Table of Contents
| Foreword | |
| Preface to the Third Edition | |
| Ch. 1 | Is There a Security Problem in Computing? | 1 |
| Ch. 2 | Elementary Cryptography | 35 |
| Ch. 3 | Program Security | 95 |
| Ch. 4 | Protection in General-Purpose Operating Systems | 179 |
| Ch. 5 | Designing Trusted Operating Systems | 229 |
| Ch. 6 | Database Security | 309 |
| Ch. 7 | Security in Networks | 363 |
| Ch. 8 | Administering Security | 491 |
| Ch. 9 | Legal, Privacy, and Ethical Issues in Computer Security | 553 |
| Ch. 10 | Cryptography Explained | 629 |
| Bibliography | 691 |
| Index | 727 |
Forewords & Introductions
Preface to the Third Edition
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 2002, the Washington Post included three important articles about security. On the front page, one article described the possibility that a terrorist group was plotting to—and actually could—invade computer systems and destroy huge dams, disable the power grid, or wreak havoc with the air traffic control system. A second article, also on the front page, considered the potential loss of personal privacy as governments and commercial establishments begin to combine and correlate data in computer-maintained databases. Further back, a third article discussed yet another software flaw that could have widespread effect. Thus, computer security is no longer relegated to esoteric discussions of what might happen; it is instead a hot news topic, prominently featured in newspapers, magazines, radio talk shows, and documentary television programs. The audience is no longer just the technical community; it is ordinary people, who feel the effects of pervasive computing.
In just a few years the world's public has learned the terms "virus," "worm," and "Trojan horse" and now appreciates the concepts of "unauthorized access," "sabotage," and "denial of service." During this same time, the number of computer users has increased dramatically; with those new users have come new uses: electronic stock trading, sharing of medical records, and remote control of sensitive equipment, to name just three. It should be no surprise that threats to security in computing have increased along with the users anduses.
Why Read This Book?
Are your data or programs at risk? If you answer "yes" to any of the following questions, you have a potential security risk.
- Do you connect to the Internet?
- Do you read e-mail?
- Have you gotten any new programs—or any new versions of old programs—within, say, the last year?
- Is there any important program or data item of which you do not have a second copy stored somewhere other than on your computer?
Almost every computer user today meets at least one of these conditions, and so you, and almost every other computer user, are at risk of some harmful computer security event. Risk does not mean you should stop using computers. You are at risk of being hit by a falling meteorite or of being robbed by a thief on the street, but you do not hide in a fortified underground bunker all day. You learn what puts you at risk and how to control it. Controlling a risk is not the same as eliminating it; you simply want to bring it to a tolerable level.
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 style—as a user, developer, manager, consumer, and voter—that balances security and risk.
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 use 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, whereas 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: implementing and maintaining a computing style
- Law, privacy, ethics: nontechnical 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. 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 for users of encryption, not designers of new encryp 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 finding an acceptable balance between threats and controls. Chapter 9 covers the way society at large addresses computer security, through its laws and ethical systems and through its concern for privacy. Finally, Chapter 10 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 nontechnical 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. Chapter 10 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 students or that relate well to the rest of a curriculum.
What Is New in This Book?This is the third 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 networks and encryption. Networking has evolved even since the second edition was published, and there are many new concepts to master, such as distributed denial-of-service attacks or scripted vulnerability probing. As a consequence, the networks chapter is almost entirely new. Previous editions of this book presented encryption details in the same chapter as encryption uses. Although encryption is a fundamental tool in computer security, in this edition the what is presented straightforwardly in Chapter 2, while the how is reserved for the later Chapter 10. This structure lets readers get to the technical uses of encryption in programs and networks more quickly.There are numerous other additions, of which these are the most significant ones:
- the Advanced Encryption System (AES), the replacement for the Data Encryption System (DES) from the 1970s
- programming flaws leading to security failures, highlighting buffer overflows, incomplete mediation, and time-of-check to time-of-use errors
- recent malicious code attacks, such as Code Red
- software engineering practices to improve program quality
- assurance of code quality
- authentication techniques such as biometrics and password generators
- privacy issues in database management system security
- mobile code, agents, and assurance of them
- denial-of-service and distributed denial-of-service attacks
- flaws in network protocols
- security issues in wireless computing
- honeypots and intrusion detection
- copyright controls for digital media
- threats to and controls for personal privacy
- software quality, vulnerability reporting, and vendors' responsibilities
- the ethics of hacking
In addition to these major changes, there are numerous small corrective and clarifying ones, ranging from wording changes to subtle notational changes for pedagogic reasons to replacement, deletion, rearrangement, and expansion of sections.
Read an Excerpt
When the first edition of this book was published in 1989, viruses and other forms of malicious code were fairly uncommon, the Internet was used largely by just computing professionals, a Clipper was a sailing ship, and computer crime was seldom a headline topic in daily newspapers. In that era most people were unconcerned about—even unaware of—how serious is the threat to security in the use of computers.
The use of computers has spread at a rate completely unexpected back then. Now you can bank by computer, order and pay for merchandise, and even commit to contracts by computer. And the uses of computers in business have similarly increased both in volume and in richness. Alas, the security threats to computing have also increased significantly.
Why Read This Book? Are your data and programs at risk? If you answer "yes" to any of the following questions, you have a potential security risk. Have you acquired any new programs within the last year? Do you use your computer to communicate electronically with other computers? Do you ever receive programs or data from other people? Is there any significant program or data item of which you do not have a second copy? Relax; you are not alone. Most computer users have a security risk. Being at risk does not mean you should stop using computers. It does mean you should learn more about the risk you face, and how to control that risk.
Users and managers of large mainframe computing systems of the 1960s and l970s developed computer security techniques that were reasonably effective against the threats ofthat era. However, two factors have made those security procedures outdated:
Personal computer use. Vast numbers of people have become dedicated users of personal computing systems, both for business and pleasure. We try to make applications "user friendly" so that computers can be used by people who know nothing of hardware or programming, just as people who can drive a car do not need to know how to design an engine. Users may not be especially conscious of the security threats involved in computer use; even users who are aware may not know what to do to reduce their risk.
Networked remote-access systems. Machines are being linked in large numbers. The Internet and its cousin, the World-Wide Web, seem to double every year in number of users. A user of a mainframe computer may not realize that access to the same machine is allowed to people throughout the world from an almost uncountable number of computing systems.
Every computing professional must understand the threats and the countermeasures currently available in computing. This book addresses that need.
This book is designed for the student or professional in computing. Beginning at a level appropriate for an experienced computer user, this book describes the security pitfalls inherent in many important computing tasks today. Then, the book explores the controls that can check these weaknesses. The book also points out where existing controls are inadequate and serious consideration must be given to the risk present in the computing situation.
Uses of This Book The chapters of this book progress in an orderly manner. After an introduction, the topic of encryption, the process of disguising something written to conceal its meaning, is presented as the first tool in computer security. The book continues through the different kinds of computing applications, their weaknesses, and their controls.
The applications areas include: general programs
operating systems
data base management systems
remote access computing
multicomputer networks
These sections begin with a definition of the topic, continue with a description of the relationship of security to the topic, and conclude with a statement of the current state of the art of computer security research related to the topic. The book concludes with an examination of risk analysis and planning for computer security, and a study of the relationship of law and ethics to computer security.
Background required to appreciate the book is an understanding of programming and computer systems. Someone who is a senior or graduate student in computer science or a professional who has been in the field for a few years would have the appropriate level of understanding. Although some facility with mathematics is useful, all necessary mathematical background is developed in the book. Similarly, the necessary material on design of software systems, operating systems, data bases, or networks is given in the relevant chapters. One need not have a detailed knowledge of these areas before reading this book.
The book is designed to be a textbook for a one- or two-semester course in computer security. The book functions equally well as a reference for a computer professional. The introduction and the chapters on encryption are fundamental to the understanding of the rest of the book. After studying those pieces, however, the reader can study any of the later chapters in any order. Furthermore, many chapters follow the format of introduction, then security aspects of the topic, then current work in the area. Someone who is interested more in background than in current work can stop in the middle of one chapter and go on to the next.
This book has been used in classes throughout the world. Roughly half of the book can be covered in a semester. Therefore, an instructor can design a one-semester course that considers some of the topics of greater interest.
What Does This Book Contain? This is the revised edition of Security in Computing. It is based largely on the previous version, with many updates to cover newer topics in computer security. Among the salient additions to the new edition are these items:
Viruses, worms, Trojan horses, and other malicious code. Complete new section (first half of Chapter 5) including sources of these kinds of code, how they are written, how they can be detected and/or prevented, and several actual examples.
Firewalls. Complete new section (end of Chapter 9) describing what they do, how they work, how they are constructed, and what degree of protection they provide.
Private e-mail. Complete new section (middle of Chapter 9) explaining exposures in e-mail, kind of protection available, PEM and PGP, key management, and certificates.
Clipper, Capstone, Tessera, Mosaic, and key escrow. Several sections, in Chapter 3 as an encryption technology, and Chapter 4 as a key management protocol, and in Chapter 11 as a privacy and ethics issue.
Trusted system evaluation. Extensive addition (in Chapter 7) including criteria from the United States, Europe, Canada, and the soon-to-be-released Common Criteria.
Program development processes, including ISO 9000 and the SEI CMM. A major section in Chapter 5 gives comparisons between these methodologies.
Guidance for administering PC, Unix, and networked environments. In addition to these major changes, there are numerous small changes, ranging from wording changes to subtle notational changes for pedagogic reasons, to replacement, deletion, rearrangement, and expansion of sections.
The focus of the book remains the same, however. This is still a book covering the complete subject of computer security. The target audience is college students (advanced undergraduates or graduate students) and professionals. A reader is expected to bring a background in general computing technology; some knowledge of programming, operating systems, and networking is expected, although advanced knowledge in those areas is not necessary. Mathematics is used as appropriate, although a student can ignore most of the mathematical foundation if he or she chooses.
Acknowledgments Many people have contributed to the content and structure of this book. The following friends and colleagues have supplied thoughts, advice, challenges, criticism, and suggestions that have influenced my writing of this book: Lance Hoffman, Marv Schaefer, Dave Balenson, Terry Benzel, Curt Barker, Debbie Cooper, and Staffan Persson. Two people from outside the computer security community were very encouraging: Gene Davenport and Bruce Barnes. I apologize if I have forgotten to mention someone else; the oversight is accidental.
Lance Hoffman deserves special mention. He used a preliminary copy of the book in a course at George Washington University. Not only did he provide me with suggestions of his own, but his students also supplied invaluable comments from the student perspective on sections that did and did not communicate effectively. I want to thank them for their constructive criticisms.
Finally, if someone alleges to have written a book alone, distrust the person immediately. While an author is working 16-hour days on the writing of the book, someone else needs to see to all the other aspects of life, from simple things like food, clothing, and shelter, to complex things like social and family responsibilities. My wife, Shari Lawrence Pfleeger, took the time from her professional schedule so that I could devote my full energies to writing. Furthermore, she soothed me when the schedule inexplicably slipped, when the computer went down, when I had writerÕs block, or when some other crisis beset this project. On top of that, she reviewed the entire manuscript, giving the most thorough and constructive review this book has had. Her suggestions have improved the content, organization, readability, and overall quality of this book immeasurably. Therefore, it is with great pleasure that I dedicate this book to Shari, the other half of the team that caused this book to be written.
Charles P. Pfleeger Washington DC
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