Abstract
Programmable Logic Controllers (PLCs) are essential for Cyber-Physical Systems (CPS) but lack a software solution for lightweight message authentication to ensure the authenticity and integrity of data. A state-of-the-art lightweight signature, called LiS, is recently proposed for continuous message authentication in CPS, based on a chameleon hash function and a universal hash function (UHF) chain. Meanwhile, the signer and verifier should synchronize the randomness in the UHF chain for message authentication. To deal with the intermittent message authentication, Yang et al. proposed a lightweight authentication scheme LARP to replace the UHF chain with a UHF tree, in which each layer is divided by a series of time slots. The signer can quickly skip some randomness rather than linearly update the randomness as in LiS. However, the computational overhead required for synchronization might be expensive in LARP when the signer is suspended for a long time. Additionally, the overhead fluctuates greatly with the growth of interruption time. In this paper, we first propose an optimized UHF tree to reduce the overhead and mitigate its growth fluctuation. In particular, we implement our optimized scheme on an Allen Bradley ControlLogix 5571, leveraging fast modular reduction of pseudo-Mersenne prime to achieve efficient modulo operation. Our results demonstrate, for the first time, the feasibility and efficiency of running a lightweight signature scheme on the PLC.