1. Beijing Key Laboratory of Security and Privacy in Intelligent Transportation, Beijing Jiaotong University, China
2. School of Computer and Information Technology, Beijing Jiaotong University, China
3. Beijing Key Laboratory of Security and Privacy in Intelligent Transportation, Beijing Jiaotong University, China and Division of Computer, Electrical and Mathematical Sciences 8 Engineering (CEMSE), King Abdullah University of Science and Technology (KAUST), Saudi Arabia