Searching for Encrypted Data on Blockchain: An Efficient, Secure and Fair Realization

Abstract

Searchable symmetric encryption (SSE) is a research hotspot in applied cryptography, with the purpose of protecting outsourced data while enabling querying of encrypted data. However, the majority of current research focuses on the scenario in which data is stored on a single server and disregards the possibility that both the clients and servers are malicious. While several existing blockchain-based SSE schemes provide solutions to the issues above, they do not simultaneously achieve security, fairness, and decentralized storage. In this paper, we explore how to efficiently solve the above problems in the blockchain setting. We build up a decentralized fair SSE framework in a layered fashion. First, we present a practical and efficient method for accessing data on the blockchain. Based on this, we craft a decentralized publicly verifiable SSE scheme in which encrypted indexes are stored on the blockchain and search operations are shifted to be executed off-chain for lightweight decentralized storage and efficient query performance. Then, we use smart contracts to confer fairness to SSE by constructing a game model that makes each party prefer to cooperate. Finally, we implement and evaluate our framework on Ethereum. The experimental results demonstrate that our design is effective and practical.