With the advent of telecommunication and IT technologies coupled with the increasingly dominant roles played by e-commerce in every major industry, the development and implementation efforts in many areas of network security have drawn technologies from more and more seemingly unrelated technical fields that did not previously have to cross path or intimately interwork. These major technical fields include cryptography, network protocols, switch/router technology and information technology, each with already fully developed theories, standards as well as well-established practices. Trying to develop expertise in all of these technical fields is a challenging task. By introducing a unique, hierarchical framework based on the fundamental network security functional elements of confidentiality, authentication, authorization, message integrity and non-repudiation, this book presents the key network security-relevant technologies in these diverse fields in an organized, easy-to-follow fashion which greatly facilitates the understanding of not only the technologies themselves but also their inter-relationships and how they interwork.