Why Isn't Trust Transitive?
10 Apr 1996-pp 171-176
TL;DR: The notion of trust is distinguished from a number of other (transitive) notions with which it is frequently confused, and it is argued that “proofs” of the unintensional transitivity of trust typically involve unpalatable logical assumptions as well as undesirable consequences.
Abstract: One of the great strengths of public-key cryptography is its potential to allow the localization of trust. This potential is greatest when cryptography is present to guarantee data integrity rather than secrecy, and where there is no natural hierarchy of trust. Both these conditions are typically fulfilled in the commercial world, where CSCW requires sharing of data and resources across organizational boundaries. One property which trust is frequently assumed or “proved” to have is transitivity (if A trusts B and B trusts C then A trusts C) or some generalization of transitivity such as *-closure. We use the loose term unintensional transitivity of trust to refer to a situation where B can effectively put things into A's set of trust assumptions without A's explicit consent (or sometimes even awareness.) Any account of trust which allows such situations to arise clearly poses major obstacles to the effective confinement (localization) of trust. In this position paper, we argue against the need to accept unintensional transitivity of trust. We distinguish the notion of trust from a number of other (transitive) notions with which it is frequently confused, and argue that “proofs” of the unintensional transitivity of trust typically involve unpalatable logical assumptions as well as undesirable consequences.
Citations
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04 Jan 2000
TL;DR: In this article, a trust model that is grounded in real-world social trust characteristics, and based on a reputation mechanism, or word-of-mouth, is proposed for the virtual medium.
Abstract: At any given time, the stability of a community depends on the right balance of trust and distrust. Furthermore, we face information overload, increased uncertainty and risk taking as a prominent feature of modern living. As members of society, we cope with these complexities and uncertainties by relying trust, which is the basis of all social interactions. Although a small number of trust models have been proposed for the virtual medium, we find that they are largely impractical and artificial. In this paper we provide and discuss a trust model that is grounded in real-world social trust characteristics, and based on a reputation mechanism, or word-of-mouth. Our proposed model allows agents to decide which other agents' opinions they trust more and allows agents to progressively tune their understanding of another agent's subjective recommendations.
1,487 citations
TL;DR: This survey examines the various definitions of trust in the literature and provides a working definition of trust for Internet applications and some influential examples of trust management systems.
Abstract: Trust is an important aspect of decision making for Internet applications and particularly influences the specification of security policy, i.e., who is authorized to perform actions as well as the techniques needed to manage and implement security to and for the applications. This survey examines the various definitions of trust in the literature and provides a working definition of trust for Internet applications. The properties of trust relationships are explained and classes of different types of trust identified in the literature are discussed with examples. Some influential examples of trust management systems are described.
1,181 citations
TL;DR: The threat model for ad hoc routing is formulated and several specific attacks that can target the operation of a protocol are presented that can provide the basis for future research in this rapidly evolving area.
Abstract: In this paper we present a survey of secure ad hoc routing protocols for mobile wireless networks. A mobile ad hoc network is a collection of nodes that is connected through a wireless medium forming rapidly changing topologies. The widely accepted existing routing protocols designed to accommodate the needs of such self-organized networks do not address possible threats aiming at the disruption of the protocol itself. The assumption of a trusted environment is not one that can be realistically expected; hence several efforts have been made towards the design of a secure and robust routing protocol for ad hoc networks. We briefly present the most popular protocols that follow the table-driven and the source-initiated on-demand approaches. Based on this discussion we then formulate the threat model for ad hoc routing and present several specific attacks that can target the operation of a protocol. In order to analyze the proposed secure ad hoc routing protocols in a structured way we have classified them into five categories; solutions based on asymmetric cryptography, solutions based on symmetric cryptography, hybrid solutions, reputation-based solutions and a category of add-on mechanisms that satisfy specific security requirements. A comparison between these solutions can provide the basis for future research in this rapidly evolving area.
807 citations
TL;DR: This article presents the first comprehensive review of social and computer science literature on trust in social networks and discusses recent works addressing three aspects of social trust: trust information collection, trust evaluation, and trust dissemination.
Abstract: Web-based social networks have become popular as a medium for disseminating information and connecting like-minded people. The public accessibility of such networks with the ability to share opinions, thoughts, information, and experience offers great promise to enterprises and governments. In addition to individuals using such networks to connect to their friends and families, governments and enterprises have started exploiting these platforms for delivering their services to citizens and customers. However, the success of such attempts relies on the level of trust that members have with each other as well as with the service provider. Therefore, trust becomes an essential and important element of a successful social network. In this article, we present the first comprehensive review of social and computer science literature on trust in social networks. We first review the existing definitions of trust and define social trust in the context of social networks. We then discuss recent works addressing three aspects of social trust: trust information collection, trust evaluation, and trust dissemination. Finally, we compare and contrast the literature and identify areas for further research in social trust.
615 citations
Proceedings Article•
10 Apr 2007TL;DR: This work identifies the four prevalent mechanisms used to inject malicious content on popular web sites: web server security, user contributed content, advertising and third-party widgets, and presents examples of abuse found on the Internet.
Abstract: As more users are connected to the Internet and conduct their daily activities electronically, computer users have become the target of an underground economy that infects hosts with malware or adware for financial gain. Unfortunately, even a single visit to an infected web site enables the attacker to detect vulnerabilities in the user's applications and force the download a multitude of malware binaries. Frequently, this malware allows the adversary to gain full control of the compromised systems leading to the ex-filtration of sensitive information or installation of utilities that facilitate remote control of the host. We believe that such behavior is similar to our traditional understanding of botnets. However, the main difference is that web-based malware infections are pull-based and that the resulting command feedback loop is looser. To characterize the nature of this rising thread, we identify the four prevalent mechanisms used to inject malicious content on popular web sites: web server security, user contributed content, advertising and third-party widgets. For each of these areas, we present examples of abuse found on the Internet. Our aim is to present the state of malware on the Web and emphasize the importance of this rising threat.
549 citations
Cites background from "Why Isn't Trust Transitive?"
...However, in practice, trust is usually not transitive [2] and the further one moves down the hierarchy the less plausible it becomes that the final entity can be trusted with controlling part of a web site’s content....
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References
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TL;DR: This paper describes the beliefs of trustworthy parties involved in authentication protocols and the evolution of these beliefs as a consequence of communication, and gives the results of the analysis of four published protocols.
Abstract: Authentication protocols are the basis of security in many distributed systems, and it is therefore essential to ensure that these protocols function correctly. Unfortunately, their design has been extremely error prone. Most of the protocols found in the literature contain redundancies or security flaws. A simple logic has allowed us to describe the beliefs of trustworthy parties involved in authentication protocols and the evolution of these beliefs as a consequence of communication. We have been able to explain a variety of authentication protocols formally, to discover subtleties and errors in them, and to suggest improvements. In this paper we present the logic and then give the results of our analysis of four published protocols, chosen either because of their practical importance or because they serve to illustrate our method.
2,638 citations
"Why Isn't Trust Transitive?" refers background in this paper
...If Ted finds himself under physical threat (eg power loss) then at least two different security policies are possible, depending upon whether disclosure or non-delivery is considered the greater threat: ( 1 ) destroy the message M (2) broadcast the message "Bob: M" Since it may be important to conceal the fact of which policy is in operation, when power is cut, Ted may well broadcast the message "Bob: Aunt Agatha will arrive ......
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Book•
06 Mar 2003TL;DR: The first edition made a number of predictions, explicitly or implicitly, about the growth of the Web and the patterns of Internet connectivity vastly increased, and warned of issues posed by home LANs, and about the problems caused by roaming laptops.
Abstract: From the Book:
But after a time, as Frodo did not show any sign of writing a book on the spot, the
hobbits returned to their questions about doings in the Shire.
Lord of the Rings
—J.R.R. TOLKIEN
The first printing of the First Edition appeared at the Las Vegas Interop in May, 1994. At that same show appeared the first of many commercial firewall products. In many ways, the field has matured since then: You can buy a decent firewall off the shelf from many vendors.
The problem of deploying that firewall in a secure and useful manner remains. We have studied many Internet access arrangements in which the only secure component was the firewall itself—it was easily bypassed by attackers going after the “protected” inside machines. Before the trivestiture of AT&T/Lucent/NCR, there were over 300,000 hosts behind at least six firewalls, plus special access arrangements with some 200 business partners.
Our first edition did not discuss the massive sniffing attacks discovered in the spring of 1994. Sniffers had been running on important Internet Service Provider (ISP) machines for months—machines that had access to a major percentage of the ISP’s packet flow. By some estimates, these sniffers captured over a million host name/user name/password sets from passing telnet, ftp, and rlogin sessions. There were also reports of increased hacker activity on military sites. It’s obvious what must have happened: If you are a hacker with a million passwords in your pocket, you are going to look for the most interesting targets, and .mil certainly qualifies.
Since the First Edition, we have been slowlylosing the Internet arms race. The hackers have developed and deployed tools for attacks we had been anticipating for years. IP spoofing Shimomura, 1996 and TCP hijacking are now quite common, according to the Computer Emergency Response Team (CERT). ISPs report that attacks on the Internet’s infrastructure are increasing.
There was one attack we chose not to include in the First Edition: the SYN-flooding denial-of- service attack that seemed to be unstoppable. Of course, the Bad Guys learned about the attack anyway, making us regret that we had deleted that paragraph in the first place. We still believe that it is better to disseminate this information, informing saints and sinners at the same time. The saints need all the help they can get, and the sinners have their own channels of communication.Crystal Ball or Bowling Ball?The first edition made a number of predictions, explicitly or implicitly. Was our foresight accurate?
Our biggest failure was neglecting to foresee how successful the Internet would become. We barely mentioned the Web and declined a suggestion to use some weird syntax when listing software resources. The syntax, of course, was the URL...
Concomitant with the growth of the Web, the patterns of Internet connectivity vastly increased. We assumed that a company would have only a few external connections—few enough that they’d be easy to keep track of, and to firewall. Today’s spaghetti topology was a surprise.
We didn’t realize that PCs would become Internet clients as soon as they did. We did, however, warn that as personal machines became more capable, they’d become more vulnerable. Experience has proved us very correct on that point.
We did anticipate high-speed home connections, though we spoke of ISDN, rather than cable modems or DSL. (We had high-speed connectivity even then, though it was slow by today’s standards.) We also warned of issues posed by home LANs, and we warned about the problems caused by roaming laptops.
We were overly optimistic about the deployment of IPv6 (which was called IPng back then, as the choice hadn’t been finalized). It still hasn’t been deployed, and its future is still somewhat uncertain.
We were correct, though, about the most fundamental point we made: Buggy host software is a major security issue. In fact, we called it the “fundamental theorem of firewalls”:
Most hosts cannot meet our requirements: they run too many programs that are too large. Therefore, the only solution is to isolate them behind a firewall if you wish to run any programs at all.
If anything, we were too conservative.Our ApproachThis book is nearly a complete rewrite of the first edition. The approach is different, and so are many of the technical details. Most people don’t build their own firewalls anymore. There are far more Internet users, and the economic stakes are higher. The Internet is a factor in warfare.
The field of study is also much larger—there is too much to cover in a single book. One reviewer suggested that Chapters 2 and 3 could be a six-volume set. (They were originally one mammoth chapter.) Our goal, as always, is to teach an approach to security. We took far too long to write this edition, but one of the reasons why the first edition survived as long as it did was that we concentrated on the concepts, rather than details specific to a particular product at a particular time. The right frame of mind goes a long way toward understanding security issues and making reasonable security decisions. We’ve tried to include anecdotes, stories, and comments to make our points.
Some complain that our approach is too academic, or too UNIX-centric, that we are too idealistic, and don’t describe many of the most common computing tools. We are trying to teach attitudes here more than specific bits and bytes. Most people have hideously poor computing habits and network hygiene. We try to use a safer world ourselves, and are trying to convey how we think it should be.
The chapter outline follows, but we want to emphasize the following:
It is OK to skip the hard parts.
If we dive into detail that is not useful to you, feel free to move on.
The introduction covers the overall philosophy of security, with a variety of time-tested maxims. As in the first edition, Chapter 2 discusses most of the important protocols, from a security point of view. We moved material about higher-layer protocols to Chapter 3. The Web merits a chapter of its own.
The next part discusses the threats we are dealing with: the kinds of attacks in Chapter 5, and some of the tools and techniques used to attack hosts and networks in Chapter 6. Part III covers some of the tools and techniques we can use to make our networking world safer. We cover authentication tools in Chapter 7, and safer network servicing software in Chapter 8.
Part IV covers firewalls and virtual private networks (VPNs). Chapter 9 introduces various types of firewalls and filtering techniques, and Chapter 10 summarizes some reasonable policies for filtering some of the more essential services discussed in Chapter 2. If you don’t find advice about filtering a service you like, we probably think it is too dangerous (refer to Chapter 2).
Chapter 11 covers a lot of the deep details of firewalls, including their configuration, administration, and design. It is certainly not a complete discussion of the subject, but should give readers a good start. VPN tunnels, including holes through firewalls, are covered in some detail in Chapter 12. There is more detail in Chapter 18.
In Part V, we apply these tools and lessons to organizations. Chapter 13 examines the problems and practices on modern intranets. See Chapter 15 for information about deploying a hacking-resistant host, which is useful in any part of an intranet. Though we don’t especially like intrusion detection systems (IDSs) very much, they do play a role in security, and are discussed in Chapter 15.
The last part offers a couple of stories and some further details. The Berferd chapter is largely unchanged, and we have added “The Taking of Clark,” a real-life story about a minor break-in that taught useful lessons.
Chapter 18 discusses secure communications over insecure networks, in quite some detail. For even further detail, Appendix A has a short introduction to cryptography.
The conclusion offers some predictions by the authors, with justifications. If the predictions are wrong, perhaps the justifications will be instructive. (We don’t have a great track record as prophets.) Appendix B provides a number of resources for keeping up in this rapidly changing field.Errata and UpdatesEveryone and every thing seems to have a Web site these days; this book is no exception. Our “official” Web site is . We’ll post an errata list there; we’ll also keep an up-to-date list of other useful Web resources. If you find any errors—we hope there aren’t many—please let us know via e-mail at .AcknowledgmentsFor many kindnesses, we’d like to thank Joe Bigler, Steve “Hollywood” Branigan, Hal Burch, Brian Clapper, David Crocker, Tom Dow, Phil Edwards and the Internet Public Library, Anja Feldmann, Karen Gettman, Brian Kernighan, David Korman, Tom Limoncelli, Norma Loquendi, Cat Okita, Robert Oliver, Vern Paxson, Marcus Ranum, Eric Rescorla, Guido van Rooij, Luann Rouff (a most excellent copy editor), Abba Rubin, Peter Salus, Glenn Sieb, Karl Siil (we’ll always have Boston), Irina Strizhevskaya, Rob Thomas, Win Treese, Dan Wallach, Avishai Wool, Karen Yannetta, and Michal Zalewski, among many others.
BILL CHESWICK
STEVE BELLOVIN
AVI RUBIN
020163466XP01302003
730 citations
07 May 1990
TL;DR: A mechanism is presented for reasoning about belief as a systematic way to understand the working of cryptographic protocols and places a strong emphasis on the separation between the content and the meaning of messages.
Abstract: A mechanism is presented for reasoning about belief as a systematic way to understand the working of cryptographic protocols. The mechanism captures more features of such protocols than that given by M. Burrows et al. (1989) to which the proposals are a substantial extension. The notion of possession incorporated in the approach assumes that principles can include in messages data they do not believe in, but merely possess. This also enables conclusions such as 'Q possesses the shared key', as in an example to be derived. The approach places a strong emphasis on the separation between the content and the meaning of messages. This can increase consistency in the analysis and, more importantly, introduce the ability to reason at more than one level. The final position in a given run will depend on the level of mutual trust of the specified principles participating in that run. >
682 citations
Book•
01 Jan 1994
TL;DR: The 2-amino-3-bromoanthraquinone which is isolated may be used for the manufacture of dyes and is at least as pure as that obtained from purified 2- aminoanthraquin one by the process of the prior art.
Abstract: In a process for the manufacture of 2-amino-3-bromoanthraquinone by heating 2-aminoanthraquinone with bromine (in the molar ratio of 1:1) in sulfuric acid, while mixing, the improvement wherein crude 2-aminoanthraquinone, in sulfuric acid of from 60 to 90 percent strength by weight, which contains from 10 to 15% by weight of an alkanecarboxylic acid of 3 or 4 carbon atoms or a mixture of such acids, is heated with from 1 to 1.05 moles of bromine per mole of 2-aminoanthraquinone at from 130 to 150 DEG C. The 2-amino-3-bromoanthraquinone which is isolated may be used for the manufacture of dyes. It is at least as pure as that obtained from purified 2-aminoanthraquinone by the process of the prior art.
356 citations
"Why Isn't Trust Transitive?" refers background in this paper
...If Ted finds himself under physical threat (eg power loss) then at least two different security policies are possible, depending upon whether disclosure or non-delivery is considered the greater threat: (1) destroy the message M ( 2 ) broadcast the message "Bob: M" Since it may be important to conceal the fact of which policy is in operation, when power is cut, Ted may well broadcast the message "Bob: Aunt Agatha will arrive ......
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