Hi, post author here. Agree that the idea isn't tricky, but it seems like many systems still get it wrong, and there wasn't an available system that had all the necessary features. I've tried many of them over the years -- XDR, JSON, Msgpack, Protobufs. When I sat down to write FOKS using protobufs, I found myself writing down "Context Strings" in a separate text file. There was no place for them to go in the IDL. I had worked on other systems where the same strategy was employed. I got to thinking, whenever you need to write down important program details in something that isn't compiled into the program (in this case, the list of "context strings"), you are inviting potentially serious bugs due to the code and documentation drifting apart, and it means the libraries or tools are inadequate.

I think this system is nice because it gives you compile-time guarantees that you can't sign without a domain separator, and you can't reuse a domain separator by accident. Also, I like the idea of generating these things randomly, since it's faster and scales better than any other alternative I could think of. And it even scales into some world where lots of different projects are using this system and sharing the same private keys (not a very likely world, I grant you).