A lot of the $10 mp3 players from China do a lot of what modern computing is (they read pdfs, play music, etc. I haven't seen one that saves text files but that doesn't seem a stretch to add). But they don't come with boot/lock screen encryption. How can this be added? (asking in a computer programming way, like How can this be approached from the coding level.)

Could mp3 players become little computers (I understand they are computers) that do a lot of what we do with a computer?