1. Research Institute, Korea Electric Power Corporation, Yuseong-Gu, Daejeon 305-706, Republic of Korea
2. Department of Computer Engineering, Korea University of Technology and Education, Cheonan, Chungnam 330-708, Republic of Korea
3. The Faculty of Liberal Arts, Korea University of Technology and Education, Cheonan, Chungnam 330-708, Republic of Korea
4. Department of Computer Engineering, Chungnam National University, Yuseong-Gu, Daejeon 305-764, Republic of Korea
5. Information Security Engineering, Soonchunhyang University, Asan, Chungnam 336-745, Republic of Korea