My sincere gratitude to my supervisor, Prof. Maode Ma from Nanyang Technological University (NTU), for his constructive guidance, technical discussions and constant encouragement throughout the course of my Master research works. The profound knowledge in network security, fluent writing skills, distinct analytical skills and high research integrity possessed by Prof. Ma have inspired my enthusiasm in research field. Prof. Ma is not only a supervisor to my research work but also a mentor of my life, who always provides me with priceless opinions for career and life. It is quite delightful and lucky to have a chance to work under Prof. Ma's supervision. Great thanks to my other group members (Mr. Cao Jin, Mr. He Tuo and Miss. Qiu Yue) and my close friends (Mr. Yew Kwang sing, Mr. Liu Pan, and Mr. Gu Chenjie) for their all-round support and friendships. I dedicate this dissertation to my parents and sister. Their precious love and support are always the motivation of my life. II