Sounds like the really cool "Stealthy Dopant-Level Hardware Trojans" paper from a few years ago. I'd forgotten about that, well worth a read for those interest

Sounds like the really cool "Stealthy Dopant-Level Hardware Trojans" paper from a few years ago. I'd forgotten about that, well worth a read for those interested. However, you must remember that as well as precise knowledge of the circuit, anyone other than an insider has close to zero chance of getting a doping change correct. Even an insider's chances are very low. And then your high-level testing is in place too. It's not common to have circuits where BIST can't give you full confidence but it happens; for things like the RNG here, also due to test tool limitations etc. So you must be doing both both general and highly targeted post-manufacturing testing also. The extent of that testing may depend on your market.