I really think the solution you’re looking for is low-tech.
Book code.
Imagine if you will 2 identically arranged bookshelves containing identical books, magazines, periodicals, etc. thousands of miles apart.
A simple substitution code identifies the shelf, book, page, and word.
Yes it’s slow, but remember, security is usually inversely proportional to convenience.
Interesting, but kinda slow, but could be very secure. Thanks.