Cactus: Obfuscating Bidirectional Encrypted TCP Traffic at Client Side

As the mainstream encrypted protocols adopt TCP protocol to ensure lossless data transmissions, the privacy of encrypted TCP traffic becomes a significant focus for adversaries. They can leverage Deep Learning (DL) models to infer the sensitive information from encrypted TCP traffic by analyzing its packet size, direction, and timing information. To defend against such DL-based traffic analysis attacks, recent advances reshape the encrypted traffic and achieve desired results. However, they typically require deploying cooperative modules on both communication endpoints and only support specific applications, such as browsers. In this paper, we propose Cactus, a client-side plug-in to obfuscate bidirectional encrypted TCP traffic for a wide range of applications transparently using the inherent TCP semantics and the emerging eBPF technique. In particular, Cactus provides four effective operations to enable bidirectional traffic obfuscation while preserving communication semantics of applications. Besides, Cactus empowers users to specify which applications to conduct traffic obfuscation and what obfuscation level for each application. We conduct comprehensive experiments to demonstrate that Cactus can effectively obfuscate encrypted TCP traffic with low overhead to hinder the traffic analysis efforts in website fingerprinting and application identification.