1. On Data-Centric Trust Establishment in Ephemeral Ad Hoc Networks Maxim Raya, Panos Papadimitratos, Virgil D. Gligor, Jean-Pierre Hubaux INFOCOM 2008

2. Ephemeral networks Definition No prior associations Short-lived contacts Volatile environment Example: VANET Trust Properties Trust in entities can be pre- established Reputation is hard to build Trust in data is important Trust establishment needs to be rethought 2

3. What is data trust?

4. Data Trust in Networks Packet forwarding Security associations Reputation A M B Data dissemination Insufficient Hard 4 Traditional ad hoc networksEphemeral networks Data Trust = Entity TrustData Trust = F(Entity Trust, context)

5. Event-specific trust Dynamic trust metric Security status A C B M General Framework Trust Computation Weights (data-centric trust levels) is the default trustworthiness Location Time Event reports of type from nodes

6. A C B M General Framework Evidence Evaluation Decision Logic Evidence Evaluation Output: Decision on Reported Event Evidence Event reports of type from nodes

7. Decision Logics (1) Most trusted report

8. Decision Logics (2) Most trusted report Weighted voting

9. Decision Logics (3) Most trusted report Weighted voting Bayesian inference – Takes into account prior knowledge

10. Decision Logics (4) Most trusted report Weighted voting Bayesian inference Dempster-Shafer Theory – probability is bounded by belief and plausibility – Uncertainty (lack of evidence) does not refute nor support evidence

11. Decision Logics (4) Most trusted report Weighted voting Bayesian inference Dempster-Shafer Theory 11 basic belief assignment trust level event report on event

12. Decision Logics (4) Most trusted report Weighted voting Bayesian inference Dempster-Shafer Theory 12 Dempster’s rule for combination: supporting evidence conflicts

13. Case Study: VANET 13 Data Trust Decision on event

14. Performance comparison MATLAB and ns2 100 simulation runs 95% confidence intervals Broadcast environment

15. Effect of Data Trust (1) Honest nodes (0.8) are more trustworthy than attackers (0.6)

16. Effect of Data Trust (2) Honest nodes (0.6) are less trustworthy than attackers (0.8)

17. Effect of Uncertainty Honest nodes (0.4) are more trustworthy than attackers (0.2)

18. Evolution in Time Highway scenario; 50% of reports are false (received first); Honest nodes (0.8) are more trustworthy than attackers (0.6)

19. Conclusions Trust in traditional MANETs pertains exclusively to entities Data-centric trust is more representative and useful in ephemeral networks (e.g., VANETs) Several decision logics can be used, notably: – Bayesian inference if there is prior knowledge – Dempster-Shafer Theory if there is uncertainty

20. Effect of Prior Knowledge 10 nodes vs. 50 before