Internet Besieged: Countering Cyberspace Scofflaws / Edition 1

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Overview

Break-ins on the Internet! Assaults on privacy! Theft of information!

Break-ins, assaults, and thefts are prohibited. Yet they happen. How is this so? Just how clever are the invaders? What are the holes in supposedly secure systems? Internet Besieged explains the ingenious strategies employed by intruders. It shows how security experts must be both defensive and proactive to protect information, privacy, and electronic commerce.

Internet Besieged consists of over thirty original and recently published chapters written by leading figures in security. They range from technical explanations of encryption and intrusion-detection systems to popular accounts of hacker attacks.

Internet Besieged is organized for the general reader as well as the practicing professional. It covers:

  • The emergence of the Internet-the evolution of security problems and required countermeasures
  • Major patterns of weakness in Internet-connected computer systems and methods for preventing and detecting attacks
  • The use of cryptography to secure computers and data on the Internet
  • Electronic commerce and secure transactions-authentication and integrity-checking technologies; foiling identity theft
  • Ethics, laws, practices, and policies that govern human interaction on the Internet

For software developers, system managers and engineers, students, and concerned citizens, this book provides a broad awareness of Internet security risk while exploring the social, legal, political, and ethical implications of security breaches and suggested countermeasures.

Contributors include: Steve Bellovin, Matt Bishop, Bill Cheswick, Jim Christy, Stephen T. Kent, Steven Levy, Teresa Lunt, Peter G. Neumann, E. Eugene Schultz, Eugene H. Spafford, and Bruce Sterling.

0201308207B04062001

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Product Details

  • ISBN-13: 9780201308204
  • Publisher: Addison-Wesley
  • Publication date: 9/30/1997
  • Series: ACM Press Series
  • Edition number: 1
  • Pages: 560
  • Product dimensions: 6.20 (w) x 9.00 (h) x 1.40 (d)

Meet the Author

Peter J. Denning is vice provost for continuing professional education at George Mason University. Denning was president of the Association for Computing (ACM) and is now chair of the ACM Publications Board. His two most recent books are Computers Under Attack and Beyond Calculation: The Next 50 Years of Computing.

Dorothy E. Denning is Professor of Computer Science at Georgetown University. She is the author of a classic book in the field, Cryptography and Data Security, a coeditor (with Peter J. Denning) of a more recent work, Internet Besieged: Countering Cyberspace Scofflaws , and the author of 100 papers on computer security. Dr. Denning has shared her special expertise on encryption in testimony before the U.S. Congress.

0201308207AB04062001

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Read an Excerpt

PREFACE:

The year 1992 was an historical divide for the Internet. In that year, the number of Internet users surged past one million, enough to form a critical mass for public interest. The Clinton administration made promotion of the "information superhighway" a top priority and formed a National Information Infrastructure advisory council. The World Wide Web and the first browsers, Mosaic and Netscape, seized the public fancy. Since then, multitudes of new businesses, and even new professions, have taken shape-with such names as Internet identity designers, browser builders, electronic marketeers, search engineers, network computers, virtual shopping malls, workflow coordinators, and intranets, to name a few. Business people now routinely include Internet e-mail and Web addresses in their cards, stationery, and advertisements.

Yet the Internet is a risky place to conduct business or store assets. Hackers, crackers, snoops, spoofers, spammers, scammers, shammers, jammers, intruders, thieves, purloiners, conspirators, vandals, Trojan horse dealers, virus launchers, and rogue program purveyors run loose, plying regularly their nasty crafts and dirty deeds. Many do so shamelessly, enjoying near perfect anonymity-using forged addresses, untraceable links, and unbreakable codes. Analogies to the Old American West, populated by unruly cowboys and a shoot-first-ask-later mentality, are more appropriate than the coiners of the phrase "electronic frontier" ever imagined. Many law-abiding citizens, who simply want to conduct their business in peace, are demanding that the marshal come to cyberspace.

But the marshal must be more than a courageous, upright, fair, and toughupholder of the law, for most of the criminals employ high-tech methods that the ordinary person has trouble understanding. The criminals post detailed instructions on bulletin boards on how to test systems for vulnerabilities and then attack them, and the experts among them have made sophisticated "burglar's tool kits" available on Web pages. The marshal must be technologically smarter than the criminals. In an initial attempt to help, the Defense Advanced Research Projects Agency (DARPA) formed the CERT (Computer Emergency Response Team) Coordination Center (CC) in 1988 to work with the Internet community to detect and resolve computer security problems and to help prevent future incidents. In 1996 CERT/CC received over 31,000 e-mail incident reports and 2,000 telephone reports, and they investigated nearly 2,600 of them. The most common security attacks in 1996 were of six kinds.

  1. The Web server operates as a background process on an Internet-connected computer. One of its programs, PHF, contains a weakness that can allow intruders to execute any command on the computer. Intruders use this to download a copy of the password file, which they attempt to crack; having guessed a weak password, they can log on to the victimized computer by masquerading as a legitimate account-holder. Sample scripts for exploiting this weakness were posted widely in the Internet and CERT saw several reports each week from victims.
  2. Many Internet-connected computers are controlled by Linux, a public-domain clone of the Unix operating system that can be installed on personal computers. Intruders regularly exploited well-known vulnerabilities of Linux to break into these systems as a "root" (superuser) and install packet sniffers (see number five), which collect account names and passwords. Most true Unix systems are not as vulnerable if their administrators have installed all the necessary security patches.
  3. Denial-of-service is an attack that obstructs the authorized users of a system from gaining access or from carrying out their normal work. One common attack, used frequently against Internet service providers (ISP), was to flood the ISP's machine with forged packets requesting a network connection; the ISP could not complete the task of opening the connection because the putative sender did not exist or would not respond since it had not initiated the request. As soon as the ISP's local limit on the number of open network connections is exceeded, its computer freezes up until its operators manually reboot it.
  4. Many operating systems have well-known vulnerabilities that can be exploited by intruders. An example is in the program that routes mail betweenlocal and Internet users: the "sendmail" program contains a "debugger" option that allows a remote system administrator to execute system commands without logging in. Many system administrators, however, have not installed all the security patches distributed by the vendor. Would-be intruders can easily find Web pages containing detailed descriptions of these vulnerabilities, and instructions and tool kits to exploit them.
  5. Packet sniffers are processes that a superuser can install on a computer attached to an Ethernet. Sniffers listen to all traffic on the Ethernet and collect packets containing account names and passwords into a file that can be transferred later to the intruder's site. Packet sniffers are frequently installed as part of a widely available kit that also replaces commonly used system programs with Trojan horse programs. Trojan horse programs hide the intruder's activities in the compromised system by masking files and erasing audit trails.
  6. The Internet Protocol (IP) sends data in packets that contain return addresses. Using the widely available tools, intruders can cause a compromised computer to generate IP packets with forged return addresses. The recipient system can be fooled into believing that the packets have come from a trusted system, to which it responds by releasing data or executing commands. Special routers called firewalls can filter out spoofed IP packets before they enter a system, but these routers are hard to program correctly.

While the CERT/CC goes about its job quietly, the news media have given a lot of attention to high-tech computer crimes. Here are some examples of big computer-security stories that appeared in the media:

  1. Viruses, hidden destructive programs that attach themselves to program files and the boot sectors of hard and floppy disks, have been the subject of intense anxiety since the mid-1980s. In 1995, a more serious virus problem came to the public's attention: viruses in Microsoft Word macros, which could be spread in Word documents attached to electronic mail. Business is booming for the companies that sell virus detectors and eradicators; they keep very busy fighting the new strains that malicious underground programmers continue churning out. Virus hoaxes have become as annoying as the real thing. Reports of super viruses, with such names as Good Times and Penpal Greetings, claim that simply reading certain e-mail is enough to be attacked (it isn't). The reports are so alluring that concerned recipients forward them to their friends and distribution lists. Many people have received dozens of copies of these false claims, forwarded by their own credulous friends.
  2. In 1988, Clifford Stoll published an account of the tracking of a hacker who had invaded computers at Lawrence Berkeley Laboratories; Stoll later expanded his report into a best-selling book, The Cuckoo's Egg. The hacker penetrated both military and commercial sites and attempted to steal classified or proprietary data.
  3. In 1988, Robert Tappan Morris, then a student at Cornell University, released a program which propagated itself throughout the Internet. It succeeded in invading between 3,000 and 6,000 hosts out of approximately 60,000 hosts on the Internet at the time, shutting many of them down for up to three days. Morris was subsequently convicted under the Computer Crime Act. The Defense Department formed the CERT shortly thereafter to coordinate future responses to such events and to give early warnings of system vulnerabilities.
  4. In 1995, the Java language and program execution environment of Sun Microsystems began to spread rapidly among Internet users. Using Java, a person can download a program (called an "applet") into a browser for local execution. According to the reports, the local execution environment was not well contained: it was possible for applets to read, write, modify, delete, scramble, or copy files belonging to the user who downloaded the applet, and to open secret connections to other sites that could receive purloined information. Sun and Netscape worked feverishly to remove these bugs, making considerable progress. Microsoft's Activex, designed with the same purpose as Java, was even worse because the underlying operating system was much weaker; Microsoft, too, has worked feverishly to remove these bugs.
  5. In April 1995, security experts Dan Farmer and Wietse Venema released a system called SATAN that would probe Internet sites for a number of unpatched security flaws that could initiate intrusions. The story was given big play in the national media, which predicted the collapse of the Internet at the hands of SATAN's unscrupulous users. As it turned out, nothing much happened and SATAN disappeared from the news within a week or two of its release. SATAN became a useful tool for system administrators to locate and repair weaknesses, an outcome never noted by the media.
  6. 1995 also brought announcements of weaknesses in the cryptographic protocols used for transmitting credit card numbers through Netscape. The New York Times journalist John Markoff wrote several front-page stories and Netscape quickly repaired the protocols.
  7. In 1996, a new practice called spamming came to light. Unscrupulous advertisers distribute large numbers of get-rich-quick offers, pyramid schemes, and on-line sex ads to e-mail addresses culled from search engines. They use fake return addresses so that irate recipients cannot respond with requests to be removed from the distribution list. In some cases, they flood a targeted user with harassing messages that cannot be traced. Frustrated users everywhere asked for laws and tools to stop these attacks.

We believe that these problems are a serious threat to information infrastructures everywhere. Until they are addressed satisfactorily, all the widely touted boons of the Internet-from tele-work to distance education to electronic commerce-will not be realized. We have assembled this anthology of leading experts because we want to help you and others understand the enormity of the job faced by system administrators and designers to keep the Internet safe, secure, and reliable. In short, we want to help the marshals become smarter and you to understand why their jobs are so demanding.

We also believe that the solutions to these problems cannot be achieved solely by technological means. The answers will involve a complex interplay among law, policy, and technology. There are many issues. Who should pay the sales tax on a transaction? Under what conditions can the government wiretap digital communications? Can a government prevent critical software or data from crossing national boundaries? What rights does an advertiser have to personal information gleaned from the computers of those engaged in transactions? Some groups see a secure Internet as the foundation of a new world order with government having less influence on private lives, more safeguards on speech and freedom, and more protections for individual privacy and due process. One person's free speech is another's clogged mailbox or tarnished public identity. We think the debates around these issues are healthy and need to be played out in the political and private arenas in the years ahead. Their resolutions will affect the kinds of countermeasures that can be used against the various threats. One thing is for sure: purely technological solutions cannot be defined. We cannot eliminate the marshal.

How To Read This Book

Originally, this book was intended to be an update of the anthology Computers Under Attack, prepared in 1989 and published in 1990. Yet so much has changed in the field that most of the previous essays were no longer relevant. The few that survived for this edition have been brought up to date by their authors. We retained the anthology format as a reminder that the field is new and still in great flux, and in such times it is more valuable to hear it from the original speakers.

After culling the best essays from a huge literature, we were left with about three dozen important articles. From your standpoint as a reader, this may well look like a daunting amount of information. How might you get the most out of this book in your limited time?

We suggest that you imagine yourself attending a symposium in a large hall with high, arching ceilings. Along the walls are booths, and in each booth is an author speaking on a topic. The room reverberates with the combined drone from all the speakers. You can walk from booth to booth, in any order you choose, listening to the conversations. You can listen as much or as little as suits you. You can return later to listen more and get some of your questions answered. If you are a beginner, a few hours in this forum will give you some basic familiarity with the terms used by the speakers and the capacity to ask intelligent questions. If you are already a working professional, a few hours in this forum will bring you up to date on what the experts are saying and allow you to calibrate whether your current knowledge is complete.

To assist you in navigating this forum, we have prefaced each of the five sections with a short summary of what the authors talk about and what common themes bring them together.

You may be interested in a related work. ACM has produced a new Professional Knowledge Program on Network and Data Security, edited by Matt Bishop and Peter Denning. It is a package of primary and secondary articles with study questions, editorial overviews, and a search engine. ACM will give you a certificate when you successfully complete the reading program. See www.acm.org/pkp.

Acknowledgements

This book is an outgrowth of our work on a predecessor anthology, Computers Under Attack: Intruders, Worms, and Viruses, published by Addison-Wesley and ACM Press Books in 1990. We are especially grateful to Helen Goldstein of Addison-Wesley for handling the logistics of review and production, Ellen Wollner of Addison-Wesley for masterful marketing, Jacquelyn Young of Addison-Wesley for coordinating production, Peter Gordon of Addison-Wesley for his sharp sense of what will resonate in the market, and Nhora Cortes-Comerer and Debbie Cotton of ACM for arranging for this to be part of the ACM Press Books series and obtaining permission from the previous publishers of these works.

Matt Bishop of U.C. Davis deserves a special mention for his long friendship, sharp technical knowledge, extensive familiarity with the literature, and inspirations over the years. He collaborated with Peter on a related collection, the ACM Professional Knowledge Program on Network and Data Security. ACM Director of Publications, Mark Mandelbaum, facilitated that program and this book. Peter's partner at George Mason University, Daniel Menasc'e, has also been a constant source of inspiration. Sushil Jajodia and Ravi Sandhu of George Mason University have always been freely available to provide technical knowledge and perspective about computer security.

Peter is grateful to the great editors with whom he has worked, notably Steve Mayer of American Scientist, who helped him with several essays whose updates are included here, and Bill Frucht of Springer-Verlag, who taught him much about the secrets of editorial selection.

Peter and Dorothy are grateful to each other for many years of marriage in which their ability to work together professionally was strengthened. They are grateful to their mothers, Catherine Denning and Helen Robling, and to their daughters, Anne and Diana Denning. All four individuals may not have fully understood the subject matter but fully realized its importance, and thus were endless sources of encouragement.



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Table of Contents

Preface.

Introduction.

I. THE WORLDWIDE NETWORK.

1. The Internet After Thirty Years Peter J. Denning.

2. Cyberspace Attacks and Countermeasures Dorothy E. Denning.

3. Rome Laboratory Attacks: Prepared Testimony of Jim Christy, Air Force Investigator, Before the Senate Governmental Affairs Committee, Permanent Investigations Subcommittee Jim Christy.

4. Reviewing the Risks Archives Peter G. Neumann.

5. Securing the Information Infrastructure Teresa Lunt.

6. Computer Viruses Eugene H. Spafford.

II. INTERNET SECURITY.

7. An Evening with Berferd William Cheswick.

8. Network and Internet Security Steve Bellovin.

9. Internet Sniffer Attacks E. Eugene Schultz and Thomas A. Longstaff.

10. Attack Class: Address Spoofing L. Todd Heberlein and Matt Bishop.

11. Passwords Peter J. Denning.

12. Location-Based Authentication: Grounding Cyberspace for Better Security Dorothy E. Denning and Peter F. MacDoran.

13. Tripwire: A Case Study in Integrity Monitoring Gene H. Kim and Eugene H. Spafford.

14. DIDS (Distributed Intrusion Detection System)- Motivation, Achitecture, and an Early Prototype Steven R. Snapp, James Brentano, Gihan V. Dias, Terrance L. Goan, L. Todd Heberlein, Che-Lin Ho, Karl N. Levitt, Biswanath Mukherjee, Stephen E. Smaha, Tim Grance, Daniel M. Teal, and Doug Mansur.

15. Test Driving SATAN Ted Doty.

16. Java Security: Web Browsers and Beyond Drew Dean, Edward W. Felten, Dan S. Wallach, and Dirk Balfanz.

III. CRYPTOGRAPHY.

17. A Brief History of the Data Encryption Standard Walter Tuchman.

18. Wisecrackers Steven Levy.

19. Internet Privacy Enhanced Mail Stephen T. Kent.

20. Authentication for Distributed Systems Thomas Y.C. Woo and Simon S. Lam.

21. A Taxonomy for Key Recovery Encryption Systems Dorothy E. Denning and Dennis K. Branstad.

IV. SECURE ELECTRONIC COMMERCE.

22. Electronic Commerce Peter J. Denning.

23. Atomicity in Electronic Commerce J. D. Tygar.

24. Securing the Commercial Internet Anish Bhimani.

25. Money in Electronic Commerce: Digital Cash, Electronic Fund Transfers, and Ecash Patiwat Panurach.

26. Identity-Related Misuse Peter G. Neumann.

V. LAW, POLICY AND EDUCATION.

27. Law Enforcement in Cyberspace Address The Honorable Janet Reno, United States Attorney General.

28. Encryption Policy and Market Trends Dorothy E. Denning.

29. Remarks at Computers, Freedom and Privacy Conference IV Chicago Bruce Sterling.

30. Speech to High Technology Crime Investigation Association Lake Tahoe Bruce Sterling.

31. Are Computer Hacker Break-ins Ethical? Eugene H. Spafford.

32. Georgetown University Computer Systems Acceptable Use Policy.

33. University Administrative Policy Number 60 RESPONSIBLE OFFICE: Vice Provost for Information Technology and Services.

34. Security Across the Curriculum: Using Computer Security to Teach Computer Science Principles Major Gregory White and Captain Gregory Nordstrom.

Biographies.

Index.

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Preface

The year 1992 was an historical divide for the Internet. In that year, the number of Internet users surged past one million, enough to form a critical mass for public interest. The Clinton administration made promotion of the "information superhighway" a top priority and formed a National Information Infrastructure advisory council. The World Wide Web and the first browsers, Mosaic and Netscape, seized the public fancy. Since then, multitudes of new businesses, and even new professions, have taken shape-with such names as Internet identity designers, browser builders, electronic marketeers, search engineers, network computers, virtual shopping malls, workflow coordinators, and intranets, to name a few. Business people now routinely include Internet e-mail and Web addresses in their cards, stationery, and advertisements.

Yet the Internet is a risky place to conduct business or store assets. Hackers, crackers, snoops, spoofers, spammers, scammers, shammers, jammers, intruders, thieves, purloiners, conspirators, vandals, Trojan horse dealers, virus launchers, and rogue program purveyors run loose, plying regularly their nasty crafts and dirty deeds. Many do so shamelessly, enjoying near perfect anonymity-using forged addresses, untraceable links, and unbreakable codes. Analogies to the Old American West, populated by unruly cowboys and a shoot-first-ask-later mentality, are more appropriate than the coiners of the phrase "electronic frontier" ever imagined. Many law-abiding citizens, who simply want to conduct their business in peace, are demanding that the marshal come to cyberspace.

But the marshal must be more than a courageous, upright, fair, and tough upholder of the law, for most of the criminals employ high-tech methods that the ordinary person has trouble understanding. The criminals post detailed instructions on bulletin boards on how to test systems for vulnerabilities and then attack them, and the experts among them have made sophisticated "burglar's tool kits" available on Web pages. The marshal must be technologically smarter than the criminals. In an initial attempt to help, the Defense Advanced Research Projects Agency (DARPA) formed the CERT (Computer Emergency Response Team) Coordination Center (CC) in 1988 to work with the Internet community to detect and resolve computer security problems and to help prevent future incidents. In 1996 CERT/CC received over 31,000 e-mail incident reports and 2,000 telephone reports, and they investigated nearly 2,600 of them. The most common security attacks in 1996 were of six kinds.

  1. The Web server operates as a background process on an Internet-connected computer. One of its programs, PHF, contains a weakness that can allow intruders to execute any command on the computer. Intruders use this to download a copy of the password file, which they attempt to crack; having guessed a weak password, they can log on to the victimized computer by masquerading as a legitimate account-holder. Sample scripts for exploiting this weakness were posted widely in the Internet and CERT saw several reports each week from victims.
  2. Many Internet-connected computers are controlled by Linux, a public-domain clone of the Unix operating system that can be installed on personal computers. Intruders regularly exploited well-known vulnerabilities of Linux to break into these systems as a "root" (superuser) and install packet sniffers (see number five), which collect account names and passwords. Most true Unix systems are not as vulnerable if their administrators have installed all the necessary security patches.
  3. Denial-of-service is an attack that obstructs the authorized users of a system from gaining access or from carrying out their normal work. One common attack, used frequently against Internet service providers (ISP), was to flood the ISP's machine with forged packets requesting a network connection; the ISP could not complete the task of opening the connection because the putative sender did not exist or would not respond since it had not initiated the request. As soon as the ISP's local limit on the number of open network connections is exceeded, its computer freezes up until its operators manually reboot it.
  4. Many operating systems have well-known vulnerabilities that can be exploited by intruders. An example is in the program that routes mail betweenlocal and Internet users: the "sendmail" program contains a "debugger" option that allows a remote system administrator to execute system commands without logging in. Many system administrators, however, have not installed all the security patches distributed by the vendor. Would-be intruders can easily find Web pages containing detailed descriptions of these vulnerabilities, and instructions and tool kits to exploit them.
  5. Packet sniffers are processes that a superuser can install on a computer attached to an Ethernet. Sniffers listen to all traffic on the Ethernet and collect packets containing account names and passwords into a file that can be transferred later to the intruder's site. Packet sniffers are frequently installed as part of a widely available kit that also replaces commonly used system programs with Trojan horse programs. Trojan horse programs hide the intruder's activities in the compromised system by masking files and erasing audit trails.
  6. The Internet Protocol (IP) sends data in packets that contain return addresses. Using the widely available tools, intruders can cause a compromised computer to generate IP packets with forged return addresses. The recipient system can be fooled into believing that the packets have come from a trusted system, to which it responds by releasing data or executing commands. Special routers called firewalls can filter out spoofed IP packets before they enter a system, but these routers are hard to program correctly.

While the CERT/CC goes about its job quietly, the news media have given a lot of attention to high-tech computer crimes. Here are some examples of big computer-security stories that appeared in the media:

  1. Viruses, hidden destructive programs that attach themselves to program files and the boot sectors of hard and floppy disks, have been the subject of intense anxiety since the mid-1980s. In 1995, a more serious virus problem came to the public's attention: viruses in Microsoft Word macros, which could be spread in Word documents attached to electronic mail. Business is booming for the companies that sell virus detectors and eradicators; they keep very busy fighting the new strains that malicious underground programmers continue churning out. Virus hoaxes have become as annoying as the real thing. Reports of super viruses, with such names as Good Times and Penpal Greetings, claim that simply reading certain e-mail is enough to be attacked (it isn't). The reports are so alluring that concerned recipients forward them to their friends and distribution lists. Many people have received dozens of copies of these false claims, forwarded by their own credulous friends.
  2. In 1988, Clifford Stoll published an account of the tracking of a hacker who had invaded computers at Lawrence Berkeley Laboratories; Stoll later expanded his report into a best-selling book, The Cuckoo's Egg. The hacker penetrated both military and commercial sites and attempted to steal classified or proprietary data.
  3. In 1988, Robert Tappan Morris, then a student at Cornell University, released a program which propagated itself throughout the Internet. It succeeded in invading between 3,000 and 6,000 hosts out of approximately 60,000 hosts on the Internet at the time, shutting many of them down for up to three days. Morris was subsequently convicted under the Computer Crime Act. The Defense Department formed the CERT shortly thereafter to coordinate future responses to such events and to give early warnings of system vulnerabilities.
  4. In 1995, the Java language and program execution environment of Sun Microsystems began to spread rapidly among Internet users. Using Java, a person can download a program (called an "applet") into a browser for local execution. According to the reports, the local execution environment was not well contained: it was possible for applets to read, write, modify, delete, scramble, or copy files belonging to the user who downloaded the applet, and to open secret connections to other sites that could receive purloined information. Sun and Netscape worked feverishly to remove these bugs, making considerable progress. Microsoft's ActiveX, designed with the same purpose as Java, was even worse because the underlying operating system was much weaker; Microsoft, too, has worked feverishly to remove these bugs.
  5. In April 1995, security experts Dan Farmer and Wietse Venema released a system called SATAN that would probe Internet sites for a number of unpatched security flaws that could initiate intrusions. The story was given big play in the national media, which predicted the collapse of the Internet at the hands of SATAN's unscrupulous users. As it turned out, nothing much happened and SATAN disappeared from the news within a week or two of its release. SATAN became a useful tool for system administrators to locate and repair weaknesses, an outcome never noted by the media.
  6. 1995 also brought announcements of weaknesses in the cryptographic protocols used for transmitting credit card numbers through Netscape. The New York Times journalist John Markoff wrote several front-page stories and Netscape quickly repaired the protocols.
  7. In 1996, a new practice called spamming came to light. Unscrupulous advertisers distribute large numbers of get-rich-quick offers, pyramid schemes, and on-line sex ads to e-mail addresses culled from search engines. They use fake return addresses so that irate recipients cannot respond with requests to be removed from the distribution list. In some cases, they flood a targeted user with harassing messages that cannot be traced. Frustrated users everywhere asked for laws and tools to stop these attacks.

We believe that these problems are a serious threat to information infrastructures everywhere. Until they are addressed satisfactorily, all the widely touted boons of the Internet-from tele-work to distance education to electronic commerce-will not be realized. We have assembled this anthology of leading experts because we want to help you and others understand the enormity of the job faced by system administrators and designers to keep the Internet safe, secure, and reliable. In short, we want to help the marshals become smarter and you to understand why their jobs are so demanding.

We also believe that the solutions to these problems cannot be achieved solely by technological means. The answers will involve a complex interplay among law, policy, and technology. There are many issues. Who should pay the sales tax on a transaction? Under what conditions can the government wiretap digital communications? Can a government prevent critical software or data from crossing national boundaries? What rights does an advertiser have to personal information gleaned from the computers of those engaged in transactions? Some groups see a secure Internet as the foundation of a new world order with government having less influence on private lives, more safeguards on speech and freedom, and more protections for individual privacy and due process. One person's free speech is another's clogged mailbox or tarnished public identity. We think the debates around these issues are healthy and need to be played out in the political and private arenas in the years ahead. Their resolutions will affect the kinds of countermeasures that can be used against the various threats. One thing is for sure: purely technological solutions cannot be defined. We cannot eliminate the marshal.

How To Read This Book

Originally, this book was intended to be an update of the anthology Computers Under Attack, prepared in 1989 and published in 1990. Yet so much has changed in the field that most of the previous essays were no longer relevant. The few that survived for this edition have been brought up to date by their authors. We retained the anthology format as a reminder that the field is new and still in great flux, and in such times it is more valuable to hear it from the original speakers.

After culling the best essays from a huge literature, we were left with about three dozen important articles. From your standpoint as a reader, this may well look like a daunting amount of information. How might you get the most out of this book in your limited time?

We suggest that you imagine yourself attending a symposium in a large hall with high, arching ceilings. Along the walls are booths, and in each booth is an author speaking on a topic. The room reverberates with the combined drone from all the speakers. You can walk from booth to booth, in any order you choose, listening to the conversations. You can listen as much or as little as suits you. You can return later to listen more and get some of your questions answered. If you are a beginner, a few hours in this forum will give you some basic familiarity with the terms used by the speakers and the capacity to ask intelligent questions. If you are already a working professional, a few hours in this forum will bring you up to date on what the experts are saying and allow you to calibrate whether your current knowledge is complete.

To assist you in navigating this forum, we have prefaced each of the five sections with a short summary of what the authors talk about and what common themes bring them together.

You may be interested in a related work. ACM has produced a new Professional Knowledge Program on Network and Data Security, edited by Matt Bishop and Peter Denning. It is a package of primary and secondary articles with study questions, editorial overviews, and a search engine. ACM will give you a certificate when you successfully complete the reading program. See www.acm.org/pkp.

Acknowledgements

This book is an outgrowth of our work on a predecessor anthology, Computers Under Attack: Intruders, Worms, and Viruses, published by Addison-Wesley and ACM Press Books in 1990. We are especially grateful to Helen Goldstein of Addison-Wesley for handling the logistics of review and production, Ellen Wollner of Addison-Wesley for masterful marketing, Jacquelyn Young of Addison-Wesley for coordinating production, Peter Gordon of Addison-Wesley for his sharp sense of what will resonate in the market, and Nhora Cortes-Comerer and Debbie Cotton of ACM for arranging for this to be part of the ACM Press Books series and obtaining permission from the previous publishers of these works.

Matt Bishop of U.C. Davis deserves a special mention for his long friendship, sharp technical knowledge, extensive familiarity with the literature, and inspirations over the years. He collaborated with Peter on a related collection, the ACM Professional Knowledge Program on Network and Data Security. ACM Director of Publications, Mark Mandelbaum, facilitated that program and this book. Peter's partner at George Mason University, Daniel Menasc'e, has also been a constant source of inspiration. Sushil Jajodia and Ravi Sandhu of George Mason University have always been freely available to provide technical knowledge and perspective about computer security.

Peter is grateful to the great editors with whom he has worked, notably Steve Mayer of American Scientist, who helped him with several essays whose updates are included here, and Bill Frucht of Springer-Verlag, who taught him much about the secrets of editorial selection.

Peter and Dorothy are grateful to each other for many years of marriage in which their ability to work together professionally was strengthened. They are grateful to their mothers, Catherine Denning and Helen Robling, and to their daughters, Anne and Diana Denning. All four individuals may not have fully understood the subject matter but fully realized its importance, and thus were endless sources of encouragement.

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Introduction

The year 1992 was an historical divide for the Internet. In that year, the number of Internet users surged past one million, enough to form a critical mass for public interest. The Clinton administration made promotion of the "information superhighway" a top priority and formed a National Information Infrastructure advisory council. The World Wide Web and the first browsers, Mosaic and Netscape, seized the public fancy. Since then, multitudes of new businesses, and even new professions, have taken shape-with such names as Internet identity designers, browser builders, electronic marketeers, search engineers, network computers, virtual shopping malls, workflow coordinators, and intranets, to name a few. Business people now routinely include Internet e-mail and Web addresses in their cards, stationery, and advertisements.

Yet the Internet is a risky place to conduct business or store assets. Hackers, crackers, snoops, spoofers, spammers, scammers, shammers, jammers, intruders, thieves, purloiners, conspirators, vandals, Trojan horse dealers, virus launchers, and rogue program purveyors run loose, plying regularly their nasty crafts and dirty deeds. Many do so shamelessly, enjoying near perfect anonymity-using forged addresses, untraceable links, and unbreakable codes. Analogies to the Old American West, populated by unruly cowboys and a shoot-first-ask-later mentality, are more appropriate than the coiners of the phrase "electronic frontier" ever imagined. Many law-abiding citizens, who simply want to conduct their business in peace, are demanding that the marshal come to cyberspace.

But the marshal must be more than a courageous, upright, fair, and tough upholder ofthe law, for most of the criminals employ high-tech methods that the ordinary person has trouble understanding. The criminals post detailed instructions on bulletin boards on how to test systems for vulnerabilities and then attack them, and the experts among them have made sophisticated "burglar's tool kits" available on Web pages. The marshal must be technologically smarter than the criminals. In an initial attempt to help, the Defense Advanced Research Projects Agency (DARPA) formed the CERT (Computer Emergency Response Team) Coordination Center (CC) in 1988 to work with the Internet community to detect and resolve computer security problems and to help prevent future incidents. In 1996 CERT/CC received over 31,000 e-mail incident reports and 2,000 telephone reports, and they investigated nearly 2,600 of them. The most common security attacks in 1996 were of six kinds.

  1. The Web server operates as a background process on an Internet-connected computer. One of its programs, PHF, contains a weakness that can allow intruders to execute any command on the computer. Intruders use this to download a copy of the password file, which they attempt to crack; having guessed a weak password, they can log on to the victimized computer by masquerading as a legitimate account-holder. Sample scripts for exploiting this weakness were posted widely in the Internet and CERT saw several reports each week from victims.
  2. Many Internet-connected computers are controlled by Linux, a public-domain clone of the Unix operating system that can be installed on personal computers. Intruders regularly exploited well-known vulnerabilities of Linux to break into these systems as a "root" (superuser) and install packet sniffers (see number five), which collect account names and passwords. Most true Unix systems are not as vulnerable if their administrators have installed all the necessary security patches.
  3. Denial-of-service is an attack that obstructs the authorized users of a system from gaining access or from carrying out their normal work. One common attack, used frequently against Internet service providers (ISP), was to flood the ISP's machine with forged packets requesting a network connection; the ISP could not complete the task of opening the connection because the putative sender did not exist or would not respond since it had not initiated the request. As soon as the ISP's local limit on the number of open network connections is exceeded, its computer freezes up until its operators manually reboot it.
  4. Many operating systems have well-known vulnerabilities that can be exploited by intruders. An example is in the program that routes mail betweenlocal and Internet users: the "sendmail" program contains a "debugger" option that allows a remote system administrator to execute system commands without logging in. Many system administrators, however, have not installed all the security patches distributed by the vendor. Would-be intruders can easily find Web pages containing detailed descriptions of these vulnerabilities, and instructions and tool kits to exploit them.
  5. Packet sniffers are processes that a superuser can install on a computer attached to an Ethernet. Sniffers listen to all traffic on the Ethernet and collect packets containing account names and passwords into a file that can be transferred later to the intruder's site. Packet sniffers are frequently installed as part of a widely available kit that also replaces commonly used system programs with Trojan horse programs. Trojan horse programs hide the intruder's activities in the compromised system by masking files and erasing audit trails.
  6. The Internet Protocol (IP) sends data in packets that contain return addresses. Using the widely available tools, intruders can cause a compromised computer to generate IP packets with forged return addresses. The recipient system can be fooled into believing that the packets have come from a trusted system, to which it responds by releasing data or executing commands. Special routers called firewalls can filter out spoofed IP packets before they enter a system, but these routers are hard to program correctly.

While the CERT/CC goes about its job quietly, the news media have given a lot of attention to high-tech computer crimes. Here are some examples of big computer-security stories that appeared in the media:

  1. Viruses, hidden destructive programs that attach themselves to program files and the boot sectors of hard and floppy disks, have been the subject of intense anxiety since the mid-1980s. In 1995, a more serious virus problem came to the public's attention: viruses in Microsoft Word macros, which could be spread in Word documents attached to electronic mail. Business is booming for the companies that sell virus detectors and eradicators; they keep very busy fighting the new strains that malicious underground programmers continue churning out. Virus hoaxes have become as annoying as the real thing. Reports of super viruses, with such names as Good Times and Penpal Greetings, claim that simply reading certain e-mail is enough to be attacked (it isn't). The reports are so alluring that concerned recipients forward them to their friends and distribution lists. Many people have received dozens of copies of these false claims, forwarded by their own credulous friends.
  2. In 1988, Clifford Stoll published an account of the tracking of a hacker who had invaded computers at Lawrence Berkeley Laboratories; Stoll later expanded his report into a best-selling book, The Cuckoo's Egg. The hacker penetrated both military and commercial sites and attempted to steal classified or proprietary data.
  3. In 1988, Robert Tappan Morris, then a student at Cornell University, released a program which propagated itself throughout the Internet. It succeeded in invading between 3,000 and 6,000 hosts out of approximately 60,000 hosts on the Internet at the time, shutting many of them down for up to three days. Morris was subsequently convicted under the Computer Crime Act. The Defense Department formed the CERT shortly thereafter to coordinate future responses to such events and to give early warnings of system vulnerabilities.
  4. In 1995, the Java language and program execution environment of Sun Microsystems began to spread rapidly among Internet users. Using Java, a person can download a program (called an "applet") into a browser for local execution. According to the reports, the local execution environment was not well contained: it was possible for applets to read, write, modify, delete, scramble, or copy files belonging to the user who downloaded the applet, and to open secret connections to other sites that could receive purloined information. Sun and Netscape worked feverishly to remove these bugs, making considerable progress. Microsoft's ActiveX, designed with the same purpose as Java, was even worse because the underlying operating system was much weaker; Microsoft, too, has worked feverishly to remove these bugs.
  5. In April 1995, security experts Dan Farmer and Wietse Venema released a system called SATAN that would probe Internet sites for a number of unpatched security flaws that could initiate intrusions. The story was given big play in the national media, which predicted the collapse of the Internet at the hands of SATAN's unscrupulous users. As it turned out, nothing much happened and SATAN disappeared from the news within a week or two of its release. SATAN became a useful tool for system administrators to locate and repair weaknesses, an outcome never noted by the media.
  6. 1995 also brought announcements of weaknesses in the cryptographic protocols used for transmitting credit card numbers through Netscape. The New York Times journalist John Markoff wrote several front-page stories and Netscape quickly repaired the protocols.
  7. In 1996, a new practice called spamming came to light. Unscrupulous advertisers distribute large numbers of get-rich-quick offers, pyramid schemes, and on-line sex ads to e-mail addresses culled from search engines. They use fake return addresses so that irate recipients cannot respond with requests to be removed from the distribution list. In some cases, they flood a targeted user with harassing messages that cannot be traced. Frustrated users everywhere asked for laws and tools to stop these attacks.

We believe that these problems are a serious threat to information infrastructures everywhere. Until they are addressed satisfactorily, all the widely touted boons of the Internet-from tele-work to distance education to electronic commerce-will not be realized. We have assembled this anthology of leading experts because we want to help you and others understand the enormity of the job faced by system administrators and designers to keep the Internet safe, secure, and reliable. In short, we want to help the marshals become smarter and you to understand why their jobs are so demanding.

We also believe that the solutions to these problems cannot be achieved solely by technological means. The answers will involve a complex interplay among law, policy, and technology. There are many issues. Who should pay the sales tax on a transaction? Under what conditions can the government wiretap digital communications? Can a government prevent critical software or data from crossing national boundaries? What rights does an advertiser have to personal information gleaned from the computers of those engaged in transactions? Some groups see a secure Internet as the foundation of a new world order with government having less influence on private lives, more safeguards on speech and freedom, and more protections for individual privacy and due process. One person's free speech is another's clogged mailbox or tarnished public identity. We think the debates around these issues are healthy and need to be played out in the political and private arenas in the years ahead. Their resolutions will affect the kinds of countermeasures that can be used against the various threats. One thing is for sure: purely technological solutions cannot be defined. We cannot eliminate the marshal.

How To Read This Book

Originally, this book was intended to be an update of the anthology Computers Under Attack, prepared in 1989 and published in 1990. Yet so much has changed in the field that most of the previous essays were no longer relevant. The few that survived for this edition have been brought up to date by their authors. We retained the anthology format as a reminder that the field is new and still in great flux, and in such times it is more valuable to hear it from the original speakers.

After culling the best essays from a huge literature, we were left with about three dozen important articles. From your standpoint as a reader, this may well look like a daunting amount of information. How might you get the most out of this book in your limited time?

We suggest that you imagine yourself attending a symposium in a large hall with high, arching ceilings. Along the walls are booths, and in each booth is an author speaking on a topic. The room reverberates with the combined drone from all the speakers. You can walk from booth to booth, in any order you choose, listening to the conversations. You can listen as much or as little as suits you. You can return later to listen more and get some of your questions answered. If you are a beginner, a few hours in this forum will give you some basic familiarity with the terms used by the speakers and the capacity to ask intelligent questions. If you are already a working professional, a few hours in this forum will bring you up to date on what the experts are saying and allow you to calibrate whether your current knowledge is complete.

To assist you in navigating this forum, we have prefaced each of the five sections with a short summary of what the authors talk about and what common themes bring them together.

You may be interested in a related work. ACM has produced a new Professional Knowledge Program on Network and Data Security, edited by Matt Bishop and Peter Denning. It is a package of primary and secondary articles with study questions, editorial overviews, and a search engine. ACM will give you a certificate when you successfully complete the reading program.

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