Comment by jedberg

You don't need multiple security protocols (and in fact that is almost always a bad idea). You just need one good protocol and a way to securely exchange the keys. What signal solved for the most part is the secure key exchange.

If you want to talk to one person, you can give them a USB key in person with a set of crypto keys and then use that to encrypt your messages over any transit method and it will be secure.

The hard part is the key exchange.