VQL: Providing Query Efficiency and Data Authenticity in Blockchain Systems

Blockchain, as the underlying technique of cryptocurrency, has triggered a wave of innovation in decentralized computing. Despite some research on blockchain data query, a primary concern for blockchain to be fully practical is to combat the data query inefficiency and query result authenticity. To provide both efficient and verifiable data query services for blockchain-based systems, we propose a Verifiable Query Layer (VQL). The middleware layer extracts transactions stored in the underlying blockchain system and efficiently reorganizes them in databases to provide various query services for public users. To prevent falsified data being stored in the middleware, a cryptographic hash value is calculated for each constructed database. The database fingerprint including the hash value and some database properties will be first verified by miners and then stored in the blockchain. We implement VQL and conduct extensive experiments based on a practical blockchain system Ethereum. The evaluation results demonstrate that VQL can effectively support various data query services and guarantee the authenticity of query results for the blockchain system.