Organization

The organization of this book reflects its philosophy. It begins with mathematical fundamentals and principles that provide boundaries within which security can be modeled and analyzed effectively. The mathematics provides a framework for expressing and analyzing the requirements of the security of a system. These policies constrain what is allowed and what is not allowed. Mechanisms provide the ability to implement these policies. The degree to which the mechanisms correctly implement the policies, and indeed the degree to which the policies themselves meet the requirements of the organizations using the system, are questions of assurance. Exploiting failures in policy, in implementation, and in assurance comes next, as well as mechanisms for providing information on the attack. The book concludes with the applications of both theory and policy focused on realistic situations. This natural progression emphasizes the development and application of the principles existent in computer security.

Part 1, "Introduction," describes what computer security is all about and explores the problems and challenges to be faced. It sets the context for the remainder of the book.

Part 2, "Foundations," deals with basic questions such as how "security" can be clearly and functionally defined, whether or not it is realistic, and whether or not it is decidable. If it is decidable, under what conditions is it decidable, and if not, how must the definition be bounded in order to make it decidable?

Part 3, "Policy," probes the relationship between policy and security. The definition of "security" depends on policy. In Part 3 we examine several types of policies, including the ever-present fundamental questions of trust, analysis of policies, and the use of policies to constrain operations and transitions.

Part 4, "Implementation I: Cryptography," discusses cryptography and its role in security. It focuses on applications and discusses issues such as key management and escrow, key distribution, and how cryptosystems are used in networks. A quick study of authentication completes Part 4.

Part 5, "Implementation II: Systems," considers how to implement the requirements imposed by policies using system-oriented techniques. Certain design principles are fundamental to effective security mechanisms. Policies define who can act and how they can act, and so identity is a critical aspect of implementation. Mechanisms implementing access control and flow control enforce various aspects of policies.

Part 6, "Assurance," presents methodologies and technologies for ascertaining how well a system, or a product, meets its goals. After setting the background, to explain exactly what "assurance" is, the art of building systems to meet varying levels of assurance is discussed. Formal verification methods play a role. Part 6 shows how the progression of standards has enhanced our understanding of assurance techniques.

Part 7, "Special Topics," discusses some miscellaneous aspects of computer security. Malicious logic thwarts many mechanisms. Despite our best efforts at high assurance, systems today are replete with vulnerabilities. Why? How can a system be analyzed to detect vulnerabilities? What models might help us improve the state of the art? Given these security holes, how can we detect attackers who exploit them? A discussion of auditing flows naturally into a discussion of intrusion detection—a detection method for such attacks.

Part 8, "Practicum," presents examples of how to apply the principles discussed throughout the book. It begins with networks and proceeds to systems, users, and programs. Each chapter states a desired policy and shows how to translate that policy into a set of mechanisms and procedures that support the policy. Part 8 tries to demonstrate that the material covered elsewhere can be, and should be, used in practice.

Each chapter in this book ends with a summary, descriptions of some research issues, and some suggestions for further reading. The summary highlights the important ideas in the chapter. The research issues are current "hot topics" or are topics that may prove to be fertile ground for advancing the state of the art and science of computer security. Interested readers who wish to pursue the topics in any chapter in more depth can go to some of the suggested readings. They expand on the material in the chapter or present other interesting avenues.