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.