This answer to the Chinese Language SE question Historical: How was Chinese written in telegrams and early computers? says (in part):

Following is a telegram code "dictionary" used by Japan military that already decoded the Chiang Kai-shek KMT army telegram code during World war 2. Even USA military know about such "open code", but USA never notify Chiang Kai-shek about the issue of leaking military secret, because USA itself want to know KMT army movement.

and contains the image below.

Question: How frequently did the KMT used telegrams to communicate, from where (roughly) and to whom?

As pointed out in comments (1, 2) the data may never have been considered particularly "secret" as the code book in the image was used primarily to change Chinese characters encoded as numbers (a form transmittable via telegram; a method of endoding) into Japanese. See also Ciphers vs. Codes.

enter image description here

  • 1
    You and your source are conflating codes and ciphers. I suggest you research the difference (see the link) and clarify your question. – Pieter Geerkens Sep 20 '18 at 2:39
  • @PieterGeerkens Yes I see what you mean. Encoding something is not always done to obscure it's meaning; morse code, ASCII etc. simply facilitate communication. From your source: "...What is the difference between codes and ciphers?...A code is stored as a mapping in a codebook, while ciphers transform individual symbols according to an algorithm." At the same time, in some cases codebooks were used to keep messages private, but perhaps not as effectively as a cipher or encryption method would have. – uhoh Sep 20 '18 at 3:17
  • @PieterGeerkens I think you have answered my question nicely and clarified a bit of history to me, but the problem is that the clarification may not be a bit of history. Thus the clarification is needed to better fit the question to the site's constraints? – uhoh Sep 20 '18 at 3:21
  • 1
    The image you've given is a Japanese code book. – congusbongus Sep 20 '18 at 3:30
  • 1
    @congusbongus since it is used by Japanese military to decode KMT code, it is definitely written in Japanese. – mootmoot Sep 20 '18 at 7:58

You might be interested in a paper "Decryption in Progress: The Sino-Japanese War of 1894-1895" appearing in pp. 9-20 of an issue of The Cryptologic Quarterly by Greg Nedved. This well-documented paper describes use of code books for encryption purposes by the Chinese government half a century before the time frame of the OP's question.

I am not myself an expert in the period or the region, but will bravely hazard: that the KMT used such cryptography often, between various headquarters for all official business. As did all armies throughout the world at the time. For various reasons military organizations prefer written orders and reports to spoken ones, and the telegraph (in the forms of manual Morse or teleprinter, carried by land line or radio) were the timeliest and (hence) main means of sending them. The nature of the Chinese writing system makes the use of code books, whose digital code groups might be subject to so-called superencipherment, more practical than then the use of cipher machines like the famous Enigma machine used in Germany up to the end of the Second World War.

  • Thank you for the clarification and the linked article, I'll give it a read today. – uhoh Sep 21 '18 at 0:16

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