Back in 2018, I wrote "The Gronsfeld Cipher before Count Gronsfeld". The cipher was for for Silvio Calandra (c.1540-1590), ambassador of the Duke of Mantua involved in diplomatic missions with Savoy and Milan in 1560s-1570s.
Now, I noticed a second instance for "Andreasi". Although the specific date is not known, it seems significant that this is again associated with Mantua.
See a new section "Gronsfeld Cipher" in "Italian Cryptography (Stub)".
Gabriel de Lavinde's collection of ciphers (1379) preserved in the Vatican archives is well-known as early specimens of Western cryptography. I was inspired by Daniel Bourdeau's writing about a cipher of Avignon pope Benedict XIII to re-read the relevant section in Meister (1906) and learned Gabriel de Lavinde was affiliated with the antipope Clement VII in Avignon.
A natural question in discussing this topic is whether it formed the basis of later papal ciphers and whether it had anything to do with the pope's ciphers at Vatican at the time. Meister (1906) tells us that the papal ciphers in Avignon were more advanced than the primitive ciphers at Vatican but ceased to be used with the end of the Avignon papacy.
See my new article, "Papal Ciphers during the Western Schisma".
For a change, it's about modern cryptography.
AI not only breaks or otherwise deciphers historical ciphers. Recently, Anthropic's Claude identified the origin of parameters used in elliptic curve cryptography. This does not mean the widely used encryption scheme is compromised. To the contrary, it alleviates the concern that the system parameters might have been intentionally chosen to provide a backdoor for the NSA.
First, I thought of reporting this in a few lines, but while reading the announcement, I felt like adding some basics for people (like me) not versed in computing/programming.
See my new article, "Anthropic's Claude Identifies Origin of Seed for Elliptic Curve Encryption".
I uploaded a new article, "Italian Cryptography (Stub)".
This is like a note of references that I should read but in collecting these from my memo, I realized how homophonic substitution was already common early in the fifteenth century. And it is impressive that a 1424 Milanese cipher already had representation of syllables.
I uploaded a new article, "A Numerical Cipher of the Imperial Japanese Army (1902-1904)", which describes one numerical cipher of the Imperial Japanese Army in the Meiji Era reconstructed by Harumi-Matsuba.
The relevant materials were found in JACAR (Japan Center for Asian Historical Records). Although I worked on this database more than ten years ago, I didn't notice this. Come to think of it, I think my scope then was limited to what were found with the search term 暗号 (code/cipher), which already returned quite a few hits.
As noted yesterday, recent studies found a substantial collection of cipher materials related to Sun Yat-sen that escaped my notice. Hopefully, there will be a lot more to be found about Japanese (and Chinese) ciphers from this database.
The other day, I reported Daniel Bourdeau solved and deciphered many telegrams related to Sun Yat-sen. Now Brice Dudout are discovering more keys and deciphering many more telegrams. Among them, there are three indicated with "X密", which scramble codebook digits rather than converting them into Roman letters.
For two of them, Dudout identified scrambling formulae combining subtraction/addition with table mapping. I now suggest they can be reformulated as simple renumbering of pages/columns/rows in the mingmi style codebook as in the case of the third. I described this in a new section, "Mingmi (明密) Format Code: Gongmi (共密), Rongmi (容密), Chenmi (辰密)", here.
I uploaded a new article, "An Imperial Cipher from 1496?".
This is about a cipher recently identified independently by Daniel Bourdeau and George Lasry. Lasry dated it to 1496, to which Bourdeau concurs. If this is indeed from 1496, this may be related to the beginning of use of symbol ciphers by the Habsburgs.
My article concludes with two desiderata. First, crucial evidence of the dating seems to be G. A. Pecci (1755), but I could not see the correspondence. Secondly, if the cipher is shared with Sienese, the Habsburgs may have learned the cipher from them. I wonder whether the letter is really addressed to Sienese envoys.
If someone can find out anything, I'd like to know.
I uploaded a new article, "Verification of AI Decipherment and Verification by AI".
It first deals with how one can verify a decipherment. This is a matter of course for crypto-people but I recently received an inquiry about this. The case of symbols occurring only once that I mentioned yesterday is worth some consideration in this regard.
The latter half gives techniques AI use to verify their own results. This is something I read in many AI solutions that have emerged these days.
Again, two people independently achieved codebreaking with AI almost at the same time. They decoded telegrams between Napoleon III and Empress Eugénie in June 1859.
Geoge Lasry notified me of his solution (one in a batch of no less than 56 solutions) on 10 October 2026 and I published his results here on 12 October 2026. Jimmy Apples had published his results on X on 5 October 2026 and provided me with details on 13 October 2026. I now mentioned him in my report of George's results.
Two of the decoded telegrams are from Eugénie to Napoleon and the others are from the Emperor to the Empress.
Eugénie's telegram on 23 June 1859 reads:
Je suis désolée de vous avoir fait de la peine. Ce n'était pas mon intention. Ne vousinquiétez pas du petit, il va à merveille. J'écris aujourd'hui par la poste.
(I am so sorry to have caused you pain. It was not my intention. Do not worry about the little one, he is doing wonderfully. I am writing today by post. (Apples' translation))
The short telegram of the Empress is about personal matters, though the Empress acted as regent during the Emperor's absences in 1859, 1865, and 1870 (Wikipedia). In 1859, Napoleon III was with the army in the Italian campaign, which culminated in the Battle of Solferino on 24 June.
In terms of cryptanalysis, this is interesting in two points.
(1) No plaintext is found and this is a ciphertext-only achievement.
(2) One telegram has a sequence in which many figures occur only once:
677(je) 1074(re) 310 925 357(des) 381 708(le) 81 1099 123 495 656 257 914(par) 439(ennemi)Apples succeeded in filling these:
677(je) 1074(re) 310([cueille]) 925([partout]) 357(des) 381([do]) 708(le) 81([ances]) 1099([relatives]) 123([aux]) 495([exact]) 656([ions]) 257([commises]) 914(par) 439(ennemi)
The readings identified for these code groups fit in appropriate places in the alphabetically ordered code list. So this is not just a fabrication from nowhere. But it is not straightforward to find out whether this is the only candidate.
It has been known from Karl de Leeuw's work that Dutch diplomatic ciphers provided multiple substitution tables.
Now, in deciphering a ciphertext in Thurloe State Papers, Paolo Rosson found it switches among five tables in one letter. Though the plaintext was found in a Dutch publication, the scheme he found out is interesting.
The ciphertext is something like "113. 10. 26. 13. 13. 19. 29. 29. 26. 11. 222. 31. 17. 21. 22. 23. 23. 22.13. 30. 20. 18. 22. 23. 15. 13. 24. 22. 13. 24. 22. 17. 10. 15. 25. 23. 13. 329. 28. 15. 22. 20. 25. 20. 15. 25. 27. 28. 20. 27. 27. 20. 22. 17. 20. 15. 527. 16. 20. 21. 12. 19. 21. 29. 26. 20. 16. 27. 16. 19...." Although the specimen is a bit short, I thought solving this would not be difficult.
As it turned out, this short letter switches tables multiple times. No wonder it couldn't be solved with ordinary attacks. (I said the plaintext might not be in Dutch but in French. Some may have been misled by this.)
The first digit of three-digit group indicates one of tables 1-5.
I uploaded a new article about this, "Table Switching in Dutch Diplomatic Ciphers".
It is well-known that the cipher in the third book of Trithemius' Steganographia was solved in the 1990s. But it was only recently that I learned the cipher was broken in the seventeenth century by one Wolfgang Ernst Heidel, who declared it in his 1676 book but re-enciphered his solution in his own polyalphabetic cipher!
Thomas Ernst, who had solved Trithemius' cipher, deciphered Heidel's cipher and thus proved that Heidel indeed had the solution of Trithemius' cipher. Since Heidel's cipher had apparent word boundaries, a breakthrough was made when he identified the matching ciphertext for "gaza frequens libicos carthago duxit triumphos" known from the solution of Trithemius' cipher.
Thomas Ernst had succeeded in deciphering Trithemius cipher in 1993 and published it in 1996. In 1998, Jim Reeds independently solved it and then found it was already solved before him. Cryptologia (1998, issue 4) carried Jim Reeds' paper together with Thomas Ernst's brief English summary of his original paper in German.
Since it may take time before I have time to study further details, references are given below:
Thomas Ernst, "Schwarzweiße Magie: Der Schlüssel zum dritten Buch der Steganographia des Trithemius", Daphnis: Zeitschrift für Mittlere Deutsche Literatur, 25/1 (1996), pp. 1-205
Thomas Ernst, "The Numerical-Astrological Ciphers in the Third Book of Trithemius’s Steganographia", Cryptologia, XXII/4 (1998), pp. 318-341
Jim Reeds, "Solved: the Ciphers in Book III of Trithemius's Steganographia", Cryptologia, XXII/4 (1998), pp.291-317
Thomas Ernst's information about Heidel is on a wordpress-site: Restoring the Steganographia of Trithemius
Thomas Ernst analysed a forged manuscript of the "Steganographia" presumedly from 1521: "Anatomie einer Fälschung: ‘Johannis Trithemij [...] Steganographiæ Lib· 3. cum Clave, tàm generalj, quàm specialj [...] M.D.XXI’", Daphnis: Zeitschrift für Mittlere Deutsche Literatur und Kultur der Frühen Neuzeit (1400–1750), 30/3-4 (2001), pp. 513-595
A cipher with superscripts with word elements are now solved by Paolo Rosson. A few hours after his email, I received a report of solution from George Lasry.
This is what I listed as "Venetian? Cipher with Superscript Digits (1528)". As it turned out, the writer was a Genoese with the pseudoonym "Hieronimo Ranzo", apparently different from "Hieronimo Ranzo" known in history. Only yesterday, I gave this one that remains intractable by AI!
I uploaded a new article about this, "A Cipher with Superscripts for Word Elements ("Hieronimo Ranzo") Solved by AI".
I uploaded a new article, "Codebreaking with AI".
In the past month, I received many solutions for pieces in my list of unsolved ciphers. I suppose most of them were achieved with the assistane of AI.
Although I'm not versed in technical details, I tried to sort out what AI did in these achievements.
While Daniel Bourdeau is known to have solved many ciphers by using AI, his simulated-annealing homophonic solver didn't work for Ormonde-Maltravers Cipher (1634-1635). The ciphertext looks too short for ordinary algorithmic analysis. His solution seems more like human ingenuity. It can be seen as an interesting example of good old codebreaking. (Github records are difficult for me to decipher, and I don't know how far he was helped by AI in this.)
I uploaded a new article to describe his solution: "Ormonde-Maltravers Cipher (1634-1635)".
I reported Paolo Rosson's full decipherment of two letters in a polyphonic cipher in a new article, "An Intercepted Report of Henry IV's Upcoming Attendance at Mass in a Polyphonic Cipher". When I identified the key from deciphered materials back in 2017, I reported these as undeciphered. The fresh decipherment reveals reporting of the prospect of Henry IV's attending Mass.
Rosson noted that these were among the intercepted letters but were recorded as left undeciphered. Probably, because the letters to the Pope and the Bishop of Lizieux from the same date were deciphered, deciphering these was not considered important. Since Rosson provides the full text, I hope someone will compare it with the known letters to see if there is some new content. (Maybe AI can do such a specific task?)
From the viewpoint of cryptography, it is wondered who deciphered the letters to the Pope and the bishop. It is exciting to speculate whether it was François Viète.
A wave of codebreaking by/with AI now hit unsolved Enigma messages. Three people independently reported solutions of Enigma messages on a list of Enigma messages in Frode Weierud's CryptoCellar. (Some messages used for his coauthored paper (Olaf Ostwald and Frode Weierud (2017), "Modern breaking of Enigma ciphertexts" (Cryptologia)) are here.)
(1) A message dated 10 July 1941 with a discriminant (Kenngruppe) MVUEH was broken by Carter Leffen (X), who used OpenAI GPT-6 Astra. He communicated his solution to Weierud on 15 September 2026 (see Weierud's report).
As with the case of Vals AI's solution of Cyphral Distich reported yesterday, Leffen only told AI to see if it could break any of the unbroken Enigma messages on the CryptoCellar web page. All by itself, AI picked up Nr.172 (MVUEH) and assumed that its content might be related to the known plaintext of Nr.173 (SIPVX) from the same date. After many failed attempts, AI took up the repeated place name ROSENOW ROSENOW as a crib. AI then autonomously developed necessary Python and C++ software for an Enigma simulator and an Enigma Bombe and finally it successfully identified the key. Its plaintext turned out to be almost identical with Nr.173 (SIPVX). Actually, the SIPVX key had been tried before but it didn't work. As it turned out, the MVUEH key is completely different from the SIPVX key.
One more amazing thing about this solution gleaned from the log is that AI discovered relevant documents in the archives by itself, though it is not yet clear how far AI used the archival materials.
(2) Solution of Nr.285 (FMNGI), dated 31 July 1941, by Jack Willis using Anthropic's Claude Opus 5 was reported to Weierud on 21 September 2021. Unlike the case of MVUEH, this solution was "more directed and relied on strong human guidance" (see Weierud's report).
AI made the transcription of the message and used an already broken message ALQFI between the same two stations as a control to check the transcription.
Several messages (including ALQFI) from the same sender suggested a crib XHARTJENSTEINX (the sender was SS-Obersturmbannführer, Friedrich Hartjenstein). Variants of this name had already been given in Geoff Sullivan and Frode Weierud (2005), "Breaking German Army Ciphers", Cryptologia (pdf).
As it happened, Weierud had found a plaintext in July 2026 and put a notice of it on his website but not the plaintext itself. So the solutioin did not use the known plaintext.
(3) Solution of messages Nr.187 (AWTZK) and Nr.189 (ZNLZT) from 11 July 1941 by John Woodhouse (pdf) using Anthropic's Claude was reported to Weierud on 26 September 2026 (Weierud's report).
Again, a crib was the key to the success. Twelve cribs, harvested from messages with close dates, were "tested with a Bombe-style search that tolerates one garbled letter." The fifth crib XOSTROWXOSTROWX (again, a repeated place name) succeeded for ZNLST, and the key obtained therefrom could read AWTZK.
The search was helped by an observation from 1941 key sheets that "no wheel sits in the same slot on cnsecutive days". This reduced 60(=5*4*3) wheel orders to 14 for 11 July because 10 July employed V-II-I and 12 July emplyoed II-V-IV.
(By the way, I learned of this topic by newsfeeds in Japanese: GIGAZINE, netlife.)
A short numerical ciphertext called Cyphral Distich in an edition of Logopandecteision by Sir Thomas Urquhart was solved by AI (Claude Fable 5.1), as announced by Geby Jaff (Vals AI) on 31 August 2026.
It is remarkable that Fable 5.1 was simply told to solve an unsolved cryptogram (one that is deterministic and not ultra-hard) and autonomously picked up this and solved it without any human intervention. What looks like an ordinary numerical cipher turned out to be a book cipher.
Right after the announcement, sceptics pointed out that the ciphertext is not present in the 1653 edition available online and the decryption could not be reproduced.
Actually, the ciphertext is found at least in an 1834 edition and using its text (different from that of the 1653 edition) reproduces the decryption. This was pointed out at least by Jozef Krajčovič（facebook, 5 September 2026), kjfriedo (comments on Bruce Schneier's blog, 9 September 2026), AI時短ラボ (17 September 2026). But because sceptic views continued to be professed, I prepared my own verification here, and uploaded a new article in Japanese, "AIが人間の介在なしに17世紀の暗号Cyphral Distichを解読したのは本物だった".
Urquhart also left a second ciphertext called Cyphral Octastich and solved it in a similar way. Daniel Bourdeau, who also used Fable 5.1 to solve many ciphers including those on my list, verified the solution. He independently applied the rule found by Vals AI to reproduce the announced reading, though some numbers were "one word off".
kjfriedo (comments on Bruce Schneier's blog, 10 September 2026) had also partially verified the solution.
I uploaded a new article about a pigpen cipher used in letters from Thomas Wilkes to Sir Francis Walsingham. See "Walsingham's Pigpen Cipher (1586-1587)"
I wrote the most part of this some weeks ago but I didn't have time to complete it until now.
During the sixteenth century, numerical ciphers were not common in France. One letter from London to Francis I (1530) is the earliest French numerical cipher I know, though, as expected, the letter is in Italian.
For a long time, I have been wondering what kind of cipher this is. Now Daniel Bourdeau deciphered it. I uploaded a new article about this, "A Numerical Cipher in a Letter to Francis I (1530)".
Louise of Savoy, mother of Francis I, acted as regent from 1525 to 1526 when the king went to war in Italy and during his captivity in Spain (Wikipedia).
I learned from Ryan Turner that a letter to her (25 October 1525) from Nicolas Raince, secretary of the French ambassador to Rome, in Dupuy 452 used Nicolas Raince's cipher (1526) I reconstructed in "French Ciphers during the Reign of Francis I" and that the letter is printed in Jacqueton (1892), La politique extérieure de Louise de Savoie, XXXIII, pp.366-370 (Internet Archive). He points out that this identification shows that the 1526 cipher had been used as early as 1525 (his github). Although it is now known that cipher was used in France much earlier than this (see my blogpost), the year 1525 is interesting because nonsporadic records in cipher start to appear in 1525.
BnF Dupuy 452 includes the following letters partly in cipher, all using the same cipher and printed in Jacqueton (1892):
f.20 Alberto Pio de Carpi to Louise of Savoy, Rome, 22 October 1525, deciphered on f.22
f.24 Nicolas Raince to treasurer Florimond Robertet, Rome, 24 October 1525, deciphered on f.25
f.28 Nicolas Raince to Louise of Savoy, Rome, 25 October 1525, deciphered on f.31
Turner also published reading of some letters mentioned in my articles by using the respective keys mentioned:
Gramont's letter from BnF fr.2980 I mentioned in "French Ciphers during the Reign of Francis I" (his github); and
Danzay's letter to the Cardinal of Lorraine I mentioned in "Danzay's Ciphers: Ciphers of a French Diplomat with a Long Tenure" (his github)
The earliest users of cipher in England include Catherine of Aragon, John Stile, Thomas Spinelly, and Cuthbert Tunstall (see "Earliest English Diplomatic Ciphers"). To this may be added Richard Pace (Letters and Papers, Henry VIII, vol.2 (BHO), Wolsey's envoy.
On the receiving side, Brian Tuke is mentioned as the one who deciphered Spinelly's letters to Henry VIII or Wolsey (ibid. (BHO)). The cipher in a letter, dated 14 June 1516, from Matthew Schiner, Cardinal of Sion, to Henry VIII (ibid. (BHO) no.2044-2045) may also have been deciphered by Tuke.
I learned of the latter letter in a write-up by Daniel Bourdeau, who found that the letter is printed with decipherment in A. Büchi (ed.), Korrespondenzen und Akten zur Geschichte des Kardinals Matth. Schiner, vol. II (1516-1527), Basel 1925. It is amazing how his bot searches many sources to find a specific letter in a relevant volume, though it cannot get inside sources with "a bot check".
According to Bourdeau, Büchi tells in the preface that the volume includes 29 letters partly in cipher and names five kinds of cipher used by Schiner and his agents "above all in dealings with England". Inspection of the original materials is desired to see exactly what kind of ciphers were used in these. (At least, the original of some letters by Schiner and Pace are preserved in Cotton MS, Vitellius B XIX.)
It will shed light not only on possible influence on the earliest English ciphers but also on Vatican ciphers at this early stage. One letter addressed to Schiner in 1520 was written as a continuous stream of digits similar to, but much simpler than, later Vatican ciphers (see "An Early Vatican Cipher (1520)"). It would be interesting to know whether schiner's official correspondence used such a simple cipher.
It has been known that Adrian of Utrecht and Chares V used cipher as early as 1520. When I saw a cipher between them in 1522-1523, after Adrian became Pope, reconstructed by Olga Kolossova (Ko.4) is a typical Spanish cipher, I wondered whether the cipher used in 1520 was so complex as this.
Now, I find that Adrian and Charles used a simple homophonic cipher in 1520 by cryptanalysis by Mikel García Larragan.
Also, the cipher used in October-December 1521 mentioned by Daniel Bourdeau appears to be the same as Ko.4. If so, it indicates that Adrian and Charles V used the same cipher before and after Adrian became Pope in January 1522. Inspection of the original images is desired. (I couldn't locate PTR 2/1/94, 99, 100, and 101 in PARES.)
Daniel Bourdeau also found that a letter jointly sent by Adrian and two other governors of Castile in December 1520 was deciphered in the nineteenth century by Claudio Pérez Gredilla. From his write-up, we see this is a typical Spanish cipher with three-letter code. I suppose Adrian learned this type of code in Spain.
See the new section I added in "Scholarly Studies on Ciphers in the Reign of Emperor Charles V".
A few days after identifying the code condenser to decipher the telegram to Sun Yat-sen (reported the other day), Daniel Bourdeau found that the telegram was only part of a larger collection. He succeeded in deciphering many of them. One is a report of assassination of Chen Qimei (陳其美) sent the day after the event. I wonder whether these telegrams reached the recipient and are preserved for historians. If not, his achievements will shed new light for historians.
Two pieces of news for crypto people. First, Bourdeau found telegrams that cannot be read with the family of code condensers he found combined with the standard character code. I added this in my list of unsolved ciphers.
Secondly, I successfully determined the mapping between the character code and the three-kana code identified by Bourdeau.
See the new section in "Solution of Two Chinese Cipher Telegrams Archived in Japan (1916)".
I have been interested in ciphers written in a continuous sequence digits without a break. To solve such ciphers, the first step is parsing the digit stream into cipher units. I uploaded a new article, "Solutions of Ciphers in a Continuous Digit Stream" to describe recent solutions of such ciphers .
Of these, the Soglia cipher solved by Daniel Bourdeau is one for which a reward was offered in 1848.
The Starhemberg cipher solved by by Andrew Aymeloglu employs a fairly complicated scheme, for which he found the key among numerous keys in the DECODE database.
I was told by Andrew Aymeloglu that plaintext of two of the Bishop of Worcester's letters in cipher is printed in publications. When I put them in my list of unsolved ciphers, I thought there was not much to be done to complete the decryption. As it turned out, however, many of the unidentified symbols represent whole words. It would have been hard to identify them from scratch. See "Bishop of Worcester's Latin Cipher with Superscripts (1526, 1529)".
One anonymous letter seems to employ the same cipher but has many yet unidentified symbols, many of which would be nulls or words. I re-marked this as yet unsolved.
Some letters from Louis XIV to Pierre Villars, Marquis de Villars, are put on auction at Spink (I thank Patrick Hayes for the information). They are interesting in the study of codes and ciphers early in the reign of Louis XIV.
One (1669) seems to use "Colbert-Croissy Cipher (1668-1674) (DE=68) but there still remain many unidentified symbols.
I reconstructed the cipher used in another (1671). As far as I know, it is the only French cipher that had no regularity in arrangement before Louvois' in 1676.
See "Two Diplomatic Ciphers of Marquis de Villars (1669, 1671)".
PS. Patrick Hayes also discovered a letter part of which is in "Cipher with Prince Rupert, Digby, and Ormonde (1644-1645)" ("King Charles I's Ciphers"). The letter is Digby to Prince Rupert, dated 12 July 1644. He provided additional elements:
83=.
87=:
h3=now
Many thanks for the info!
Daniel Bourdeau solved "French Cipher Despatch received by General Catinat (1691)" in my list of "Unsolved Historical Ciphers".
He has been solving so many items in the past few days (he told me he solved 26, with avg 1-2 hours per problem) that I cannot catch up in updating my list. So I put a notice in my list that people about to start working should first check his website. As far as I have seen, his solution and analysis are of very high quality.
For this particular case, automatic codebreaking by AI failed. He found another ciphertext in the same cipher with a paraphrased translation, in which matching ciphertext-plaintext portions could be found from recurring symbols.
See "Solution of Louvois's Petit Chiffre (1690-1691)" and his github quoted therein.
Two Chinese cipher telegrams from 1916 presented in "Chinese Cryptography: 1871-1945" are now solved by Daniel Bourdeau.
The one is a telegram to Sun Yat-sen, for which he identified the code condenser (kind of superencryption) by brute force attack after cleverly narrowing down the search scope.
The second was not technically "unsolved" because the decryption is attached, but the encryption scheme has not been known. Bourdeau found it is a three-kana code. It still remains to be found out how the three-kana code groups are mapped to character numbers in a codebook.
See "Solution of Two Chinese Cipher Telegrams Archived in Japan (1916)" and Bourdeau's github pages quoted therein.
An undeciphered letter from Le Tellier to Marquis de Castelnau, dated 12 May 1657, is presented in "Ciphers Early in the Reign of Louis XIV". From other letters in Le Tellier's correspondence at the time, it is considered to be in a syllabic cipher. The ciphertext spanning a little over half a page seemed too short for a conventional solver for general syllable assignment.
To my pleasant surprise, it was solved by Robert Pitt. I guess the regularity of the assignment was given as a constraint or training data. The solution is described in a new short article, "Solution of Le Tellier-Castelnau Cipher (1657)".
IonQ published a blueprint for breaking 256-bit elliptic curve signatures used in blockchain technology including Bitcoin (press release). Unlike prior work, they "compiled every operation down to the actual error-correction primitives our architecture runs. Today's paper proved - rather than assumed - a lower bound on the probability that the full computation succeeds." They estimated that solution of 256-bit ECDLP (elliptic curve discrete logarithm problem, the classically intractable mathematical problem underlying elliptic curve cryptography) on secp256k1 (parameters specifying a specific elliptic curve on which mathematical operations are done) takes 25.7 days per attempt, by using 19397 physical qubits (quantum bits) implementing 1457 logical qubits and 39 million Toffoli gates (means for operating on qubits). (Use of quantum states necessitates complicated error correction schemes, which inflates the number of physical qubits required to implement logical qubits.)
I was reminded of an issue of potentially compromising authenticity of documents by their remark, "The cryptographic exposure this work describes relates to authentication and integrity rather than to confidentiality.... Unlike an attack on encrypted data, a signature compromise is exploitable going forward rather than retroactively against traffic recorded today. "
The threat to confidentiality is already quietly underway through a strategy known as "Harvest Now, Decrypt Later" (my blogpost). On the other hand, breaking of the signature scheme does not allow tampering with a document already signed with the scheme. Instead, it allows an attacker to derive a private key from a public key, which means that the attacker can put an authentic digital signature to a forged document. Suppose there is a digitally signed document stating "The President is very unpopular." Even with the knowledge of the private signature key, the attacker cannot falsify it to read "The President is very popular." Instead, however, it will be possible to create a new document stating "The President is very popular." and put a digital sign to authenticate it.
The same applies for digital timestamping because digital timestamping works by putting a digital signature to a combination of a hash of a document and a timestamp by a trusted timestamping authority to prove that the document was present at the time indicated by the timestamp. If the signature scheme is broken as of 2030, the attacker can create a document stating "The President is very popular." and add to it a valid timestamp of 2026.
Experts are aware of the issue and one (cenceptually) simple solution is timestamp renewal, whereby a document with a timestamp as a whole is wrapped in another layer of digital timestamping with a new (e.g., quantum-resistant) signature scheme. But this renewal need to be done before the original signature scheme is broken.
Some months ago, I wrote about a British book cipher during the American Revolutionary War. This time, I uploaded a new article about Wellington's dictionary code: "Wellington's Polyalphabetic Cipher with a Dictionary Code". For words/names not found in the dictionary, a polyalphabetic cipher with heavy nulls was used.
My observations are based on Wellington's despatch to General Maitland dated 2 September 1812. I thank George Lasry for the information of the auction of the letter at Spink.
Two undecoded telegrams to Union General Milroy were solved by Richard Bean, who had Claude Opus 5 solve them. While there are many papers about codebreaking with AI (see my blogpost for some), this is the first case that I see commonly available generic AI solve a real historical cryptogram.
I note the transposition route is the same as that of Stager Cipher No.7 albeit with a different number of lines. I uploaded a new article "Stager Cipher No.7 Continued in Use after Abandonment" about this.
I updated my recent article "Korean Cryptography" with additional specimens from John Milmore (2002), #1 Code Break Boy. The book, written like an unedited memorandum of an eyewitness, is interesting in recording US codebreaking activities on North Korean traffic during the Korean War, in which the author was "the principle cryptanalyst" (p.3).
It is more interesting to me because the codebreaking unit was headquartered in Tokyo (Japan was still under occupation after WWII). The photo below is a recent view of the building used as the headquarter (from Wikipedia).
How long did it take for a secretary to decipher a despatch? Sometimes we see a reply to a ciphered despatch received the night before, in which case we know that the deciphering of the original letter and the enciphering of the reply were done in a day. It is desired to find such an instance for which the original letter in cipher is available. If the letter is a long one, a better upper bound estimate can be made.
An informal experiment I recently read about this (I thought it was in Desenclos and Clinet (2025) (BDN) but apparently I misremembered it) induced me to try it myself. It took me twenty minutes to decipher a page.
But of course, this depends on many factors.
(i) The page is almost entirely in cipher but the number of symbols on the page (about 340) is modest. (One instance of a letter of Mary, Queen of Scots, has more than 4000 symbols on a page.)
(ii) Of these, almost 80% are single letters, with only about 20% being symbols for syllables and names. While the cipher has three or four homophones for each letter of the alphabet, after getting familiar with the cipher, one can work with this much (as well the most frequent syllables and code numbers such as "re", "de", "se", "que", "luy", "dit") from memory. If the cipher used syllables and codes more extensively, it would have taken more time in consulting the cipher table.
(iii) I was familiar with the cipher because I had been working with it for two weeks before the experiment. When one works with a new cipher, much longer time is necessary.
(iv) The deciphering work may be delayed if symbol shapes are hard to identify. In this regard, this particular case posed difficulty because of ink bleed-through. For this experiment, however, its influence was negligible beause I simply skipped the hardest cases for the experiment.
(v) There is interlinear decryption, but I did not refer to it for the experiment. (Actually, I had worked on this particular page before but I'm sure I did not remember the content.)
(vi) I worked on a pdf file, which is not very convenient as far as writing deciphered text is concerned. If I had worked on paper, it would have taken much less time.
Mirabeau's undecoded letter (1787) (see my blogpost) reminded me of the famous cipher devised by him, which is now described in a new article, "Mirabeau's Cipher".
It includes several open questions. If someone have any ideas, please let me know.
In Western history, there are many prominent historical figures who used code/cipher. But in China, Korea, or Japan, use of code/cipher was not common before the modern era. So an episode from the Tang period as an introduction for a narrative of Korean patriot codes in the Japanese colonial period on a Korean website I cited recently caught my attention. As expected, it is more like a riddle than code/cipher.
The episode is recorded in Memorabilia of the Three Kingdoms (三國遺事) (Wikipedia):
又古記云。總章元年戊辰〈若總章戊辰則李勣之事而下文蘇定方誤矣。若定方則年號當龍朔二年壬戌來圍平壤之時也〉國人之所請唐兵屯于平壤郊而通書曰。急輸軍資。王會群臣問曰。入於敵國至唐兵屯所。其勢危矣。所請王師糧匱而不輪其料。亦不宜也。如何。庾信奏曰。臣等能輸其軍資。請大王無慮。於是庾信仁問等率數萬人入句麗境。輸料二萬斛乃還。王大喜。又欲興師會唐兵。庾信先遣然起兵川等一人問其會期。唐帥蘇定方紙畫鸞犢二物迴之。國人未解其意。使問於元曉法師。解之曰。速還其兵。謂畫犢畫鸞二切也。於是庾信迴軍。欲渡浿江。今日後渡者斬之。軍士爭先半渡。句麗兵來掠。殺其未渡者。翌日信返追句麗兵。捕殺數萬級。(text from Database of East Asian World History Research Center (東アジア世界史研究センター))
Korea was divided into three major kingdoms: Goguryeo (高句麗), Paekche (百済), and Silla (新羅) for several centuries. Silla, allied with Tang (China), conquered Paeckche in 660 and then Goguryeo in 668. Kim Yu-sin (金庾信) (Wikipedia) was a leading figure in the unification of the Korean Peninsula under Silla.
In 668, when a Tang army under General Su Dingfang (蘇定方) (Wikipedia) (so goes the record, but either the year or the name of the general must be wrong because Su died in 667) was camped near Pyongyang, capital of Goguryeo deep behind the border, Silla was to join the Tang army. General Kim Yu-sin sent forward a small detachment to ask for a schedule. General Su Dingfang replied by drawing a young phoenix (鸞) and a calf (犢). When Kim's staff was puzzled by this mysterious letter from the ally, an eminent scholar-monk Wonhyo (元曉) (Wikipedia) figured out that the riddle can be solved by fanqie (反切), a technique whereby the pronuciation of a character is indicated by the initial consonant of a first character and the ending of a second character.
With this technique, the drawing of a calf (畫犢) (hwa-dok) reads hok, and the drawing of a young pohenix (hwa-ran) (畫鸞) reads hwan. That is, the two drawings refer to hok-hwan, which is somehow understood to be sok-hwan (速還), meaning "Retrun quickly". (I relied on the Hangul rendering of the characters in the transliterations here. Maybe we need to check the old pronunciation of these characters.)
This saved General Kim Yu-sin's army from annihilation.
Similar stories, if not fanqie, may abound in the world. In the Warring States Period in Japan, when warlord Oda Nobunaga was attacking the Asakura clan in 1570, his back was threatened by the Azai clan, supposed to be an ally. Nobunaga is said to have been warned of the imminent danger by his sister Oichi, wedded to Azai Nagamasa. She sent a pack of beans with both ends tied, which revealed the pincer movement by his enemies. While one might deplore such crucial information not being conveyed in a more straightforward message, this episode is considered apocryphal (Wikipedia).
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 no 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 of 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.
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 Sr Blatier in the Low Countries (1584) in BnF fr.16127 (f.196 ff.) do not include cipher.)
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.
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)).
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.)
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.
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.
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 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)
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".
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.)
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)
For contemporary Spanish ciphers, see "Spanish Ciphers during the Reign of Philip II".
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.
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.
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)".
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."
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.
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.
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.)
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.
