The document discusses trust networks and methods for determining trustworthiness. It begins by providing real-life examples where trust is important, such as deciding who to leave children with or which sensor data to rely on. It then defines trust and related concepts, and presents a trust ontology with elements like trust type, value, and scope. The document also discusses challenges around gleaning trustworthiness and provides practical examples using metrics like reputation over time or among communities. The goal is to better understand and represent trust to help make important decisions with incomplete information.
Cory Henson and Amit Sheth, Active Perception Over Machine and Citizen Sensing, SemTech 2011, June 2011.
http://semtech2011.semanticweb.com/sessionPop.cfm?confid=62&proposalid=3825
http://semantic-sensor-web.com
Given the growth of social media and rapid evolution of Web of Data, we have unprecedented opportunities to improve crisis response by extracting social signals, creating spatio-temporal mappings, performing analytics on social and Web of Data, and supporting a variety of applications. Such applications can help provide situational awareness during an emergency, improve preparedness, and assist during the rebuilding/recovery phase of a disaster. Data mining can provide valuable insights to support emergency responders and other stakeholders during crisis. However, there are a number of challenges and existing computing technology may not work in all cases. Therefore, our objective here is to present the characterization of such data mining tasks, and challenges that need further research attention for leveraging social media and Web of Data to assist crisis response coordination.
This tutorial presents tools and techniques for effectively utilizing the Internet of Things (IoT) for building advanced applications, including the Physical-Cyber-Social (PCS) systems. The issues and challenges related to IoT, semantic data modelling, annotation, knowledge representation (e.g. modelling for constrained environments, complexity issues and time/location dependency of data), integration, analy- sis, and reasoning will be discussed. The tutorial will de- scribe recent developments on creating annotation models and semantic description frameworks for IoT data (e.g. such as W3C Semantic Sensor Network ontology). A review of enabling technologies and common scenarios for IoT applications from the data and knowledge engineering point of view will be discussed. Information processing, reasoning, and knowledge extraction, along with existing solutions re- lated to these topics will be presented. The tutorial summarizes state-of-the-art research and developments on PCS systems, IoT related ontology development, linked data, do- main knowledge integration and management, querying large- scale IoT data, and AI applications for automated knowledge extraction from real world data.
Related: Semantic Sensor Web: http://knoesis.org/projects/ssw
Physical-Cyber-Social Computing: http://wiki.knoesis.org/index.php/PCS
This is a brief a brief review of current multi-disciplinary and collaborative projects at Kno.e.sis led by Prof. Amit Sheth. They cover research in big social data, IoT, semantic web, semantic sensor web, health informatics, personalized digital health, social data for social good, smart city, crisis informatics, digital data for material genome initiative, etc. Dec 2015 edition.
Krishnaprasad Thirunarayan, Trust Management: Multimodal Data Perspective,
Invited Tutorial, The 2015 International Conference on Collaboration
Technologies and Systems (CTS 2015), June 2015
Smart Data - How you and I will exploit Big Data for personalized digital hea...Amit Sheth
Amit Sheth's keynote at IEEE BigData 2014, Oct 29, 2014.
Abstract from:
http://cci.drexel.edu/bigdata/bigdata2014/keynotespeech.htm
Big Data has captured a lot of interest in industry, with the emphasis on the challenges of the four Vs of Big Data: Volume, Variety, Velocity, and Veracity, and their applications to drive value for businesses. Recently, there is rapid growth in situations where a big data challenge relates to making individually relevant decisions. A key example is personalized digital health that related to taking better decisions about our health, fitness, and well-being. Consider for instance, understanding the reasons for and avoiding an asthma attack based on Big Data in the form of personal health signals (e.g., physiological data measured by devices/sensors or Internet of Things around humans, on the humans, and inside/within the humans), public health signals (e.g., information coming from the healthcare system such as hospital admissions), and population health signals (such as Tweets by people related to asthma occurrences and allergens, Web services providing pollen and smog information). However, no individual has the ability to process all these data without the help of appropriate technology, and each human has different set of relevant data!
In this talk, I will describe Smart Data that is realized by extracting value from Big Data, to benefit not just large companies but each individual. If my child is an asthma patient, for all the data relevant to my child with the four V-challenges, what I care about is simply, “How is her current health, and what are the risk of having an asthma attack in her current situation (now and today), especially if that risk has changed?” As I will show, Smart Data that gives such personalized and actionable information will need to utilize metadata, use domain specific knowledge, employ semantics and intelligent processing, and go beyond traditional reliance on ML and NLP. I will motivate the need for a synergistic combination of techniques similar to the close interworking of the top brain and the bottom brain in the cognitive models.
For harnessing volume, I will discuss the concept of Semantic Perception, that is, how to convert massive amounts of data into information, meaning, and insight useful for human decision-making. For dealing with Variety, I will discuss experience in using agreement represented in the form of ontologies, domain models, or vocabularies, to support semantic interoperability and integration. For Velocity, I will discuss somewhat more recent work on Continuous Semantics, which seeks to use dynamically created models of new objects, concepts, and relationships, using them to better understand new cues in the data that capture rapidly evolving events and situations.
Smart Data applications in development at Kno.e.sis come from the domains of personalized health, energy, disaster response, and smart city.
Cory Henson and Amit Sheth, Active Perception Over Machine and Citizen Sensing, SemTech 2011, June 2011.
http://semtech2011.semanticweb.com/sessionPop.cfm?confid=62&proposalid=3825
http://semantic-sensor-web.com
Given the growth of social media and rapid evolution of Web of Data, we have unprecedented opportunities to improve crisis response by extracting social signals, creating spatio-temporal mappings, performing analytics on social and Web of Data, and supporting a variety of applications. Such applications can help provide situational awareness during an emergency, improve preparedness, and assist during the rebuilding/recovery phase of a disaster. Data mining can provide valuable insights to support emergency responders and other stakeholders during crisis. However, there are a number of challenges and existing computing technology may not work in all cases. Therefore, our objective here is to present the characterization of such data mining tasks, and challenges that need further research attention for leveraging social media and Web of Data to assist crisis response coordination.
This tutorial presents tools and techniques for effectively utilizing the Internet of Things (IoT) for building advanced applications, including the Physical-Cyber-Social (PCS) systems. The issues and challenges related to IoT, semantic data modelling, annotation, knowledge representation (e.g. modelling for constrained environments, complexity issues and time/location dependency of data), integration, analy- sis, and reasoning will be discussed. The tutorial will de- scribe recent developments on creating annotation models and semantic description frameworks for IoT data (e.g. such as W3C Semantic Sensor Network ontology). A review of enabling technologies and common scenarios for IoT applications from the data and knowledge engineering point of view will be discussed. Information processing, reasoning, and knowledge extraction, along with existing solutions re- lated to these topics will be presented. The tutorial summarizes state-of-the-art research and developments on PCS systems, IoT related ontology development, linked data, do- main knowledge integration and management, querying large- scale IoT data, and AI applications for automated knowledge extraction from real world data.
Related: Semantic Sensor Web: http://knoesis.org/projects/ssw
Physical-Cyber-Social Computing: http://wiki.knoesis.org/index.php/PCS
This is a brief a brief review of current multi-disciplinary and collaborative projects at Kno.e.sis led by Prof. Amit Sheth. They cover research in big social data, IoT, semantic web, semantic sensor web, health informatics, personalized digital health, social data for social good, smart city, crisis informatics, digital data for material genome initiative, etc. Dec 2015 edition.
Krishnaprasad Thirunarayan, Trust Management: Multimodal Data Perspective,
Invited Tutorial, The 2015 International Conference on Collaboration
Technologies and Systems (CTS 2015), June 2015
Smart Data - How you and I will exploit Big Data for personalized digital hea...Amit Sheth
Amit Sheth's keynote at IEEE BigData 2014, Oct 29, 2014.
Abstract from:
http://cci.drexel.edu/bigdata/bigdata2014/keynotespeech.htm
Big Data has captured a lot of interest in industry, with the emphasis on the challenges of the four Vs of Big Data: Volume, Variety, Velocity, and Veracity, and their applications to drive value for businesses. Recently, there is rapid growth in situations where a big data challenge relates to making individually relevant decisions. A key example is personalized digital health that related to taking better decisions about our health, fitness, and well-being. Consider for instance, understanding the reasons for and avoiding an asthma attack based on Big Data in the form of personal health signals (e.g., physiological data measured by devices/sensors or Internet of Things around humans, on the humans, and inside/within the humans), public health signals (e.g., information coming from the healthcare system such as hospital admissions), and population health signals (such as Tweets by people related to asthma occurrences and allergens, Web services providing pollen and smog information). However, no individual has the ability to process all these data without the help of appropriate technology, and each human has different set of relevant data!
In this talk, I will describe Smart Data that is realized by extracting value from Big Data, to benefit not just large companies but each individual. If my child is an asthma patient, for all the data relevant to my child with the four V-challenges, what I care about is simply, “How is her current health, and what are the risk of having an asthma attack in her current situation (now and today), especially if that risk has changed?” As I will show, Smart Data that gives such personalized and actionable information will need to utilize metadata, use domain specific knowledge, employ semantics and intelligent processing, and go beyond traditional reliance on ML and NLP. I will motivate the need for a synergistic combination of techniques similar to the close interworking of the top brain and the bottom brain in the cognitive models.
For harnessing volume, I will discuss the concept of Semantic Perception, that is, how to convert massive amounts of data into information, meaning, and insight useful for human decision-making. For dealing with Variety, I will discuss experience in using agreement represented in the form of ontologies, domain models, or vocabularies, to support semantic interoperability and integration. For Velocity, I will discuss somewhat more recent work on Continuous Semantics, which seeks to use dynamically created models of new objects, concepts, and relationships, using them to better understand new cues in the data that capture rapidly evolving events and situations.
Smart Data applications in development at Kno.e.sis come from the domains of personalized health, energy, disaster response, and smart city.
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Social life in digital societies: Trust, Reputation and Privacy EINS summer s...i_scienceEU
Ralph Holz (Technische Universitat Munchen)
Pablo Aragon (Barcelona Media)
Katleen Gabriels (IBBT-SMIT, Vrije Univeriteit Brussel)
Janet Xue (Macquaire University)
Anna Satsiou (Centre for Research and Technology Hellas- Information Technologies Institute)
Sorana Cimpan (Universite De Savoie)
Norbert Blenn (Delft University of Technology)
More information: http://www.internet-science.eu/
In this presentation: interpersonal trust and trust forming process
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- Building benevolence, integrity, and ability based trust
- Routes for trust building
- Swift trust
- Some practical guidelines
- Elaboration likelihood model
Trustlet, Open Research on Trust MetricsPaolo Massa
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Trustlet.org is a cooperative environment (wiki) for research of trust metrics on social networks, sharing of social network datasets and of trust metrics code as Free Software
C-DeepTrust A Context-Aware Deep Trust Prediction Model in Online Social Netw...OKOKPROJECTS
https://okokprojects.com/
IEEE PROJECTS 2023-2024 TITLE LIST
WhatsApp : +91-8144199666
From Our Title List the Cost will be,
Mail Us: okokprojects@gmail.com
Website: : https://www.okokprojects.com
: http://www.ieeeproject.net
Support Including Packages
=======================
* Complete Source Code
* Complete Documentation
* Complete Presentation Slides
* Flow Diagram
* Database File
* Screenshots
* Execution Procedure
* Video Tutorials
* Supporting Softwares
Support Specialization
=======================
* 24/7 Support
* Ticketing System
* Voice Conference
* Video On Demand
* Remote Connectivity
* Document Customization
* Live Chat Support
As the scope of current distributed computing model envisioned by the contemporary cloud computing environment enlarges to future federated Intercloud and ubiquitous & pervasive computing models such as Internet of Things (IoT), many difficult problems and challenges arise. Security is one of the most important and paramount concerns of such a computing environment. Current security mechanisms are very static, inflexible and not granular enough to make efficient and informed decisions in the Service Provider based computing environment. The conventional trust mechanisms in place are inadequate at addressing granular level trust issues in the highly distributed open environments. In this paper, we explore various Trust Management schemes and blueprints for enabling a framework that interested parties can use to determine the trustworthiness of disparate and heterogeneous computing entities. The paper also enumerates various business use case scenarios articulating how such a Trust Management framework would be highly invaluable for addressing the current as well as future computing environments needs.
Social life in digital societies: Trust, Reputation and Privacy EINS summer s...i_scienceEU
Ralph Holz (Technische Universitat Munchen)
Pablo Aragon (Barcelona Media)
Katleen Gabriels (IBBT-SMIT, Vrije Univeriteit Brussel)
Janet Xue (Macquaire University)
Anna Satsiou (Centre for Research and Technology Hellas- Information Technologies Institute)
Sorana Cimpan (Universite De Savoie)
Norbert Blenn (Delft University of Technology)
More information: http://www.internet-science.eu/
In this presentation: interpersonal trust and trust forming process
- organizational context, cognition-based trust
- Building benevolence, integrity, and ability based trust
- Routes for trust building
- Swift trust
- Some practical guidelines
- Elaboration likelihood model
Trustlet, Open Research on Trust MetricsPaolo Massa
Presentation of a paper at 11th Business Information Systems conference - 2nd Workshop on Social Aspects of the Web (SAW 2008).
Trustlet.org is a cooperative environment (wiki) for research of trust metrics on social networks, sharing of social network datasets and of trust metrics code as Free Software
C-DeepTrust A Context-Aware Deep Trust Prediction Model in Online Social Netw...OKOKPROJECTS
https://okokprojects.com/
IEEE PROJECTS 2023-2024 TITLE LIST
WhatsApp : +91-8144199666
From Our Title List the Cost will be,
Mail Us: okokprojects@gmail.com
Website: : https://www.okokprojects.com
: http://www.ieeeproject.net
Support Including Packages
=======================
* Complete Source Code
* Complete Documentation
* Complete Presentation Slides
* Flow Diagram
* Database File
* Screenshots
* Execution Procedure
* Video Tutorials
* Supporting Softwares
Support Specialization
=======================
* 24/7 Support
* Ticketing System
* Voice Conference
* Video On Demand
* Remote Connectivity
* Document Customization
* Live Chat Support
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1. Trust Networks
Krishnaprasad Thirunarayan (T. K. Prasad)
Professor, Department of Computer Science and Engineering
Kno.e.sis - Ohio Center of Excellence in Knowledge-enabled Computing
Wright State University, Dayton, OH-45435
(Collaborators: Pramod Anantharam, Cory Henson, and Professor Amit Sheth)
IICAI-2011
Dec 15, 2011 Trust Networks: T. K. Prasad 1
2. Broad Outline
• Real-life Motivational Examples (Why?)
• Trust : Characteristics and Related Concepts (What?)
• Trust Ontology (What?)
– Type, Value, Process, Scope
• Gleaning Trustworthiness (How?) + Security
– Practical Examples of Trust Metrics
– Comparative Analysis of Bayesian Approaches to Trust
• Research Challenges (Why-What-How?) + Our Contributions
– Sensor Networks
– Social Networks
– Interpersonal
– Bayesian Approach to Multi-level Trust
Dec 15, 2011 Trust Networks: T. K. Prasad 2
4. Interpersonal
• With which neighbor should we leave our
children over the weekend when we are
required to be at the hospital?
• Who should be named as a guardian for our
children in the Will?
Dec 15, 2011 Trust Networks: T. K. Prasad 4
5. Social
• In Email:
– SUBJECT: [TitanPad] Amit Sheth invited you to an
EtherPad document.
– CONTENT: View it here:
http://knoesis.titanpad.com/200
• Issue: Is the request genuine or a trap?
Dec 15, 2011 Trust Networks: T. K. Prasad 5
6. Social
• To click or not to click a http://bit.ly-URL
• To rely or not to rely on a product review
(when only a few reviews are present)?
Dec 15, 2011 Trust Networks: T. K. Prasad 6
7. Sensors
• Weather sensor network predicts a potential tornado in
the vicinity of a city.
• Issue: Should we mobilize emergency response teams
ahead of time?
• Van’s TCS (Traction Control System) indicator light came
on intermittently, while driving.
• Issue: Which is faulty: the indicator light or the traction
control system?
• Van’s Check Engine light came on, while driving.
• Issue: Which is faulty: the indicator light or the
transmission control system ?
Dec 15, 2011 Trust Networks: T. K. Prasad 7
8. Common Issues and Context
• Uncertainty
– About the validity of a claim or
assumption
–Past Experience : Vulnerability
• Need for action
• Critical decision with potential for loss
Dec 15, 2011 Trust Networks: T. K. Prasad 8
9. Commonality among Trust Definitions*
• a Trustor
– someone who must choose whether, and how much, to
trust
• a Trustee
– someone or something that is to be trusted
• an Action
– by which the trustor is choosing to be vulnerable to the
trustee based on an assessment of trustee’s nature
• a Context
– in which the potential negative consequences of betrayal
outweigh any perceived positive results.
*http://www.iarpa.gov/rfi_trust.html
Dec 15, 2011 Trust Networks: T. K. Prasad 9
10. Sources of uncertainty
• In social network, trustor’s incomplete
knowledge or trustee’s devious intentions.
• In sensor network, unpredictable environment
(e.g., random phenomenon), or sensor faults
(e.g., due to aging), leading to corrupt data.
• In cognitive radio networks, unpredictable
channel noise or traffic.
• Interpersonal examples
– Irresponsible / selfish / greedy / vengeful
Dec 15, 2011 Trust Networks: T. K. Prasad 10
11. Why Track Trust?
• In Mobile Ad Hoc Networks (MANETs),
trust enables dynamic determination of
secure routes.
– Efficiency: To improve throughput
• By avoiding nodes facing bad channel condition
– Robustness : To detect malicious nodes
• When attackers enter the network in spite of
secure key distribution/authentication
Dec 15, 2011 Trust Networks: T. K. Prasad 11
12. Why Track Trust?
• In sensor networks, it allows detection of
faults and transient bad behavior due to
environmental effects.
• In cognitive radio networks, it can enable
selection of optimal channel (less noisy,
less crowded channels).
Dec 15, 2011 Trust Networks: T. K. Prasad 12
13. Why Track Trust?
• In E-commerce:
–To predict future behavior in a
reliable manner.
–To incentivize “good” behavior and
discourage “bad” behavior.
–To detect malicious entities.
Dec 15, 2011 Trust Networks: T. K. Prasad 13
14. Risk/uncertainty mitigation
• Compensating factors that alter trust
threshold
• In e-commerce, warranties and insurance
reduce risk.
• In sensor networks, redundancy enables
filtering of corrupt data.
• In interpersonal situations, close ties
help.
Dec 15, 2011 Trust Networks: T. K. Prasad 14
15. Trust and Related Concepts
(What is trust?)
Dec 15, 2011 Trust Networks: T. K. Prasad 15
16. Trust Definition : Psychology slant
Trust is the psychological state
comprising a willingness to be
vulnerable in expectation of a
valued result.
Ontology of Trust, Huang and Fox, 2006
Josang et al’s Decision Trust
Dec 15, 2011 Trust Networks: T. K. Prasad 16
17. Trust Definition : Psychology slant
Trust in a person is a commitment to
an action based on a belief that the
future actions of that person will
lead to good outcome.
Golbeck and Hendler, 2006
Dec 15, 2011 Trust Networks: T. K. Prasad 17
18. Trust Definition : Probability slant
Trust (or, symmetrically, distrust)
is a level of subjective probability
with which an agent assesses
that another agent will perform
a particular action, both before
and independently of such an
action being monitored …
Can we Trust Trust?, Diego Gambetta, 2000
Josang et al’s Reliability Trust
Dec 15, 2011 Trust Networks: T. K. Prasad 18
19. Trustworthiness Definition :
Psychology Slant
Trustworthiness is a collection of
qualities of an agent that leads them
to be considered as deserving of
trust from others (in one or more
environments, under different
conditions, and to different degrees).
http://www.iarpa.gov/rfi_trust.html
Dec 15, 2011 Trust Networks: T. K. Prasad 19
20. Trustworthiness Definition :
Probability slant
Trustworthiness is the objective
probability that the trustee
performs a particular action on
which the interests of the
trustor depend.
Solhaug et al, 2007
Dec 15, 2011 Trust Networks: T. K. Prasad 20
21. Trust vs Trustworthiness : My View
Trust Disposition
Depends on
Potentially Quantified Trustworthiness Qualities
+
Context-based Trust Threshold
E.g.*, In the context of trusting strangers, people in
the West will trust for lower levels of trustworthiness
than people in the Gulf. *Bohnet et al, 5/2010
Dec 15, 2011 Trust Networks: T. K. Prasad 21
22. Qualitative Trust Dispositions
(depends on Trust Threshold?)
http://paulenglish.com/trust.html
Dec 15, 2011 Trust Networks: T. K. Prasad 22
23. (Community-based) Reputation
• Reputation* is the community or public
estimation of standing for merit,
achievement, reliability, etc. *dictionary.com
• Reputation** is the opinion (or a social
evaluation) of a community toward a
person, a group of people, or an
organization on a certain criterion. **Wikipedia
• Cf. Brand-value, PageRank, eBay profile, etc.
Dec 15, 2011 Trust Networks: T. K. Prasad 25
24. Trust vs. (Community-based)
Reputation
Reputation can be a basis for trust.
However, they are different notions*.
• I trust you because of your good reputation.
• I trust you despite your bad reputation.
• Do you still trust Toyota brand?
*Josang et al, 2007
Dec 15, 2011 Trust Networks: T. K. Prasad 26
25. Trust vs. (Community-based)
Reputation
Trust :: Reputation
::::
Local :: Global
::::
Subjective :: Objective
(Cf. Security refers to resistance to attacks.)
Dec 15, 2011 Trust Networks: T. K. Prasad 27
26. Reputation is Overloaded
Community-based Reputation
vs.
Temporal Reputation
(Cf. Sustained good behavior over time elicits
temporal reputation-based trust.)
Dec 15, 2011 Trust Networks: T. K. Prasad 28
27. Trust is well-known,
but is not well-understood.
The utility of a notion
testifies not to its clarity but
rather to the philosophical
importance of clarifying it.
-- Nelson Goodman
(Fact, Fiction and Forecast, 1955)
Dec 15, 2011 Trust Networks: T. K. Prasad 31
28. Trust Ontology
(What is trust?)
Illustration of Knowledge Representation and Reasoning:
Relating Semantics to Data Structures and Algorithms
Dec 15, 2011 Trust Networks: T. K. Prasad 32
29. Example Trust Network -
Different Trust Links with Local Order on out-links
• Alice trusts Bob for recommending good car
mechanic.
• Bob trusts Dick to be a good car mechanic.
• Charlie does not trust Dick to be a good car
mechanic.
• Alice trusts Bob more than Charlie, for
recommending good car mechanic.
• Alice trusts Charlie more than Bob, for
recommending good baby sitter.
*Thirunarayan et al, IICAI 2009
Dec 15, 2011 Trust Networks: T. K. Prasad 33
30. Digression: Illustration of Knowledge
Representation and Reasoning
• Abstract and encode clearly delineated “subarea”
of knowledge in a formal language.
– Trust Networks => node-labeled, edge-labeled
directed graph (DATA STRUCTURES)
• Specify the meaning in terms of how “network
elements” relate to or compose with each other.
– Semantics of Trust, Trust Metrics => using logic or
probabilistic basis, constraints, etc. (SEMANTICS)
• Develop efficient graph-based procedures
– Trust value determination/querying (INFERENCE
ALGORITHMS)
Dec 15, 2011 Trust Networks: T. K. Prasad 34
31. (In recommendations)
(For capacity to act)
(For lack of
capacity to act)
Dec 15, 2011 Trust Networks: T. K. Prasad 35
32. Trust Ontology*
6-tuple representing a trust relationship:
{type, value, scope, process}
trustor trustee
Type – Represents the nature of trust relationship.
Value – Quantifies trustworthiness for comparison.
Scope – Represents applicable context for trust.
Process – Represents the method by which the value is
created and maintained.
*Anantharam et al, NAECON 2010
Dec 15, 2011 Trust Networks: T. K. Prasad 36
33. Trust Ontology:
Trust Type, Trust Value, and Trust Scope
Trust Type*
Referral Trust – Agent a1 trusts agent a2’s ability to
recommend another agent.
(Non-)Functional Trust – Agent a1 (dis)trusts agent a2’s
ability to perform an action.
Cf. ** trust in belief vs. trust in performance
Trust Value
E.g., Star rating, numeric rating, or partial ordering.
Trust Scope*
E.g., Car Mechanic context. *Thirunarayan et al, IICAI 2009
** Huang and Fox, 2006
Dec 15, 2011 Trust Networks: T. K. Prasad 37
34. Trust Ontology:
Trust Process
Represents the method by which the value
is computed and maintained.
Primitive (for functional and referral links)*
Reputation – based on past behavior (temporal) or
community opinion.
Policy – based on explicitly stated constraints.
Evidence – based on seeking/verifying evidence.
Provenance – based on lineage information.
Composite (for admissible paths)**
Propagation (Chaining and Aggregation)
*Anantharam et al, NAECON 2010
**Thirunarayan et al, IICAI 2009
Dec 15, 2011 Trust Networks: T. K. Prasad 40
36. Example Trust Network illustrating Ontology Concepts
Dick is a
Bob is a car certified
aficionado mechanic
type: referral
process: reputation
scope: car mechanic
value: TAB Bob type: functional
process: policy
TAB > TAC scope: car mechanic ASE certified
value: 10
type: referral
Alice
process: reputation
scope: car mechanic type: non-functional
value: TAC process: reputation
scope: car mechanic Dick
value: 3
Charlie
37. Unified Illustration of Trust Processes
Scenario : Hiring Web Search Engineer - An R&D Position
Various Trust Processes :
• (Temporal-based) Reputation: Past job experiences
• (Community-based) Reputation: Multiple
references
• Policy-based: Scores on screening test
• Provenance-based: Department/University of
graduation
• Evidence-based: Multiple interviews (phone, on-
site, R&D team)
Dec 15, 2011 Trust Networks: T. K. Prasad 44
38. Gleaning Trustworthiness :
Practical Examples
(How to determine trustworthiness?)
Dec 15, 2011 Trust Networks: T. K. Prasad 45
39. Trust Metrics and Trust Models
• Trust Metric => How is primitive trust
represented?
• E.g., Real number, Finite levels, Partial Order, Opinion =
(belief, disbelief, uncertainty), etc.
• Trust Model => How is composite trust
computed or propagated?
Y. L. Sun, et al, 2/2008
Dec 15, 2011 Trust Networks: T. K. Prasad 46
40. Ideal Approach
• Capture semantics of trust using
– axioms for trust propagation, or
– catalog of example trust networks that are
equivalent.
• Develop trust computation rules for
propagation (that is, chaining and
aggregation) that satisfy the axioms or
equivalence relation.
Dec 15, 2011 Trust Networks: T. K. Prasad 47
41. Direct Trust : Functional and Referral
Reputation-based Process
(Using large number of observations)
Dec 15, 2011 Trust Networks: T. K. Prasad 48
42. Reputation-based Frameworks
• Centralized Trust Authority
– E.g., E-commerce systems, etc.
• Distributed Trust Representation and
Computation (using Bayesian analytics)
– E.g., MANETs, peer-to-peer networks, etc.
Dec 15, 2011 Trust Networks: T. K. Prasad 49
43. Using Large Number of Observations
• Over time (<= Referral + Functional) :
Temporal Reputation-based Process
– Mobile Ad-Hoc Networks
– Sensor Networks
• Quantitative information
(Numeric data)
• Over agents (<= Referral + Functional) :
Community Reputation-based Process
– Product Rating Systems
• Quantitative + Qualitative information
(Numeric + text data)
Dec 15, 2011 Trust Networks: T. K. Prasad 50
44. Desiderata for Trustworthiness
Computation Function
• Initialization Problem : How do we get initial value?
• Update Problem : How do we reflect the observed
behavior in the current value dynamically?
• Trusting Trust* Issue: How do we mirror uncertainty
in our estimates as a function of observations?
• Law of Large Numbers: The average of the results obtained from a
large number of trials should be close to the expected value.
• Efficiency Problem : How do we store and update
values efficiently?
*Ken Thompson’s Turing Award Lecture: “Reflections on Trusting Trust”
Dec 15, 2011 Trust Networks: T. K. Prasad 51
45. Mathematical Background
Beta PDF for Reputation
Dec 15, 2011 Trust Networks: T. K. Prasad 52
46. Beta-distribution : Gently
• Consider a (potentially unfair) coin that comes up
HEADS with probability p and TAILS with probability
(1 – p).
• Suppose we perform ( r + s ) coin tosses and the coin
turns up with HEADS r times and with TAILS s times.
• What is the best estimate of the distribution of the
probability p given these observations?
=> Beta-distribution with parameters ( r+1, s+1 )
f(p; r+1, s+1)
Dec 15, 2011 Trust Networks: T. K. Prasad 53
47. Beta Probability Density Function(PDF)
x is a probability,
so it ranges from 0-1
If the prior distribution of x is
uniform, then the beta
distribution gives posterior
distribution of x after
observing a-1 occurrences
of event with probability x
and b-1 occurrences of the
complementary event with
probability (1-x).
Dec 15, 2011 Trust Networks: T. K. Prasad 54
48. a = b, so the pdf’s are symmetric w.r.t 0.5.
Note that the graphs get narrower as (a+b) increases.
a= 2
a= 1
b= 2
b= 1
a= 5 a= 10
b= 5 b= 10
Dec 15, 2011 Trust Networks: T. K. Prasad 55
49. a ≠ b, so the pdf’s are asymmetric w.r.t . 0.5.
Note that the graphs get narrower as (a+b) increases.
a= 5 a= 5
b= 25 b= 10
a= 25 a= 10
b= 5 b= 5
Dec 15, 2011 Trust Networks: T. K. Prasad 56
50. Beta-distribution - Applicability
• Dynamic trustworthiness can be
characterized using beta probability
distribution function gleaned from total
number of correct (supportive) r = (a-1)
and total number of erroneous
(opposing) s = (b-1) observations so far.
• Overall trustworthiness (reputation) is its
mean: a/a +b
Dec 15, 2011 Trust Networks: T. K. Prasad 58
51. Why Beta-distribution?
• Intuitively satisfactory, Mathematically precise, and
Computationally tractable
• Initialization Problem : Assumes that all probability values
are equally likely.
• Update Problem : Updates (a, b) by incrementing a for
every correct (supportive) observation and b for every
erroneous (opposing) observation.
• Trusting Trust Issue: The graph peaks around the mean, and
the variance diminishes as the number of observations
increase, if the agent is well-behaved.
• Efficiency Problem: Only two numbers stored/updated.
Dec 15, 2011 Trust Networks: T. K. Prasad 59
52. Information Theoretic Interpretation
of Trustworthiness Probability
• Intuitively, probability values of 0 and 1 imply
certainty, while probability value of 0.5 implies
a lot of uncertainty.
• This can be formalized by mapping probability
in [0,1] to trust value in [–1,1], using
information theoretic approach.
Y. L. Sun, et al, 2/2008
Dec 15, 2011 Trust Networks: T. K. Prasad 60
53. Information Theoretic Interpretation
of Trustworthiness Probability
• T(trustee : trustor, action) =
if 0.5 <= p
then 1 – H(p) /* 0.5 <= p <= 1 */
else H(p) – 1 /* 0 <= p <= 0.5 */
where
H(p) = – p log2(p) – (1 – p) log2(1 – p)
Dec 15, 2011 Trust Networks: T. K. Prasad 61
54. Plot of T(trustee : trustor, action) vs. p
Trust portion (p in [0.5,1]) Distrust portion (p in [0,0.5])
Dec 15, 2011 Trust Networks: T. K. Prasad 63
55. Direct Trust : Functional
Policy-based Process
(Using Trustworthiness Qualities)
Dec 15, 2011 Trust Networks: T. K. Prasad 64
56. General Approach to Trust Assessment
• Domain dependent qualities for determining
trustworthiness
– Based on Content / Data
– Based on External Cues / Metadata
• Domain independent mapping to trust values
or levels
– Quantification through abstraction and
classification
Dec 15, 2011 Trust Networks: T. K. Prasad 65
57. Example: Wikipedia Articles
• Quality (content-based)
– Appraisal of information provenance
• References to peer-reviewed publication
• Proportion of paragraphs with citation
– Article size
• Credibility (metadata-based)
– Author connectivity
– Edit pattern and development history
• Revision count
• Proportion of reverted edits - (i) normal (ii) due to vandalism
• Mean time between edits
• Mean edit length.
Sai Moturu, 8/2009
Dec 15, 2011 Trust Networks: T. K. Prasad 66
58. (cont’d)
• Quantification of Trustworthiness
– Based on Dispersion Degree Score
(Extent of deviation from mean)
• Evaluation Metric
– Ranking based on trust level (determined from
trustworthiness scores), and compared to gold
standard classification using Normalized
Discounted Cumulative Gain (NDCG)
• RATINGS: featured, good, standard, cleanup, and stub.
• NDCG: penalizes more heavily errors at the top.
Dec 15, 2011 Trust Networks: T. K. Prasad 67
59. Example: Websites
• Trustworthiness estimated based on criticality
of data exchanged.
• Email address / Username / password
• Phone number / Home address
• Date of birth
• Social Security Number / Bank Account Number
• Intuition: A piece of data is critical if and only
if it is exchanged with a small number of
highly trusted sites.
Dec 15, 2011 Trust Networks: T. K. Prasad 68
60. Indirect Trust : Referral + Functional
Variety of Trust Metrics and Models
(Using Propagation – Chaining and Aggregation over Paths)
Dec 15, 2011 Trust Networks: T. K. Prasad 69
61. Collaborative Filtering
• Collaborative Filtering: Item-rating by a user
predicted on the basis of user’s similarity to
other users.
• Similarity Measures:
• Profile-based
• Item-ratings-based
• Item-category-based
Dec 15, 2011 Trust Networks: T. K. Prasad 72
62. Collaborative Filtering
• Pros:
– Items-agnostic
– Scales well over time with large number of items
• Cons:
– Data Sparsity Problem: Small number of
common items between users.
– Cold Start Users: Small number of items rated
by a user.
– Prone to Copy-Profile Attack: An attacker can
create a targeted-user-like profile to
manipulate recommendations.
Massa-Avesani, 2007
Dec 15, 2011 Trust Networks: T. K. Prasad 73
63. Trust-aware Recommender System
• TaRS uses explicit/direct trust between users to
predict implicit/indirect trust between users
through chaining.
• Collaborative Filtering Limitations Overcome:
– Mitigates Data Sparsity: Trust propagation is more
general and improves coverage.
– Bootstraps Cold Start Users: A single trust link from a
new user can enable the user to inherit several
“parental” recommendations.
– Robust w.r.t Copy-Profile Attack: Fake identities are
not trusted by an active user.
Massa-Avesani, 2007
Dec 15, 2011 Trust Networks: T. K. Prasad 74
64. Trust Propagation Frameworks
• Chaining, Aggregation, and Overriding
Golbeck – Hendler, 2006 Massa-Avesani, 2005 Sun et al, 2006
Bintzios et al, 2006 Thirunarayan et al, 2009
• Trust Management Richardson et al, 2003
• Abstract properties of operators
• Reasoning with trust Guha et al., 2004
• Matrix-based trust propagation
• The Beta-Reputation System
• Algebra on opinion = (belief, disbelief, uncertainty)
Josang and Ismail, 2002
Dec 15, 2011 Trust Networks: T. K. Prasad 75
65. Trust Propagation Algorithms
• Top-down
• 1: Extract trust DAG (eliminate cycles)
• 2: Predict trust score for a source in a target by
aggregating trust scores in target inherited
from source’s “trusted” parents weighted with
trust value in the corresponding parent.
–Computation is level-by-level
–Alternatively, computation can be based on
paths.
Golbeck – Hendler, 2006
Dec 15, 2011 Trust Networks: T. K. Prasad 76
66. Trust Propagation Algorithms
• Bottom-up
• 1: Extract trust DAG (eliminate cycles)
• 2: Predict trust score for a source in a target by
aggregating trust scores in target inherited
from target’s “trusted” neighbors weighted
with trust value in the corresponding neighbor.
–Computation is level-by-level
–Alternatively, computation can be based on
paths. Massa-Avesani, 2005
Bintzios et al, 2006
Dec 15, 2011 Trust Networks: T. K. Prasad 77
67. Top-down vs Bottom-up (visualized)
Target
w1 w3
Target w2
Trust-Network
w1 w2 w3
source source
Dec 15, 2011 Trust Networks: T. K. Prasad 78
68. Example: Comparative Analysis
Different Interpretation:
q distrusts s (Bintzios et al’s)
vs
q has no information about
the trustworthiness of s (our’s,
Golbeck rounding algorithm)
Dec 15, 2011 Trust Networks: T. K. Prasad 79
69. Example: Well-founded
Cyclic Trust Network
Thirunarayan and Verma, 2007
Dec 15, 2011 Trust Networks: T. K. Prasad 81
71. Indirect Trust : Referral + Functional
Variety of Bayesian Trust Models
With Applications to Mobile Ad hoc Networks
Wireless Sensor Networks, etc.
Dec 15, 2011 Trust Networks: T. K. Prasad 83
72. Direct Trust : Functional and Referral
• Trust link: {subject : agent, action}
• For MANETs (resp. cognitive radio)
– Functional => Packet Forwarding (resp. quality of
spectrum / channel)
– Referral => Recommendations
Based on beta-reputation model:
Probability for trust = (S + 1) / (S + F +2)
where S = Number of good actions
F = Number of bad actions
Dec 15, 2011 Trust Networks: T. K. Prasad 84
73. Direct Trust : Functional and Referral
• Direct Trust for Packet Forwarding
• S = Number of packets forwarded
• F = Number of packets dropped
• S + F = Total number of requests for packet forwarding
• Direct Trust for Recommendations
• S = Number of times observed direct trust for packet
forwarding approximates expected indirect trust for
packet forwarding (trust over transit path : r+f)
• F = Number of times observed direct trust for packet
forwarding does not approximate expected indirect
trust for packet forwarding (trust over transit path : r+f)
Dec 15, 2011 Trust Networks: T. K. Prasad 85
74. Indirect Trust : Functional and Referral
• Indirect Trust for Packet Forwarding
– Used when direct trust is not available
»(overriding behavior)
• Chain links for a path from a recommender to the target
– Multiplicative
• Aggregate over multiple (parallel) paths from
recommenders to the target
– Unclear, in general
• Indirect Trust for Recommendations
• Obtained implicitly through computed referral trust
Dec 15, 2011 Trust Networks: T. K. Prasad 86
75. Trust Propagation Rules :
Axioms for Trust Models
Rule 1: Concatenation
propagation does
not increase trust. |T(A1,C1)| <= min(|R(A1,B1)|, |T(B1,C1)|)
Rule 2: Multipath
propagation does
not reduce trust. 0<=T(A1,C1) <= T(A2,C2) for R1 > 0 and T2 >= 0
0>=T(A1,C1) >= T(A2,C2) for R1 > 0 and T2 < 0
Dec 15, 2011 Trust Networks: T. K. Prasad
Sun et al, 2006 87
76. (cont’d)
Rule 3: Trust based on multiple referrals from a
single source should not be higher than that
from independent sources.
0<=T(A1,C1) <= T(A2,C2) for R1, R2, R3 > 0 and T2 >= 0
0>=T(A1,C1) >= T(A2,C2) for R1, R2, R3 > 0 and T2 < 0
Dec 15, 2011 Trust Networks: T. K. Prasad
Sun et al, 2006 88
77. Trust Propagation Rules :
Implementation
1 2
Dec 15, 2011 Trust Networks: T. K. Prasad
Sun et al, 2006 89
78. Trust Paths Visualized for Scalability:
Semantics unclear based on Sun et al’s spec
Bottom-up computation
reflects our needs better?
Dec 15, 2011 Trust Networks: T. K. Prasad 95
79. Trust : Functional and Referral
• Direct Trust for Primitive Actions based on
• S = Number of success actions
• F = Number of failed actions
• S + F = Total number of actions
• Indirect Trust via Recommendations based on
summing direct experiences of recommenders
• Sk = Number of success actions for kth recommender
• Fk = Number of failed actions for kth recommender
• No chaining for referrals Denko-Sun 2008
Dec 15, 2011 Trust Networks: T. K. Prasad 98
80. Cumulative Trust using
Direct Experience and Recommendations
• Cumulative Trust is obtained by using total
number of success actions and failed actions
from direct experience (ns,nu) and from i
(indirect experiences through)
recommendations (nsr,nur).
Dec 15, 2011 Trust Networks: T. K. Prasad 99
81. Contents of [Ganeriwal et al, 2007] Paper
• (a,b)-parameters to compute trust of i in j is
obtained by combining direct observations
(aj,bj) with indirect observations (ajk,bjk) from
k weighted by (ak,bk) using [Josang-Ismail,
2002] chaining/discounting rule.
• Obtains cumulative trust by combining direct trust from
a functional link and indirect trusts using paths
containing one referral link and one functional link.
• However, it does not distinguish functional and referral
trust.
Dec 15, 2011 Trust Networks: T. K. Prasad 100
82. Trust Propagation Rules :
Beta Reputation System
1 2
Dec 15, 2011 Trust Networks: T. K. Prasad
Josang and Ismail, 2002
101
83. Trust Propagation Rules :
Beta Reputation System
1 2
Rule 1: Concatenation propagation (reputation
discounting)
r = 2*r1 * r2 / (s1+2)(r2+s2+2)+2*r1
s = 2*r1 * s2 / (s1+2)(r2+s2+2)+2*r1
Rule 2: Multipath propagation (combining
feedback)
r = r1 + r2 s = s1 + s2
Rule *: Temporal Decay (Forgetting)
Dec 15, 2011 Trust Networks: T. K. Prasad
Josang and Ismail, 2002
102
84. Contents of [B-Trust, 2006] Paper
• Uses generic K-level discrete trust metric (as
opposed to 2-level metric)
– E.g., (very untrustworthy, untrustworthy, trustworthy, very trustworthy)
– E.g., reminiscent of Amazon recommendation ratings
• Distributed (local), robust, lightweight,
computational trust that takes into account
context, subjectivity, and time
– a la reputation-based approach
• Application: Pervasive computing
Dec 15, 2011 Trust Networks: T. K. Prasad 103
85. BUG -> FLAWED LEARNING?
• The approach does not clearly separate the
use of stable background knowledge for
applying Bayes’ rule, from the need to
dynamically learn background knowledge for
gleaning trust from experience.
• As a result, the initial trust values do not
change in response to experience.
Dec 15, 2011 Trust Networks: T. K. Prasad 104
86. Comparative Analysis
[Menko-T.Sun] : Beta-distribution based
• Direct functional trust and indirect functional
trust (through direct referrals).
– Trivial chaining.
– One fixed context, local and distributed.
• Robustness improved by dropping extreme
recommendations, though recommenders not
distinguished.
Dec 15, 2011 Trust Networks: T. K. Prasad 105
87. Comparative Analysis
[Ganeriwal et al]: Beta-distribution based
• Functional and Referral trust mixed up.
– Context glossed over, local and distributed.
• Robustness improved by chaining trust links of
length 2, using Josang-Ismail opinion
composition.
– Recommenders distinguished.
– Chaining weighs recommendations by
recommender trust.
Dec 15, 2011 Trust Networks: T. K. Prasad 106
88. Comparative Analysis
[Y. Sun et al]: Beta-distribution based
• Functional and Referral trust separated.
• One Context, hybrid (dynamically formed trust
network) and distributed.
• Information-theoretic approach
• Axiomatic specification and implementation of
trust propagation (chaining and aggregation)
• Incomplete w.r.t. arbitrary trust networks
• Robustness and Quality improved by analyzing
dynamically formed trust network.
Dec 15, 2011 Trust Networks: T. K. Prasad 107
89. Comparative Analysis
[B-Trust et al]: Multi-valued trust - Bayesian
• Functional and Referral trust separated.
– Context-based, local and distributed.
• Individualized aggregation, trivial chaining.
• Nice roadmap for theory, specification, and
implementation of trust networks
– Multi-valued Trust evolution : novel but buggy.
Dec 15, 2011 Trust Networks: T. K. Prasad 108
90. Comparative Analysis
[MLT-Approach]: Multi-level trust using Dirichlet
Distribution
• Functional and Referral trust separated.
– Context-based, local and distributed.
• Individualized aggregation, trivial chaining.
• Based on B-Trust roadmap but MLT evolution
based on Dirichlet distribution: conceptually
satisfactory and computationally efficient
• Example-based analysis for insights
Dec 15, 2011 Trust Networks: T. K. Prasad 109
91. Security Issues:
Threats and Vulnerabilities
Attacks and Robustness Analysis
Dec 15, 2011 Trust Networks: T. K. Prasad 110
92. Attacks
• Trust Management is an attractive target for
malicious nodes.
Bad mouthing attack (Defamation)
Dishonest recommendations on good nodes (calling them
bad)
Ballot stuffing attack (Collusion)
Dishonest recommendations on bad nodes (calling them
good)
Sybil attack
Creating Fake Ids
Newcomer attack
Registering as new nodes
Dec 15, 2011 Trust Networks: T. K. Prasad 111
93. Attacks
• Inconsistency in time-domain
On-Off attack
Malicious node behaves good and bad alternatively to
avoid detection
Sleeper attack
Malicious node acquires high trust by behaving good
and then striking by behaving bad
Inconsistency in node-domain
Conflicting Behavior Attack
Provide one recommendation to one set of peers and a
conflicting recommendation to a disjoint set of peers
Dec 15, 2011 Trust Networks: T. K. Prasad 112
94. Security : Robustness w.r.t Attacks
Bad mouthing attack
Example: Competent nodes downplay competitions.
Example: Can diminish throughput due to lost capacity.
Approach:
Separate functional and referral trust, updating
referral trust to track good recommendations
Trust composition rules ensure that low or
negative referral trust does not impact decision
Low trust nodes can be branded as malicious and
avoided. (Not viable if majority collude.)
Dec 15, 2011 Trust Networks: T. K. Prasad 113
95. Security : Robustness w.r.t Attacks
Ballot stuffing attack
Example: Malicious nodes collude to recommend each
other.
Example: Can cause unexpected loss of throughput.
Approach:
Feedback : Cross-check actual functional
performance with expected behavior via referral,
and update (reward/penalize) referral trust (in
parent) accordingly (in addition to updating
functional trust (in target))
Dec 15, 2011 Trust Networks: T. K. Prasad 114
96. Security : Robustness w.r.t. Attacks
Sybil attack
Create Fake Ids to take blame for malicious
behavior (dropping packets)
Newcomer attack
Register as new node to erase past history
Approach
Requires separate (key-based) authentication
mechanism (with TTP) to overcome these attacks.
Dec 15, 2011 Trust Networks: T. K. Prasad 115
97. Security : Robustness w.r.t Attacks
On-Off attack
Sleeper attack
Example: Due to malice or environmental changes
Approach:
Use forgetting factor (0<=b<=1):
k good/bad actions at t1
= k * b(t2 – t1) good/bad actions at t2 (> t1)
Dec 15, 2011 Trust Networks: T. K. Prasad 116
98. Forgetting Factor
k good/bad actions at t1 = k * b(t2 – t1) good/bad actions at t2 (> t1)
• High b value (0.9) enhances memorized time
window, while low b value (0.001) reduces it.
– High b enables malicious nodes (on-off/sleeper
attackers) to use prior good actions to mask
subsequent intentional bad actions.
• Reduces reliability.
– Low b forces legitimate nodes to be avoided due
to short spurts of unintentional bad actions.
• Reduces throughput.
Dec 15, 2011 Trust Networks: T. K. Prasad 117
99. Adaptive Forgetting Factor
• Intuition: Bad actions are remembered for a
longer duration than good actions.
• Actions performed with high trust forgotten quicker than
actions performed with low trust.
Choose b equal to ( 1 – p )
Choose b = 0.01 when p in [0.5,1] else 0.9
Example: Similar ideas used in Ushahidi
Note: Effectively, more good actions are
necessary to compensate for fewer bad actions,
to recover trust.
Dec 15, 2011 Trust Networks: T. K. Prasad 118
100. Security : Robustness w.r.t. Attacks
Conflicting Behavior Attack
Malicious node divide and conquer, by behaving
differently (resp. by providing different
recommendations) to different peers, causing
peers to provide conflicting recommendations to
source about the malicious node (resp. about
some target), reducing source’s referral trust in
some peers.
Eventually, this causes recommendations of some peers
to be ignored incorrectly.
Dec 15, 2011 Trust Networks: T. K. Prasad 119
101. Example
• Peer Node Set 1: 1, 2, 3, and 4
• Peer Node Set 2: 5, 6, 7, and 8
• Malicious node 0 behaves well towards nodes in
Set 1 but behaves badly towards nodes in Set 2.
• When node 9 seeks recommendations from
nodes in Set 1 U Set 2 on node 0, node 9 receives
conflicting recommendations on malicious node
0, causing referral trust in nodes in Set 1 or
nodes in Set 2 to be lowered.
=> Eventually throughput lowered
Dec 15, 2011 Trust Networks: T. K. Prasad 120
102. Security : Robustness w.r.t. Attacks
Conflicting Behavior Attack
Issue: Can recommenders get feedback
to reduce trust in malicious node?
Otherwise, referral trust cannot be
relied upon for detecting malicious
nodes.
Dec 15, 2011 Trust Networks: T. K. Prasad 121
103. Security : Robustness w.r.t. Attacks
If cumulative referral trust in B is computed using
direct experiences of several recommenders,
then it is possible to weed out extreme
experiences using deviation from the mean trust
value, where S is some chosen threshold.
Dec 15, 2011 Trust Networks: T. K. Prasad
Denko-Sun 2008 122
104. Contents of [Ganeriwal et al, 2007] Paper
• Combined trust of i in j is obtained from direct
observations (aj,bj) of j by i and indirect
observations (ajk,bjk) from k to i weighted by
(ak,bk) using [Josang-Ismail, 2002]
chaining/weighting/discounting rule.
• This discounting rule makes the local trust
computation resilient to bad mouthing ajk << bjk
and ballot stuffing ajk >> bjk attacks from
unreliable/malicious nodes ak << bk.
• It requires aging to be resilient to sleeper attacks.
Dec 15, 2011 Trust Networks: T. K. Prasad 123
105. Research Challenges
(What-Why-How of trust?)
HARD PROBLEMS
Dec 15, 2011 Trust Networks: T. K. Prasad 125
106. Generic Directions
• Finding online substitutes for traditional cues
to derive measures of trust.
• Creating efficient and secure systems for
managing and deriving trust, in order to
support decision making.
Josang et al, 2007
Dec 15, 2011 Trust Networks: T. K. Prasad 126
107. Trust : Social Networks vs
Machine Networks
• In social networks such as Facebook, trust is
often subjective, while in machine networks
and social networks such as Twitter, trust can
be given an objective basis and approximated
by trustworthiness.
• Reputation is the perception that an agent
creates through past actions about its
intentions and norms.
– Reputation can be a basis for trust.
Dec 15, 2011 Trust Networks: T. K. Prasad 127
109. Our Research
Abstract trustworthiness of sensors and
observations to perceptions to obtain actionable
situation awareness!
Web
T
observe perceive
T T
“real-world”
Dec 15, 2011 Trust Networks: T. K. Prasad 130
110. Trust
Strengthened Trust
Dec 15, 2011 Trust Networks: T. K. Prasad 131
111. Concrete Application
• Applied Beta-pdf to Mesowest Weather Data
– Used quality flags (OK, CAUTION, SUSPECT)
associated with observations from a sensor
station over time to derive reputation of a sensor
and trustworthiness of a perceptual theory that
explains the observation.
– Perception cycle used data from ~800 stations,
collected for a blizzard during 4/1-6/03.
Dec 15, 2011 Trust Networks: T. K. Prasad 132
112. Concrete Application
• Perception Cycle
– http://harp.cs.wright.edu/perception/
• Trusted Perception Cycle
– http://www.youtube.com/watch?v=lTxzghCjGgU
Dec 15, 2011 Trust Networks: T. K. Prasad 133
113. Mean of beta pdf vs. Time (for stnID = SBE)
1.2
1
0.8
Mean Beta
0.6
Value
0.4
0.2
0
3/31/2003 0:00 4/1/2003 0:00 4/2/2003 0:00 4/3/2003 0:00 4/4/2003 0:00 4/5/2003 0:00 4/6/2003 0:00 4/7/2003 0:00
Time
Dec 15, 2011 Trust Networks: T. K. Prasad 134
114. Research Issues
• Outlier Detection
– Homogeneous Networks
• Statistical Techniques
– Heterogeneous Networks (sensor + social)
• Domain Models
• Distinguishing between abnormal phenomenon
(observation), malfunction (of a sensor), and
compromised behavior (of a sensor)
– Abnormal situations
– Faulty behaviors
– Malicious attacks Ganeriwal et al, 2008
Dec 15, 2011 Trust Networks: T. K. Prasad 135
116. Our Research
• Study semantic issues relevant to trust
• Proposed model of trust/trust metrics to
formalize indirect trust
Dec 15, 2011 Trust Networks: T. K. Prasad 137
117. Quote
• Guha et al:
While continuous-valued trusts are
mathematically clean, from the standpoint
of usability, most real-world systems will
in fact use discrete values at which one
user can rate another.
• E.g., Epinions, Ebay, Amazon, Facebook, etc all
use small sets for (dis)trust/rating values.
Dec 15, 2011 Trust Networks: T. K. Prasad 139
118. Our Approach
Trust formalized in terms of partial orders
(with emphasis on relative magnitude)
Local but realistic semantics
Distinguishes functional and referral trust
Distinguishes direct and inferred trust
Direct trust overrides conflicting inferred trust
Represents ambiguity explicitly
Thirunarayan et al , 2009
Dec 15, 2011 Trust Networks: T. K. Prasad
119. Formalizing the Framework
• Given a trust network (Nodes AN, Edges RL U
PFL U NFL with Trust Scopes TSF, Local
Orderings ⪯ ANxAN), specify when a source can
trust, distrust, or be ambiguous about a
target, reflecting local semantics of:
• Functional and referral trust links
• Direct and inferred trust
• Locality
Dec 15, 2011 Trust Networks: T. K. Prasad 141
120. (In recommendations)
(For capacity to act)
(For lack of
capacity to act)
Dec 15, 2011 Trust Networks: T. K. Prasad 142
123. Similarly for Evidence in support of Negative Functional Trust.
Dec 15, 2011 Trust Networks: T. K. Prasad 145
124. Benefits of Formal Analysis
• Enables detecting and avoiding
unintended consequences.
– An earlier formalization gave priority to “certain“
conclusion from less trustworthy source over
“ambiguous“ conclusion from more trustworthy
source.
The whole problem with the world is
that fools and fanatics are always so
certain of themselves, but wiser people
so full of doubts. — Betrand Russell
Dec 15, 2011 Trust Networks: T. K. Prasad 146
125. Practical Issues
• Refinement of numeric ratings using
reviews in product rating networks
– Relevance : Separate ratings of vendor or about
extraneous features from ratings of product
• E.g., Issues about Amazon’s policies
• E.g., Publishing under multiple titles (Paul Davies’ “The Goldilock’s
Enigma” vs. “Cosmic Jackpot”)
– Polarity/Degree of support: Check consistency
between rating and review using sentiment
analysis; amplify hidden sentiments
• E.g., rate a phone as 1-star because it is the best
Dec 15, 2011 Trust Networks: T. K. Prasad 147
126. Research Issues
• Determination of trust / influence from
social networks
– Text analytics on communication
– Analysis of network topology
• E.g., follower relationship, friend relationship, etc.
• Determination of untrustworthy and
anti-social elements in social networks
• HOLY GRAIL: Direct Semantics in favor of
Indirect Translations
Dec 15, 2011 Trust Networks: T. K. Prasad 149
127. Research Issues
• Improving Security : Robustness to Attack
– How to exploit different trust processes to detect
and recover from attacks?
• Bad mouthing attack
• Ballot stuffing attack
• Sleeper attack
– Temporal trust discounting proportional to trust value
– Using policy-based process to ward-off attack using
reputation-based process
• Sybil attack
• Newcomer attack
Dec 15, 2011 Trust Networks: T. K. Prasad 152
128. Research Issues
• Intelligent integration of mobile sensor and
social data for situational awareness
– To exploit complementary and corroborative
evidence provided by them
– To obtain qualitative and quantitative context
– To improve robustness and completeness
– To incorporate socio-cultural, linguistic and
behavioral knowledge as part of ontologies to
improve semantic processing and analysis of data
Dec 15, 2011 Trust Networks: T. K. Prasad 153
129. Complementary and Corroborative
Information
Sensors observe
slow moving
traffic
Complementary
information
from social
networks
Dec 15, 2011 Trust Networks: T. K. Prasad 154
130. Corroborative Evidence
Evidence for
reported
observations
Dec 15, 2011 Trust Networks: T. K. Prasad 155
132. Research Issues
• Linguistic clues that betray
trustworthiness
• Experiments for gauging interpersonal
trust in real world situations
– *Techniques and tools to detect and amplify
useful signals in Self to more accurately predict
trust and trustworthiness in Others
*IARPA-TRUST program
Dec 15, 2011 Trust Networks: T. K. Prasad 157
133. Research Issues
• Other clues for gleaning
trustworthiness
– Face (in photo) can effect
perceived trustworthiness and
decision making
–Trust-inducing features of e-
commerce sites can impact buyers
Dec 15, 2011 Trust Networks: T. K. Prasad 158
134. Research Issues
• Study of cross-cultural differences in
trustworthiness qualities and trust thresholds
to better understand
– Influence
• What aspects improve influence?
– Manipulation
• What aspects flag manipulation?
Dec 15, 2011 Trust Networks: T. K. Prasad 159
135. Bayesian Trust Management Framework :
Multi-level Trust Metric
Illustrating a General Approach
Dec 15, 2011 Trust Networks: T. K. Prasad 160
136. Outline
• Motivation : Multi-level trust management
• Mathematical Foundation: Dirichlet
Distribution
• Implementation and Behavior Details:
– Local Trust Data Structures
– Trust Formation
– Bayesian Trust Evolution
• Analysis of Robustness: Security
• Evaluation: Example trace vs. experiment
Dec 15, 2011 Trust Networks: T. K. Prasad 161
137. Motivation
• Uses K-level discrete trust metric
– E.g., Amazon’s 5-star trust metric can be
interpreted as signifying (very untrustworthy,
untrustworthy, neutral, trustworthy, very
trustworthy) or (very dissatisfied, dissatisfied,
neutral, satisfied, very satisfied).
Dec 15, 2011 Trust Networks: T. K. Prasad 162
138. Approach
• Multi-level trust management approach
formalizes a distributed, robust,
lightweight, computational trust that
takes into account context, subjectivity,
and time.
• Applies Dirichlet distribution, a
generalization of Beta-distribution.
Dec 15, 2011 Trust Networks: T. K. Prasad 163
140. K-level Trust Metric
• K-level trust probability vector:
x = (x1, . . ., xK)
where (x1 + . . . + xK = 1).
• Example: If a 5-star rating system has 50 people
giving 5-stars, 20 people giving 4-stars, 5 people
giving 3-stars, 5 people giving 2-stars, and 20 people
giving 1-star, then the 5-level trust metric probability
vector is (0.5,0.2,0.05,0.05,0.2).
Dec 15, 2011 Trust Networks: T. K. Prasad 165
141. Trust and Experience
• Experience is a realization of the latent trust,
and helps predicting trust.
• Probability of an experience-level sequence,
with a1 - 1 counts of level 1 experience, …, aK - 1
counts of level K experience is:
* ( (a1 +…+ aK – K) ! / (a1-1 ! *…* aK-1 !) )
Dec 15, 2011 Trust Networks: T. K. Prasad 166
142. Dirichlet Distribution
• The Dirichlet distribution is the probability
density function for x = (x1, . . ., xK) given
(a1,…,aK):
Dec 15, 2011 Trust Networks: T. K. Prasad 167
143. Why use Dirichlet Distribution?
• If the prior distribution of x is uniform, then
the Dirichlet family of distribution shown
below gives posterior distribution of x after
ai-1 occurrences of level i experience with
probability xi, for each i in [1, K]:
Dec 15, 2011 Trust Networks: T. K. Prasad 168
144. Why use Dirichlet Distribution?
• Dirichlet distribution is a conjugate prior for
multinomial distribution.
• Consequence:
– Estimated distribution updated for a new experience
at level i, by just incrementing ai parameter.
– In contrast: if prior distribution is different from
Dirichlet, then it is conceptually hard to comprehend
and computationally inefficient to compute posterior
distribution, in general.
– Icing on the cake: Uniform distribution (signifying
ignorance) is Dirichlet!
Dec 15, 2011 Trust Networks: T. K. Prasad 169
145. Dirichlet distribution is a conjugate prior
for multinomial distribution.
Dec 15, 2011 Trust Networks: T. K. Prasad 170
146. Why use Dirichlet Distribution?
• Convenient Abstraction
–Abstraction of K-level Dirichlet
distribution by combining different
levels still yields Dirichlet distribution
with the corresponding parameters
merged.
• Conceptually and computationally
pleasing property
Dec 15, 2011 Trust Networks: T. K. Prasad 171
148. Dynamic Trustworthiness
• Best estimate of trust for Dir(a1,...,aK) (gleaned
from (ai-1) experiences at level i, for all i in [1,K])
is the mean vector (a1/a0,…,aK/a0), and the
associated confidence is the variance vector.
Dec 15, 2011 Trust Networks: T. K. Prasad 173
150. Local Data Structures
• To store relevant information to compute
direct (functional) and indirect (referral) trust.
• Each node maintains locally, for each peer and
each context, four vectors of length K.
Dec 15, 2011 Trust Networks: T. K. Prasad 175
151. Local Data Structures
• Direct Trust Vector: Peers X Contexts X Peers -> Probability-Vector-K
• dtv(px,c,py) = (d1,d2,…,dK)
• Direct Experience Matrix: Peers X Contexts X Peers -> Count-Vector-K
• dem(px,c,py) = (ec1,…,ecK)
Dec 15, 2011 Trust Networks: T. K. Prasad 176
152. Local Data Structures
• Recommended Trust Vector: Peers X Contexts X Peers -> Probability-
Vector-K
• rtv(px,c,py) = (r1,r2,…,rK)
• Sent Recommendation Matrix: Peers X Contexts X Peers -> Count-Vector-K
• srm(px,c,py) = (sr1,…,srK)
Dec 15, 2011 Trust Networks: T. K. Prasad 177
153. Local Data Structures
• Initialization: To reflect complete
ignorance via uniform distribution, we
set the probability vectors dtv and rtv to
(1/K,…,1/K), and the elements of the
count vector dem and srm to (0,…,0).
• These are Dirichlet distributed in the
limiting case where ai’s are 1.
Dec 15, 2011 Trust Networks: T. K. Prasad 178
154. Trust Formation
• Overall trust vector is weighted combination
of direct trust vector and recommended trust
vector.
• Weights determined using
– Objective confidence values using variance
(deviation from the mean)
– Subjective relative preference for direct
experience over recommendations
• Dependence on recommended trust yet to be explored
Dec 15, 2011 Trust Networks: T. K. Prasad 179
155. Trust Decision
• Assuming that trust-level scale is linear, the
trust distribution vector (d1,d2,…,dK) can be
mapped to the closed interval [0,1], or to
consolidated trust level, in order to act.
• Trust threshold should be determined based
on the context and risk tolerance.
Dec 15, 2011 Trust Networks: T. K. Prasad 180
156. Trust Evolution
• Direct/recommended trust vectors are updated
for a new experience/received recommendation.
• Key Idea: Dirichlet distribution is the conjugate
prior of the multinomial distribution. So it is
adequate to maintain counts of direct experience
and sent recommendations, to best estimate
direct trust and recommended trust vectors
respectively.
Dec 15, 2011 Trust Networks: T. K. Prasad 181
157. Trust Evolution
• Simple Scheme (Direct Trust)
For a new experience at level i,
dem(px,x,py) = (ec1,…,ecK) becomes
demnew(px,x,py) = (ec1,…, eci+1,…,ecK)
and dtv(px,c,py) becomes
dtvnew(px,c,py) = (d1,d2,…,dK)
where di = eci+1 / (ec1 + … + eck+1) and
dj = ecj / (ec1 + … + eck+1)
for each j in [1,K] and j =/= i.
Dec 15, 2011 Trust Networks: T. K. Prasad 182
158. Trust Evolution
• Robust Scheme
To incorporate differential aging of experience
counts as a function of their level (and to
incorporate “long term memory for low-level
experience and short term memory for high-
level experience”), we use a decay vector
(l1,…,lK), where 1 >= l1 >= … >= lK > 0, that
modifies update rule as:
Dec 15, 2011 Trust Networks: T. K. Prasad 183
159. Trust Evolution
• Robust Scheme (Direct Trust)
For a new experience at level i,
dem(px,x,py) = (ec1,…,ecK) becomes
demnew(px,x,py) = (ec1,…, eci + 1,…,ecK).
For every clock tick (with context-based delay),
dem(px,x,py) = (ec1,…,ecK) becomes
demnew(px,x,py) = (l1*ec1,…, lK*ecK)
Dec 15, 2011 Trust Networks: T. K. Prasad 184
160. Trust Evolution
• Robust Scheme (Direct Trust)
For every clock unit and new experience,
dtv(px,c,py) becomes
dtvnew(px,c,py) = (d1,d2,…,dK)
where di = eci / (ec1 + … + eck)
for each i in [1,K].
• Subtlety: Experience counts should saturate at
1 rather than diminish to 0 with time. (See code)
Dec 15, 2011 Trust Networks: T. K. Prasad 185
161. Trust Evolution Illustrated
Final Trust Distribution Final Trust Distribution
Experience Sequence
(Simple Scheme) (Robust Scheme)
[1,1,1] (0.57,0.14,0.14,0.14)
(0.55,0.15,0.15,0.15)
[1,4,1,4] (0.375,0.125,0.125,0.375)
(0.42,0.14,0.14,0.29)
[1,1,4,4,4,4,1,1] (0.42,0.08,0.08,0.42)
(0.5,0.1,0.1,0.3)
[1,1,4,4,4,4,1,1,1] (0.53,0.07,0.07,0.33)
(0.64,0.1,0.1,0.17)
[2,3,2,3] (0.125,0.375,0.375,0.125)
(0.16,0.4,0.3,0.14)
Dec 15, 2011 Trust Networks: T. K. Prasad 186
162. Trust Evolution Illustrated
Experience Trust Distribution Trace Trust Distribution Trace Beta-pdf
Sequence Value (Simple Scheme) (Robust Scheme) (cf. n =2)
(0.25,0.25,0.25,0.25) (0.25,0.25,0.25,0.25) 0.5
1 (0.4,0.2,0.2,0.2) (0.4,0.2,0.2,0.2) 0.33
1 (0.5,0.17,0.17,0.17) (0.53,0.165,0.155,0.15) 0.25
1 (0.57,0.14,0.14,0.14) (0.55,0.15,0.15,0.15) 0.2
n (0.5,0.125,0.125,0.25) (0.5,0.13,0.12,0.25) 0.33
n (0.44,0.11,0.11,0.33) (0.46,0.135,0.135,0.27) 0.43
n (0.4,0.1,0.1,0.4) (0.42,0.12,0.11,0.35) 0.5
n (0.36,0.1,0.1,0.45) (0.37,0.12,0.12,0.38) 0.55
1 (0.42,0.08,0.08,0.41) (0.47,0.11,0.11,0.31) 0.5
1 (0.46,0.08,0.08,0.38) (0.53,0.11,0.11,0.24) 0.45
1 (0.5,0.07,0.07,0.35) (0.6,0.1,0.1,0.2) 0.41
1 (0.53,0.07,0.07,0.33) (0.65,0.1,0.1,0.14) 0.38
n (0.5,0.0625,0.0625,0.375) (0.6,0.1,0.1,0.2) 0.43
1 (0.53,0.06,0.06,0.35) (0.64,0.1,0.1,0.17) 0.4
Dec 15, 2011 Trust Networks: T. K. Prasad 187
166. Salient Properties
• Symmetry
– Simple Scheme is symmetric w.r.t.
trust/experience levels while Robust Scheme is
somewhat asymmetric because of non-uniform
decay.
– Experience levels are “preserved” in that
extreme/controvertial behavior (credulous
interpretation) is treated differently from
ignorance (skeptical interpretation).
Dec 15, 2011 Trust Networks: T. K. Prasad 191
167. Salient Properties
• Effect of Order of Experience
– Simple Scheme is sensitive to the counts of
various experience levels, but not to the order of
experience.
– Robust Scheme is sensitive to the order of
experience.
Dec 15, 2011 Trust Networks: T. K. Prasad 192
168. Salient Properties
• Differential Aging of experience levels
• It exhibits limited and selective
memory.
–It retains low-level experiences
much longer than high-level
experiences.
»Parameters: Decay rate and
saturation
Dec 15, 2011 Trust Networks: T. K. Prasad 193
169. Related Work on Multi-level Trust
with Applications
The described approach is similar to Dirichlet Reputation
System [Josang-Haller, 2007].
Applications:
• Browser toolbar for clients to see the user ratings and
for users to provide ratings (critical surfer model)
[Josang-Haller, 2007]
• Evaluating partners in Collaborative Environments
[Yang and Cemerlic, 2009]
• Formalizing Multi-Dimensional Contracts [Reece, et al,
2007]
• In Collaborative Intrusion Detection System [Fung et al,
2011 ]
Dec 15, 2011 Trust Networks: T. K. Prasad 194
170. Conclusion
• Provided simple examples of trust (Why?)
• Explained salient features of trust (What?)
• Showed examples of gleaning trustworthiness
(How?)
• Touched upon research challenges in the
context of
• Sensor Networks
• Social Networks
• Interpersonal Networks
• Collaborative Environments
Dec 15, 2011 Trust Networks: T. K. Prasad 196