1. Kemal AkkayaWireless & Network Security 1 Department of Computer Science Southern Illinois University Carbondale CS 591 – Wireless & Network Security Lecture 12: Trust Dr. Kemal Akkaya E-mail: kemal@cs.siu.edu

2. Kemal AkkayaWireless & Network Security 2Trust  Definition:  The belief that an entity is capable of acting reliably, dependably, and securely in a particular case  A well studied concept in sociology and psychology.  Need for trust  Traditional schemes focus on preventing attackers from entering the network through security protocols.  Those schemes, however, are not effective when: Malicious nodes have gained access to the network Some nodes in the network have been compromised  Trust function:  Provide an incentive for good behavior.  Provide a prediction of one’s future behavior.  Detect malicious and selfish entities.  Examples:  E-commerce : risk estimation  P2P : reducing free riding  Mobile ad hoc networks : mitigating nodes selfish behavior

3. Kemal AkkayaWireless & Network Security 3 Trust Models  Trust models entails collecting the information necessary to establish a trust relationship and dynamically monitoring and adjusting the existing truth relationship.  Two models:  Policy-based Trust Based on access control Restricting access to resources according to application-defined policies PolicyMaker, Keynote, REFEREE  Reputation-based Trust a peer requesting a resource may evaluate its trust in the reliability of the resource and the peer providing the resource Trust value assigned to a trust relationship is a function of the combination of the peer’s global reputation SPORAS, HISTOS, XREP, NICE, DCRC/CORC, Beta, EigenTrust  Others: Social network-based Trust  Utilize social relationships between peers when computing trust and reputation values

4. Kemal AkkayaWireless & Network Security 4 Policy-based Trust

5. Kemal AkkayaWireless & Network Security 5 Policy-based Trust: virtual  Problems  They do not provide a complete generic trust management solution for all decentralized applications  Scalability

6. Kemal AkkayaWireless & Network Security 6 Reputation-based Trust  Community of cooks (200 people)  Need to interact with someone you don’t know,  To extablish trust: you ask your friends –and friends of friends »... some recommendations are better than other you check the record (if any)  After success trust increases  p2p community of hackers (2000 people)  Exchange programs & scripts  Need to interact with someone you don’t know, ...  Difference with concrete community:  Larger, faster Trust establishment has to be to some extent automatic

7. Kemal AkkayaWireless & Network Security 7 Challenges  Trust metrics  How to model and compute trust  Evaluating initial trust value  Combining evidences, recommendations, reputation  Management of reputation data  Secure & efficient retrieval of reputation data  Automating trust based decision  Closing the circle: using experience as feedback

8. Kemal AkkayaWireless & Network Security 8 Reputation vs Policy-based Trust  open system (different security domains)  trust is a measure & changes in time  risk-based  recommendation based (NOT identity-based)  peers are not continuously available  Some systems: PGP TBD  open system (different security domains)  trust is boolean & less time-dependent  no risk  rule (credential) based (NOT identity-based)  peers are not continuously available  Some systems: keynote, Trust-X

9. Kemal AkkayaWireless & Network Security 9 Distributed Trust Models  Distributed Trust:  The representation of inputs to, and the process of making, trust decisions based on resources shared among multiple entities  Without Trust, either parties refuse to interact or require severe restrictions and complex controls – increased costs.  Trust is required for multiple entities to co-operate and share resources, and thus achieve some application value.  Conditional transitivity of trust  if A trusts B & B trusts C then A trusts C if B recommends its trust in C to A explicitly A trusts B as a recommender A can judge B’s recommendation and decide how much it will trust C, irrespective of B’s trust in C  Will look at different models separately  MANETs  P2P Networks

10. Kemal AkkayaWireless & Network Security 10 Comparison of TM Approaches ApproachTarget Environ.Idea AT&T labs(1996, 1998)PKIA lot like Access Control – Policy-based Abdul-Rahman & Hailes (2000) Virtual comm. Intro to Reputation-based Trust Models & agents autonomy Aberer & Despotovic (2001) P2P Attempts distributed Storage of Trust info. – Reputation-based CONFIDANT (2002)MANET Attempts incorporation of Detection & isolation of misbehavior SECURE (2003) Ubiquitous roaming entities Attempts Incorporation of risk model with Trust hTrust(2004)MANET Trust Management & dispositional trust. Detection & isolation of malicious recommenders. McNamara et al. (2006)MANETMobility introduced as a factor STRUDEL (2006)CPD Combat Tragedy of the commons (Selfishness of Nodes) MATE (2006)MANET Attempts integrated management of trust and risk (an element of dispositional trust).