I'm using Android to start with, i went through the link you shared but i wasn't able to download the app to my phone, or am i doing it wrong.
I'll appreciate if you spare sometime to put me through, i really wanna get this.
I should recomend to use Termux in android and install the gnupg, I know its a command line tool and not everybody like it but IMHO its the best way to do it.