Say you wanted to communicate openly and effectively to multiple people through cypher both in plan sight and hidden. Print a book, maybe a few special editions. Each layer in the web or hierarchy gets a different cypher based on edition. If you were good enough sometimes the same message could be sent to everyone and each layer would get different instructions.

Almost impossible to crack without the cyphers, Caesar was a genius. Hillary was not.

I wonder what the enemies book cyphers were, they sure write a lot of books. If our side has Q drops theirs does too.