ScanPUF: Robust ultralow-overhead PUF using scan chain

Physical Unclonable Functions (PUFs) have emerged as an attractive primitive to address diverse hardware security issues, such as chip authentication, intellectual property (IP) protection and cryptographic key generation. Existing PUFs, typically acquired and integrated in a design as a commodity, often incur considerable hardware overhead. Many of these PUFs also suffer from insufficient challenge-response pairs. In this paper, we propose ScanPUF, a novel PUF implementation using a common on-chip structure used for improving circuit testability, namely scan chain. It exploits path delay variations between the scan flip-flops in a scan chain to create high-quality (in terms of uniqueness and robustness) secret keys. Furthermore, since a scan chain provides large pool of scan paths to create a signature, we can achieve high volume of secret keys from each chip. Since it uses a prevalent on-chip structure, the overhead is extremely small (2.3% area of the RO-PUF), primarily contributed by small additional logic in the signature-generation cycle controller. Circuit-level simulation results with 1000 chips under inter- and intra-die process variations show high uniqueness of 49.9% average inter-die Hamming distance and good reproducibility of 5% intra-die Hamming distance below 85 °C. The temporal variations due to device aging effect e.g. bias temperature instability (BTI) lead to only 4% unstable bits for ten-year usage. The experimental evaluation on FPGA (Altera Cyclone-III) exhibits 47.1% average inter-Hamming distance, as well as 3.2% unstable bits at room temperature.