Authenticated Subgraph Matching in Hybrid-Storage Blockchains

Graphs serve as an essential data structure to model complex relationships in a variety of applications, such as social networks, web graphs, and chemical informatics. Due to the high cost of maintaining large-scale graph data and executing graph queries, data owners often outsource their graph data to a third-party service provider for graph processing. In this scenario, it is crucial to ensure the integrity of query results, as the provider may have the incentive to return only partial or tampered results to save computing resources or serve their own interests. Blockchain, as a promising solution for secure data storage and retrieval, opens up new opportunities for data management in such scenarios. To scale the blockchain, many works have been conducted using off-chain storage while ensuring the integrity of query results for key-value data in hybrid-storage blockchain architectures. To our knowledge, there is no work to enable the blockchain to support subgraph matching queries. In this paper, we present a novel approach to support authenticated subgraph matching queries for large graphs kept off-chain. We first design the authenticated data structure as MELTree and keep the digests of the roots on-chain. We propose the verification object (VO) construction algorithm AMatching for queries to ensure the completeness and soundness of the results. To further reduce the cost, we propose AMatching* based on a bidirectional search including forward search and reverse search. Moreover, we further optimize the on-chain storage cost by proposing MVPTree, which organizes the structures for vertices and only needs to keep one root digest on-chain for verification. Experimental results show that the proposed algorithms and the optimizations improve the performance significantly.