1. Tianjin Key Laboratory of Advanced Networking (TANK), School of Computer Science and TechnologyTianjin University Tianjin 300350 China
2. State Key Laboratory of Information Security, Institute of Information EngineeringChinese Academy of Sciences Beijing 100093 China
3. Institute of Cybersecurity and Cryptology, School of Computing and Information TechnologyUniversity of Wollongong Wollongong, NSW 2522 Australia