StatSAT: a boolean satisfiability based attack on logic-locked probabilistic circuits

The outsourcing of chip designs for fabrication has raised concerns regarding the protection of Intellectual Property (IP) from an untrustworthy foundry. Logic locking is a design-for-security technique that has the potential to thwart attacks from such an adversary. On the other hand, the notions of approximate and probabilistic computing have been popularized due to their low energy consumption characteristics and their potential application in error-tolerant frameworks. Prior work has looked into and exposed the vulnerability of logic-locked circuits using concepts of Boolean Satisfiability (SAT), but mostly from the perspective of deterministic designs. Despite existing attack frameworks not being directly applicable, we show in this work that circuits exhibiting probabilistic behavior also face the same threat. We propose StatSAT, an attack methodology incorporating statistical techniques into the existing SAT attack, that can overcome the hurdles imposed by the probabilistic behavior. Our attack results show that the adversary is capable of unlocking the circuit to an extent good for all practical purposes.