Well, you could fill all of the unused storage space on the system with random noise specified by you, then ask the system to regurgitate that noise to you (or

Well, you could fill all of the unused storage space on the system with random noise specified by you, then ask the system to regurgitate that noise to you (or more practically, tell you a function calculated from some set of bytes you specify). That would require that an attacker physically alter the hardware to defeat your verification process. You can maybe come up with a version of this that uses a HSM, or simply some part of the firmware that is read-only.