I’ve concluded that open hardware is precisely as trustworthy as closed hardware. Which is to say, I have no inherent reason to trust either at all. While open hardware has the opportunity to empower users to innovate and embody a more correct and transparent design intent than closed hardware, at the end of the day any hardware of sufficient complexity is not practical to verify, whether open or closed. Even if we published the complete mask set for a modern billion-transistor CPU, this “source code” is meaningless without a practical method to verify an equivalence between the mask set and the chip in your possession down to a near-atomic level without simultaneously destroying the CPU.
So where does this leave us? Do we throw up our hands in despair? Is there any solution to the hardware verification problem?
I’ve pondered this problem for many years, and distilled my thoughts into 3 core principles:
- Complexity is the enemy of verification
- Verify entire systems, not just components
- Empower end-users to verify and seal their hardware
2023-03-11: The next step, inspecting the hardware itself
The Infra-Red, In Situ (IRIS) inspection method is capable of seeing through a chip already attached to a circuit board, and non-destructively imaging the construction of a chip’s logic. Each pixel corresponds to 1.67 micron. While these images cannot precisely resolve individual logic gates, the overall brightness of a region will bear a correlation to the type and density of logic gate used. With a reasonable amount of design-level hardening, we may be able to up the logic footprint for a hardware trojan into something large enough to be detected with IRIS. Fortunately, there is an existing body of research on hardening chips against trojans, using a variety of techniques including logic locking, built in self test (BIST) scans, path delay fingerprinting, and self-authentication methods
Gregor J. Rothfuss 