Affiliation: | 1. College of Mathematics and Information Science, Northwest Normal University, Lanzhou, Gansu 730070, PR China;2. State Key Lab. of Integrated Service Networks, Xidian University, Xi?an, Shaanxi 710071, PR China;3. Department of Mathematics, Putian University, Putian, Fujian 351100, PR China;4. State Key Laboratory of Information Security, Graduate School of Chinese Academy of Sciences, Beijing 100049, PR China |