Trust Model Based Self-Organized Routing Protocol For Secure Ad Hoc Networks

1. Trust Model Based Self-Organized Routing Protocol For Secure Ad Hoc Networks Li Xiaoqi CSE Department, CUHK 29/04/2003

2. Outline • Introduction to Ad Hoc Networks • Motivation and Design Goals • Trust Model for Ad Hoc Networks • Trusted Self-Organized Routing Protocol • Conclusion • Research Plan and Future Work

3. Now Come to: • Introduction to Ad Hoc Networks • Motivation and Design Goals • Trust Model for Ad Hoc Networks • Trusted Self-Organized Routing Protocol • Research Plan and Future Work • Conclusion

4. What is Ad Hoc Network • A kind of network without fixed infrastructure such as base stations or access points, which performs communications through wireless media • Wireless applications in: • Military Operations • Disaster Relief • Meeting Room Setup for Conference • Personal Area Networking

5. Characteristics of Ad Hoc Networks • No fixed infrastructure • Each node is a router • Multi-hop routing by nodes cooperation • Self-organization nature • High mobility • Prone to be attacked

6. Routing Protocols for Ad Hoc Networks • AODV: -Ad Hoc On-Demand Distance Vector Protocol • DSR: -The Dynamic Source Routing Protocol • DSDV: -Destination-Sequenced Distance Vector Protocol

7. Overview of AODV • Discover routes when needed • Mainly two types of routing messages: • RREQ: Route Request • RREP: Route Reply • Fixed-length messages • Only one mutable field: Hop Count

8. Route Discovery in AODV RREQ Broadcast S D RREP RREP

9. Now Come To: • Introduction to Ad Hoc Networks • Motivation and Design Goals • Trust Model for Ad Hoc Networks • Trusted Self-Organized Routing Protocol • Conclusion • Research Plan and Future Work

10. Security Requirements in Ad Hoc Networks • Confidentiality • Authenticity • Integrity • Availability • Non-repudiation • Access Control

11. Attacks to Ad Hoc Networks

12. Common Solutions for Security • Often assume • A trusted authority to issue certificates. • A centralized server to monitor the networks. • A secret association between certain nodes. • Disadvantages • Destroy the self-organization nature of ad hoc networks. • Limit the mobility of nodes. • Single point of failure • Less of efficiency and availability

13. Self-Organized Solutions for Security • Properties • Authenticate each other in a self-organized way • Often issue certificate of a public key by nodes cooperation • Often need node monitoring mechanism • Disadvantages • Need at least k neighbors to cooperate • Monitoring mechanism is difficult to implement and is performance-consuming

14. Current Issues in Ad Hoc Networks • Lack of security consideration • Centralized server or trusted third parties destroy the self-organization nature • Pure cryptographic solutions bring high overhead • Current self-organized solutions lose flexibility

15. Our Solutions and Design Goals • Design a suitable decentralized trust model that can be used for the security solutions of ad hoc networks. • Apply this trust model to design a flexible self-organized key management scheme. • Apply this trust model to design a secure and flexible self-organized routing protocol with lower overhead. • Demonstrate the principle of the trust model and the security advantages of the resulting ad hoc networks.

16. Now Come To: • Introduction to Ad Hoc Networks • Motivation and Design Goals • Trust Model for Ad Hoc Networks • Trusted Self-Organized Routing Protocol • Research Plan and Future Work • Conclusion

17. Trust Model for Ad Hoc Networks • Overview of trust theory • Trust is a basic aspect of human life. • Trust is regarded as a measurable variable. • Trust theory has been applied into the fields of E-Commerce • Organization of nodes in ad hoc networks is similar as human society • Apply trust theory to secure ad hoc networks

18. Previous Trust Models • Direct and recommendation trust model • Continuous value to represent trust • Basis of many other trust models • Recommendation protocol model • Focus on the exchange of trust information • Dempster-Shafer Theory based model • Upper and lower bound pair to represent trust • Trust matrix to represent trust relationship • Combine two matrices using Dempster-Shafer theory

19. Previous Trust Models (Con’d) • Model using Fuzzy Logic • Trust matrix to represent trust relationship • Fuzzy logic to verify transactions • Fuzzy logic to combine trust matrices • Model using Subjective Logic • Use Opinion to represent trust • Opinion includes belief, disbelief, uncertainty • Combine trust using subjective logic

20. Comparison of Trust Models • Single trust value vs. Opinion • Opinion with belief, disbelief and uncertainty can express more information • Fuzzy logic vs. Subjective logic • Fuzzy logic operates on certain measures about fuzzy propositions • Subjective logic operates on uncertain measures about crisp propositions

21. Comparison of Trust Models (Con’d) • Shafer theory vs. Subjective logic • Both introduce uncertainty • No need to set upper or lower bounds of trust described in Shafer theory

22. Design Issues of Trust Model • Definition of Trust • Representation of Trust • Combination of Trust • Exchange of Trust Information

23. Our Trust Model • Use ‘Opinion’ to define and represent trust • Combine trust opinions using subjective logic • Define a trust recommendation protocol to exchange trust information

24. Definition and Representation of Trust • Opinion: a three-dimensional metric • The opinion about the trustworthiness of x, denoted by ωx , is the triple defined by: • b(x) represent belief: probability of believing x. • d(x) represent disbelief: probability of disbelieving x • u(x) represent uncertainty: probability of uncertainty about x’s trustworthiness

25. Definition and Representation of Trust (Con’d) • Property of Opinion: • b, d, u is in [0,1] • b+d+u = 1 • Opinion ωx (0.4,0.1,0.5) can be represented in the right figure.

26. Combination of Trust • Discounting Combination • Combine trusts along one path • Combine • Consensus Combination • Combine trusts from several paths • Combine

27. A want to know B’s trustworthiness An Example of Combining Trust

28. Trust Recommendation Protocol • Exchange trust information • Three types of message: • TREQ: Trust Request • TREP: Trust Reply • TWARN: Trust Warning • Message structure

29. Our Trust Model vs. Subjective Logic Trust Model • Simplify the representation of trust, which is more suitable for ad hoc networks • Propose a trust recommendation protocol to exchange trust information • Handle the dynamic of trust which is not mentioned in subjective logic

30. Now Come To: • Introduction to Ad Hoc Networks • Motivation and Design Goals • Trust Model for Ad Hoc Networks • Trusted Self-Organized Routing Protocol • Research Plan and Future Work • Conclusion

31. Assumption of Our Trusted Routing Protocol • Ability to recover node’s neighbors. • Reliability of broadcasting one-hop messages • Uniqueness of node’s ID • Capability of monitoring behaviors of one-hop neighbors • Key management has been done before

32. Node Model • One node has an opinion about others • Each node maintains a trust table. For Example, A’s trust table is: • Initial opinion of a node in others’ eyes is (0,0,1)

33. C r y p t o g r a p h i c R o u t i n g D i s c o v e r y a n d M a i n t e n a n c e T r u s t T r u s t T r u s t R e c o m m e n d a t i o n U p d a t i n g C o m b i n a t i o n T r u s t e d R o u t i n g D i s c o v e r y P r o t o c o l A L g o r i t h m A l g o r i t h m a n d M a i n t e n a n c e T r u s t M o d e l T r u s t e d R o u t i n g P r o t o c o l B a s i c A O D V R o u t i n g P r o t o c o l General Framework

34. Cryptographic Technologies • Use cryptographic schemes to do routing in the beginning of this network • Adopt ideas in SAODV [42] • Digital signature: authenticate the non-mutable fields of the messages • Hash chains: secure the only mutable field ‘hop count’

35. Overview of Trusted Self-Organized Routing Protocol • Effective when trust relationships have been established among most nodes • Based on AODV routing protocol • Criteria to determine whether a node can be trusted or not is: • belief≥0.5, disbelief<0.5, uncertainty<0.5 • Nodes cooperate to decide a opinion

36. Trusted Routing Discovery

37. Trust Update Algorithm • Each value in a opinion is logically divided into 5 levels. Every 0.25 is one level. • Successful verification for ten times: • belief+=0.25, disbelief-=0.125, uncertainty-=0.125 • Failed verification for each time: • belief-=0.125, disbelief+=0.25, uncertainty-=0.125 • No verification during expiry time • belief-=0.375, disbelief+=0.125, uncertainty+=0.25

38. Trust Update Algorithm (Con’d) • If in opinion A to B, belief<0 or disbelief>1 • Opinion(AB) will be changed to (0,1,0) • Node A broadcast this opinion using TWARN message • Neighbors will re-calculate the opinion using trust combination algorithm • B will be denied from A’s communication

39. Trusted Key Management • Use trust model into key management • Advantages: • Self-organization • Flexible: no limitation of at least k neighbors • Lower overhead

40. Analysis • Performance is increased • No need to perform cryptographic calculations for every packet  lower overhead • Security is enhanced • Combination of trust model, cryptographic schemes and monitor mechanism • More reasonable and flexible • Good nodes who become bad will be denied from network eventually • Bad nodes who turn to good will be allowed accessing network again soon

41. Now Come To: • Introduction to Ad Hoc Networks • Motivation and Design Goals • Trust Model for Ad Hoc Networks • Trusted Self-Organized Routing Protocol • Conclusion • Research Plan and Future Work

42. A promising idea to apply trust model to secure ad hoc networks Node uses ‘opinion’ to judge if another node is trustable Nodes cooperate to obtain a more accurate opinion Trusted routing protocol is Self-organized Lower-overhead More reasonable More secure More flexible Conclusion

43. Research Plan and Future Work • A better trust combination algorithm • A better way to apply trust model into key management • Study monitor or intrusion detection issues • Improve trusted routing protocol to make it prevent or stand more attacks • A detailed simulation evaluation using NS-2 or Glomosim simulators

44. Q&A Thank you !