2) Key signature Since the server side doesn't store the key of the user, I would like a way to still be able to tell the user if their password is wrong. I ne

2) Key signature Since the server side doesn't store the key of the user, I would like a way to still be able to tell the user if their password is wrong. I need a way to generate something that can be stored on the server, that the user can sent when generating the initial key, and then can resend when logging in, that the server can reply true/false if the master key/password is correct. My initial thought was to simply hash the master key and store that. I was going to use SHA-256 but since I might use that to get the AES key, I had to revisit it. Would simply generating a low-entropy/length hash from say MD5, and storing that, be a good option? I'm not worried about collisions, since the chance the user gets a collision for their own password is extremely low.