Rethinking Practical Blockchain-Based Symmetric Searchable Encryption Services

Blockchain-based cloud storage is one of the areas which have been developing rapidly in both academia and industry in recent years. As a key feature to improve the usability of such systems, keyword search is yet missing in existing blockchain-based cloud storage systems due to the encryption of uploaded files. To enable this important feature for blockchain-based cloud storage systems while preserving privacy, blockchain-based Symmetric Searchable Encryption schemes have attracted a lot of research interest. In this research, we pinpoint three important requirements for blockchain-based SSE systems to be practical. The first two requirements are fast query response and low on-chain storage cost. They are the key for a blockchain-based SSE system to be usable and feasible. The third requirement is soundness, which guarantees that dishonest behaviours from both users and service providers can be detected and prevented. To the best of our knowledge, none of the existing studies achieves these properties at the same time. To fill in this gap, we present a novel construction of the blockchain-based SSE system. We provide both theoretical analysis and empirical evaluation to show that the system achieves all the desired properties.