used between Granvelle and Renard, in contrast with the wide usage of the first cipher. It was used in Granvelle's five letters from August to November 1553. This cipher is the focus of Pich-Ponce (2023a).

The third cipher was used from 1549 to 1554 by the Emperor, Mary of Austria, Nicolas Perrenot and Antoine Perrenot, and Renard (with a less wide distribution than the first cipher).

The second cipher is much simpler than the first. In particular, it lacks syllables as found in the first cipher. Moreover, the second cipher was only used sparingly. The longest passage in this cipher I spotted is "s-o-n i-n-c-l-i-n-a-c-i-o-n e-t c-o-n-t-e-n-t-e-m-e-n-t" (f.40). This is in contrast to the first cipher, wihch was used to encipher the substantial portion of the whole letters, apparently by a professional secretary. The third cipher (to be treated in Pich-Ponce's coming paper) seems to be closer to the first cipher both in structure and use.

Why did this second cipher have to be introduced, when the first and third ciphers were already available? It was not that the latter ciphers were obsolete or compromised, given that they continued in use after the span of the second cipher. Pich-Ponce considers it was because of the Emperor's desire for strict secrecy, without even letting his closest circle know the content (p.116-117). Her explanation of the historical situation (the Emperor had to be sure of Mary Tudor's inclination before formally broaching the subject of her marriage to Philip) is very interesting. But given the weak nature of the second cipher (both in structure and use), there might have been other factors. (I'd like to know in what situation the Emperor (or Mary of Austria on his behalf) directly wrote to Renard (by a secretary) and in what situation Granvelle wrote to him (personally?).)

The vocabulary of the nomenclature seems to indicate the cipher was prepared for the issue of Mary Tudor's marriage. 40 (étranger) and 45 (mariage) are used to express "mariage étranger" (foreign marriage), as opposed to marrying an Enlishman (such as Edward Courtenay, a great-grandson of Edward IV).

Her study revealed 1553 was a year when the lifespans of the three ciphers overlap. I look forward to her coming paper about the third cipher.

A Cipher Used by Margaret of Austria (1508) (Not Properly Scanned)

Speaking of Mary of Austria, the Governor of the Netherlands before her, Margaret of Austria, also used ciphers. I mentioned a very simple one in "Ciphers during the Reign of Emperor Charles V". Correspondence de Marguerite d'Autriche (Google) also records use of cipher in her correspondence. It has an appendix of cipher, but regrettably the fold-out is not properly scanned (in all the copies I found).

It should include:

N^o. I. Chiffre latin de l'empereur Maximilien et d'André de Burgo. V. les lettres N^o. 45 et 49.
N^o. II. Chiffre français de Jean de Courteville. V. les lettres N^o. 2, 10, 15, 16, 18.
N^o. III. Chiffre gueldrois de Jean van der Horst. V. la lettre N^o. 155.
N^o. IV. La lettre N^o. 155.

The cipher no. I should be the one used in the letter from Emperor Maximilian to Margaret dated 23 July 1508 (N^o. 49).

The transcription of IV allows reconstruction of the cipher III used by Jean van der Horst (who is considered to be an "officier" of Charles, Duke of Guelders.)

 

A Cipher Used by Mary of Austria (1546)

I mentioned ciphers used by Mary of Austria, Governor of the Netherlands and sister of Emperor Charles V, in "Ciphers during the Reign of Emperor Charles V" but have not seen an actual specimen. A cipher used in two letters from her to [Nicolas Perrenot de] Granvelle in 1546 is reconstructed in Francisco Javier Reales Pérez (2025), "Déchiffrer l'histoire : présentation et description d'un chiffre employé par Marie de Hongrie dans sa correspondance en langue française", Estudios Románicos, vol. 34, pp.159-177 (DOI: https://doi.org/10.6018/ER.614131 ).

The cipher has a homophonic substitution alphabet, symbols for double letters, nulls, syllables, and words. Syllables such as ba, be, bi, bo, bu are generally represented by some base symbol plus an indicator to distinguish the vowels. However, unlike the regular vowel indicators in Spanish ciphers under Philip II, the indicators are not regular. This is a characteristic (better than in the next reign!) also seen in other Spanish ciphers during the reign of Charles V (see my article quoted above).