An enhanced searchable encryption scheme for secure data outsourcing

In the cloud environment, where the cloud server cannot always be fully trusted, both data and query privacy should be well protected for secure data outsourcing. Searchable encryption provides a more practical solution to secure data storage while enabling efficient search queries. In this paper, four important problems of public key encryption with keyword search (PEKS), namely, a scheme without secure channels, conjunctive keyword search, (offline) outside and inside keyword guessing attack (full KGA) resistance and proof in the standard model, are considered. We provide an in-depth analysis of the reasons behind (offline) full KGA by considering two types of PEKS schemes as examples. In particular, we introduce the concept of server-aided secure channel free public key encryption with conjunctive keyword search (SA-SCF-PECKS) which can resist (offline) full KGA. Furthermore, we provide a concrete and efficient construction of SA-SCF-PECKS, and prove its security in the standard model. To the best of our knowledge, our proposal is the first PECKS scheme to address these four problems simultaneously. We compare the security and efficiency of our scheme with those of other related PECKS schemes in theoretical and practical ways. In general, compared with other schemes, our SA-SCF-PECKS scheme shows better performance in terms of security and efficiency.