Ultra-Lightweight and Reconfigurable Tristate Inverter Based Physical Unclonable Function Design

A physical unclonable function (PUF) is a promising security primitive which utilizes the manufacturing process variations to generate a unique unclonable digital fingerprint for a chip. It is especially suitable for resource constrained security applications, e.g. internet of things (IoT) devices. The ring oscillator (RO) PUF and the static RAM (SRAM) PUF are two of the most extensively studied PUF designs. However, previous RO PUF designs require a lot of hardware resources for ROs to be robust and SRAM PUFs are not suitable for authentication. The previous research by the author proposed a tristate static RAM (TSRAM) PUF which is a highly flexible challenge response pair (CRP) based SRAM PUF design. In this paper, a novel configurable PUF structure based on tristate inverters, namely a tristate configurable ring oscillator (TCRO) PUF is proposed. A configurable delay unit, composed of a tristate matrix, is used to replace the inverters in the RO PUF. The configurable bits are able to select a subset of the tristate inverters in the delay unit. Each tristate inverter is completely utilized by using the configurable delay unit and thus the approach enhances the flexibility and entropy of the proposed PUF design. The proposed PUF design can generate an exponential number of CRPs compared with the conventional RO PUF. Moreover, the proposed design significantly reduces the hardware resource consumption of the RO PUF. Delay models of both the TSRAM PUF and the proposed TCRO PUF designs are presented. A comprehensive evaluation of the TSRAM PUF is proceeded. To validate the proposed TSRAM PUF and TCRO PUF designs, a simulation based on UMC 65nm technology and a hardware implementation on a Xilinx Virtex-II FPGA are presented. The experimental results demonstrate good uniqueness and reliability as well as high efficiency in terms of hardware cost.