12/03/2025
D'Estrades' Ciphers with Mazarin and Others
28/02/2025
Chinese Telegraphic Codebook for Phrases (1948)
I got a copy of a Chinese telegraphic codebook (1948) including not only single characters but also phrases. It is Cheng yu Dian ma (成語電碼) already described in 「電碼――中国の文字コード」 (an abridged English version), but I now added three photos.
26/02/2025
A Cipher in Italian used between Cardinal Gualterio and the French Foreign Minister Torcy (1718)
21/02/2025
Yardley's Diplomatic Novel, Red Sun of Nippon (1934)
14/02/2025
Substitution Cipher in Hangul
Japanese text can be written with some fifty kana, which can be enciphered with substitution ciphers. (Historical examples can be seen e.g., at 明治日本の暗号いろいろ). The Chinese language employs thousands of characters, so any practical encryption in Chinese is based on numerical code of those Chinese characters.
What about Korean? I have long wondered whether substitution cipher is possible in Korean script (Hangul). This is because Hangul text is not simply a series of Hangul letters. Instead, two or three Hangul letters (consonant+vowel or consonant+vowel+consonant) are combined to form a syllabic block, which is the unit of writing (morphemic block). Moreover, placement of letters within a block differs depending on the vowel. The vowels for A, E, I (which have a vertical axis) are written to the right of the initial consonant, but the vowels for O and U (which have a horizontal axis) are written under the initial consonant. So, simply substituting one Hungul letter for another may result in a letter sequence that cannot be formed into morphemic blocks.
Now, I learned possible simple solutions to my question. There may be two ways for substitution ciphers to work in Hangul.
(i) Substitution is applied in separate groups for consonants and vowels. This way, the "consonant-vowel" grouping is preserved in substitution. This is the approach that AI (Copilot) on my new PC gave to my question. Actually, AI at first gave an example of a Caesar cipher of consonants alone. When I asked about vowels, AI gave a separate substitution table for vowels. I do not know whether this simple scheme really works for actual Hangul text. (For example, I hear not every consonant can be the third element in a block; there are letters that are not simple vowels or consonants.) To my repeated requests to give actual examples, AI simply ignored "in Hangul" and gave websites for the Caesar cipher in Japanese!
(ii) Substitution is applied to morphemic blocks rather than to letters. Unicode registers 11,172 Hangul morphemic blocks (399 consisting of two leters + 10,773 consisting of three letters). If we think this whole set as a single alphabet, substitution cipher can be used. (An attempt to use the Vigenere cipher in Hangul (pdf in Indonesian?) seems to use this approach.)
Googling now finds applications to use cipher in Hangul, but I still cannot find actual examples of substitution ciphers in Hangul. Considering that Hangul was not used in official documents until 1894 and that I have seen use of numerical codes for telegraphy (posted here), substitution in Hangul may not have been common historically.
09/02/2025
Yardley's Codebreaking of a Chinese Book Cipher (1939)
08/02/2025
Yardley's "Device" to Convey a Secret Message under an Ostensible Plaintext?
Yardley tells such a feat in The Chinese Black Chamber posthumously published, though no details are given (p.152-153).
He was teaching his Chinese students how to evade the censor in sending out a secret message in an apparently innocent message encoded with the standard codebook for Chinese characters. Whether the message passed the censor could be known by addressing it to a fictitious recipient in Hong Kong, because they got inquiries as to the unknown addressee.
When the censor (a general) came to confront Yardley directly, the ostensible message he questioned was "Please tell my cousin to send me airmail two hundred quinine tablets." while the "secret message, encrypted by a device I showed them" was "New airfield completed six miles up Little River."
His interpreter demonstrated to the general how to derive the true meaning by using the public codebook and succeeded in satisfying the censor.
To the astonished Yardley, the interpreter explained that he revealed a fake secret message, "Your first born is a male.," adding that "I can make it say that as easily as anything else." Actually, he didn't understand the method himself but he knew the general (censor) wouldn't understand it, either, and he was too proud to request further explanation by saying he couldn't understand!
04/02/2025
Secret Chinese Codebooks Preserved in US
Compared with commercially available standard telegraphic codebooks, not much is known about secret Chinese codebooks. The photos of the secret codebooks on the Libraries' website are invaluable. The photo of a page from the Li Zongren codebook shows it included not only characters but also words. The photo of the Wellington Koo codebook shows a list of proper names with sequential numbers (probably to be combined with page numbers to form numerical code).
I added mention of this in "Chinese Cryptography: 1871-1945" and "中国の暗号:1871-1945".
03/02/2025
Undeciphered Letters of Richelieu and Mazarin
02/02/2025
Variable-length Figure Cipher between Henry de la Tour and Duke of Nevers (1589, 1591)
The cipher used is no.23 (f.46-47) of the Nevers Collection (BnF fr.3995), in which the letters A-I are assigned single digits and M-U are assigned two-digit figures (with a dot over the digit in the tens place). Although the cipher includes instructions to write figures continuously ("Aussi fault aduertir de ne separer les mots come lon fait comunem[ent] ains escrire tout aulong le chifre sans aucuns distinction"), chuncks of two digits are barely visible in the ciphertext.
De la Tour joined the Protestant party of Henry of Navarre in 1576 (Wikipedia). At first, I thought use of Arabic figures came from Navarre (see "A Cipher of Henry of Navarre before Accession to the French Throne (1587)"), but in view of the 1571 instance, it may be more natural to think it came from the Duke of Nevers at least for this case.
31/01/2025
French Code at the time of Peace Talk at Geertruidenberg (1710)
Not only single letters but also some short words/syllables have homophones, though this is not an innovation at this time because a similar feature is seen at least as early as Greater Cipher (1691).
27/01/2025
French Diplomatic Code Shortly before the Peace of Rijswijk (1694)
01/12/2024
Instructions for Code Switching in a Set of Codes in English (1792)
Of the motley of materials presented, the most interesting to me is a set of four codes in English (1792). The instructions prescribe that the codes could be switched even in one letter. Such code switching is what I observed in French diplomatic correspondence about that time ("Code Switching in French Diplomatic Correspondence and Intercepted Letter of Barbé-Marbois (1782)").
02/11/2024
Codebreaking without Command of the Language
I saw similar observations in two books I recently read.
Elonka Dunin and Klaus Schmeh, Codebreaking: A Practical Guide, which I reviewed yesterday:
"Experience shows that breaking an encrypted message does not necessarily require command of the language used."
(p.76 in Japanese, p.74 in English)
Liza Mundy, Code Girls: The Untold Story of the American Women Code Breakers of World War II, which I mentioned last month:
"What Friedman had also taught them during their training is that you can break a foreign cipher without understanding the language, as long as you know how the letters in that language behave."
(p.138 in Japanese)
01/11/2024
Japanese Edition of Codebreaking: A Practical Guide by Elonka Dunin and Klaus Schmeh
Although I'm mentioned as one of contributors to the original English version (p.16 of the translation), I believe the following is not too partial.
Use of the polite style in Japanese (cf. Hiragana Times), as well as presenting personal names in the original roman alphabet, is, I believe, the style commonly adopted in textbooks/manuals in the field of computing and cybersecurity where the expertise of the translator belongs.
The translator, who accepted the offer of this project after seeing the high rating of the original edition abroad and endorsements by experts, got absorbed in classical cryptography through reading the book. The numerous translator's notes inserted between paragraphs attest to the zeal to help beginners understand the content. Sometimes, the translator's note runs half of a page (e.g., p.229). Given the evident zeal, it could have been better but for the occasional typos and a few relevant errors.
The translator's notes are more than just a guide for beginners. I myself found useful the explanation of the very first steps of CrypTool 2 on p.7-8! At times, additional information is given, like the solution of the Silk Dress cryptogram in 2024 (p.153). I found interesting the episode of a Lorenz machine being sold on eBay for 9.5 pounds in 2016! (The news received media coverage at the time: NPR, BBC, The Guardian).
With so many topics about paper-and-pencil ciphers with many worked-out examples, numbering the sections adopted in the Japanese verion (including in the running head) is convenient for referencing and navigating. I never thought such a voluminous work (nearly 500 pages) can be published in Japanese at such an affordable price (3,480 yen before tax).
I enjoyed re-reading this book in Japanese, with occasional reference to the original in English.
Congratulations to the authors on the publication!
26/10/2024
A Great Cipher Left Undeciphered by William Blencowe
Filed with it is another letter from Marshal Villars to the Abbé de Polignac, dated 1 June 1710. This also seems to be undeciphered.
I uploaded a new article "A Great Cipher Left Undeciphered by William Blencowe" describing BL Add MS 61575 including these. I also added references to these undeciphered pieces in "Unsolved Historical Ciphers"
25/10/2024
Frederick I of Prussia's Transposition Cipher
See my new article "Frederick I of Prussia's Transposition Cipher". I also listed them in "Unsolved Historical Ciphers."
24/10/2024
Cardinal Richelieu Used a Porta-like Pairing Cipher?
Just as I wrote about the outage of the British Library's online services the other day, another important source, Internet Archive, went down about 10 October because of a DDoS attack. It's a sad realization that online services we take for grated may be attacked anytime and the attackers may have success sometimes.
Thankfully, it seems Internet Archive (at least archive.org that I need) appears to be working now.
Thus, I could access Wits Interpreter (1, 2), attributed to John Cotgrave (Wikipedia), which I learned printed Richelieu's cipher the other day. (Somehow, at that time, before the attack on Internet Archive, my search could not find this on Internet Archive.)
The cipher attributed to Richelieu (p.491) is a Porta-like pairing-based cipher. But the other ciphers following this all seem to be taken from Porta's book. So, a more reliable source is needed to confirm Richelieu really used this cipher. (After writing this, I noticed the section on Richelieu in "French Ciphers during the Reign of Louis XIII" already mentions Wits Interpreter from a secondary source.)
19/10/2024
Some Ciphers from Henry IV's Time
ciphers of Seguier, Buzanval, and an informant to Henry IV (1601) in "French Ciphers during the Reign of Henry IV of France"; and
Francesco Guicciardini's Cipher (1597) in "Florentine Ciphers of Guicciardini (ca.1590-1593)".
It is notable that the three ciphers used in 1601 are of different nature. Buzanval (ambassador in The Hague) employed a symbol cipher with a seemingly large nomenclature in symbols. Seguier (ambassador to Venice) employed a symbol cipher, but his nomenclature was in Arabic figures with diacritics. The cipher of the king's informant employs Arabic figures both in the substitution table and the nomenclature, the character reminiscent of a cipher used with the Landgrave of Hesse-Cassel.