I'm writing a story set partially in historic China, and it involves a network of secret agents who seek to communicate over the mail in innocuous-looking letters. So I need a description of a pen-and-paper cipher that works for the Chinese language and (traditional) writing system. The story is not ultimately about the language or the cipher, it is just an element that I want to describe accurately.
For the plot I need to use a null cipher; a way to conceal the secret message in a large amount of regular text by interspersing the secret stuff with lots of random stuff that together looks like it is about something different entirely.
In alphabetical scripts that would work by taking every n'th word, or every n'th letter, and putting them behind each other. This example from Wikipedia:
HE GOT A GOOD HEART. SHOULD YOU BE HAVING PROBLEMS BE ASSURED THAT WHEN YOU HIT THE STREETS...
Taking every 5th word:
HE SHOULD BE HIT
I'm considering, for this story, to say that this particular cipher mixed and matched components. That is to say, if the agent wanted to encrypt "steal", 偷; he would find another character starting with 人 (e.g. 仔) and another character ending with 俞 (e.g. 瑜), and write some text between to make it flow as a sentence. Then he'd just need to do so in a regular manner; let's say picking the first component of every 3rd character, then the second component of every 5th character, and maybe some extra cases for characters with even more components. Another agent who reads the text can read it selectively and get the secret message.
That is the level of explanation I'd use in the story; so the question is basically whether that, on the surface, looks feasible. I'm not going to write any actual ciphered text. I just don't want to do disrespect to any speaker of Chinese who comes across the story when I eventually put it online.
Rather than invent my own, I would have used an actual historic cipher, but they seem hard to find. The only one I could find attested is a grille cipher. That too is a null cipher, but it operates on the level of whole characters; and I presume that hiding the entire word "steal" in a text would be more suspicious than just hiding its components. Plus using components I can use it in a scene where someone explains the Chinese script itself, for a nice little educational bonus.
