Keybase.io now offers private folders where you can store data, shared private folders to privately exchange files with other Keybase.io users and public folders which files are automatically signed to prove their validity.
If you’d like to get an invitation for keybase.io, I still have a few to spare. Or if you want to send me encrypted messages, even better, just get my key here and let’s encrypt!
Last but not least: I’ve been using the OpenKeychain app for Android and it is really neat, lots of nice bells and whistles! And they have this step-by-step tutorial to get you started: Email Encryption with Android — A Quick Start Guide