Intersection of light cones, the expansion of the universe, and the Margolus–Levitin limit of computation is truly the ultimate secret.

5 picoseconds to respond, then you are disconnected from the system by the laws of physics.

No amount of frame-jacking via time dilation using black holes can cheat that captcha, or brute force that keyspace.

By the time you find the key, we are no longer connected in space-time/causality