Practical Multi-Source Multi-Client Searchable Encryption With Forward Privacy: Refined Security Notion and New Constructions

Multi-source multi-client (M/M) searchable encryption has drawn increasing attention as data sharing becomes prevalent in the digital economics era. It allows data from multiple sources to be securely outsourced to third parties and queried by authorized clients. In response to these demands, various schemes sprung up in the last few years. However, empirical results show that they suffer from performance limitations. Specifically, they either require per-interaction in per-query between data sources and clients or time-consuming public-key encryption. To address these issues, we propose a searchable encryption scheme that allows authorized clients to efficiently search encrypted data from multiple sources. Compared to previous schemes, our design reduces the interaction overhead of authorization and query with the aid of a set-constrained pseudo-random function. Given practical considerations in the M/M setting, we further refine the forward privacy (FP) as "FP with client" and "FP with server" for data addition. To achieve these new security notions, we construct a new M/M scheme only with efficient symmetric cryptographic tools. We perform a formal security analysis of the proposed schemes and implement them to compare with prior arts. The theoretical and experimental results confirm that our designs are practical with lower communication and computation overhead.