International Journal of Computer Applications (0975 – 8887)
Volume 12– No.6, December 2010
1
Security in Wireless Sensor Networks using Frequency
Hopping
ABSTRACT
A Wireless Sensor Network (WSN) is a collection of thousands of
tiny sensor nodes having the capability of wireless
communication, limited computation and sensing. These networks
are vulnerable to internal and external attacks due to the lack of
tamper-resistant packaging and the insecure nature of wireless
communication channels. Since most of the existing routing
protocols are application specific and hence do not satisfy the
security constraints of wireless sensor networks. Whenever any
device comes within the frequency range can get the access to the
transmitting data and may affect the transmission. In this paper,
we simulated the concept of frequency hopping and proved it a
better approach to provide security in WSN..
General Terms
Wireless Sensor Networks, Security, Frequency Hopping.
1. INTRODUCTION
Sensors are small nodes which are capable of data processing and
communication. The sensor node measures ambient conditions
from environment, transform it into electrical signals and sends
via radio transceiver to a sink and then this aggregated
information is sent back to a base station through a gateway [2].
Sensor networks are distributed sensors to monitor conditions like
temperature, sound, vibration, pressure and pollutants etc. WSN
links physical world and digital data network and provide a
distributed network having the constraint of scalability, lifetime
and energy efficiency. WSN was initially developed for military
and disaster rescue purposes but because of the availability of
ISM band (2.4 GHz), the technology is now developing in public
applications. The significant features in Wireless Sensor Network
makes it different from other network; as they are self-organizing,
consumes low power, requires low memory for storage and low
bandwidth for communication, consists of large number of nodes,
self-configurable, wireless, and infrastructure-less. Therefore, in
order to provide a reliable network, WSN design must encounter
the above mentioned features. However each sensor node in the
network is equipped with its own sensor, processor and radio
transceiver, so that a node has the ability of sensing, data
processing and communicating to other node in the network.
Nodes are deployed densely throughout the area where they
monitor specific phenomena and communicate with each other
and with one or more sink nodes; that interact with a remote user.
The user can insert commands into the sensor network via the sink
to assign data collection; data processing and data transfer tasks to
the sensors in order to receive the data sensed by the network.
However, these networks are vulnerable to internal and external
attacks due to the lack of tamper-resistant packaging and the
insecure nature of wireless communication channels.
Figure 1. A Wireless Sensor Network
WSN are susceptible to failure and malicious user attack since the
network is not physically strong. A normal sensor node is very
easy to be captured to convert it into a malicious node. The
insertion of a malicious node in the network is a quite easy task if
security is not upto the mark. The malicious nodes or adversaries
try to disrupt the network operation by modifying, fabricating, or
injecting extra packets; they may mislead the operation of packet
forwarding or will try to consume the resources of the nodes by
making them believe that the packets are legitimate. The
malicious node will not unite in the network operation resulting in
the malfunction of the network operation. As we are aware that
wireless communication only affects the physical, data link and
network layers of the OSI layer, then getting access is not a
difficult job for an adversary by attaining the same frequency
band.
2. SECURITY IN WIRELESS SENSOR
NETWORKS
Due to inherent limitations in wireless sensor networks, security is
a crucial issue and a sensor network is highly vulnerable against
any external or internal attack, thus the infrastructure and
protocols of the network must be prepared to manage these kinds
of situations. This section looks at the security problems that
sensor networks face due to node resource limitations like
memory and energy, sensor network constraints like unreliable
communication, collisions and latency and physical limitation like
unattended after deployment and remotely managed [4, 8, 9, 14].
2.1 Security Goals for Wireless Sensor
Networks
The security goals [4, 8, 9, 14] comprise both traditional networks
and goals suited to the unique constraints of sensor networks. The
security goals for sensor networks are:
Gaurav Sharma
ABES Engineering College
Ghaziabad, India
Suman Bala
Thapar University,
Patiala, India
A. K. Verma
Thapar University,
Patiala, India
Tej Singh
Dept. of Mathematics
AIT, Ghaziabad, India
International Journal of Computer Applications (0975 – 8887)
Volume 12– No.6, December 2010
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2.1.1 Confidentiality
It confirms the ability to the concealment of messages from a
passive attacker so that any message communicated via the sensor
network remains confidential.
2.1.2 Integrity
It confirms the reliability of the data and refers to the ability to
confirm a message has not been tampered with, altered or changed
while on the network.
2.1.3 Authentication
It confirms the reliability of the message by identifying its origin.
Data authentication verifies the identity of senders.
2.1.4 Availability
It confirms the ability to use the resources and whether the
network is available for the messages to communicate.
2.2 Secure Routing in Wireless Sensor
Networks
The major concern in WSN is not only the routing of information
from source to destination through the network but also to take
care of security measures which are necessary for transmission [8,
9]. Indeed; limited resources like energy, is one of the primary
design requirements for these routing protocols. Moreover, the
transmission range of a sensor is severely limited to save energy
so that information that should be transmitted across the network
have to be forwarded via multiple hops. Additionally, the energy
of each single node has to be taken into account for the routing
algorithm, so that overburdened nodes will run out of energy.
While, the routing of information in sensor networks is an
essential service, which makes communication possible in the first
place, security issues in the area of routing were mostly ignored.
Instead, most of the current routing protocols aiming at metrics
such as reliability, robustness, responsiveness and preserving
energy. However, security issues are not considered in the area of
routing. As the sensor nodes are deployed in a hostile or in an
unattended environment, this provides the opportunity for
adversaries to launch certain attacks against sensor nodes, mainly,
the capturing and compromising of the nodes. Reason is the
physical access of the sensor nodes. This results in the
transmission of wrong data in the network.
3. PROBLEM STATEMENT
Most current WSN routing protocols assume that the wireless
network in benign and every node in the network strictly follow
the routing behavior and is willing to forward packets for other
nodes. Dynamic behavior of nodes in the network is also an
addressable issue because most of the protocols do not send any
information regarding misbehavior of any adversary node.
A commonly observed misbehavior is packet dropping. Basically,
in a WSN, most devices have limited computing and battery
power though packet forwarding consumes a lot of such
resources. Consequently some devices would not like to forward
the packet for the benefit of others and they drop packets not
destined to them. In contrast, they still make use of other nodes to
forward packets that they originate. These misbehaved or
malicious nodes are very difficult to examine; whether the packet
dropping is intentionally by malicious node or dropped due to link
error. WSNs have many characteristics that make them vulnerable
to malicious attacks. These are:
Due to open wireless channel (radio) to everyone, an interface is
configured on same frequency band anyone can monitor or
partake in communications. This provides a convenient way for
attackers to break into the network.
Due to standard activity many routing protocols for WSNs are
well-known in public; furthermore these do not include potential
security considerations at the design stage. Thus, attackers can
easily launch attacks by exploiting security holes in the protocols.
Due to the complexity of the algorithms, the constrained resources
make it difficult to implement strong security algorithms on a
sensor platform. It is difficult to design such security protocol. A
stronger security protocol needs more resources on sensor nodes,
which can lead to the performance degradation of applications. In
most cases, a balance must be made between security and
performance.
Due to deployment of nodes in the hostile areas, it is difficult to
perform continuous monitoring. Thus, a WSN may face various
attacks.
The problem of detection of the malicious nodes has been
addressed separately in different protocols, which are either
extensions or based on secure routing protocols. There are various
approaches for providing security to networks. These are
encryption, steganography, securing access to the physical layer;
frequency hopping, etc. can provide security service to sensor
networks.
Table 1. Network Parameter Definition
Parameter Name Parameter Value
Channel Type Channel/Wireless Channel
Radio Model TwoRayGround
Netif Phy/WirelessPhy/802_15_4
Mac Protocol Mac/802_15_4
Number of Nodes 25
Number of malicious nodes 1
Routing Protocol AODV
Grid Size 50 x 50 sq.m
Packet Size 70
Simulation Time Varies
Traffic Type CBR
4. SIMULATION
We use simulation to evaluate the performance of the proposed
AODV routing protocol [1, 13] with and without the malicious
node. We simulate a sensor network consisting of 25 nodes
randomly deployed in a field of 50m × 50m square area. The base
station is located in the middle of one edge. Nodes have same
transmission range in our experiment. The simplest and usually
the first thing to setup a network is creating a node. A network is
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build up from its layer components such as Link layer, MAC layer
and PHY layer. The components have to be defined before a node
can be configured. Table 1 show the parameters used in the
simulation.
5. RESULTS, PERFORMANCE
EVALUATION & ANALYSIS
The analysis is being done on the basis of the results of *.nam file
and the *.tr file with the help of Network Animator (NAM) [11]
and tracegraph [18] by plotting the 2D and 3D graphs. We also
evaluate the performance of the protocol by using AWK
Programming [3]. With the help of AWK programming we obtain
the results in percentage. Simulation has been divided in four
parts (i) AODV, (ii) AODV with frequency hopping, (iii) AODV
with malicious node, and (iv) AODV with malicious node and
frequency hopping.
5.1 Simulation of AODV
In the simulation of simple AODV [1], experiment is carried over
25 nodes. In the ns2-allinone package NAM is a build-in
program. NAM helps us to see the flow of Route REQuest
(RREQ) and Route REPly (RREP). It also shows the packets are
dropping or reaching to the destination properly. When the TCL
(Tool Command Language) [15] file is written, NAM is invoked
inside that file. Figure 2 and figure 3 are animation capture of
WSN with 25 nodes.
Figure 2. Source node broadcasts RREQ
The source (node 10) is broadcasting RREQ message to all its
neighbors and Node 1 which is the destination node, is sending
RREP (route reply) back to the source. The nodes with the same
frequency will receive the message and forward it to its neighbor,
while the nodes with different frequency will drop the packet. In
figure 3, a packet of blue color is on transmission from the source
(node 10) to the destination (node 1). Since there is peer-to-peer
communication between source node (10) and destination node
(1), so no packet will be dropped. In figure 4 tracegraph proves
that dropped packets are zero. This high throughput is expected
because all the nodes are using the same frequency.
Figure 3. Transmission of data packets from source node to
destination node
Figure 4. No packet dropping
5.2 Simulation of AODV with Frequency
Hopping
A data packet is received by the destination only when source and
destination are using the same frequency. When frequency
hopping [16, 19, 21] is applied in the AODV without malicious
node, throughput decreases because due to two frequencies in the
network all the packets do not reach to the destination and drops
in between. The throughput varies as two frequencies are hopped
with different period of simulation time. The throughput is
increased when period of simulation becomes longer. The
throughput has been analyzed with awk script and tracegraph. In
table 2, tracegraph shows the received packets on the destination
node. The table shows how the throughput changes with different
simulation time.
5.3 Simulation of AODV with Malicious Node
When malicious node (25) is inserted into the network as shown
in the figure 5, it receives the broadcast packets and tries to
behave like regular node of the network. In figure 5, malicious
node 25 is broadcasting to all network nodes.
Now malicious node (25) receives RREP packet from the
destination node and sends its own data to the destination node 1.
In figure 6, malicious node and source node both are sending their
own data to the destination node. The packet from malicious node
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is of black color and it sends more packets than source node. The
malicious node tries to jam the channel by sending more and more
packets so that the throughput decreases. Figure 7 shows the
throughput of dropping packets with malicious node.
Table 2. Percentage Of Received Packets At The Destination
Node
Simulation Time (sec) Throughput (percentage)
50 58.8
100 79.4
200 89.7
300 93.1
400 94.8
500 95.8
1000 97.9
1500 98.6
2000 98.9
Figure 5. Malicious node broadcasts a RREQ
Figure 6. Malicious node attacks the network
Figure 7. Throughput of dropping packet with malicious
node
5.4 Simulation of AODV with Malicious Node
and Frequency Hopping
When frequency hopping is applied to the network (with
malicious node), the network performance increases as the
simulation time increases. Table 3, explains how the throughput
increases as the simulation time increases. Figure 8 shows the
throughput of dropping packets with malicious node and
frequency hopping.
Figure 8. Throughput of dropping packet with malicious
node and frequency hopping
5.5 Evaluation and Analysis
In the presented work, we have discussed all the modes of AODV
(simple mode, frequency hopping and malicious node) along with
their working. We sincerely hope that our work will contribute in
providing further research directions in the area of security based
on frequency hopping. In this paper, AODV over WSN is
simulated with different operation modes. An important
contribution of this paper is the comparison of the WSN with and
without malicious node using the frequency hopping technique.
With the results of AWK programming and tracegraph, we can
conclude that in the case of simple AODV there is no packet drop
International Journal of Computer Applications (0975 – 8887)
Volume 12– No.6, December 2010
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and throughput is 100%. But when two frequencies are hopped in
the network with different simulation times, throughput is less
than 100% but increases continuously with respect to simulation
time. After a simulation time of 2000 seconds (~33 minutes)
almost 98 percent packets reach the destination safely.
Table 3. Table captions should be placed above the table
Simulation Time
(sec)
Throughput
(percentage) (10-1)
Throughput
(percentage) (25-1)
50 60 0.4272
100 80 0.2132
200 90 0.1065
300 93.3 0.0709
400 95 0.0532
500 96 0.0425
1000 98 0.0212
1500 98.6 0.0141
2000 99 0.0106
As the malicious node enters into the network, it tries to capture
the network. The performance of the network is affected badly.
But, after applying frequency hopping, as the simulation time
increases, the throughput at the destination node also increases,
which means that the network is secure enough to overpower the
malicious node. After 1500 seconds throughput is 98.66 percent
and after 2000 seconds it is exactly 99 percent. Even malicious
node 25 is about not able to affect the network performance for
long period of time. So, frequency hopping works well and can be
used as a reliable method for IEEE 802.15.4 [7, 10, 20]. Practical
WSN security is a balancing act that is constantly in search of the
highest level of protection that can be squeezed out of the
judicious use of limited resources. A large number of security
problems are still open in WSN. One of the open problems is
authentication of sensor nodes. To secure the sensor network
when a new node enters into the network, it should be
authenticated. Another, aspect of future research direction can be
a non-beacon enabled WSN. Further, path hopping is another
optional concept that can be used to secure the sensor network.
6. REFERENCES
[1] Ad hoc on-demand distance vector (AODV) routing. Online
Available: http://www.ietf.org/rfc/rfc3561.txt
[2] Bisdikian, C. 2001. An overview of the Bluetooth Wireless
technology. IEEE Communication Magazine, vol. 39.
[3] Bruce Barnett. AWK – A Tutorial and Introduction.
http://www.grymoire.com/Unix/Awk.html
[4] Carman, D., Krus, P., and Matt, B., 2000. Constraints and
approaches for distributed sensor network security. Technical
Report 00-010, NAI Labs.
[5] Crow, B., Widjaja, I., Kim, J., and Sakai, P. 1997. IEEE
802.11 Wireless Local Area Networks. IEEE
Communication Magazine, Vol. 35.
[6] Ganesan, R., Govindan, S., Shenker, and Estrin, D., 2001.
Highly-resilient, energy-efficient multipath routing in
wireless sensor networks. Mobile Computing and
Communications Review, vol. 4.
[7] IEEE 802.15.4 WPAN-LR Task Group Website:
http://www.ieee802.org/15/pub/TG4.html
[8] Jones, K., Waada, A., Olaniu, S., Wison, L., and Eltoweissy,
M. 2003. Towards a new paradigm for Securing Wireless
Sensor Networks. New Security Paradigms workshop 2003.
[9] Karlof, C., and Wagner, D., 2003. Secure routing in wireless
sensor networks: attacks and countermeasures. University of
California at Berkeley, USA, Ad Hoc Networks 1 (2003).
[10] Koubaa,A., Mario, A., Bilel, N., SONG, Y. Improving the
IEEE 802.15.4 Slotted CSMA-CA MAC for Time-Critical
Events in Wireless Sensor Network.
[11] Marc Greis. Ns Tutorial. http://www.isi.edu/nsnam/
ns/tutorial/index.html
[12] Roosta, T., Shieh, S. and Sastry, S., 2006. Taxonomy of
Security Attacks in Sensor Networks and Countermeasures.
Berkeley, California, University Press.
[13] Royer, E., and Perkins, C. An Implementation of the AODV
Routing Protocols. http://reference.kfupm.edu.sa/content/i/m/
an_implementation_study_of_the_aodv_rout_2328699.pdf
[14] Sastry, N., and Wagner, D., 2004. Security considerations for
ieee 802.15.4 networks. In Proceedings of ACM workshop
on Wireless security.
[15] TCL Tutorial. http://www.tcl/man/tcl8.5/tutorial/
tcltutorial.html
[16] Torrieri, D., 1989. Fundamental limitations on repeater
jamming of frequency-hopping communications. IEEE
Journal on Selected Areas in Communications, vol. 7, no. 4.
[17] Tovmark, K., 2002. Frequency Hopping Systems (Rev. 1.0).
Chipcon Application Note AN014. http://electronix.ru/forum
/index.php?act=Attach&type=post&id=3712
[18] Tracegraph http://www.tracegraph.com/download.html
[19] Vanninen, T., Tuomivaara, and H., Huovinen, J., 2008. A
Demonstration of Frequency Hopping Ad Hoc and Sensor
Network Synchronization Method on WARP Boards.
WinTech’08, ACM 978-1-60558-187-3/08/09.
[20] Zheng, J., and Lee, M. 2006. A comprehensive performance
study of IEEE 802.15.4 – Sensor Network Operations. Wiley
Interscience. IEEE Press Chapter 4. 218-237.
[21] Zyren, J., Godfrey T., and Eaton, D. Does frequency
hopping enhance security? http://www.packetnexus.com/
docs/20010419_frequencyHopping.pdf
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