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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TL;DR: This work defines two models for trustworthiness management starting from the solutions proposed for P2P and social networks and shows how the proposed models can effectively isolate almost any malicious nodes in the network at the expenses of an increase in thenetwork traffic for feedback exchange.
Abstract: The integration of social networking concepts into the Internet of things has led to the Social Internet of Things (SIoT) paradigm, according to which objects are capable of establishing social relationships in an autonomous way with respect to their owners with the benefits of improving the network scalability in information/service discovery. Within this scenario, we focus on the problem of understanding how the information provided by members of the social IoT has to be processed so as to build a reliable system on the basis of the behavior of the objects. We define two models for trustworthiness management starting from the solutions proposed for P2P and social networks. In the subjective model each node computes the trustworthiness of its friends on the basis of its own experience and on the opinion of the friends in common with the potential service providers. In the objective model, the information about each node is distributed and stored making use of a distributed hash table structure so that any node can make use of the same information. Simulations show how the proposed models can effectively isolate almost any malicious nodes in the network at the expenses of an increase in the network traffic for feedback exchange.
427 citations
Cites background from "Why Isn't Trust Transitive?"
...The main properties of trust are well defined and many works contribute to describe them ([36], [37], [38], [39] and [40])....
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...Indeed, it has been demonstrated in [40] that in real life trust is not always transitive but depends on the particular service requested....
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TL;DR: The model is that agents use their social network to reach information and their trust relationships to filter it and it is identified that network density, preference heterogeneity among agents, and knowledge sparseness to be crucial factors for the performance of the system.
Abstract: In this paper, we present a model of a trust-based recommendation system on a social network. The idea of the model is that agents use their social network to reach information and their trust relationships to filter it. We investigate how the dynamics of trust among agents affect the performance of the system by comparing it to a frequency-based recommendation system. Furthermore, we identify the impact of network density, preference heterogeneity among agents, and knowledge sparseness to be crucial factors for the performance of the system. The system self-organises in a state with performance near to the optimum; the performance on the global level is an emergent property of the system, achieved without explicit coordination from the local interactions of agents.
413 citations
Cites background from "Why Isn't Trust Transitive?"
...From the perspective of network security (where transitivity would, for example, imply accepting a key with no further verification based on trust) or formal logics (where transitivity would, for example, imply updating a belief store with incorrect, impossible, or inconsistent statements) it may make sense to assume that trust is not transitive [11,20,22]....
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TL;DR: The article reviews the most popular peer-to-peer key management protocols for mobile ad hoc networks (MANETs) and discusses and provides comments on the strategy of each group separately.
Abstract: The article reviews the most popular peer-to-peer key management protocols for mobile ad hoc networks (MANETs). The protocols are subdivided into groups based on their design strategy or main characteristic. The article discusses and provides comments on the strategy of each group separately. The discussions give insight into open research problems in the area of pairwise key management.
373 citations
Cites background from "Why Isn't Trust Transitive?"
...Inherently a chain of trust provides weak authentication [Christianson 1996; Abdul-Rahman and Hailes 1997]....
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...This has been shown to be generally untrue [Christianson 1996]....
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01 Jan 2006
TL;DR: A method for trust network analysis using subjective logic (TNA-SL), which provides a simple notation for expressing transitive trust relationships, and defines a method for simplifying complex trust networks so that they can be expressed in a concise form and be computationally analysed.
Abstract: Trust networks consist of transitive trust relationships between people, organisations and software agents connected through a medium for communication and interaction. By formalising trust relationships, e.g. as reputation scores or as subjective trust measures, trust between parties within the community can be derived by analysing the trust paths linking the parties together. This article describes a method for trust network analysis using subjective logic (TNA-SL). It provides a simple notation for expressing transitive trust relationships, and defines a method for simplifying complex trust networks so that they can be expressed in a concise form and be computationally analysed. Trust measures are expressed as beliefs, and subjective logic is used to compute trust between arbitrary parties in the network. We show that TNA-SL is efficient, and illustrate possible applications with examples.
345 citations
Cites background from "Why Isn't Trust Transitive?"
...Moreover, most traditional cues for assessing trust in the physical world are not available through those media....
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TL;DR: This paper proposes a novel agent-based trust and reputation management scheme (ATRM) for wireless sensor networks, and proves its correctness and extensive performance evaluation results, which clearly show thatTrust and reputation can be computed in wireless Sensor networks with minimal overhead.
282 citations
Cites background from "Why Isn't Trust Transitive?"
...The properties of trust are summarized as: subjectivity [30,35], non-transitivity [12], temporalness, [4], contextualness and dynamicity, as well as non-monotonicity [2]....
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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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