1. Key Laboratory of Aerospace Information Security and Trusted Computing, Ministry of Education, School of Cyber Science and EngineeringWuhan University Wuhan China
2. Guangdong Provincial Key Laboratory of Data Security and Privacy Protection Guangzhou 510632 China
3. Jiangsu Key Laboratory of Big Data Security and Intelligent Processing, School of Computer Science, Nanjing University of Posts and Telecommunications Nanjing 210023 China
4. Division of Computer ScienceUniversity of Aizu Aizu‐Wakamatsu Japan