Title: TAPPFL: TASK-AGNOSTIC PRIVACY-PRESERVING REPRESENTATION LEARNING FOR FEDERATED LEARNING AGAINST ATTRIBUTE INFERENCE ATTACKS. Abstract: Federated learning (FL), a new collaborative learning paradigm, has been widely studied recently due to its property to collaboratively train data from different sources without needing to share the raw training data. Nevertheless, recent studies show that an adversary (e.g., an honest-but-curious server) can still be possible to infer private information about the training data, e.g., sensitive information such as income, race, and sexual orientation. To mitigate the attribute inference attacks, various existing privacy-preserving FL methods can be adopted/adapted. However, all these existing methods have key limitations: they need to know the FL task in advance, or have intolerable computational overheads or utility losses, or do not have provable privacy guarantees. We aim to address all these issues and design a task-agnostic privacy-preserving FL (short for TAPPFL) method against attribute inference attacks from the information-theoretic perspective. Specifically, we formally formulate TAPPFL via two mutual information goals, where one goal learns task-agnostic data representations that contain the least information about the private attribute in each device’s data, and the other goal includes as much information as possible about the training data to maintain utility. However, it is intractable to compute exact mutual information in general. Then, we derive tractable variational mutual information bounds, and each bound can be parameterized via a neural network. Next, we alternatively train these parameterized neural networks to approximate the true mutual information and learn privacy-preserving representations for device data. We also derive theoretical privacy guarantees of our TAPPFL against worst-case attribute inference attacks. Extensive results on multiple datesets and applications validates the effectiveness of our TAPPFL to protect data privacy, maintain the FL utility, and be efficient as well.