1. State Key Laboratory of Software Development Environment, School of Computer Science and Engineering; Beihang University; Beijing 100191 China
2. School of Computer Science and Engineering; Hunan University of Science and Technology; Xiangtan 411201 China
3. Department of Mathematics, Agra College; Dr. B. R. A. University; Agra 282002 Uttar Pradesh India
4. Center of Excellence in Information Assurance; King Saud University; Riyadh Saudi Arabia