[Ma, Huifang;Zhang, Di;Wang, Yanru] Northwest Normal Univ, Coll Comp Sci & Engn, Lanzhou 730070, Gansu, Peoples R China.^[Ma, Huifang] Guilin Univ Elect Technol, Guangxi Key Lab Trusted Software, Guilin 541004, Guangxi, Peoples R China.^[Zhao, Weizhong] Cent China Normal Univ, Sch Comp, Wuhan 430079, Hubei, Peoples R China.^[Shi, Zhongzhi] Chinese Acad Sci, Inst Comp Technol, Key Lab Intelligent Informat Proc, Beijing 100190, Peoples R China.