SCONE: A Logic Locking Technique Utilizing SMT Solver and Circuit Encoding Scheme for Efficient Hardware IP Protection

Multiple intellectual property (IP) protections have emerged to defeat security threats in integrated circuit (IC) supply chain. Among these, logic locking is regarded as a promising IP protection for its security. A state-of-the-art work uses stripped-functionality logic locking (SFLL) technique with protected input patterns (PIPs) satisfying the distance of at least 2 (Dist2) property, or D2PIPs, for ensuring resilience against both input-output (I/O)-based and structural attacks. However, this approach has research challenges in scalability, flexibility, and security, as stated and discussed in our paper. Our paper solves these challenges by (i) utilizing a satisfiability modulo theories (SMT) solver and (ii) developing a secure circuit encoding scheme. SCONE, our secure logic locking technique, combines the two methods and meets all three challenges simultaneously. Our results show that SCONE improves scalability 350× on the IBEX processor (16 K gates) and remains resilient against five I/O or structural attacks. Index Terms-logic locking, encoding scheme, SMT solver.