Security for Wireless Sensor Networks in Military

Operations

Rajat Gupta

Student, B.Tech IT

VIT University

Vellore , India

Rajat.gupta2010@vit.ac.in

Pallavi Singh Student, B.Tech IT

VIT University

Vellore,India

Pallavi.singh2010@vit.ac.in

Kaushal Sultania Archit Gupta

Student, B.Tech IT Student, B.Tech CSE

VIT University VIT University

Vellore , India Vellore, India

Kaushal.sultania2010@vit.ac.in Archit.Gupta2011@vit.ac.in

Abstract:- The communication in military is vital for distribution

of commands, logistical information and proper functionality of

all units. It is must to have a secure channel through which

critical information is exchanged in real time and privacy of

information is maintained. Wireless sensor network can be used

in military application for monitoring militant activities like

tracking enemies and force protection. Wireless sensor network

has set of distributes sensors nodes which are connected to each

other. These sensor nodes are low powered, low cost, small in size

and can do limited amount of computation. But wireless sensor

network is vulnerable to various kinds of attacks like node

capturing, eavesdropping in communication links and man in the

middle or reply to a message. To ensure security, messages from

wireless sensor networks must be encrypted. Many key

agreement schemes have been proposed to ensure security but

most of them are quite complex. In this paper we are proposing

pre key distribution scheme for public key cryptography in

military communication by establishing secure key arrangement

between set of nodes in sensor network. This will improve

performance in term of memory usage, resource consumption,

resiliency against node capturing, scalability, resistant against

node replication and security in information sharing.

Keywords—Wireless sensor network; public key cryptosystem;

Elliptical Curve Cryptography; Military; Security.

I. INTRODUCTION

Enormous amount of research is going on in the field of

wireless sensors network these days. The significant amount

of development has been achieved over years and more is yet

to be achieved. Its involvement is growing in the field of

military services where communication is inevitable. But

wireless sensors are prone to various kinds of node capturing,

reply attacks and DOS attacks. If attacked node is not declared

dead and exchange of information is continued then

information is compromised. Therefore, there is more security

challenges involved where transmission of information takes

place through wireless medium.

Military communication should be resistant to

jamming, direction finding and other type of threats involved

during transmission of information. It should have medium

which must deliver message end-to-end securely. But

transmitting information over wireless sensor need encryption

so that data authentication, data confidentiality and data

integrity is achieved and maintained throughout the

transmission. Secure key agreement and distribution of key is

major issue regarding key management. It requires trusted

third party, KDC or a master station, which assure key

agreement between two nodes. An open research problem in

wireless sensor security is to design a bootstrapping

protocol[4] that establishes a secure communication

infrastructure for sensors where the nodes are pre-initialized

with secret keys without any prior direct contact with other

participating nodes. The complexity of the bootstrapping

problem statement complexity arises from various hardware

restrictions in the deployment of wireless sensor networks.

Since sensor nodes are resource constrained devices, they

can’t work using traditional key management techniques.

Even though public key cryptography is widely believed to

require high computational power, high memory several

recent researches have demonstrated an acceptable

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performance using public key architecture [6], [7], [8], [9].

Considering the resource limitations, elliptic curve based

cryptography is considered to be most suitable public key

algorithm for deployment in sensor network [10].

The focus of this paper is to propose a secure pre key

distribution scheme for wireless sensor network in military by using public key cryptography. In the proposed scheme all the

nodes are initialized with master public key and a set of

corresponding public and private key before their deployment.

Since every node has limited communication range, they

broadcast an empty message (ping protocol) and collects reply

from the nodes which are in their communication range and

later communicate using session keys (private key

cryptography) which is unique and private to them. But before

communication between any two nodes starts they must get

authenticated by the base station.

A sensor network is military is shown in figure. It has

a hierarchical network with three layers. Sensor Network

layer, coordination network layer and back end network layer.

Sensor Network Layer - This layer is used to monitor

environmental and physical conditions, such as pressure,

temperature etc. This layer co-operatively passes their data

through the network to a required location. These sensors

make use of ZigBee or Bluetooth technology and so they have

a short communication range. Therefore their power must be

enhanced in order to deliver sensed data to military personnel.

This can be done by connecting more powerful devices in

coordination network layer.

Coordination network layer – As the sensor network layer

does not have support for data storage over a long period so

coordination network layer is used to collect and analyze data

from it. A number of devices such as PDA, mobile phones,

laptops etc are connected to fixed or remote station using ad

hoc network or infrastructure based network.

Back end network layer – this layer consist of a number of

station which are fixed and servers which are structured on the

internet to provide application level services. The physical

records from the sensor layer are stored in the server side

database for long term period. The key distribution centre

(KDC) or the master station can be trusted to have access to

military camps, weapons storage centre or support centre for

the military services. The job of KDC/master station is to

issue certificates and keys to valid sensor network and

coordination network nodes.

This paper is organized as follow: Section II deals with

background knowledge required to understand the RSA

algorithm , Section III discusses related work done regarding

efficient encryption , decryption and factoring of Public key N,

Section IV describes our implemented algorithm, Section V do

a performance analysis of our method with the brute force one.

Section VI gives conclusion and Section VII describes Future

work.

II. PROBLEM STATEMENT

Key distribution refers to the problem of establishing

shared secrets on sensors nodes such that secret symmetric

keys for communication, privacy, integrity and

authentication can be generated. Due to bootstraping

problem, the difficulty level is raised higher due to various

limitations of sensor nodes. The following issues must be

addressed for the security of sensor networks.

1. A secure communication must be established after the

deployment of sensor nodes.

2. The establishment of connection by unauthorized

nodes should be prohibited.

3. When a new node is added to the existing nodes, it

should form a secure connection.

4. The method should be functional for all conditions

without any prior knowledge of communication range

of nodes which will communicate with each other.

5. The resource requirement such as storage and

computational power should be low and the method

should be protected against denial of service (DOS)

attack.

These issues are to be dealt in detail to overcome security

problems and design robust security mechanisms for sensor

networks. Sensor network have the limitation of

computational, storage and energy resources. But due to

many other additional limitations, it is very complicated to

design new security protocol. These problems are as

follows.

Environment-Sensor node can be deployed in remote

hostile environment, such as battle field. Hence, sensor

nodes are exposed to physical attacks by an adversary. So,

node replication attack and node capturing is and easy

attack.

Medium-Sensor network communicates through radio

Waves where everybody has an access. An attacker can

easily listen to the data being transferred and hence, the

network is exposed to active and passive attacks.

Resources- Sensor nodes always have limited resources.

They have low storage, processing, communication, energy

capabilities due to which the costly key management

infrastructure cannot be used. Sensor nodes are battery-

driven and it is infeasible to visit every node and replace

their batteries. Communication absorbs the most of the

energy in sensor nodes.

Topology- Sensor network do not have any prior

knowledge of post deployment network of nodes. In

military, sensor nodes are deployed in the hostile

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environment using random methods like dropping from

airplane etc.[5]. Therefore, in these situations, storing

encryption keys on nodes to establish secure link among

neighbours is difficult and insecure.

III. PROPOSED SECURITY SCHEME

Following is our proposed security scheme for deployment of

sensor nodes in military.

Key establishment phase: The foremost requirement is to

establish keys between the nodes. For this purpose, we choose

Elliptical Curve Cryptography method which is one of the

methods of Public key cryptosystem. Elliptical curve

cryptography is more scalable and requires less storage space

when compared to symmetric key cryptography or other

public key cryptography methods. It requires less key length

when compared to other public key cryptosystem. Elliptical

curve cryptography with 160 bit key length has equivalent

security level when compared to RSA with 1024 bit key

length. It has low communication overhead, requires less cost

and is easily deployable.

The first phase starts with initialization and is

performed offline before deploying the sensor nodes in the

physical environment. First, a Master public key and

corresponding private key is generated. Master station selects

an elliptical curve over a finite field GF(P) and release a base

point P of large order Q.Q must be a prime number. Next, it

selects a random number r as its private key.

PR ∈ GF(P)

Master public key

PU= r * P

These keys will be used for secure communication by

all the sensor nodes with base station. The master public key

will be stored in node’s memory and only base station has

knowledge about the corresponding private key.

It then generates a random number ri ∈ GF(P) which act as

private key for sensor Si and generate a corresponding public

key PUi = ri *P. The key pair (ri, PUi) is then loaded to the

sensor si. Now,each node in the network has an elliptical key

pair and the master public key PU ,which serves to establish

secret(symmetric) key for secure communication.

Neighbour discovery phase: In this phase, handshake protocol

is followed. Each sensor node performs a neighbour discovery

operation in the network. Since the sensor nodes have limited

communication range, we assume that sensor nodes will be

able to communicate only with the nodes in range. This

operation can be performed using ping protocol. The sensor

node broadcast a HELLO message for eg, Node 1 broadcast a

HELLO message. Those nodes which are in communication

range of Node 1 will receive this HELLO message. Suppose

Node 2 is a neighbour node, i.e, in communication range of

Node 1 and receives a HELLO message sent from node

1.Since the HELLO message from node 1 doesn’t have the

address of Node 2, after receiving this message node 2 will

register node 1 as its asymmetric neighbour and then send a

Hello message back to Node 1 declaring Node 1 as its

neighbour. Since, This Hello Message contains address of

Node 1, Node 1 registers Node 2 as its symmetric neighbour.

It then sends a Hello message to Node 2 declaring it as its

symmetric neighbour. Upon receiving this message, this time

node 2 will register Node 1 as a symmetric neighbour.

Hence neighbour discovery operation is complete and now

each node has knowledge about the nodes which are in its

communication range. Now the sensor nodes will send their

respective public keys to all the nodes which are their

symmetric neighbours. This public key will be used by the

nodes to encrypt a message. This ciphertext can only be

decrypted by the node which in intended since only that node

will be knowing about its private key used to decrypt the

ciphertext.

Secure communication phase:- In this phase, a secure

symmetric communication link is established between sensor

nodes in the entire network. In sensor network communication

occurs between the neighbouring nodes only rather than all the

nodes in the network.

Let’s understand this phase using an example

Alice requests for access list from the master station.

Master station checks for the authentication of Alice and

based on her privileges, issues her a proper access control list

Per(Alice). Per(Alice) comprises of Id and user access list.

Master station generates a certificate of the Alice’s access list

and public key by signing with its private key ( lice =

MS(Per( lice) || PU lice) where Per(Alice) is the access

list, PUAlice is the public key of Alice and MS the

signature of Master Station.

Bob requests for access list from the master station.

Master station checks for the authentication of Bob and based

on his priviledges, issues him a proper access control list

Per(Bob). Per(Bob) comprises of Id and user access list.

Master station generates a certificate of the Bob’s access list

and public key by signing with its private key ( Bob =

MS(Per(Bob) || PUBob) where Per(Bob) is the access list,

PUBob is the public key of Alice and MS the signature of

Master Station.

Both, Alice and Bob will send their own id and the id of the

corresponding communicating node to the base station. For

sending the Ids, the message will be encrypted using master

station’s public key PU. On receiving, master station will

verify both the node’s id and certificate and ensure that these

nodes are authorized member of the network and that they are

allowed to communicate with each other.

This authentication by the master station provides resiliency

against node replication and node capturing attacks.

After receiving the approval from the base station, Alice

selects a random number x∈ (P). x will be used as a session

key for

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communication with neighboring node Bob. It then creates a

secret key =ℎ(r liceBob⊕ ) (where is the current

timestamp generated by Alice), and encrypts the session key x

with the key (i.e. (x) ). Alice then signs this encrypted value

along with its certificate (i.e. lice= lice( (x) ||

lice)), encrypts lice with the public key of Bob PUBob

and sends the af combination x, , , to the node Bob. The

encryption with the private key of Alice provides

authentication (Digital Signature) and encrypting the message

with public key of Bob ensures the confidentiality of the

session key.

After receiving this, Bob will first decrypt the session key

using its own private key rBob which will result in signed

session key. Bob will then checks if the timestamp TAlice is

valid(i.e by verifying if TAlice < Tnow, where Tnow is the

current timestamp). Then it verifies Alice’s signature lice .

If valid, the Alice is authentic to C. Alice’s certificate

lice is also verified to check the validity of the access

list Per(Alice) which was assigned to her. Alice is authorized

if lice is valid. Now bob will compute the secret key

=ℎ( liceBob⊕ ), and decrypts (x) to get x. now, both of

the nodes have established a session key, x, and now they can

proceed for further communication using this symmetric

session key.

IV. SECURITY ANALYSIS

Wireless sensor networks are more prone to attacks in

comparison to other traditional networks.

So, in the scope of this paper, we focus on the possible

vulnerabilities to the proposed method.

1. Node Capture – The network is said to be perfectly

resilient against node capture if a compromised node do

not reveal any information about the links it is not

directly involved with

The weakest point for sensor nodes are that mostly

they are physically available. Hence, it is possible for an

attacker to mount an attack by capturing any node

physically. Resilience of a node is defined as how much

extra information is revealed if a node is

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compromised.in our proposed architecture, each node

communicates by establishing a session key and session

key is established only between the nodes which are

first authorized by the base station. Also, the

communication between two nodes is done using

session key which is first encrypted using the intended

node’s public key. Since, only the related node can has

the knowledge of the corresponding private key, only it

can decrypt the message. The proposed security

architecture provides perfect secrecy against node

capturing since even if the node is captured, no

additional information about the node which is not

involved is released. Capturing a node will only reveal

information about the links which are directly involved

with the node being captured.

2. Node Replication:- Node capturing means whether or

not an attacker can put additional hostile nodes in the

network after attaining some secret information

through node capture. The proposed scheme provides

resistance against replication of node through the use

of base station. In order to ensure security in the

network, the node replicated should be detected as soon

as possible and should be declared dead immediately.

In node replication attack, an attacker can use keys of

the compromised node to form communication with all

the other nodes in the network. But, in our proposed

method, each nodes needs to get authentication from

the master station before communicating and sharing

session key with the other node. Also, each node must

get the certificate from the base station to know all the

nodes with which they are allowed to communicate.

So, if a node is replicated and another node detects that

some node is compromised, it could immediately

inform the same to the master station. Also, since

master station monitors the communication between

the nodes all the time, any node which is compromised

will be having unusual amount of traffic to gain the

most from the compromised node, the base station can

immediately revoke the node assuming it is a

compromised node. Since before deployment base

station generates keys for all the nodes, it has

knowledge about all the node’s identity in the network.

Before approving any node for communication, base

station check for the identity of the node if it belongs to

the same network or not, i.e., the communicating node

is authentic or not. Hence, we can say that even if in

some way, a node is replicated, there is more than

likely chances that base station will catch the replicated

node and immediately revoke it.

3. Remove the compromised node: Since base station

monitors all the communication between all the nodes,

any compromised node can be easily detected by the

base station and can be immediately revoked.

4. Consumption of resources:- Sensor nodes are limited in

terms of resources. They have less memory, less

computational ability, less bandwidth etc. In the

proposed method, the public key cryptography scheme

used is Elliptical Curve cryptography which is widely

believed to be fast and has smaller key length than

RSA and provides the same security as provided by

RSA. Hence, memory requirements are satisfied using

the Elliptical curve cryptography. In the proposed

method, the keys are generated before the deployment

of nodes in the network. Hence, the computation is

reduced once the nodes are deployed in the network

since there is no involvement of computation for large

keys. Although, in comparison to symmetric key

algorithm, public key cryptography requires more

computation power. But since the computation for keys

is being done before the deployment of nodes, we need

not worry about the computation power of the nodes

much. Once the keys are distributed, the nodes can

achieve symmetric link which further reduces the

computational power. Also, for satisfying the memory

requirements of sensor nodes, the nodes are

communicating only with the nodes which are in range

of the communicating nodes. Hence every node just

needs to store master station public key, its own private

key and all the neighboring nodes public key. Suppose

there are n nodes in the communicating range of a

node, a maximum of n+2 keys needs to be saved in any

node. Comparing to the pair-wise key scheme which

requires N-1 keys to store where N is the size of the

network, the proposed method uses n+2 keys which is

<<N. Hence memory consumption is significantly

improved.

5. Scalability: The proposed method is fully scalable

since no part of the algorithm depends on the size of

the network.

6. Mutual Authentication:- Since, communicating nodes

are sent their certificates from the master station, the

master station sent the certificating when both the

communicating nodes are allowed to communicate

with each other and are present in each other’s

certificate.

7. Replay Attacks:- The nodes check the timestamps

before communicating with each other and encrypt the

timestamp while sending a message to other node. The

receiving node can check the time stamp. If the

received timestamp is older than the threshold

timestamp (a particular value, maximum number of

seconds, will be decided after which a message will be

declared void), the proposed method provides total

prevention against replay attacks.

V. CONCLUSION

Secrecy of information in military is vital. But using

wireless sensor network can lead to different kind of attacks

which can compromise our information. Therefore In this

paper we have demonstrated pre distribution of key for

military communication using public key cryptography.

Here communication is taking place between nodes only

after verifying authentication by master station. Therefore it

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is resilience to node capturing because communication

between nodes are encrypted using session key which is

secret between both the nodes. It prevents node replication

as base station detect replicated node and block it. Various

other attacks are also eliminated. It also helps us develop

scalable network as security of the method doesn’t depend

on network size.

ACKNOWLEDGMENT

We would like to express our sincere gratitude towards Prof

Vincent PM, IT dept., VIT University who guided us

throughout this project. I would like to thank our each team

members for their support, hard work and equal contribution

to make this project a success.

.

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