> scheme using digital signatures The simpliest one would be to have "CHIP S/N: XXXX MFG DATE: YY/MM/DD" signed by some CA and watermarked on each chip. That

> scheme using digital signatures The simpliest one would be to have "CHIP S/N: XXXX MFG DATE: YY/MM/DD" signed by some CA and watermarked on each chip. That doesn't prevent for a counterfeit manufacturer from grabbing a handful of original chips and watermarking a series of their counterfeit chips with it. So it boils down to: a) no watermark on a chip what should be watermarked: obvious counterfeit b) one watermark on all chips: obvious counterfeit c) a valid watermarks on a shipment of chips: if you order a ton of them AND you bothered to setup both the tests and means to store and compare the results, so it would be obvious when you receive the shipment of chips with watermarks what you already has tested. for anyone else it would be c2) chips with a valid watermarks: not a counterfeit