18 August 2006
12 th IEEE RTCSA Conference
Riaz Ahmed Shaikh
Dep. of Computer Eng., KyungHee University
Republic of Korea riaz@oslab.khu.ac.kr

• Introduction
• Motivation
• Problem Statement
• Proposed Solution
• Conclusion
• Future Work
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• Definition of Trust:
“the quantified belief by a trustor with respect to the competence, honesty, security and dependability of a trustee within a specified context”
(T. Grandison and M. Sloma, 2000)
• Traditionally trust is applied in various diverse domains such as e-commerce systems, ad-hoc networks, and peerto-peer networks. u-Security Research Group
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• A wireless sensor network is an emerging technology that is used in various application areas such as health, military, and home etc .
• It typically consists of tiny sized sensor nodes that are densely deployed in an environment. The basic objective of a sensor network is to sense, gather and propagate information about the environmental phenomena.
• Recent widespread uses of sensor networks have evoked the need of proper lightweight trust management schemes.
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• Establishing trust in a network gives two main benefits such as;
– Trust, helps to make traditional security mechanism more robust and reliable.
– Trust can also solve the problems that can not be solved through traditional security mechanisms.
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• Traditional research work in wireless sensor networks is mostly based on the assumption of a trusted environment which may not be realistic for every application.
• Traditional trust management schemes that have been developed for wired and wireless ad-hoc networks are not suitable for wireless sensor networks because of higher consumption of resources such as memory and power.
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Classification of Trust Management Schemes
Centralized
Advantages

Less computational overhead.

Consume Less memory.
Distributed
Hybrid
 Reliable means no single point of failure.
 Scalable.

Less communication overhead than centralized.

Less memory consumption than distributed.

Less computational overhead than distributed.

More reliable and scalable than centralized.

Disadvantages

Single Point of failure.

Increase communication overhead.
Increase computational overhead.
 Consume large memory.

Large computational overhead then centralized.

Large memory requirement than centralized.

Less scalable and reliable than distributed.
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• By looking at the advantages and disadvantages of all three approaches we conclude that neither completely centralized nor completely distributed trust management schemes are appropriate for wireless sensor networks .
• Therefore, hybrid trust management schemes are more suitable for wireless sensor networks.
• Hybrid Approach can be used with the help of clustering topology.
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• Wireless sensor networks use various clustering schemes such as LEACH, HEED, etc, that are used in real world scenarios. The basic objective of these clustering schemes is to reduce the communication cost.
• Moreover, sensor nodes can also be deployed in the form of groups.
• This highlights the fact that these clustering schemes and group deployment, enable sensor nodes to fulfill their responsibilities in a cooperative manner rather than individually .
• Thus one should also consider the trust management as a cooperative business rather than an individual task.
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• Research on trust management scheme for wireless sensor networks is in the infancy state. Hence, in this work, we propose a novel lightweight group based trust management scheme (GTMS) for distributed wireless sensor networks that is based on hybrid trust management approach.
• We focus on following problem.
How to establish secure lightweight group based trust
Management scheme for large scale distributed wireless sensor networks?
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• Research challenges for this problem are:
– How to make our trust management scheme lightweight ?
– How to make our trust management scheme flexible and robust?
– How to make our trust management scheme resilient against security threats ?
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Base Station
Cluster head
Sensor Node
Un-Trusted Group
Un-Certain Group
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Trusted Group u-Security Research Group

• At Node level, trust value is calculated by using time based past interaction as well as peer recommendations.
• Time based Past Interactions Evaluation:
PI w s
1 max[{ w SI
,
 w UI
,




 h m l t s



T current


T
ST


, t u


 t s t s t s

1


2

2
T current


T
UT

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• Peer Recommendations Evaluation:
PR
 n i

1 

1
[ Tv * Tv n

1
]
• Formation of Trust Value:
Tv


PI

PR
2
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• Memory Requirement
• Each node maintains the small trust database as shown in table 1.
Past Interactions
Node ID
Peer
Recommendations
Trust value
SI x,y
2 bytes
ST x,y
UI x,y
4 bytes 2 bytes
UT x,y
4 bytes
2 bytes 4 bytes 4 bytes
• The size of each record is 22 bytes. Therefore memory requirement for GTMS at each sensor node is (n-1)*22 bytes, where n is number of nodes in the cluster u-Security Research Group
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• Here we assume that Cluster Head is the sensor node that has higher power and memory as compare to other sensor nodes.
• In response all group member nodes forward their trust values of other member nodes to cluster head. The trust vector of cluster head node is defined as
Tv ch

( Tv ch ,1
, Tv ch ,2
, , Tv )
• Where Tv ch,i represent the trust of node i. It is calculated as
Tv ch ,1

( n

1) i


1
Tv i ,1
( n

1)
, Tv ch ,2

( n

1) i


1
Tv i ,2
( n

1)
, , Tv

( n

1) i


1
Tv
( n

1)
• This Trust vector is forwarded to BS.
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Trust Calculation at Cluster Head (Cont…)
• Formation of Trust Value:
Tv


PI

BR
2

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Trust Calculation at Cluster Head (Cont…)
• Cluster head maintains two databases; one is similar to individual’s sensor node trust database and in second CH maintains the trust values of other groups as shown in table 2.
Group ID
2 bytes
SI x,y
2 bytes
Past Interactions with Groups
ST x,y
4 bytes
UI x,y
2 bytes
UT x,y
4 bytes
Recommendations from BS
4 bytes
Trust value
4 bytes
• The size of each record is 22 bytes. Therefore the total size of table 2 is (m-
1)*22 . Here ‘m’ is the total number of groups in the network.
• In order to save all trust values in both database cluster head needs (n+m-2)*22 bytes of memory space.
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Tv
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 i m 
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, Tv
)



 trusted uncertain untrusted
Tv
Tv
Tv
0.6

Tv
0.3

Tv
0

Tv
Tv
Tv
Tv
, 2
 i m 

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Tv m
, 2
, , Tv
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 i m 

1
Tv m u-Security Research Group
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• Research on trust management scheme for wireless sensor networks is at very infancy state and current sensor network security solutions are based on assumption of trusted environment.
• Therefore in this work, we have proposed novel group based trust management scheme (GTMS) for distributed wireless sensor networks that is based on hybrid trust management approach.
• GTMS is very simple and flexible and doesn ’ t require any large storage of data and complex computations at single sensor node.
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• Our work is in initial phase, Now are now in the phase of implementation of GTMS scheme that will gives us the information about computation and communication overhead.
• Our Trust model is based on the assumption that every node has a unique id but the following challenging problem is still open:
“how to assign identities and trust values to sensor nodes in a large scale anonymous environment where nodes have no unique id?” u-Security Research Group
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Email: riaz@oslab.khu.ac.kr
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