ChainDB: Ensuring Integrity of Querying Off-Chain Data on Blockchain

Enterprise blockchain applications have been widely adopted and the data scale on blockchain increases rapidly in recent years. In practical application, participants prefer to store most of the business data in local database systems and only provide when queried by others due to privacy concerns, high storage cost, or constraints of on-chain space. However, this makes that the integrity of query results cannot be guaranteed and participants cannot fully trust others, and data owner has the opportunity to provide falsified records. In this paper, we present ChainDB, a relational database that can ensure integrity of querying off-chain data on blockchain. The key insight behind is using Merkle B+ tree as index structure, thus has being able to provide Merkle proof and keep all the records in order. Since the index structure is extended on B+ tree, ChainDB is compatible with common SQL operations and it is easy for enterprises to migrate from classic database systems to ChainDB. The experimental results show that ChainDB not only provides the ability to ensure integrity of querying off-chain data on blockchain, but also performs better than existing solutions.