Fault-tolerant Verifiable Encrypted Search on Blockchain

Verifiable Dynamic Searchable Symmetric Encryption (VDSSE) enables search and update functionalities over encrypted data, allowing users to utilize encrypted data outsourced to an untrusted server. The verifiable property ensures that users do not accept incorrect search results returned by the server. Recent works on VDSSE have focused on the forward-privacy property, which requires that an update operation cannot be linked to previous search queries. However, the majority of existing schemes focus on preventing curious or malicious behavior from the server but ignore faulty update operations by the client. Moreover, most current schemes store data on a single server or in centralized storage, which, in an untrusted environment, raises concerns over data storage reliability and integrity.In this paper, we explore how to solve the above problems with blockchain. First, we introduce a pragmatic approach to storing and accessing data on the blockchain while ensuring forward-privacy. Then, we use a smart contract to build a forward-private keyword mapping for verifying keyword search. Building upon these foundations, we formulate a decentralized, verifiable dynamic SSE scheme featuring a lightweight client and robust fault-tolerant properties. Following this, we use smart contract to establish fairness by devising a model that incentivizes each party to adopt honest behavior. We provide the prototype implementation on Ethereum. Experiments and evaluations demonstrate the practicability of our blockchain VDSSE scheme.