[1] Tsinghua Univ, Grad Sch Shenzhen, Shenzhen 518055, Peoples R China
[2] Chinese Acad Sci, Grad Univ, State Key Lab Informat Secur, Beijing 100049, Peoples R China
[3] Chinese Acad Sci, Inst Comp Technol, Key Lab Network Sci & Technol, Beijing 100190, Peoples R China