Trust and Grid Computing Systems Presented By: Woodas Lai.
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Transcript of Trust and Grid Computing Systems Presented By: Woodas Lai.
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
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
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.