Coward: Collision-based OOD Watermarking for Practical Proactive Federated Backdoor Detection

ArXi:2508.02115v4 Announce Type: replace-cross Backdoor detection is currently the mainstream defense against backdoor attacks in federated learning (FL), where a small number of malicious clients can upload poisoned updates to compromise the federated global model. Existing backdoor detection techniques fall into two categories, passive and proactive, depending on whether the server proactively intervenes in the