Random Coding Responses for Resisting Side-Channel Attacks in Client-Side Deduplicated Cloud Storage

Side-channel attacks are widespread in client-side deduplication systems, compromising the privacy of outsourced data. The adversary may infer the existence status of data via the deterministic relations between duplication requests and responses to launch side-channel attacks. Random Response (RARE) is one of the state-of-the-art approaches to overcome this issue, where the cloud server returns the randomized deduplication response for two requests at once to mitigate the risk of side-channel attacks. However, it still has some inherent limitations on communication efficiency and security. In this paper, we propose Random Coding Responses (RACORE), a lightweight and secure multi-chunk coding algorithm to address the limitations of RARE. RACORE achieves efficient multi-chunk coding and obfuscation based on the linear mapping induced by a specially constructed pseudo-random matrix. Compared to existing schemes, RACORE can strike a flexible balance between security and performance by adjusting parameters. Further, we present an enhanced composite matrix generation strategy to extend the coding matrix. Based on this strategy, we design an enhanced coding algorithm RACORE$^+$ to improve efficiency. Besides, we put forward a novel redundant chunk selection method to enhance the security of RACORE and RACORE$^+$. Rigorous security analysis and extensive experimental evaluation demonstrate that both RACORE and RACORE$^+$ can effectively resist side-channel attacks while reducing overhead compared to existing schemes.