EPPVChain: An Efficient Privacy-Preserving Verifiable Query Scheme for Blockchain Databases

Blockchain databases have been exploited in many applications to construct trust and share data among multiple participants. However, maintaining the entire blockchain locally will cause heavy communication and storage overhead for users with limited resources. Alternatively, the user could act as a light node that stores block headers only and delegates queries to full nodes that maintain the entire blockchain. However, introducing a light node raises several concerns about query integrity and privacy. In this paper, we propose EPPVChain, the first scheme that simultaneously achieves efficient, privacy-preserving and verifiable conjunctive query for blockchain databases. EPPVChain resorts to a novel symmetric cryptographic primitive named Symmetric Hidden Vector Encryption (SHVE), and deploys several new techniques to achieve the desired goals. In specific, we design a new SHVE-based authenticated data structure to support privacy-preserving verifiable conjunctive queries. We further propose two improved schemes to aggregate data records to optimize query performance. Finally, we propose a dual-chain key escrow protocol to securely escrow the symmetric key of SHVE without relying on any trusted third party. The security analysis and evaluation confirm EPPVChain's ability to achieve query privacy and integrity with high efficiency.