A new method for enhancing variety and maintaining reliability of PUF responses and its evaluation on ASICs

Physically unclonable functions (PUFs) are expected to provide a breakthrough in anti-counterfeiting devices for secure ID generation and authentication, etc. Factory-manufactured PUFs are generally more secure if the number of outputs (the variety of responses) is larger (e.g., a 256-bit full-entropy response is more secure than a 128-bit response). In Yamamoto et al. (J Cryptogr Eng 3(4):197–211, 2013), we presented a latch-based PUF structure, which enhances the variety of responses by utilizing the location information of the RS (Reset-Set) latches outputting random numbers. We confirmed the effectiveness of this method using two kinds of different Xilinx FPGA chips: Spartan-3E and Spartan-6. In this paper, we propose a novel method of further enhancing the variety of responses while maintaining the reliability of responses, i.e., consistency over repeated measurements. The core idea in this method is to effectively utilize the information on the proportion of ‘1’s in the random number sequence output by the RS latches. This proportion information is determined during the manufacturing process, making it relatively stable and reliable once PUFs are manufactured. We estimated the variety of responses generated by the PUFs to which the proposed method was applied. According to our experiment with 73 ASIC chips fabricated by a 0.18-\(\upmu \)m CMOS process, latch-based PUFs with 256 RS latches can improve the variety of responses to as much as \(2^{379}\). This is much larger than \(2^{220}\) for conventional methods, and \(2^{314}\) for our previous method presented in Yamamoto et al., J Cryptogr Eng 3(4):197–211, 2013). The average error rate (reliability) of responses is only 0.064 when both temperature and voltage are changed to \(-20 \sim 60^\circ \)C and \(1.80 \pm 0.15\mathrm{V}\), respectively. Our proposed PUF enhances the variety of responses dramatically while maintaining reliability.