  In many Industry Internet of Things (IIoT) 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.
However, traditional weak PUFs such as Ring Oscillator (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 this issue, we propose a PUF-based key sharing
method for the first time. 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 of RO PUF. 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.
