1551-3203 (c) 2017 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TII.2017.2786307, IEEE Transactions on Industrial Informatics 1 Consortium Blockchain for Secure Energy Trading in Industrial Internet of Things Zhetao Li, Member, IEEE, Jiawen Kang, Rong Yu, Member, IEEE, Dongdong Ye, Qingyong Deng, Yan Zhang, Senior Member, IEEE,. Abstract—In Industrial Internet of Things (IIoT), Peer-to-Peer (P2P) energy trading ubiquitously takes place in various scenar- ios, e.g., microgrids, energy harvesting networks, and vehicle-to- grid networks. However, there are common security and priva- cy challenges caused by untrusted and nontransparent energy markets in these scenarios. To address the security challenges, we exploit the consortium blockchain technology to propose a secure energy trading system named energy blockchain. This energy blockchain can be widely used in general scenarios of P2P energy trading getting rid of a trusted intermediary. Besides, to reduce the transaction limitation resulted from transaction confirmation delays on the energy blockchain, we propose a credit-based payment scheme to support fast and frequent energy trading. An optimal pricing strategy using Stackelberg game for credit-based loans is also proposed. Security analysis and numerical results based on a real dataset illustrate that the proposed energy blockchain and credit-based payment scheme are secure and efficient in IIoT. Index Terms—Blockchain, industrial Internet of things, energy trading, security and privacy, Stackelberg game. I. I NTRODUCTION I NDUSTRIAL Internet of Things (IIoT) has attracted enor- mous attention from academics and industries, which is a significant component of the future transformation of industrial systems [1], [2]. IIoT offers interconnection and intelligence to industrial systems through sensing devices and actuators with ubiquitous networking and computing abilities [3]. However, it is a great challenge for the industrial systems to satisfy the ever-increasing energy demands of IIoT applications, while IIoT nodes continue to grow in both numbers and performance requirements [4], [5]. To address this challenge, previous stud- ies have presented Peer-to-Peer (P2P) energy trading among This work was supported in part by programs of NSFC under Grant nos. 61379115, 61422201, 61370159 and U1301255, U1501251, the Sci- ence and Technology Program of Guangdong Province under Grant no. 2015B010129001, Special-Support Project of Guangdong Province under grant no. 2014TQ01X100, Science and Technology Program of Guangzhou under grant no. 2014J2200097, and is partially supported by the projects 240079/F20 funded by the Research Council of Norway. (Corresponding author: Yan Zhang.) Zhetao Li is with College of Information Engineering, Xiangtan University, Xiangtan 411105, Chian (e-mail: liztchina@gmail.com). Jiawen Kang, Rong Yu, and Dongdong Ye are with School of Automation, Guangdong University of Technology, Guangzhou 510006, China (e-mail: {jiawenkang, yurong and Dongdongye}@ieee.org). Qingyong Deng is with School of Information and Communication Engi- neering, Beijing University of Posts and Telecommunications, Beijing 100876, China, and also with College of Information Engineering, Xiangtan University, Xiangtan, Hunan 411105, China (dengqingyong@xtu.edu.cn). Yan Zhang is with University of Oslo, Norway, and also with Simula Research Laboratory, Norway (e-mail: yanzhang@ieee.org) IIoT nodes, such as electric vehicles [6]. The IIoT nodes can trade their surplus energy with other nodes in a P2P manner to locally satisfy energy demands, improve energy efficiency, and decrease transfer losses for promoting green industrial systems. Many emerging technologies have been introduced into green industrial systems, e.g., energy harvesting, wireless power transfer, and vehicle-to-grid [7]. Combined with these technologies, industrial systems develop various efficient and sustainable P2P energy trading scenarios [6]. There are three typical P2P energy trading scenarios for IIoT as following. • Microgrids: Smart buildings with solar panels or wind generators can form microgrids, in which the buildings harvest ambient energy and trade energy with each other by a P2P manner among the microgrids. • Energy harvesting networks: Industrial nodes with ener- gy harvesting ability can obtain energy from renewable energy, also charge themselves through a mobile charger using wireless power transfer by P2P energy trading. • Vehicle-to-grid networks: Electric vehicles acted as ener- gy storage devices perform charging operations at load valley, and feed their energy back into the power grid to reduce load peaks. Vehicles can also sell their energy to neighboring charging vehicles in a P2P manner with the help of local aggregators [8], [9]. Although P2P energy trading plays a vital role in IIoT, there are common security and privacy challenges for general P2P energy trading scenarios. I) It is insecure for IIoT nodes to carry out large-scale decentralized energy trading in untrusted and nontransparent energy markets. II) IIoT nodes with surplus energy may be not willing to participate as energy suppliers due to their concerns about privacy [10]. In this case, energy supply and demand are unbalanced among IIoT nodes. III) In P2P energy trading, there is an intermediary to audit and verify transaction record among IIoT nodes. This intermediary suffers from problems such as single point of failure and privacy leakage [11]. Therefore, it is important to design a unified and secure energy trading system for various energy trading scenarios in IIoT [11]. In addition, it is necessary to encourage more IIoT nodes with surplus energy to act as energy sellers by designing proper incentives. Recently, blockchain technology is studied in energy trading because of its advantages of decentralization, anonymity and trust. Blockchain is an open, distributed ledger that records transactions in a verifiable and permanent way, which is the underlying fabric for Bitcoin. A digital currency named