Stealthy Attacks on Multi-Agent Reinforcement Learning in Mobile Cyber-Physical Systems

Due to their mobility, real-time requirements, energy limitations, and safety considerations, the complexities involved in Mobile Cyber-Physical Systems (MCPSs) surpass those of traditional computing systems. To address these challenges, the use of multi-agent reinforcement learning (MARL) algorithms is gaining significance in the field of MCPS. MARL enables precise, instantaneous, and coordinated decision-making to maximize cumulative rewards through systematic trial and error, even in unfamiliar environments. While MARL algorithms can effectively learn scalable and efficient control policies for MCPSs, their resilience against security and safety attacks has not been thoroughly explored, severely limiting their real-world applications. This paper investigates the robustness of MARL-based MCPS against stealthy adversarial attacks which involve targeting and manipulating a specific mobile node in order to generate deceptive observations that adversely affect the behavior of other MCPS nodes. We adopt the FGSM (Fast Gradient Sign Method) adversarial example technique from deep learning to incorporate a detection evasion mechanism as a new stealth feature. The objective is to entice the compromised node to adopt an adversarial policy that deviates the activations of policy networks in its cooperative nodes from the expected distribution, while evading detection. We empirically demonstrate the susceptibility of MARL algorithms commonly employed in MCPSs, namely MADDPG, to our proposed attack strategies. The evaluation is conducted in three MCPSs, considering both white and black-box settings. By targeting a single node, our attacks have a significantly detrimental impact on the overall performance of the MCPS, resulting in a minimum reduction of 33% and a maximum reduction of 89.6% in the system's overall reward, with an evasion rate ranging from 16% to 36%.