DScanPUF: A Delay-Based Physical Unclonable Function Built Into Scan Chain

Physical unclonable function (PUF) has emerged as an attractive primitive to address diverse hardware security issues in integrated circuits, such as authentication and cryptographic key generation. Most of the existing PUFs rely on dedicated circuit structure for generating random signatures. It often causes concerns due to extra design efforts and hardware overhead. Moreover, the hardware complexity increases with higher entropy requirement, which may be unacceptable in area-constrained applications. In this paper, we propose DScanPUF, a novel PUF structure that leverages on the scan chain, a prevalent design-for-test structure in a chip. It is based on a low-overhead delay measurement structure consisting of a phase-locked loop and multiple clock delay lines to measure scan path delays at high resolution. A method is proposed to transform the responses into robust binary signatures. We note that the area of DScanPUF is only 18% of the ring-oscillator (RO) PUF with 1024 ROs. Moreover, it can be easily integrated into a design without any influence on testability. DScanPUF is evaluated with test results from 31 field-programmable gate array chips, which show good randomness, uniqueness and reproducibility under temperature, and supply voltage fluctuations. We also show that the signature is robust under aging effects on scan paths through a simulation at 45-nm CMOS process. Finally, we propose a simple structural modification to further improve the signature robustness.