Forward Secure Conjunctive-Keyword Searchable Encryption

Searchable symmetric encryption (SSE) has been applied in constructing secure cloud storage for its simplicity, high-efficiency, and practicality. Recent works show that forward privacy has become a fundamental property required for SSE, and several forward secure dynamic SSE schemes supporting single-keyword search have been proposed. However, to the best of our knowledge, there is no forward secure searchable encryption scheme supporting conjunctive-keyword search. In this paper, we propose two forward secure SSE schemes with conjunctive-keyword search functionality. Technically, in our basic scheme, we introduce a bloom filter on the client side to check the existence of keywords in a file. This also makes it easy to delete a file in locality rather than on the server side. In order to avoid the false positive probability of the bloom filter and reduce the redundant search results, we further propose a construction by applying secret-key inner-product encryption. Both of our schemes achieve sub-linear efficiency and one-round communication in the search protocol. Moreover, our methods are generic, as they can be applied to any forward secure single-keyword searchable encryption scheme to obtain a conjunctive-keyword one.