Mr. Scott Mix, The North American Electric Reliability Corporationtion configurations. On the other hand, the prototype system SecureSCL has a potential of being developed into a realistic application for power substations. iii To my beloved wife Ying Wang iv Acknowledgement First and foremost, I would like to express my great appreciation to my supervisor, Professor Carl A. Gunter, for his guidance, assistance, encouragement during this research and many years Ph.D. study. The opportunities and learning experiences he has given me are deeply appreciated. My experience at University of Illinois at Urbana-Champaign and University of Pennsylvania is especially rewarding and helpful in my future career because of his patient and strong supports not only in the research work but also in the career design. I’m grateful for his unconditional moral support, which is one of the factors that led me to completion of my Ph.D. studies. I would like to thank my thesis committee members. Professor Roy Campbell raised my attention to some problems I missed at the beginning. Professor William Sanders not only offered good advice to the dissertation but also created a great environment in the TCIP group, which is a strong backup for my research. Professor Samuel King provided insightful comments for the system analysis of PCES-HS. Mr. Scott Mix helped me identify the real problems in power industry. Their efforts to my thesis work help me accomplish the Ph.D. study with solid output. I have a great research group. Micheal LeMay was a wonderful office-mate for many years and I enjoyed our joint research efforts and interesting technical talks. The conversation to Alwyn Goodloe helped me thoroughly understand IPsec and related topics. I would also like to acknowledge the support and the friendship from others working in the group, in particular, Raja Afandi, Jodie Boyer, Sonia Jahid, Hee-