The 'Secrets' app has been updated thanks to Mario, so you can now exchange private messages in the lovely Salsa20 instead of boring old AES. Nothing wrong with AES but the Stanford library is unmaintained and that's usually bad news for encryption. It's also possible to use custom algorithms between specific friends that are theoretically unbreakable -- if you've been following some of my earlier encryption work. But I can't legally talk about that, so I'll leave these things for you to discover.