Error-tolerant bit generation techniques for use with a hardware-embedded path delay PUF

Cryptographic and authentication applications in application-specific integrated circuits (ASICs) and FPGAs, as well as codes for the activation of on-chip features, require the use of embedded secret information. The generation of secret bitstrings using physical unclonable functions, or PUFs, provides several distinct advantages over conventional methods, including the elimination of costly non-volatile memory, and the potential to increase the number of random bits available to applications. In this paper, we propose a Hardware-Embedded Delay PUF (HELP) that is designed to leverage path delay variations that occur in the core logic macros of a chip to create random bitstrings. The bitstrings produced by a set of 30 FPGA boards are evaluated with regard to several statistical quality metrics including uniqueness, randomness, and stability. The stability characteristics of the bitstrings are evaluated by subjecting the FPGAs to commercial-level temperature and supply voltage variations. In particular, we evaluate the reproducibility of the bitstrings generated at 0°C, 25°C, and 70°C, and at nominal and ±10% of the supply voltage. An error avoidance scheme is proposed that provides significant improvement against bit-flip errors in the bitstrings.