I'm interested in learning how this works. i.e. how do you encrypt the data client side? is it a randomly generated key? (I guess not since the user would need

I'm interested in learning how this works. i.e. how do you encrypt the data client side? is it a randomly generated key? (I guess not since the user would need to know it to decrypt the data on another machine). If the user picks a key, is it the same as their password? If the key is the same as their password, do you store the password in localStorage? etc etc? (Sorry, just thinking out loud here and not sure how this'll work)