arXiv Machine Learning By Motoki Nakamura

Dynamic Free-Rider Detection in Cross-Silo Federated Learning via Simulated Attack Patterns

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The paper introduces S2-WEF, a dynamic free‑rider detection method for cross‑silo federated learning. It simulates weight‑evolving‑frequency (WEF) patterns of global‑model‑mimicking attacks on the server side and compares them with clients’ submitted WEFs, combining this similarity with a deviation score from mutual WEF comparisons. Using two‑dimensional clustering and per‑score classification, S2‑WEF can identify clients that switch to free‑riding during training, achieving robust detection across four datasets and five attack types without requiring proxy datasets or pre‑training.

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arXiv AI
Sep 24

When Clients Are Orchestrated: Strategic Gradient Manipulation to Defeat Federated Learning Servers with Efficient Defense

The paper introduces Fed-ADR, a coordinated attack framework where a malicious orchestrator server directs heterogeneous adversarial clients to adapt their gradient updates in real time, thereby evading existing federated learning defenses and drastically reducing global model accuracy. It also presents a lightweight detection mechanism that estimates true client gradients from historical data to spot coordinated attacks, and an in-situ recovery method that restores model performance without restarting training. Experiments on MNIST, Fashion‑MNIST, and CIFAR‑10 show the attack can drop accuracy from over 90% to below 10%, while the defense can recover accuracy to above 90% within a few rounds at a computational cost at least 20× lower than retraining from scratch.

By Mohamed Shaaban, Ahmed Abdelnaby, Mohamed Elmahallawy