Secure Cloud Storage Service with an Efficient DOKS Protocol

Storage services based on public clouds provide customers with elastic storage and on-demand accessibility. However, moving data to remote cloud storage also raises privacy concerns. Cryptographic cloud storage and search over encrypted data have attracted attentions from both industry and academics. In this paper, we present a new approach to constructing efficient oblivious keyword search (OKS) protocol, which permits fast search (i.e., sub-linear time) and relatively short ciphertext, while providing provably strong privacy for both users and cloud storage service providers. Previous OKS protocols have ciphertext size linear in the number of keywords, which consume much storage space and relatively long searching time. We formally define a Disjunctively Oblivious Keyword Search (DOKS) protocol realizing oblivious keyword search with the ciphertext size constant in size of keywords, which is significantly less than that of previous OKS protocols. Our approach improves both the privacy and efficiency of existing OKS protocols. With DOKS, adversary cannot distinguish two search keywords submitted by users, and cannot know the relations between ciphertext of documents and search keywords. A search keyword cannot be reused by adversaries. Users can get the matching documents without revealing statistical information on search keywords.