1. Trust and Grid Computing Systems Presented By: Woodas Lai

2. Agenda What is Grid? What is Trust? Our Trust Model Future Work

3. What is Grid? Two facts: Advanced Technologies lead to the large, complex and resource-intensive applications Moore ’ s Law: power of network, storage, and computing resources is projected to double every 9, 12, and 18 months, respectively  Network performance outperforms CPU performance

4. What is Grid? Conclusion: Difficult to gather enough computational resources for running applications at a single location How to overcome?

5. What is Grid? Grid is a technology which brings together a set of resources distributed over wide-area networks that can support large-scale distributed applications Grid coordinates resource sharing and problem solving in dynamic, multi-institutional, virtual organizations

6. Gird Example

7. Grid Computing Each company could be regarded as a domain Each domain will have its own security policy The primary goal of Grid environment is to encourage domain-to-domain interactions to share the resources

8. How to share the resources? To encourage the controlled sharing of resources: The security overhead should be minimized so that the sharing is appealing The security mechanism applied should be scalable Domains should not lose control over their own resources  This is where our trust model comes and is applied

9. What is Trust Trust is to model the human social behavior When I use a credit card to pay the bill, the bank trust me that I will pay back the money later When I use the e-banking service to perform a transaction, I trust the bank that it will perform the transaction for me

10. Definition of Trust Trust is the firm belief in the competence of an entity to behave as expected such that this firm belief is a dynamic value associated with the entity and is subject to the entity ’ s behavior and applies only within a specific context at a given time

11. Trust Trust value is a continuous and dynamic value in the range of [0,1] 1 means very trustworthy 0 means very untrustworthy It is built on past experience It is context based (under different context may have different trust value)

12. Reputation When making trust-based decisions, entities can rely on others for information regarding to a specific entity. The information regarding to a specific entity x is defined as the reputation of entity x.

13. Definition of Reputation The reputation of an entity is an expectation of its behavior based on other entities ’ observations or information about the entity ’ s past behavior within a specific context at a given time.

14. Evaluating Trust and Reputation Trusts decays with time Entities may form alliances and they may trust their allies and business partners more than others Trust value is based on the combination of direct trust and reputation

15. Let D i and D j be two domains of entities The trust relationship based on a specific context c at a given time t is T(D i,D j,t,c) Let the direct trust relationship for the context c at time t be dT(D i,D j,t,c) Let the reputation of D j for the context c at time t be R(D j,t,c) Evaluating Trust and Reputation

16. T(D i,D j,t,c) =  x dT(D i,D j,t,c) +  x R(D j,t,c) where  and  are the weights given to direct and reputation relationships respectively Evaluating Trust and Reputation

17. Direct trust relationship is computed as a product of the trust level in the direct trust table (DTT) and the decay function  (t-t ij,c) where c is the specific context t is the current time t ij is the time of the last update or the last transaction between D i and D j Evaluating Trust and Reputation

18. dT(D i,D j,t,c) = DTT(D i,D j,c) x  (t-t ij,c) Evaluating Trust and Reputation

19. The reputation of D j is computed as the average of the product of the trust level in the reputation trust table (RTT), the decay function (  (t-t kj,c)), and the recommender trust factor (r(D k,D j )) for all domains k. Evaluating Trust and Reputation

20. Recommender trust factor It is used to prevent cheating via collusions among a group of domains It is a value between 0 and 1 Higher value if D k and D j are unknown or have no prior relationship Lower value if D k and D j are allies or business partner

21. R(D j,t,c) =  RTT(D k,D j,c) x r(D k,D j ) x  (t-t kj,c)  D k Evaluating Trust and Reputation

22. Each Domain will maintain its own Direct Trust Table (DTT) and Reputation Trust Table (RTT). Trust Model

23. ContextDomains D1D1 D2D2 ……DjDj C1C1 Trust Value ……Trust Value …… CiCi Trust Value ……Trust Value Direct Trust Table maintained By D k

24. Trust Model Time duration for this service invocation = t4-t1 In Grid Computing, there is always a chain of service calls

25. Trust Model We define another time decay function: (t expected -t duration,c) Where t expected is the expected time duration for this service call t duration is the actual time duration for this service call C is the context

26. Trust Model Our Direct Trust Relationship will be modified as follows: dT(D i,D j,t,c) = DTT(D i,D j,c) x  (t-t ij,c) x (t expected -t duration,c)

27. Updating Direct Trust Table Our formula is: DTT(D i,D j,c) = (1-  )x DTT(D i,D j,c) +  x Tv(t ij,c) where Tv(t ij,c) is the trust value for context c resulted from the direct trust relationship between D i and D j  is between 0 and 1. If  > 0.5, more preference will be given to current direct trust value

28. Required Trust Value The required trust value is defined as a value between 0 and 1, such that if T(D i,D j,t,c) >= RTv, the interaction is trusted and the request is granted if T(D i,D j,t,c) < RTv, the interaction is not trusted and enhance security mechanism is enforced (authentication using X.509 certificate)

29. Initial Trust Value Itv is define as the initial trust value. At the very beginning, D i and D j may not know each other. D j will then send the X.509 certificate to D i so as to verify the identity, if the verification is successful, Dj will be assigned the trust value of Itv and then the transaction starts. After the transaction, some trust metrics like last transaction time and duration time will be updated. After that, our trust model will continue to evolve as described before.

30. Future Work Simulation or Experiments should be done in order to test our trust model. In this model, the behavior of the entity is not monitored. (Like the entity consumes more resources than requested or reading some memory out of the allocated boundary). Intrusion Detection Systems (IDSs) may be studied so as to address this behavioral issue.

31. Thanks for your attention Q&A