Client-side data deduplication enables cloud storage services (e.g., Dropbox) to achieve both storage and bandwidth savings, resulting in reduced operating cost and high level of user satisfaction. However, the deduplication checks (i.e., the corresponding essential message exchange) create a side channel, exposing the privacy of file existence status to the attacker. In particular, the binary response from the deduplication check reveals the information about the existence of a copy of the file in the cloud storage. This behavior can be exploited to launch further attacks such as learning the sensitive file content and establishing a covert channel. While current solutions provide only weaker privacy or rely on unreasonable assumptions, we propose RAndom REsponse (RARE) approach to achieve stronger privacy. The idea behind our proposed RARE solution is that the uploading user sends the deduplication request for two chunks at once. The cloud receiving the deduplication request returns the randomized deduplication response with the careful design so as to preserve the deduplication gain and at the same time minimize the privacy leakage. Our analytical results confirm privacy guarantee and results show that both deduplication benefit and privacy of RARE can be preserved.
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