This book constitutes the refereed proceedings of the 15th International Conference on Network and System Security, NSS 2021, held in Tianjin, China, on October 23, 2021.The 16 full and 8 short papers presented in this book were carefully reviewed and selected from 62 submissions.

Full papers.- RLTree: Website Fingerprinting through ResourceLoading Tree.- Re-check Your Certificates! Experiences and Lessons Learnt from Real-world HTTPS Certificate Deployments.- ZERMIA - A Fault Injector framework for testing Byzantine Fault Tolerant protocols.- Revocable Data Sharing Methodology Based on SGX and Blockchain.- On the Analysis of the Outsourced Revocable Identity-Based Encryption from Lattices.- Preventing Fake News Propagation in Social Networks using a context Trust-based security model.- A Lightweight Android Malware Detection Framework based on Knowledge Distillation.- Federated learning-based intrusion detection in the context of IIoT networks: Poisoning Attack and defense.- A Simplified and Effective Solution for Hybrid SDN Network Deployment.- Group Key Exchange Compilers from Generic Key Exchanges.- An architecture for processing a dynamic heterogeneous information network of security intelligence.- The Complexity of Testing Cryptographic Devices on Input Faults.- A Malware Family Classification Method Based on the Point Cloud Model DGCNN.- Collection of the main Anti-Virus detection and bypass techniques.- Profiled Attacks against the Elliptic Curve Scalar Point Multiplication using Neural Networks.- Deep Cross-modal Supervised Hashing based on Joint Semantic Matrix.- Short papers.- Accurate Polar Harmonic Transform-based Watermarking Using Blind Statistical Detector.- Cloud Key Management Based on Verifiable Secret Sharing.- A Scheme for Sensor Data Reconstruction in Smart Home.- Privacy-preserving and Auditable Federated Deep Reinforcement Learning for Robotic Manipulation.- HALNet: A Hybrid Deep Learning Model for Encrypted C&C Malware Traffic Detection.- Tracing Software Exploitation.- A Secure and Privacy Preserving Federated Learning Approach for IoT Intrusion Detection System.- Cryptanalysis of A Fully Anonymous Group Signature with Verifier-Local Revocation from ICICS 2018.

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