 Open Access
 Total Downloads : 70
 Authors : H. S. Prakruthi, Veena. S
 Paper ID : IJERTV4IS040922
 Volume & Issue : Volume 04, Issue 04 (April 2015)
 DOI : http://dx.doi.org/10.17577/IJERTV4IS040922
 Published (First Online): 28042015
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
Robust Heterogeneity in WMN: Powerful Neighbor Pair wise Scheme
Prakruthi H S
PG in DECS
SJC Institute of Technology Chickaballapur, India
Veena S
Asst. prof. ECE Dept.
SJC Institute of Technology Chickaballapur,India
Abstract – The security plays an important role in WMN due to vulnerability of network. Powerful neighbour pair wise scheme is one of the fundamental issue in securing WMNs. This paper presents the new pair wise key establishment scheme. The pair wise key is required for the secure communication link between the two nodes which are ready for communicating. Predistribution of secrete key for all the nodes in a larger area of network consumes more memory so to avoid this we proposed a random key predistribution scheme that exploits the deployment knowledge and avoids unnecessary usage of memory. We show that the performance including communication, usage of memory and network resilience against the node capture attack of the mesh network can be improved with our proposed scheme. The scheme and detailed performance evaluation is presented in this paper.
Keywords – Wireless mesh network, pair wise key, sensor nodes, deployment knowledge.

INTRODUCTION
Key establishment is the first step to provide the security mechanisms. Because some security mechanisms depends on keys to operate correctly and provide desirable security measures. sensor networks are networks that consist of tiny electronic devices called sensor nodes that are capable of sensing the environmental conditions such as temperature, pressure, humidity, sound, vibration, fog level and monitors pollution levels, etc. [2]. the sensor network consist of: sensor nodesdevice designed to sense various environmental conditions, microcontrollerdevice which is used to interface with the sensor node, radio transceiver used to transmit and receive the data using external and internal antenna, energy source a battery that provide energy for working of sensor nodes [1].
WMN are self configured and self organized, with the nodes in the network participating in routing by forwarding data for other node and maintain mesh connectivity [3]. Mesh network consist of two types of nodes: mesh clients and mesh routers. Mesh clients are either stationary or mobile stations and mesh router is a back bone to the mesh clients. Different types of key distribution scheme that exist are: (1) network keying (2) pair Wise keying (3) group keying [6]. In this paper we are using the pair wise key distribution scheme. Because this is the best keying in terms of robustness, authentication as well as in Storage efficiency. We have proposed a key management scheme that is based on Bloms scheme [3].
Fig 1: wireless sensor network
The key distribution scheme proposed by bloms allow any pair of nodes in a network can find the secrete pair wise key [5]. The network consists of N number of nodes termed as N users. is a threshold treated as a security parameter i.e., larger the value more will the security provided to the network. Another use of is that amount of memory needed to store key information. Higher value leads to higher memory usage. The network is said to be secure as long as no more than node is compromised. This is called the secure property.

REVIEW ON RELATED RESEARCH
Key management protocol based on either symmetric or asymmetric key functions. Asymmetric key cryptographic algorithms are infeasible for computations and communication. Because sensor nodes are not able afford asymmetric cryptographic operation. Hence symmetric key management functions are favorable to WMN [6].
Different key management protocols base on pair wise key establishment scheme are [7]:
Eschenauer and Gligor proposed a random key pre distribution scheme, here they predistribute a random subset of key to all the nodes from a large pool of keys before the deployment. To agree on a key for communication, two node find a common key from their subset and use that key as a shared secrete key for communication [7]. Though it is robust and require less storage it suffer from less authentication and low accessibility with no support to cluster operation.
Chan, Perrig and Song [8]. This scheme is based on q composite random key predistribution. In this scheme they used q common keys (q>=1) instead of a single one, for the establishment of communication between the pair of nodes. This scheme provides a better security for small scale attack while trading off increased vulnerability in the case of large scale physical attack on network node.
Due, Dan, Hang and Vershney proposed a new key pre distribution scheme [9]. Where they used the number of private matrices instead of one and use k key matrices in each node.
Perrig et al. proposed SPINS [10]. In SPINS each sensor nodes shares a secrete key with the base station. Two sensor nodes cannot directly establish secret key. However they use the base station as a trusted third party to set up a secret key.
Apart from these many other schemes have been proposed. Our scheme is based on Bloms scheme [3] and we use this scheme as a basic scheme throughout the paper. Blom presented a symmetric key generation system based on MD5. In a network of N users K users as to cooperate to get the information. The public matrix G is choose from the field GF(q) and central authority generate the symmetric secrete matrix D and computes the key and distribute to all users. The public matrix is generated using vandermonde matrix [12].
Modified Bloms scheme [6]: instead of using the Vandermonde matrix as a public matrix here we use the adjacency matrix. Adjacency matrix is a matrix in which the neighboring nodes of a particular node are filled with 1s and other nodes are filled with q1 value. q is a prime number chosen from GF(q) and q should be (q>N).
Fig 2: Adjacency matrix

PROPOSED SYTEM
This section briefly describes the steps from the network creation to till the pair wise key establishment phase.
Figure3 shows the block diagram of the proposed system. Here the network creation indicates the creation of the sensor nodes. Once the sensor nodes are created it is necessary to initialize the sensor nodes with the configuration details. Then a group of sensor nodes are assigned with the cluster head, which is designated as region. Next the total target development area is divided into regular hexagons. Then the base station generates the key seeds for each nodes in the region. After this the central authority (base station) generates a secrete matrix G
and also generates the symmetric matrix D for pair wise key establishment. This pair wise key will be established using the modified bloms algorithm. After all these the the nodes can communicate with each other.
Fig3: block diagram of proposed system
Fig4: target development area divided into regular hexagons

KEY ESTABLISHMENT IN WMN
This section denotes the description of our full scheme. In this section will see the preliminaries requrired for the scheme, basic Blom scheme and then our full scheme.
A.PRELIMINARIES
There are three phase in Bloms scheme: system setup phase, key predistribution phase and pair wise key establishment phase.
System setup phase: the central authority generates the required parameters and the matrices.
Key predistribution phase: the central authority pre load each node including mesh router and mesh client with a key information.
Pair wise key establishment phase: with the use of mesh router the two senso nodes can establish pair wise secrete key.

ASIC SCHEME
Our basic scheme is a bloms scheme [13]. In bloms scheme with as a security parameter it takes large storage cost [14]. To reduce the storage cost at each sensor node, we modified the Bloms scheme as follows.
System setup: central authority

The central authority choose N independent key seeds s1,s2sN and use the identifier to indicate the key seed, let idi be the identifier of key seed si .

Generate a public matrix G of size (+1)Ã—N: S1 S2 … SN
G = (S1)2 (S2)2(SN)2
(S1)3 (S2)3(SN)3

Generate a symmetric matrix D of size (+1)Ã—(+1) in GF(q).
Key predistribution phase: In this phase the central authority completes the following operations.

Operation associated with sensor nodes: store each key seeds si and its identifier idi to the ith sensor node.

After the generation of symmetric matrix computes the public matrix A=(D.G)T.

Preload the mesh router with a matrix A.
Pair wise key establishment phase:

After the deployment all sensor node broadcast the key seed identifier idi and keeps track of neighbours key seed identifier.

Any two sensor nodes can directly establish the pair wise key after broadcasting the matrix A by the mesh router.

Suppose node i and node j want to establish a pair wise key with each other then,
Calculation at the ith node:

node i uses its key seed si to generate the ith column of the G matrix (si s 2.s +1)T.


UR FULL SCHEME
In our scheme we use the adjacency matrix as a public matrix G. from figure2 we can see that the adjacency matrix consist of only two numbers 1s and q1. q is the prime number. The key generation is same as that in bloms scheme. The following steps are use for calculating keys.
Generation of matrices:
First select a prime number q (q>N). Then generate a G matrix of size N. Then generate a G matrix of size NÃ—N. Modify the G matrix by selecting +1 row and N columns from the original G matrix.
Gj is the jth column of the G matrix it is loaded to the node j in original bloms scheme but in our scheme each node knows its neighbor nodes so there is no need of storing it once again. This avoids the large 0memory consumption.
The central authority generates random secrete symmetric matrix D1 D2D of size (+1)Ã—(+1). Then computes Ai=(Di.Gi)T.
Computation of key:
The central authority will stores each row of matrix A to all the nodes in the region. If node I want to communicate with node j then node i multiply ith row of A matrix and the jth column of G matrix.
Implementation:
The following example shows the working of the modified Bloms scheme. Let the number of nodes are N=6, security parameter =3 and the prime number q=29. Which says no more than 3 nodes in the network are compromised it is not possible to find the keys of other
i i users (nodes).
j
j

Let (aj a 2a +1) be the jth row of the A matrix
j j i i
which is broadcast by the mesh router. Kji=(aj a 2a +1) . (si s 2..s +1)T Calculation at jth node:

node j uses its key seed sj to generate the jth
j
j
column of the G matrix (sj s 2s +1)T.
Consider the node structure,
i
i

Let (ai a 2.a +1) be the ith row of the A
matrix which is broadcast by mesh router.
i
i
j
j
Kij= (ai a 2.a +1) . (sj s 2s +1)T

From this we can say that Kij=Kji.

Fig5: example of sensor nodes structure
From fig5 the adjacency matrix is,
0
1
1
0
0
0
1
0
0
1
0
0
1
0
0
0
1
0
0
1
0
0
0
0
0
0
1
0
0
1
0
0
0
0
1
0
Modified adjacency matrix is,
Key generation:
Suppose let node3 want to communicate with node5, in order to obtain the shared secrete key node3 multiplies its private row which is provided to it by matrix A which is 3rd row of A with the column of public matrix G which is 5th column of G.
K35=A3G5
K35= 18 18 14 26 28 = 175mo29
28
1
28
28
1
1
28
28
28
1
28
28
1
28
28
1
28
28
28
1
28
28
1
28
28
28
28
28
28
1
28
28
1
28
28
28
28
1
28
K35 = 10
Similarly,
Public matrix G of size (4Ã—6),
28
1
1
28
28
28
1
28
28
1
28
28
1
28
28
28
1
28
28
1
28
28
28
28
Secrete symmetric matrix D of size (4Ã—4), 3 5 2 7
5 6 9 1
2 9 3 5
7 1 5 4
A=(DÃ—G)T mod 29 is,
26
9
5
24
3
20
24
5
18
18
14
26
22
20
28
14
16
26
16
22
12
8
10
12
Once matrix A is calculated each sensor nodes are filled with the row corresponding to the index.
K53 = 16 26 16 22 1 = 1808 mod29
28
28
28
K53 = 10
We can observe that K35=K53 which is node3 and node5 share a common secrete key therefore they can communicate with each other.

LINK ESTABLISHMENT
In wireless mesh network, according to the bloms scheme the keys are generated and distributed randomly to each sensor nodes in the network. The node which shares a common key will establish link between the nodes. In this scheme a new approach has been proposed to establish a secure communication between the nodes with desire scalability and resiliency.
When two nodes share more than one shared key, the amount of data transferred will be high when compared to one shared key and bandwidth consumption will also less when compared to others.
Fig6 shows how link will be establish between the nodes using the bloms algorithm. If there is a common key then link will be establish ,if there is no common key between the nodes then no link will be establish, it will look again with other nodes for the common key.
Flow chart that describes the link establishment s,
Fig6: Flowchart for link establishment
Fig6 shows how link will be establish between the nodes using the bloms algorithm. If there is a common key then link will be establish ,if there is no common key between the nodes then no link will be establish, it will look again with other nodes for the common key.

ANALYSIS
This section devote the analysis of our scheme, by comparing it with others [6],[7],[8].
Consider total number of sensor nodes N=100, the security parameter is taken as =29, target area divided into 10 sub regions r=10 and the total number of nodes in each sub region is =100. Figure7 shows how the number of sensor nodes spread over network size of 5000.
Fig7: sensor nodes spread across the network
Fig8: probability of at least one key space being broken after x nodes are compromised
Figure8 indicates that: when the system security parameter is =19, the adversaries have to randomly capture about 300 nodes in order to break at least one key space with reasonably high probability. When security parameter increase to =29 the adversary have to randomly capture minimum of 600 nodes to break at least one key space. From this we can say that larger the security parameter more will be the security.
Fig9: storage cost
Figure9 indicates that: the storage cost of mesh router is high when the total target area is divided into square. When the total target area is divided into regular hexagons the storage cost is comparatively low.

OTHER ANALYSIS
SCALABILITY: new node can be added to the network to replace the old node or to extend the network.
To add the new node to replace an existing node in region Rj, central authority follow these steps:

Select a new key seed Sj(+1) and an identifier idj(+1)

Update G matrix associated with Rj and its 6 neighbouring regions

Update A matrices stored in router.

Load each node with Sj(+1) , idj(+1) and with set identifier Nj(+1).
After all these the new node can establish pair wise key with other nodes as described in key establishment phase.
KEY UPDATING: we can update the pair wise keys when needed to increase the network resilience.


CONCLUSION
Security by establishing a pair wise key is a fundamental issue in WMN. This paper presents a new design of pair wise key establishment scheme. This new scheme reduce the computational cost of sensor nodes for their communication and reduce memory required for storage. Furthermore our scheme has the ability perform even in nonuniform condition and neighbor nodes can directly establish pair wise keys. Our scheme can be scalable, updateable and it gives robust heterogeneity in wireless mesh network.

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