Making it harder to unlock an LSIB: Honeytraps and misdirection in a P1687 network

Today´s chips often contain a wealth of embedded instruments and data, including sensors, hardware monitors, built-in self test (BIST) engines, and chip IDs, among others. IEEE P1687 was specifically designed to provide access to such instruments in an efficient manner, and some companies are already implementing the proposed standard on their chips. However, while instruments provide valuable information and features to authorized users who need to harness them for test, debug, diagnosis, and possibly counterfeit detection, it may be desirable to restrict unauthorized access to certain instruments through the P1687 network. Previous work proposed replacing some of the segment insertion bits (SIBs), which add scan path segments in a P1687 network, with locking SIBs (LSIBs). LSIBs use the data that is naturally scanned through the network as keys to hide instruments from attackers. However, that previous work did not investigate many of the techniques and structures that can be used to significantly increase the time an attacker is likely to need to unlock LSIBs and gain access to hidden instruments. In this work, we explore some of these techniques and show how simple modifications to a P1687 network protected with LSIBs can significantly increase the difficulty an attacker faces in attempting to access protected instruments.