Post-SAT 1: Point Function-Based Logic Locking

This chapter presents point function-based logic locking techniques, namely SARLock, Anti-SAT, and AND-tree detection that thwart the SAT attack by controlling the distinguishing ability of the DIPs. All these techniques integrate with the original netlist a point function that sets a limit on the number of incorrect key values that a DIP can eliminate. While these techniques cost-effectively thwart the SAT attack, their main limitation is the susceptibility to removal attacks. Moreover, these techniques fail to achieve a high output error rate. This chapter is about point function-based logic locking techniques that remain the earliest countermeasures against the SAT attack. The chapter presents three techniques, SARLock [5], Anti-SAT [4], and AND-tree detection [1]. All three techniques harness point functions to control the distinguishing ability of individual DIPs and ultimately render the required number of required DIPs exponential in the key size. Section 5.1 describes the common principle underlying these techniques. Section 5.2 describes the architecture and operation of SARLock. Section 5.3 explains how Anti-SAT makes use of point functions to circumvent the SAT attack. Section 5.4 elaborates on the effectiveness of AND-tree detection. Section 5.5 compares the three approaches in terms of the attack resilience and the implementation cost. Section 5.6 highlights the limitations of the point function-based logic locking.