Blockchain-Based Secure and Fair IoT Data Trading System with Bilateral Authorization

These days, data is regarded as a valuable asset in the era of the data economy, which demands a trading platform for buying and selling data. However, online data trading poses challenges in terms of security and fairness because the seller and the buyer may not fully trust each other. Therefore, in this paper, a blockchain-based secure and fair data trading system is proposed by taking advantage of the smart contract and matchmaking encryption. The proposed system enables bilateral authorization, where data trading between a seller and a buyer is accomplished only if their policies, required by each other, are satisfied simultaneously. This can be achieved by exploiting the security features of the matchmaking encryption. To guarantee non-repudiation and fairness between trading parties, the proposed system leverages a smart contract to ensure that the parties honestly carry out the data trading protocol. However, the smart contract in the proposed system does not include complex cryptographic operations for the efficiency of on-chain processes. Instead, these operations are carried out by off-chain parties and their results are used as input for the on-chain procedure. The system also uses an arbitration protocol to resolve disputes based on the trading proof recorded on the blockchain. The performance of the protocol is evaluated in terms of off-chain computation overhead and on-chain gas consumption. The results of the experiments demonstrate that the proposed protocols can enable the implementation of a cost-effective data trading system.