Dynamic Dual-level Defense Routing for Continual Adversarial Training

As adversarial attacks continue to evolve, defense models face the risk of recurrent vulnerabilities, underscoring the importance of continuous adversarial training (CAT). Existing CAT approaches typically balance decision boundaries by either data replay or optimization strategy to constrain shared model parameters. However, due to the diverse and aggressive nature of adversarial examples, these methods suffer from catastrophic forgetting of previous defense knowledge after continual learning. In this paper, we propose a novel framework, called Dual-level Defense Routing or DDeR, that can autonomously select appropriate routers to integrate specific defense experts, thereby adapting to evolving adversarial attacks. Concretely, the first-level defense routing comprises multiple defense experts and routers, with each router dynamically selecting and combining suitable experts to process attacked features. Routers are independently incremented as continuous adversarial training progresses, and their selections are guided by an Adversarial Sentinel Network (ASN) in the second-level defense routing. To compensate for the inability to test due to the independence of routers, we further present a Pseudo-task Substitution Training (PST) strategy, which leverages distributional discrepancy in data to facilitate inter-router communication without storing historical data. Extensive experiments demonstrate that DDeR achieves superior continuous defense performance and classification accuracy compared to existing methods.