Abstract
In the globalized semiconductor supply chain, increasing outsourcing to external contractors, e.g., offshore foundry, results in possible exposure of hardware designs to adversaries. Consequently, security threats such as integrated circuit (IC) overproduction, intellectual property (IP) piracy and hardware Trojans have emerged, which poses a serious impact on the technology industry as well as the national security. Logic locking is a holistic Design-for-Trust method that can address those issues. By inserting key-controlled logic, logic locking allows locking the circuit functionality with a key only known by the IP/IC owner. The requirements for logic locking are to secure the logic locking key as well as effectively disrupting the circuit functionality. The security of logic locking is greatly challenged by oracle-guided attacks, notably the SAT attack. The attack is based on SAT solver and takes advantages of open scan chain access. Ensuring functionality disruption necessitates sufficient corruption at outputs, which is influenced by the insertion strategy of key-controlled logic. In this thesis, we develop secure and effective logic locking schemes, by focusing on three aspects, insertion strategy, SAT-secure logic lock and scan chain protection. For optimizing output corruption, we propose a key-gate insertion strategy called KIP. Based on signal probability analysis, the strategy selects nodes where corruption at such location is highly observable at multiple outputs. Furthermore, we propose a secure logic locking technique called SKG-Lock. It consist of inserting so-called switchable key-gates that are controlled by a switch controller. The technique provides provable SAT resilience and significant output corruption, especially when using KIP for insertion. Finally, we propose a scan controller for protecting logic locking against oracle-guided attacks. The scan controller introduces a key-based authentication mechanism, thus, prevents unauthorized access to the scan chains once the IC is deployed in the field.