Lope de Soria's Cipher Letters (1523)

Once I was particularly interested in ciphers of Lope de Soria, a Spanish ambassador in Genoa in the 1520s (see "Tracing the Origin of Vowel Indicators in Spanish Ciphers"). Now some of his cipher letters (1523) are in the DECODE database. They use two keys, printed in Galende Diaz (1992). I added reference to these letters in "Ciphers during the Reign of Emperor Charles V".

(The two recent additions to DECODE, R9531, R9530, are the cipher letters from which I reconstructed the keys in "Spanish Ciphers before Accession of King Ferdinand: 1470-1479" (Academia.edu).)

Oral Cipher in Yoshiwara Pleasure Quarters in Edo

Women in the Yoshiwara pleasure quarters in Edo in the late eighteenth century used a cipher, called the Fukagawa Speak, in their conversation. I learned this from a contemporary novel depicted in a scene in a historical drama I watched on TV the other day. The scheme is simple enough: meaningless syllables "ka", "ke", "ki", "ko", "ku" are inserted in the message. But when used in conversation, the resulting sound would have been unintelligible to untrained ears.
Similar schemes, typically known as the tanuki cipher, have also been used in riddles for kids. (Tanuki means a raccoon dog, but may also be interpreted as "drop ta".)

And, of course, it's not limited to Japan. Even John Wilkins' Mercury (1641) mentions an example of a similar scheme: Ougour plogot igis digiscogovegereged.
A Japanese translation of a mystery novel in English uses the Fukagawa Speak to render secret conversation in "King Tut English" among kids: A-bub-shush-o-lul-u-tut-e-lul-ylum.

I described these in a new article in Japanese, 深川言葉　―　大河ドラマ「べらぼう」に出てきた遊里の暗号.

Substitution Cipher for Hangul Text in a Book for Kids

The other day, I said I was looking for a cipher in Hangul. Now, I've found the book I have been looking for. It is a Korean translation of a book in Japanese, which features a cipher. Although the ciphertext is not in Hangul but in graphic symbols, this is the first ciphertext for Korean I encountered. I uploaded a new article, "Substitution Cipher for Hangul", which supersedes my post the other day.
(There is also a Chinese version of the book. It would be interesting to see how the cipher was adapted into Chinese. The Taiwan version skips the relevant volume (vol.11), so we need to look for Hong Kong or Mainland Chinese version.)

D'Estrades' Ciphers with Mazarin and Others

I added ciphers used in the correspondence of Comte D'Estrades in "Ciphers Early in the Reign of Louis XIV". Most of the keys are now identified, but a key for a letter in Italian (BnF Clair. 577, p.629) is not. The interlinear decipherment of the first few words (wihch I partly parse as `41(L) ¨33(AR) ¨36(MA) ′56(TA) ¨56(NA) ′61(VA) `42(LO)) may allow one to reconstruct the whole code.

(15 Mary 2025: I uploaded the key for the remaining Italian cipher reconstructed by George Lasry and Norbert Biermann. My parsing should be corrected in various ways: `41(LA) ¨33(R) ¨36(MA) ′56(TA) ¨41(NA) ′61(VA) `42(LE).)

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.

 

A Cipher in Italian used between Cardinal Gualterio and the French Foreign Minister Torcy (1718)

I added a section "Gualterio-Torcy Cipher (1718)" for a cipher used in a letter from Cardinal Gualterio to the French Foreign Minister Torcy in "A Syllabic Cipher (ca.1715) of Cardinal Gualterio Reconstructed Manually".

Yardley's Diplomatic Novel, Red Sun of Nippon (1934)

I enjoyed reading Yardley's diplomatic novel, Red Sun of Nippon (1934). It is a story of a young American diplomat and his half-Chinese, half-white girlfriend, set in the contemporary Washington D.C. It develops around an important document which would be evidence of the Japanese intention of establishing a buffer state in Manchuria. As expected from Yardley, breaking of Japanese diplomatic code plays some role. See my new article, "Yardley's Diplomatic Novel, Red Sun of Nippon (1934)".

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. 

 

Yardley's Codebreaking of a Chinese Book Cipher (1939)

Herbert O. Yardley wrote The Chinese Black Chamber after Word War II, posthumously published in 1983. It describes his days in China from 1938 to 1940, where he was invited by the Chiang Kai-shek's government to work on Japanese codes and ciphers. Codebreaking of one particular cipher is described in some detail, which I described in a new article, "Yardley's Codebreaking of Book Cipher used by Pro-Japanese Traitors in China (1939)".

Yardley's "Device" to Convey a Secret Message under an Ostensible Plaintext?

I'm interested in encryption that allows more than one reading (see posts about Venetian, J.F.W. Herschel).
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!

Secret Chinese Codebooks Preserved in US

Secret codebooks of statesmen of the Republic of China are preserved in the Li Zongren (李宗仁) papers (covering 1944-1951) and the V. K. Wellington Koo (Weijun Gu, 顧維鈞) papers (covering 1932-1966) in Columbia University Libraries in New York.
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".

Undeciphered Letters of Richelieu and Mazarin

I added mentions of undeciphered letters of Richelieu (BnF fr.3829), Mazarin (Melanges de Colbert 11), and the Duke of Lorraine (BnF fr.3621) in "Undeciphered Historical Ciphers". I solved the last one, but the first two remain unsolved.

Variable-length Figure Cipher between Henry de la Tour and Duke of Nevers (1589, 1591)

Speaking of variable-length figure ciphers mentioned recently, BnF fr.3619 (catalogue), f.103 (DECODE 9442), is a letter of Henry de la Tour (viscount of Turennes), to the Duke of Nevers dated 29 November 1591. For the most part, the ciphertext consists of Arabic figures.
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.

French Code at the time of Peace Talk at Geertruidenberg (1710)

I added a French Code at the time of the Peace Talk at Geertruidenberg (1710) in "French Ciphers during the Reign of Louis XIV".
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).

French Diplomatic Code Shortly before the Peace of Rijswijk (1694)

I added a Louis XIV's Code (1694) with Harlay and Callières, who sounded peace during the War of the Grand Alliance in "French Ciphers during the Reign of Louis XIV". Harlay and Callieres are two of the French representatives who signed the final Peace of Rijswijk in 1697, at which time they used two codes with code switching. The new specimen shows that code switching was not introduced as of 1694.

Instructions for Code Switching in a Set of Codes in English (1792)

I uploaded a new article "Specimens from Papers of Francis Willes".
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)").

Codebreaking without Command of the Language

Suppose we have a ciphertext in a letter in, say, Spanish. Can we break it without command of Spanish? The answer is yes. Back in 2019, I gave a quotation from 1737 to this effect in "Is Codebreaking Possible without Knowing 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)

Japanese Edition of Codebreaking: A Practical Guide by Elonka Dunin and Klaus Schmeh

Codebreaking: A Practical Guide is now available in Japanese! The book is by Elonka Dunin and Klaus Schmeh and was first published in UK in 2020 (as I reported before). In US, a new expanded edition was published in September 2023 (announced here). The translation is based on the 2020 version, with additional appendices for reprint: Appendix D for the solution of the famous Zodiac killer cryptogram Z340, released right after the first publication plus Appendix E showing the Morse table. According to the translator's preface, the translation project started soon after the initial publication.

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!

A Great Cipher Left Undeciphered by William Blencowe

An intercepted letter from the French foreign minister Torcy to French ministers sent to the peace talk at Geertruidenberg, dated 3 April 1710, is endorsed "M Blencow cannot decypher them."
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"

Frederick I of Prussia's Transposition Cipher

I noticed three transposition ciphertexts (two of which are attributed to King Frederick I of Prussia) in DECODE. Two appeared to be non-decrypted, and I could solve them without much difficulty.
See my new article "Frederick I of Prussia's Transposition Cipher". I also listed them in "Unsolved Historical Ciphers."