Using Smart Contracts to Improve Searchable Symmetric Encryption

In this paper, we propose a smart contract based searchable symmetric encryption scheme. The existing searchable symmetric encryption protocol can resist malicious servers when using the MAC algorithm; however, it is more effective only under the assumption that the server is running. If the server receives a user’s money but does not provide a service to the user (or if the server shuts down after receiving the user’s money), the user cannot withdraw the money paid. In addition, if the server wants to reduce computing costs, bandwidth, etc., then it may reduce the number of documents to be searched or omit part of the search results. As a result, there is no guarantee that all files have been searched. We use the Merkle tree to construct search integrity verification. Implementing search integrity verification ensures that it is nearly impossible for searchers to provide integrity verification without searching all documents. Smart contracts use computing resources effectively and help us better search the blockchain. All information is recorded on the blockchain and will not be tampered with. In addition, integrity verification and smart contracts slightly reduce the efficiency but are feasible in practice. Finally, we have theoretically and experimentally verified the safety and feasibility of the proposed scheme.