An xray or optical inspection would never be able to detect the doping of the silicon so it's possible to alter the behavior of the chip in such a way as to all

An xray or optical inspection would never be able to detect the doping of the silicon so it's possible to alter the behavior of the chip in such a way as to allow an attacker to cripple something like Intel's random number generator RdRand yet have this be basically undetectable in software.