SCOOP: Scalable On-Chain-Off-Chain Storage in Blockchain-Based Decentralized Identity for Cyber-Physical-Social Systems

Blockchain-based decentralized identity (DID) technology provides a more secure and efficient paradigm for identity verification. However, along with the promotion of applications, data storage of DID has gradually become one of the restrictions for the implementation due to the dramatically increasing size of the distributed ledger, and the issue becomes more complicated when considering the diversity of practical conditions and interoperability. In this article, we propose a scalable on-chain-off-chain storage for decentralized identity (SCOOP) scheme to minimize the total storage cost of blockchain-based DID while guaranteeing the efficiency of the implementation. The proposed scheme consists of a two-phase decision-making process, and a method that integrates the on-chain storage with off-chain storage in a scalable manner, so that an optimal storage task scheduling can be generated. In addition, to reduce on-chain storage overhead, we propose a multilinear tree-based commitment scheme that supports sublinear proof aggregation and updates. Our experiment evaluations have demonstrated that the proposed scheme can successfully achieve a superior performance in storage saving for DID while considering the time constraint.