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Trust and reputation in mobile environments

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  • 1. Trust and Reputation in Mobile Environments Trust and Reputation in Mobile Environments Andrada A¸tef˘noaie s a Computer Science Faculty of Ia¸i s December 14, 2012 1/41
  • 2. Trust and Reputation in Mobile EnvironmentsContents 1 Introduction 2 Social perspective 3 Trust in MANETs and WSNs 4 Overview of Reputation and Trust Based Systems 5 Components of Reputation and Trust Based Systems Information Gathering Information Sharing Information Modelling Decision Making 6 Examples of Reputation and Trust-based Systems Core Confidant 7 Open problems 8 Conclusions 9 Bibliography 2/41
  • 3. Trust and Reputation in Mobile Environments IntroductionMANETs and WSNs - Problems Mobile Ad Hoc Networks and Wireless Sensor Networks ⇒ tremendous technological advances over the last few years ⇒ risk of newer threats and challenges and the responsibility of ensuring safety, security, and integrity of information communication over these networks. MANETs ⇒ vulnerable to different types of attacks and security threats (complete autonomy of the member nodes, lack of any centralized infrastructure). WSNs ⇒ unique problems due to their usual operations in unattended and hostile areas. Also, it is imperative to produce sensors at very low costs⇒ to produce tamper-resistant sensors ⇒ very easy for an adversary to physically capture a sensor node and bypass its limited cryptographic security. 3/41
  • 4. Trust and Reputation in Mobile Environments IntroductionTrust and Reputation ⇒ resolved by modelling MANETs and WSNs as reputation and trust-based systems. As in real life, we tend to believe and interact only with people who we see as having a good reputation. Reputation can be defined as a person’s history of behaviour, and can be positive, negative, or a mix of both. Based on this reputation, trust is built. Trust can be seen as the expectation that a person will act in a certain way. Reputation: opinion of one entity about another ⇒ trustworthiness of an entity. Trust: expectation of one entity about the actions of another. 4/41
  • 5. Trust and Reputation in Mobile Environments Social perspectiveTrust and uncertainty Trust: important factor affecting consumer behaviour, especially in the e-commerce context where uncertainty abounds. Uncertainty: ⇒ originates from two sources: information asymmetry and opportunism. ⇒ degree to which an individual or organization cannot anticipate or accurately predict the environment 5/41
  • 6. Trust and Reputation in Mobile Environments Social perspectiveTrust beliefs and trust intention Trust means that the trustor believes in, and is willing to depend on, the trustee. Theory of reasoned action ⇒ trusting beliefs and trusting intention. Trusting beliefs ⇒ multidimensional, representing one’s beliefs that the trustee is likely to behave in a way that is benevolent, competent, honest, or predictable in a situation. Most frequently: competence, benevolence, and integrity. Trusting intention is the extent to which one is willing to depend on the other person in a given situation. 6/41
  • 7. Trust and Reputation in Mobile Environments Social perspectiveInformation asymmetry and Opportunistic behaviour Information asymmetry is defined as the difference between the information possessed by buyers and sellers. Opportunistic behaviour is prevalent in exchange relationships. In the on-line buyer-seller relationship, the seller may behave opportunistically by trying to meet its own goals without considering the consumer’s benefits. 7/41
  • 8. Trust and Reputation in Mobile Environments Social perspectiveTrust antecedents : calculus , knowledge institution based Calculus-based trust ⇒ credible information regarding the intentions or competence of the trustee. Knowledge-based trust ⇒ aggregation of trust related knowledge by the involved parties ⇒ accumulated either first-hand (based on an interaction history) or second-hand Institution-based trust ⇒ one believes the necessary impersonal structures are in place to enable one to act in anticipation of a successful future endeavour 8/41
  • 9. Trust and Reputation in Mobile Environments Trust in MANETs and WSNsMANET - Problems MANETs: nodes are autonomous and do not have any common interest ⇒ selfish behaviour ⇒ need incentive and motivation to cooperate Non-cooperative behaviour of a node: selfish intention (e.g. save power) malicious intention (e.g. denial-of-service attacks). 9/41
  • 10. Trust and Reputation in Mobile Environments Trust in MANETs and WSNsWSN - Problems WSNs - all sensors belong to a single group/entity and need to cooperate towards the same goal ⇒ incentive is less of a concern. In the same time, WSNs are vulnerable to physical capture ⇒ make the sensor nodes tamper-proof ⇒ expensive tamper-proofing the nodes ⇒ not a viable solution: An adversary might change sensors to start misbehaving and disrupt communication in the network and afterwards to launch an attack from insider ⇒ need of security mechanisms to make WSNs able to cope with insider attacks. 10/41
  • 11. Trust and Reputation in Mobile Environments Trust in MANETs and WSNsMisbehaviour of nodes Reputation and trust-based systems enable nodes to make informed decisions on prospective transaction partners. 11/41
  • 12. Trust and Reputation in Mobile Environments Trust in MANETs and WSNsEffects of nodes misbehaviour Examples of effects of the misbehaviour of nodes: packet loss increased denial-of-service experienced by honest nodes in the network There were theoretical studies that emphasized the following ides: increased cooperation more than proportionately increases the performance for small networks with fairly short routes prevention measures (encryption, authentication) reduce the success of intrusion attempts in MANETs, but cannot completely eliminate them. 12/41
  • 13. Trust and Reputation in Mobile Environments Overview of Reputation and Trust Based SystemsSystem goals 1 provide information that allows nodes to distinguish between trustworthy and non-trustworthy nodes. 2 encourage nodes to be trustworthy. 3 discourage participation of nodes that are untrustworthy. 4 cope with any kind of observable misbehaviour 5 minimize the damage caused by insider attacks. 13/41
  • 14. Trust and Reputation in Mobile Environments Overview of Reputation and Trust Based SystemsProperties In order to work effectively the system should have the following properties: 1 Long-lived entities that inspire an expectation of future interaction. 2 The capture and distribution of feedback about current interactions (such information must be visible in the future). 3 Use of feedback to guide trust decisions. 14/41
  • 15. Trust and Reputation in Mobile Environments Overview of Reputation and Trust Based SystemsProperties Properties of the trust metric: 1 Asymmetric (if node A trusts node B, then it is not necessarily true that node B also trusts node A), 2 Transitive: (if node A trusts node B and node B trusts node C, then node A trusts node C), 3 Reflexive: (node always trusts itself). 15/41
  • 16. Trust and Reputation in Mobile Environments Overview of Reputation and Trust Based SystemsInitialization Reputation and trust-based systems can be initialized in one of the following presented ways: 1 All nodes in the network are considered trustworthy. Nodes trust each other node in the network. Reputation of nodes is decreased by every bad encounter. 2 All nodes are considered to be untrustworthy and no node trusts any other node within the network. Reputation of nodes is increased with every good encounter. 3 All nodes are neither considered trustworthy nor untrustworthy. They all take a neutral reputation value to begin with. Reputation of nodes is increased or decrease with every good respectively bad encounter. 16/41
  • 17. Trust and Reputation in Mobile Environments Overview of Reputation and Trust Based SystemsClassification Classification of such systems can be done based on the following criteria: 1 Observation: First-Hand (direct observation, own experience) or second-hand (information obtained through peers). 2 Information Symmetry: Symmetric (same amount of information) or Asymmetric (different amount of information). 3 Centralization: Centralized (one entity maintains reputation of all nodes) or Distributed (each node maintains reputation of all nodes he cares about). In case of the second one reputation can be stored Local or Global. 4 Trust among peers: Credential-based or Behaviour based trust management systems . 17/41
  • 18. Trust and Reputation in Mobile Environments Overview of Reputation and Trust Based SystemsPros and cons Reputation and trust-based systems: + one of the best solutions for dealing with selfish misbehaviour. + robust solutions to curtail insider attacks. + for the most part, self maintaining. − added overhead, both in computation and communication, − a new dimension of security consideration ⇒ adversary might attack the system based on the reputation system itself. 18/41
  • 19. Trust and Reputation in Mobile Environments Components of Reputation and Trust Based SystemsInformation Gathering Information Gathering - the process by which a node collects information about nodes it cares about ⇒ concerned only with first-hand information. Most reputation and trust-based systems make use of a component called Watchdog to monitor their neighbourhood and gather information based on promiscuous observation. 19/41
  • 20. Trust and Reputation in Mobile Environments Components of Reputation and Trust Based SystemsInformation Sharing Information Sharing- concerned with dissemination of first-hand information gathered by nodes. Information can be shared among nodes in the following ways: friends list, blacklist, and reputation table. For sharing information, three important issues have to be addressed: 1 Dissemination frequency: Proactive Dissemination and Reactive Dissemination 2 Dissemination locality: Local and Global 3 Content of information disseminated: Raw and Processed. 20/41
  • 21. Trust and Reputation in Mobile Environments Components of Reputation and Trust Based SystemsInformation Modelling Information Modelling - deals with combining the first-hand and second-hand information meaningfully into a metric. It also deals with maintaining and updating this metric. 21/41
  • 22. Trust and Reputation in Mobile Environments Components of Reputation and Trust Based SystemsDecision Making Decision Making - responsible for taking all the decisions. Decisions made by this component ⇒ based on the information provided by the information modelling component. Basic decision ⇒ binary decision, on who to trust and who not to (be one of cooperate/dont-cooperate, forward/dont-forward, etc). 22/41
  • 23. Trust and Reputation in Mobile Environments Examples of Reputation and Trust-based Systems CoreCore - About A Collaborative Reputation Mechanism to enforce node co-operation in Mobile Ad hoc Networks. a distributed, symmetric reputation model uses first-hand and second-hand information for updating reputation values. uses bi-directional communication symmetry and dynamic source routing (DSR) protocol for routing. assumes wireless interfaces that support promiscuous mode operation nodes ⇒ members of a community ⇒ have to contribute on a continuing basis to remain trusted, else reputation will degrade until eventually they are excluded from the network. each node: a watchdog mechanism for promiscuous observation. 23/41
  • 24. Trust and Reputation in Mobile Environments Examples of Reputation and Trust-based Systems CoreCore - About addresses only the selfish behaviour problem. reputation ⇒ formed and updated along time ⇒ subjective reputation, indirect reputation, and functional reputation past observations are more important than the current observations. two types of protocol entities, requester (ask execution of function f ) and provider (execute f ) use of reputation table (RT), with one RT for each function: unique ID, recent subjective reputation, recent indirect reputation, and composite reputation for a predefined function. RTs are updated in two situations: during the request phase and during the reply phase. 24/41
  • 25. Trust and Reputation in Mobile Environments Examples of Reputation and Trust-based Systems CoreCore - Information gathering The reputation of a node computed from first-hand information is referred to as subjective reputation (calculated directly from a node’s observation). Subjective reputation is calculated only for the neighbouring nodes and it is updated only during the request phase. If a provider does not cooperate with a requester’s request, then a negative value is assigned to the rating factor σ of that observation and consequently the reputation of the provider will decrease (value varies between -1 and 1). New nodes, when they enter the network, are also assigned a neutral reputation value since enough observations are not available to make an assessment of their reputation. 25/41
  • 26. Trust and Reputation in Mobile Environments Examples of Reputation and Trust-based Systems CoreCore - Information sharing Indirect reputation (second-hand information) is used to model MANETs as complex societies. One node sees the others through the opinion of the society. Core adds the following restriction: only positive information can be exchanged (prevents bad mouthing attacks on benign nodes). Each reply message consists of a list of nodes that cooperated and like this indirect reputation will be updated only during the reply phase. 26/41
  • 27. Trust and Reputation in Mobile Environments Examples of Reputation and Trust-based Systems CoreCore - Information modelling Functional reputation (combined value of subjective and indirect reputation for different functions) is used to test how trustful a node is with respect to different functions. In CORE, reputation is compositional. Thus, the global reputation for each node is obtained by combining the three types of reputation. Positive reputation values are decremented along time to ensure that nodes cooperate and contribute on a continuing basis. 27/41
  • 28. Trust and Reputation in Mobile Environments Examples of Reputation and Trust-based Systems CoreCore - Decision making When a node has to make a decision: it checks the reputation value of the requester. Positive values indicates well behaved entities. If the value is negative, the node is tagged as a misbehaving entity and denied the service. A misbehaving entity is denied service unless it cooperates and ameliorates its reputation to a positive value. Reputation ⇒ hard to build (reputation decreases every time the watchdog detects a non cooperative behaviour and it also gets decremented in time to prevent malicious nodes from building reputation and then attacking the system resources. 28/41
  • 29. Trust and Reputation in Mobile Environments Examples of Reputation and Trust-based Systems CoreCore - Discussion 1 if reputation is high, a node can misbehave temporarily 2 CORE prevents false accusation attacks, confining the vulnerability of the system to only false praise 3 since only positive information is shared, the possibility of retaliation is prevented. There is a problem with combining the reputation values for various functions into a single global value. 4 CORE also ensures that disadvantaged nodes that are inherently selfish due to their critical energy conditions are not excluded from the network using the same criteria as for malicious nodes 29/41
  • 30. Trust and Reputation in Mobile Environments Examples of Reputation and Trust-based Systems ConfidantConfidant - About Cooperation Of Nodes - Fairness In Dynamic Ad-hoc NeTworks. inspired by ”The Selfish Gene” by Dawkins which states reciprocal altruism is beneficial for every ecological system when favors are returned simultaneously because of instant gratification. main purpose: make misbehaviour unattractive in MANETs based on selective altruism and utilitarianism. distributed, symmetric reputation model which uses both first-hand and second-hand information for updating reputation values. aims to detect and isolate misbehaving nodes for routing: used DSR assumes that no tamper-proof hardware is required for itselfother nodes to modify their values. 30/41
  • 31. Trust and Reputation in Mobile Environments Examples of Reputation and Trust-based Systems ConfidantConfidant - Components Confidant has four components at each node: Monitor, Trust Manager, Reputation System, and Path Manager. 31/41
  • 32. Trust and Reputation in Mobile Environments Examples of Reputation and Trust-based Systems ConfidantConfidant - Information Gathering The Monitor: helps nodes to passively observes their 1-hop neighbourhood. nodes can detect deviations by the next node on the source route ⇒ have a copy of a packet while listening to the transmission of the next node ⇒ any content change can be detected ⇒ the monitor registers these deviations ⇒ report bad behaviour to the reputation system. the monitor also forwards ALARMS to the Trust Manager for evaluation 32/41
  • 33. Trust and Reputation in Mobile Environments Examples of Reputation and Trust-based Systems ConfidantConfidant - Information Gathering Trust Manager: handles all the incoming and out-going ALARM messages. Incoming ALARMs (from any node)⇒ source has to be checked for trustworthiness⇒ looking at trust level of the reporting node. Outgoing ALARMS ⇒ generated by the node itself after it was detected a malicious behaviour. Recipients: friends ⇒ friends list by each node. The Trust Manager: contains: alarm table (information about alarms), trust table (trust levels for nodes), and friends list (all friends of node). responsible: providing or accepting routing information. 33/41
  • 34. Trust and Reputation in Mobile Environments Examples of Reputation and Trust-based Systems ConfidantConfidant - Information Modelling Reputation System ⇒ table consisting of entries for nodes and their rating. Ratings ⇒ changed when there is sufficient evidence of malicious behaviour (has occurred at least a threshold number of times to rule out coincidences) ⇒ updated according to a rate function (greatest weight: personal experience, smaller weight: observations in the neighbourhood, even smaller weight: to reported experience) ⇒ the reputation entry for the misbehaving node is updated accordingly. Node = rating below a predetermined threshold ⇒ Path Manager is summoned. 34/41
  • 35. Trust and Reputation in Mobile Environments Examples of Reputation and Trust-based Systems ConfidantConfidant - Decision Making Path Manager ⇒ the decision maker ⇒ responsible for: path re-ranking according to the security metric ⇒ deletes paths containing misbehaving nodes taking necessary actions upon receiving a request for a route from a misbehaving node. 35/41
  • 36. Trust and Reputation in Mobile Environments Examples of Reputation and Trust-based Systems ConfidantConfidant - Discussions only negative information is exchanged between nodes ⇒ system is vulnerable to false accusation of benign nodes by malicious nodes. false praise attacks are prevented since no positive information is exchanged ⇒ eliminates the possibility of malicious nodes colluding to boost the survival time of one another. since negative information = shared between nodes ⇒ an adversary gets to know his situation ⇒ change his strategy 36/41
  • 37. Trust and Reputation in Mobile Environments Examples of Reputation and Trust-based Systems ConfidantConfidant - Discussions nodes that are excluded will recover after a certain timeout failed nodes are treated like any other malicious node authors have not explained how the actual reputation is computed and how it is updated using experienced, observed and reported information. authors have not provided any evidence to support their rationale behind the differentiation of weights. 37/41
  • 38. Trust and Reputation in Mobile Environments Open problems Reputation and trust-based systems are still in the first phase when it comes to MANETs and WSNs ⇒ current open problems: the bootstrap problem. intelligent adversary strategies. 38/41
  • 39. Trust and Reputation in Mobile Environments Conclusions Reputation and trust: very important tools ⇒ used since the beginning to facilitate decision making in diverse fields from an ancient fish market to state of the art e-commerce. 39/41
  • 40. Trust and Reputation in Mobile Environments BibliographyBibliography “Reputation and Trust-based Systems for Ad Hoc and Sensor Networks”, Avinash Srinivasany, Joshua Teitelbaumy, Huigang Liangz, Jie Wuy and Mihaela Cardeiy “A Survey on Reputation and Trust-Based Systems for Wireless Communication Networks”, Jaydip Sen “Trust and Reputation Systems for Wireless Sensor Networks”, Rodrigo Roman, M. Carmen Fernandez-Gago, and Javier Lopez “Performance Analysis of the CONFIDANT Protocol (Cooperation Of Nodes: Fairness In Dynamic Ad NeT works)”, Sonja Buchegger, Jean-Yves Le Boudec 40/41
  • 41. Trust and Reputation in Mobile Environments Bibliography Thank you! 41/41

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