A Low-overhead PUF-based Secure Scan Design

Scan-based side-channel attacks have become a severe threat to the security of cryptographic chips and locking mechanisms are one of the most effective methods against these attacks. However, securing the test key that locks the scan but must be shared among test engineers arises as a new challenge. In this paper, we solve this challenge by adopting the physical unclonable function (PUF) design to generate test keys that are unique for each chip. A one-time programming structure (OTPS) is used when the PUF response is first generated to improve its reliability. The security of the PUF response is achieved by obfuscation such that it can be retrieved only when a specific validation test vector presents. We implement the proposed secure scan design by reusing the original scan chain to reduce overhead. We demonstrate that the proposed secure scan design can protect the crypto chips against all existing scan-based side-channel attacks while incurring negligibly low overhead.