1. Fujian Provincial Key Laboratory of Network Security and Cryptology, Fujian Normal University, Fuzhou, Fujian 350117, P. R. China
2. College of Mathematics and Statistics, Fujian Normal University, Fuzhou, Fujian 350117, P. R. China
3. Fujian Key Laboratory of Financial Information Processing, Putian University, Putian, Fujian 351100, P. R. China
4. Key Laboratory of Applied Mathematics of Fujian Province University, Putian University, Putian, Fujian 351100, P. R. China