This is one of the coolest anti-tamper mechanisms imho: https://spectrum.ieee.org/the-unhackable-envelope
TLDR: HSM housed within an envelope composed of layered electrodes having a unique capacitive signature used to derive its secret material.
TLDR: HSM housed within an envelope composed of layered electrodes having a unique capacitive signature used to derive its secret material.
https://www.hardwear.io/netherlands-2019/presentation/Enclos...
https://media.ccc.de/v/35c3-9611-enclosure-puf
> verifying the authenticity, integrity and/or the physical state of an item by employing the propagation behaviour of electromagnetic waves. In particular, it enables to check for any tamper attempts for larger structures, such as off-the-shelf computers and their periphery. The technology extends existing tamper proof approaches from the chip/PCB to a system level and is easily retrofittable. In this presentation, we are demonstrating exemplary tamper proofing in order to protect secret information without an attack-detection or data-deletion circuit (!), which is a known difficult problem and an imperfect undertaking. Therefore, we demonstrate the simplicity and effectiveness using a very cheap self-made testbed (using alumium foil) to protect standard hardware against invasive attacks, such as needle probing through the case. Cyber-physical systems are ubiquitous and are often located in non-trustworthy environments, in which data is processed that is both sensitive and worth protecting.
That is, they are measuring something to do with capacitance (at a very small "femto/10^-15" scale) at the place where they seal it up. Then you're supposed to be able to do that same measurement at the place where it arrives after shipping, and have identical readings. Even though origin and destination likely have different ambient temps, humidity, altitudes, and so on.