1. Department of Computer Engineering, Konkuk University, 268 Chungwondaero, Chungju, Chungcheongbuk-do 380-701, Republic of Korea
2. Information Assurance Research Group, Advanced Computing Research Centre, University of South Australia, Mawson Lakes, SA 5095, Australia
3. Department of Computer Engineering, Sungkyunkwan University, 2066 Seobu-ro, Suwon, Gyeonggi-do 440-746, Republic of Korea