1. College of Mathematics and System Sciences; Shandong University of Science and Technology; Qingdao 266590 China
2. Shandong Province Key Laboratory of Wisdom Mine Information Technology; Shandong University of Science and Technology; Qingdao 266590 China
3. College of Computer Science and Engineering; Shandong University of Science and Technology; Qingdao 266590 China
4. Computing, Digital Forensics and Cybersecurity; Canterbury Christ Church University; Canterbury Kent CT1 1QU UK