Privacy-preserving Schemes for Fog-based IoT Applications: Threat models, Solutions, and Challenges

In this paper, we present a survey of existing privacy-preserving schemes for fog-based Internet of Things (IoT) applications. We start by describing fundamentals of fog computing architecture and presenting an overview of the fog-based IoT applications. Then we discuss major attacks in fog-based IoT applications and we provide a taxonomy and a side-by-side comparison of the state-of-the-art methods towards secure and privacy-preserving fog-based IoT applications with respect to network model, specific security goals, performance, limitations, and complexity. Based on the existing security models, we classify privacy-preserving models for fog-based IoT applications in eight categories, including, holistic privacy, privacy-preserving aggregation, trajectory privacy, conditional privacy preservation, differential privacy, data privacy, user's privacy, and location privacy. In addition, we highlight open research challenges and discuss possible future research directions in the privacy-preserving for fog-based IoT applications.