Efficient Authentication Processing for Spatial Keyword Queries in Hybrid Storage Blockchain

Blockchain technology has emerged as a promising solution for secure data storage and retrieval for decentralized applications. To scale up the blockchain services, a common approach is to employ a hybrid storage architecture, where only meta-data are stored on-chain and the raw data are outsourced to an off-chain storage service provider. In this scenario, users need to query the data on-chain and off-chain at the same time, and the key issue for query processing would be how to design a gas-efficient authenticated data structure (ADS) to guarantee the completeness and soundness. In this paper, we study the spatial keyword authentication queries in the hybrid-storage blockchain, which includes on-chain and off-chain storage. We propose the GEMIR-tree index, which can significantly reduce the cost of maintenance by combing a single MIR-tree and a series of SMIR trees. Theoretical analysis and empirical evaluation are conducted to validate the performance of GEMIR-tree. Experimental results show that, compared to the baseline solution, the proposed GEMIR-tree index can efficiently reduce gas cost.