Circuit Design Obfuscation for Hardware Security
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Nowadays, chip design and chip fabrication are normally conducted separately by independent companies. Most integrated circuit (IC) design companies are now adopting a fab-less model: they outsource the chip fabrication to offshore foundries while concentrating their effort and resource on the chip design. Although it is cost-effective, the outsourced design faces various security threats since the offshore foundries might not be trustworthy. Attacks on the outsourced IC design can take on many forms, such as piracy, counterfeiting, overproduction and malicious modification, which are referred to as IC supply chain attacks. In this work, we investigate several circuit design obfuscation techniques to prevent the IC supply chain attacks by untrusted foundries. Logic locking is a gate-level design obfuscation technique that's proposed to protect the outsourced IC designs from piracy and counterfeiting by untrusted foundries. A locked IC preserves the correct functionality only when a correct key is provided. Recently, the security of logic locking is threatened by a strong attack called SAT attack, which can decipher the correct key of most logic locking techniques within a few hours even for a reasonably large key-size. In this dissertation, we investigate design techniques to improve the security of logic locking in three directions. Firstly, we propose a new locking technique called Anti-SAT to thwart the SAT attack. The Anti-SAT can make the complexity of SAT attack grow exponentially in key-size, hence making the attack computationally infeasible. Secondly, we consider an approximate version of SAT attack and investigate its application on fault-tolerant hardware such as neural network chips. Countermeasure to this approximate SAT attack is proposed and validated with rigorous proof and experiments. Lastly, we explore new opportunities in obfuscating the parametric characteristics of a circuit design (e.g. timing) so that another layer of defense can be added to existing countermeasures. Split fabrication based on 3D integration technology is another approach to obfuscate the outsourced IC designs. 3D integration is a technology that integrates multiple 2D dies to create a single high-performance chip, referred to as 3D IC. With 3D integration, a designer can choose a portion of IC design at his discretion and send them to a trusted foundry for secure fabrication while outsourcing the rest to untrusted foundries for advanced fabrication technology. In this dissertation, we propose a security-aware physical design flow for interposer-based 3D IC (also known as 2.5D IC). The design flow consists of security-aware partitioning and placement phases, which aim at obfuscating the circuit while preventing potential attacks such as proximity attack. Simulation results show that our proposed design flow is effective for producing secure chip layouts against the IC supply chain attacks. The circuit design obfuscation techniques presented in this dissertation enable future chip designers to take security into consideration at an early phase while optimizing the chip's performance, power, and reliability.