There already is a master key, or, more specifically, a master wrench. Preferably a 1 inch or larger spanner wrench.
Applied to various parts of the body it will do a wonderful job of improving certain specific memories. This isn't designed to prevent the NSA from going after you should they find that desirable (don't kid yourself, twinky). This is designed to protect yourself against two bit private investigators, your local sheriff, the creep down the block and your mother. No security is perfect, but this is lots better default security than most people ever get. Yes, Ms. Random Luser can defeat it by posting their passkey on Facebook or telling their soon to be ex boyfriend, but since security is a process, not a thing, nothing is always completely secure. And especially nothing that is designed to connect to the Internet.