Fair²Trade: Digital Trading Platform Ensuring Exchange and Distribution Fairness

Online data trading is increasingly prevalent as data are becoming valuable assets. In most common conventional data trading scenarios, three parties (seller, broker, and buyer) exist, and fairness in trading is essential. This paper discusses and solves the fairness problem in two aspects. First, we consider exchange fairness , which requires payments and data exchanged correctly between buyers and the broker. In existing solutions, keys of encrypted data are traded. However, these solutions failed to provide a complete and secure design for validating keys' correctness unless they used generic theoretical but expensive methods, e.g., zk-SNARK. We address this security issue by designing a new key verification mechanism. We also present a novel atomic exchange protocol based on Hashed Timelock Contracts on Ethereum, reducing gas consumption compared to the existing approach. Second, we consider distribution fairness , which requires correctly splitting income between the broker and sellers. Straightforward solutions are impractical, i.e., sellers participating in every transaction or traversing the blockchain. Therefore, we design a verifiable statement protocol for sellers to verify the income split efficiently. Further, analysis and experimental results indicate that extra fairness properties are securely achieved, and our protocol reduces users' on-chain participation compared to state-of-the-art protocols.