Preface

Every day, the news media give more and more visibility to the effects of computer security on our daily lives. For example, on a single day in June 2006, the Washington Post included three important articles about security. On the front page, one article discussed the loss of a laptop computer containing personal data on 26.5 million veterans. A second article, on the front page of the business section, described Microsoft's new product suite to combat malicious code, spying, and unsecured vulnerabilities in its operating system. Further back, a third article reported on a major consumer electronics retailer that inadvertently installed software on its customers' computers, making them part of a web of compromised slave computers. The sad fact is that news like this appears almost every day, and has done so for a number of years. There is no end in sight.

Even though the language of computer securityterms such as virus, Trojan horse, phishing, spywareis common, the application of solutions to computer security problems is uncommon. Moreover, new attacks are clever applications of old problems. The pressure to get a new product or new release to market still in many cases overrides security requirements for careful study of potential vulnerabilities and countermeasures. Finally, many people are in denial, blissfully ignoring the serious harm that insecure computing can cause.

Why Read This Book?

Admit it. You know computing entails serious risks to the privacy and integrity of your data, or the operation of your computer. Risk is a fact of life: Crossing the street is risky, perhaps more so in some places than others, but you still cross the street. As a child you learned to stop and look both ways before crossing. As you became older you learned to gauge the speed of oncoming traffic and determine whether you had the time to cross. At some point you developed a sense of whether an oncoming car would slow down or yield. We hope you never had to practice this, but sometimes you have to decide whether darting into the street without looking is the best means of escaping danger. The point is all these matters depend on knowledge and experience. We want to help you develop the same knowledge and experience with respect to the risks of secure computing.

How do you control the risk of computer security?

• Learn about the threats to computer security.

• Understand what causes these threats by studying how vulnerabilities arise in the development and use of computer systems.

• Survey the controls that can reduce or block these threats.

• Develop a computing styleas a user, developer, manager, consumer, and voterthat balances security and risk.

The field of computer security changes rapidly, but the underlying problems remain largely unchanged. In this book you will find a progression that shows you how current complex attacks are often instances of more fundamental concepts.

Users and Uses of This Book

This book is intended for the study of computer security. Many of you want to study this topic: college and university students, computing professionals, managers, and users of all kinds of computer-based systems. All want to know the same thing: how to control the risk of computer security. But you may differ in how much information you need about particular topics: Some want a broad survey, while others want to focus on particular topics, such as networks or program development.

This book should provide the breadth and depth that most readers want. The book is organized by general area of computing, so that readers with particular interests can find information easily. The chapters of this book progress in an orderly manner, from general security concerns to the particular needs of specialized applications, and finally to overarching management and legal issues. Thus, the book covers five key areas of interest:

• introduction: threats, vulnerabilities, and controls

• encryption: the "Swiss army knife" of security controls

• code: security in programs, including applications, operating systems, database management systems, and networks

• management: building and administering a computing installation, from one computer to thousands, and understanding the economics of cybersecurity

• law, privacy, ethics: non-technical approaches by which society controls computer security risks

These areas are not equal in size; for example, more than half the book is devoted to code because so much of the risk is at least partly caused by program code that executes on computers.

The first chapter introduces the concepts and basic vocabulary of computer security. Studying the second chapter provides an understanding of what encryption is and how it can be used or misused. Just as a driver's manual does not address how to design or build a car, Chapter 2 is not for designers of new encryption schemes, but rather for users of encryption. Chapters 3 through 7 cover successively larger pieces of software: individual programs, operating systems, complex applications like database management systems, and finally networks, which are distributed complex systems. Chapter 8 discusses managing and administering security, and describes how to find an acceptable balance between threats and controls. Chapter 9 addresses an important management issue by exploring the economics of cybersecurity: understanding and communicating the costs and benefits. In Chapter 10 we turn to the personal side of computer security as we consider how security, or its lack, affects personal privacy. Chapter 11 covers the way society at large addresses computer security, through its laws and ethical systems. Finally, Chapter 12 returns to cryptography, this time to look at the details of the encryption algorithms themselves.

Within that organization, you can move about, picking and choosing topics of particular interest. Everyone should read Chapter 1 to build a vocabulary and a foundation. It is wise to read Chapter 2 because cryptography appears in so many different control techniques. Although there is a general progression from small programs to large and complex networks, you can in fact read Chapters 3 through 7 out of sequence or pick topics of greatest interest. Chapters 8 and 9 may be just right for the professional looking for non-technical controls to complement the technical ones of the earlier chapters. These chapters may also be important for the computer science student who wants to look beyond a narrow view of bytes and protocols. We recommend Chapters 10 and 11 for everyone, because those chapters deal with the human aspects of security: privacy, laws, and ethics. All computing is ultimately done to benefit humans, and so we present personal risks and approaches to computing. Chapter 12 is for people who want to understand some of the underlying mathematics and logic of cryptography.

What background should you have to appreciate this book? The only assumption is an understanding of programming and computer systems. Someone who is an advanced undergraduate or graduate student in computer science certainly has that background, as does a professional designer or developer of computer systems. A user who wants to understand more about how programs work can learn from this book, too; we provide the necessary background on concepts of operating systems or networks, for example, before we address the related security concerns.

This book can be used as a textbook in a one- or two-semester course in computer security. The book functions equally well as a reference for a computer professional or as a supplement to an intensive training course. And the index and extensive bibliography make it useful as a handbook to explain significant topics and point to key articles in the literature. The book has been used in classes throughout the world; instructors often design one-semester courses that focus on topics of particular interest to the students or that relate well to the rest of a curriculum.

What is New in This Book?

This is the fourth edition of Security in Computing, first published in 1989. Since then, the specific threats, vulnerabilities, and controls have changed, even though many of the basic notions have remained the same.

The two changes most obvious to people familiar with the previous editions are the additions of two new chapters, on the economics of cybersecurity and privacy. These two areas are receiving more attention both in the computer security community and in the rest of the user population.

But this revision touched every existing chapter as well. The threats and vulnerabilities of computing systems have not stood still since the previous edition in 2003, and so we present new information on threats and controls of many types. Change include:

• the shift from individual hackers working for personal reasons to organized attacker groups working for financial gain

• programming flaws leading to security failures, highlighting man-in-the-middle, timing, and privilege escalation errors

• recent malicious code attacks, such as false interfaces and keystroke loggers

• approaches to code quality, including software engineering, testing, and liability approaches

• rootkits, including ones from unexpected sources

• web applications' threats and vulnerabilities

• privacy issues in data mining

• WiFi network security

• cryptanalytic attacks on popular algorithms, such as RSA, DES, and SHA, and recommendations for more secure use of these

• bots, botnets, and drones, making up networks of compromised systems

• update to the Advanced Encryption System (AES) with experience from its first several years of its use

• the divide between sound authentication approaches and users' actions

• biometric authentication capabilities and limitations

• the conflict between efficient production and use of digital content (e.g., music and videos) and control of piracy

In addition to these major changes, there are numerous small corrective and clarifying ones, ranging from wording and notational changes for pedagogic reasons to replacement, deletion, rearrangement, and expansion of sections.

Acknowledgments

It is increasingly difficult to acknowledge all the people who have influenced this book. Colleagues and friends have contributed their knowledge and insight, often without knowing their impact. By arguing a point or sharing explanations of concepts, our associates have forced us to question or rethink what we know.

We thank our associates in at least two ways. First, we have tried to include references to their written works as they have influenced this book. References in the text cite specific papers relating to particular thoughts or concepts, but the bibliography also includes broader works that have played a more subtle role in shaping our approach to security. So, to all the cited authors, many of whom are friends and colleagues, we happily acknowledge your positive influence on this book. In particular, we are grateful to the RAND Corporation for permission to present material about its Vulnerability, Assessment and Mitigation method and to use its government e-mail analysis as a case study in Chapter 8. Second, rather than name individuals, we thank the organizations in which we have interacted with creative, stimulating, and challenging people from whom we learned a lot. These places include Trusted Information Systems, the Contel Technology Center, the Centre for Software Reliability of the City University of London, Arca Systems, Exodus Communications, the RAND Corporation, and Cable & Wireless. If you worked with us at any of these locations, chances are high that you had some impact on this book. And for all the side conversations, debates, arguments, and light moments, we are grateful. For this fourth edition, Roland Trope and Richard Gida gave us particularly helpful suggestions for Chapters 9 and 10.

Authors are the products of their environments. We write to educate because we had good educations ourselves, and because we think the best response to a good education is to pass it along to others. Our parents, Paul and Emma Pfleeger and Emanuel and Beatrice Lawrence, were critical in supporting us and encouraging us to get the best educations we could. Along the way, certain teachers gave us gifts through their teaching. Robert L. Wilson taught Chuck how to learn about computers, and Libuse L. Reed taught him how to write about them. Florence Rogart, Nicholas Sterling and Mildred Nadler taught Shari how to analyze and probe.

To all these people, we express our sincere thanks.

Charles P. Pfleeger
Shari Lawrence Pfleeger
Washington, D.C.