SATAM: A SAT Attack Resistant Active Metering Against IC Overbuilding

In the horizontal semiconductor business model, a foundry can tamper or overbuild the integrated circuits (ICs) while the IC owner knows nothing about it. Active IC metering scheme has been proposed to solve this problem by enabling IC owners to uniquely identify each manufactured chip. We propose a new active metering scheme, SATAM. In the scheme, a new cell of switchable scannable flip-flop (WFF) is introduced to be inserted in the non-critical paths or replace some original scan cells. Without a correct key on these WFFs, the synchronization status of the original design is violated and hence the circuit logic is locked (obfuscated). The scan design is also obfuscated by the introduction of WFFs, which helps the locking scheme to resist the typical SAT attack and other existing attacks on logic locking. To enable each fabricated chip to have a unique key to unlock, a via-based physical unclonable function (PUF) is adopted due to its perfect reliability. A new post-processing method is proposed to improve its uniqueness and randomness. Also, we propose to modify the original finite state machine (FSM) so that the PUF response can only be retrieved by the chip designer in a secure way. The experimental results show that the locking scheme based on WFFs can well resist the SAT attack and other existing attacks on logic obfuscation. The PUF design can achieve satisfactory uniqueness and randomness while incurring lower overhead. The FSM-based retrieval scheme can secure the PUF response by slightly modifying the original FSM. The overhead due to the overall metering method is smaller than most of the existing metering methods while it can resist typical attacks.