Trust and Grid Computing Systems

Presented By: Woodas Lai

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

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

What is Grid? Conclusion:

Difficult to gather enough computational resources for running applications at a single location

How to overcome?

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

Gird Example

Company A Company ZCompany B

GridService

GridService

GridService

GridService

GridService

GridService

GridService

GridService

GridService

Grid Virtual Organisation

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

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

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

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

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)

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.

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.

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

Let Di and Dj be two domains of entities The trust relationship based on a specifi

c context c at a given time t isT(Di,Dj,t,c)

Let the direct trust relationship for the context c at time t be dT(Di,Dj,t,c)

Let the reputation of Dj for the context c at time t be R(Dj,t,c)

Evaluating Trust and Reputation

T(Di,Dj,t,c) = x dT(Di,Dj,t,c) + x R(Dj,t,c)

where and are the weights given to direct and reputation relationships respectively

Evaluating Trust and Reputation

Direct trust relationship is computed as a product of the trust level in the direct trust table (DTT) and the decay function (t-tij,c)where c is the specific context

t is the current time tij is the time of the last update

or the last transaction between Di and Dj

Evaluating Trust and Reputation

dT(Di,Dj,t,c) = DTT(Di,Dj,c) x (t-tij,c)

Evaluating Trust and Reputation

The reputation of Dj is computed as the average of the product of the trust level in the reputation trust table (RTT), the decay function ((t-tkj,c)), and the recommender trust factor (r(Dk,Dj)) for all domains k.

Evaluating Trust and Reputation

Recommender trust factor It is used to prevent cheating via collu

sions among a group of domains It is a value between 0 and 1 Higher value if Dk and Dj are unknown

or have no prior relationship Lower value if Dk and Dj are allies or b

usiness partner

R(Dj,t,c) = RTT(Dk,Dj,c) x r(Dk,Dj) x (t-tkj,c)

Dk

Evaluating Trust and Reputation

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

Trust Model

Trust Model

 

Context Domains

D1 D2 …… Dj

C1 Trust Value Trust Value …… Trust Value

…… …… …… …… ……

Ci Trust Value Trust Value …… Trust Value

 

Direct Trust Table maintained By Dk

Trust Model

Service s1 ofCompany A

Service s2 ofCompany B

Service s3 ofCompany C

Service s4 ofCompany D

t1 t2 t3 t4

Time duration for this service invocation = t4-t1

In Grid Computing, there is always a chain of service calls

Trust ModelWe define another time decay function:

(texpected-tduration,c)

Where texpected is the expected time duration for this service calltduration is the actual time duration for this service callC is the context

Trust Model

Our Direct Trust Relationship will be modified as follows:

dT(Di,Dj,t,c) = DTT(Di,Dj,c) x (t-tij,c) x (texpected-tduration,c)

Updating Direct Trust Table Our formula is:

DTT(Di,Dj,c) = (1-)x DTT(Di,Dj,c) + x Tv(tij,c)where Tv(tij,c) is the trust value for context cresulted from the direct trust relationship between Di and Dj

is between 0 and 1. If > 0.5, more preference will be given to current direct trust value

Required Trust Value The required trust value is defined as a valu

e between 0 and 1, such thatif T(Di,Dj,t,c) >= RTv, the interaction is trusted and the request is granted

if T(Di,Dj,t,c) < RTv, the interaction is not trusted and enhance security mechanism is enforced (authentication using X.509 certificate)

Initial Trust Value Itv is define as the initial trust value. At the very beginning, Di and Dj may not know each

other. Dj will then send the X.509 certificate to Di 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.

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 moni

tored. (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.

Thanks for your attention

Q&A