Beyond Passive Aggregation: Active Auditing and Topology-Aware Defense in Decentralized Federated Learning
This addresses security risks in decentralized federated learning systems, offering an incremental improvement over existing defenses.
The paper tackles the vulnerability of Decentralized Federated Learning to adaptive backdoor attacks by introducing an active auditing framework with novel metrics and a topology-aware defense strategy, achieving competitive performance with state-of-the-art defenses in mitigating stealthy attacks while preserving utility.
Decentralized Federated Learning (DFL) remains highly vulnerable to adaptive backdoor attacks designed to bypass traditional passive defense metrics. To address this limitation, we shift the defensive paradigm toward a novel active, interventional auditing framework. First, we establish a dynamical model to characterize the spatiotemporal diffusion of adversarial updates across complex graph topologies. Second, we introduce a suite of proactive auditing metrics, stochastic entropy anomaly, randomized smoothing Kullback-Leibler divergence, and activation kurtosis. These metrics utilize private probes to stress-test local models, effectively exposing latent backdoors that remain invisible to conventional static detection. Furthermore, we implement a topology-aware defense placement strategy to maximize global aggregation resilience. We provide theoretical property for the system's convergence under co-evolving attack and defense dynamics. Numeric empirical evaluations across diverse architectures demonstrate that our active framework is highly competitive with state-of-the-art defenses in mitigating stealthy, adaptive backdoors while preserving primary task utility.