I'd love to know more about this, if you have the time to point me to some place to learn/read/listen. I'm an amateur backend developer(yay node), and I'm trying to figure out how to make it so that even I'm not able to read the contents of a users uploaded file/generated content without a key. Can I use the password as this key? How would I go about this?
It depends on how user-friendly you want to be. A balanced solution would be to use their password to encrypt a really long key, with which you encrypt their data by using symmetric encryption. This way you can add new computers as long as you know the password, and you only have to re-encrypt the key when the user changes their password.
A more secure, but much more cumbersome solution would be to do the same but with private keys on each computer. However, to add a new computer you'd have to have the user transfer their private key from one computer to the other without ever reaching you, so that other computer could decrypt the filesystem encryption key and re-encrypt it adding the new public key.
I can help you with this having just done it for my own startup. Send me an email and I'll shoot you over our independent security report which explains all.
