# FaDe: A Blockchain-Based Fair Data Exchange Scheme for Big Data Sharing  
[PERSON]  
1 State Laboratory of Public Big Data, GuiZhou University, Guizhou 550025, China; [EMAIL_ADDRESS]  
2 College of Computer Science and Technology, GuiZhou University, Guizhou 550025, China  
3 School of Computer Science, China University of Geosciences (Wuhan), Wuhan 430074, China; [EMAIL_ADDRESS] (J.G.); [EMAIL_ADDRESS] (C.L.)  
4 Hubei Key Laboratory of Intelligent Geo-Information Processing, China University of Geosciences (Wuhan), Wuhan 430074, China  
5 Correspondence: [EMAIL_ADDRESS]; Tel.: +86-027-67883716  
big data sharing have been proposed [3; 4], there are few comprehensive methods that can guarantee various requirements, e.g., legal data transaction, fair data sharing, and subtle privacy protection. We observe that blockchain technologies, e.g., BTC (Bitcoin), Ethereum, and especially smart contracts, can be employed for creating and implementing fair protocols in data exchanges and data transaction, by automatically executing the consented source codes and finding data in the ledger [5]. Furthermore, the blockchain network is a P2P (Point-To-Point) network, which makes data sharing easier without looking for a trusted data market. That is, data owners can conduct data transactions with data buyers autonomously, on demand, anytime and anywhere. It greatly promotes the data sharing between data owners and data buyers for utilizing data values conveniently, and avoids the leakage of data privacy to a third party as well.  
In P2P data transaction processes between data owners and data buyers, when data owners provide required data to data buyers, data buyers must pay the corresponding fee to data owners. Inversely, if data buyers pay a required fee to data owners, data owners must provide the corresponding data to data buyers. This is elementally fair. To solve this problem, simply speaking, we suggest that data buyers can choose a random part of data to read before deciding whether to continue buying it or not. The selection of such trial data has two advantages: it allows data buyers to evaluate the availability and authenticity of intended data, and it does not damage the profit of data owners due to few data leakages.  
In this approach, we still encounter two challenges: designing a protocol that can be implemented in the BTC script framework to ensure that the data and fee can be distributed to both parties at the same time without any trusted third party, in order to maintain the fairness of transactions. The second challenge is data buyers intending to justify the authenticity and availability of data before conducting guaranteed transactions by payment, and maintaining the benefit of data buyers, yet not damaging the profit of data owners. That is, we need a reasonable way to inspect trial data to be traded.  
By using bit commitment and a BTC script framework, we propose and implement a scheme called FaDe to overcome the challenges above and guarantee aforementioned requirements. The contribution of the paper is as follows:  
1. A decentralized scheme including data exchange protocol and implementation framework is proposed and designed. The proposed scheme enables data owners and data buyers to trade data directly without trusted third parties.
2. A fair data exchange protocol and the corresponding algorithm are proposed and presented, by which neither data owners lose traded data without acquiring sufficient payment, nor do data buyers finish payment without obtaining sufficient traded data.  
The rest of the paper is organized as follows: in Section 2, we review related work. Section 3 formulates research problems and challenges. Our proposed scheme is presented in Section 4. Section 5 presents evaluation and analysis, and we conclude this paper in Section 6.