Crossover RO PUF-based Key Sharing for IoT Security.

In many Internet of Things (IoT) applications, resources like CPU, memory, and battery power are limited and cannot afford the classic cryptographic security solutions. Silicon Physical Unclonable Function (PUF) is a lightweight security primitive that exploits manufacturing variations during the chip fabrication process for key generation and/or device authentication. Ring Oscillator (RO) PUF as one of the most popular silicon weak PUFs can generate secret bits by comparing the frequency difference between any two ROs. Previous RO PUFs improve flexibility and reliability through adding redundant ROs, which incurs unacceptable hardware overheads. In addition, traditional weak PUFs such as RO PUF generate chip-unique key for each device, which restricts their application in security protocols where the same key is required to be shared in resource-constrained devices. In order to address these shortcomings, we propose a crossover RO PUF (CRO PUF) that improves flexibility, reliability and reduces hardware overheads. It is the first PUF that can generate the shared key in physically. The basic idea is to implement one-to-one input-output mapping with Lookup Table (LUT)-based interstage crossing structures in each level of inverters. Individual customization on configuration bits of interstage crossing structure and different RO selections with challenges bring high flexibility. Therefore, with the flexible configuration of interstage crossing structures and challenges, CRO PUF can generate the same shared key for resource-constrained devices, which enables a new application for lightweight key sharing protocols. Experimental results show that our proposed PUF structure has much lower hardware overheads, better uniqueness and reliability than the previous configurable RO PUFs.