From Cryptography to Logic Locking: A Survey on the Architecture Evolution of Secure Scan Chains

The availability of access to Integrated Circuits' scan chain is an inevitable requirement of modern ICs for testability/debugging purposes. However, leaving access to the scan chain OPEN resulted in numerous security threats on ICs. It raises challenging concerns particularly when the secret asset, like secret information, is placed within the chip, such as the keys of cryptographic algorithms, or similarly logic obfuscation key. So, to combat these threats, numerous secure scan chain architectures have been proposed in the literature to prevent any unauthorized access to the scan chain. They also keep the availability of the scan chain for testability/debugging. In this paper, we first show why a secure scan chain architecture is required when security primitives, like logic obfuscation, are in place. Then, we provide a holistic overview of all secure scan chain architectures starting from preliminary methods introduced when cryptography is in place and the adversary threat model is very limited. It is then followed by newer and more advanced methods introduced when logic obfuscation is in place and the adversary threat model is much stronger. Hence, we have more concentration on the architecture proposed more recently on logic obfuscation. We evaluate all secure scan chain architectures in terms of security and resiliency, testability/debugging time and complexity, and area/power/delay overhead.