The Security Issues In Wireless Sensor Networks Computer Science

Wireless sensors are low powered sensing devices coupled with wireless technology. These sensors are often called as motes. The combination of these motes along with RFID, renders a powerful technical product which can change the face of the automation systems used in today's world. A lot of research is going on currently in this field as it guarantees ease of deployment and low expenditure when deployed in large scale. Mostly these devices operate using Zigbee protocol (802.15.4) and some of the companies also came up with the standard 802.11 protocol. The architecture of the protocol stack is the same and moreover they both face almost same security concerns but being a low power device it becomes the bottleneck to provide extra security measures which are available in the standard 802.11 devices. In this report we will be studying about the various attacks that can take place in the Wireless Sensor network. If one does not want its WSN to be a test subject or the victim of vandalism, the security aspect should not be overlooked. Therefore, it is useful to know how today's WSN software and protocols hold up against a variety of attacks and how likely it is that these attacks really take place.

Overview

In this report we shall see what the different known attacks in the WSN are and what the proposed remedies for them are. We will begin with the physical layer, where the tampering and jamming are the main known attacks and how they effect the WSN. Then we will move to the Data link layer, where we will study the collision attack and this is the main focus of my topic. The collision attack occurs when a listener listens to the start of the data and sends its own bytes at the same frequency to corrupt the data. We will also study the remedies in use and the remedies proposed for the same. Then we will move to the known attacks in the network layers. This report covers only the remedies for the data link layer and the physical layer. We will not be discussing the remedies for the other layers as the concentration of this paper is on the data link layer only.

Physical Layer

Tampering: As the wireless mote is mostly present in outdoor environment and is visible to human, it is possible that someone might intentionally or intentionally tamper it, the only solution to this is to try and place the mote in strategic location where it is difficult for humans to interfere with it and to properly camouflage the mote.

Jamming Attack: This is a crucial attack because when a mote is under its influence it can neither send nor receive anything from the gateway or the other motes. The mote which performs the jamming will try to prevent the reception or transmission of signals from or to other motes. This is done by listening the frequency at which the WSN is operating using a radio then continuously sending random signal at the same frequency to jam the network and case the motes in its vicinity to get isolated. The main advantage to the attacked is that it just has to know at what frequency the WSN is operating and nothing else and the disadvantage is that if the attacker is running on battery then it will soon run out of battery because of continuous transmission of random signals. One way to prevent jamming attack is to use different frequency when it is under jamming effect but it is almost impossible for the other mote to detect when the mote under attack is going to transmit on different frequency. The more promising solution is the use of frequency hopping where all the motes uses a predefined sequence of frequency. In this way the motes will transmit in different frequencies and the attacker won't be able to detect that. This solution is not seen to be incorporated because of its complexity in the hardware and it will increase the power consumption. Another solution proposed is the use of UWB (Ultra Wide Band). It is based on transmitting very short pulses in the order if nanosecond on a large part of frequency band simultaneously. [1]

Data Link Layer

Collision attack: By using a radio the attacker can come to know at what frequency the WSN is operating. The attacker listens to the start of the frame and then it sends out its own message to corrupt the message sent by the mote. This will not prevent the mote from sending or receiving data but will corrupt the data and the CRC check will render wrong result and the data will be discarded which will cause retransmission and then the same. Eventually the mote will die because of high power consumption in re-transmission over and over again. This attack is difficult to detect as the attacker is not transmitting continuously. The other point is that listening to signal consumes less power than transmission. This increases the life of the attacker if it is operating on batteries. [1]

All the countermeasures which are used for the jamming attack can be used in the collision attack but the problem is that it is difficult to detect such an attack. The error correction code seems to be a promising solution to this problem. The attacker sends out few bytes of data which corrupts few bits of data and the error detection and correcting techniques can be applied at the receiving end to fetch the data out of the corrupted pattern. This seems to be promising because the additional byte of data which will be attached to the data frame will be less and the correction codes are not that complex and are currently in use in today's world. The other alternative is use of Tiny Sec., this is an encryption technique supported by the Tiny OS. The motes generally run on Tiny Os which is an open source component based embedded Operating system for low powered wireless devices developed by UC Berkeley. It uses a shared key of 80 bit and the algorithm for the encryption is Skipjack. It can also provide integrity by using MAC, Message authentication protocol. The attacker can see the message but cannot interfere with it. The use of encryption makes only the header visible and provides good security. [2]

Network Layer

Routing: Routing protocol finds the path from source to the destination in the network from sharing of information. The routing protocols always strive to find out the best path by having the least number of hops in between, minimum energy and shortest distance. The two main routing technologies are link state routing and distance vector routing. [3]

In link state routing every node has map of all the nodes in the network and their respective connectivity. Hence, every node independently calculates the best path and uses it. The information of the other motes is placed in its routing table. The disadvantage is that it requires more data processing and more memory. [3]

To avoid this distance vector routing algorithm is used in the WSN. In this algorithm, every mote is aware of it neighbor mote only and they use the routing tables of their neighbors to decide. There are various attacks which particularly targets the routing technique used in the WSN. The most common are selective forwarding, sinkhole, HELLO flood, Routing Cycles and misdirection attacks. The above mentioned attacks are discussed in brief in the following section. [1]

Selective Forwarding:

In this type of attack, the node forwards most of the packets or messages and it drops selected packets or messages, which means that it will simply discard or throw away some messages or packets. This attack is also referred to as a neglect attack as the node simply neglects messages from some of the node or nodes. This attack can be combines with other attacks like, a sinkhole attack to increase traffic at its end and drop packets more often. [1]

Sinkhole

In this attack, the node tries to attract all the traffic or most of it by presenting itself as a lucrative option to forward data. The node manifests itself as if it is a base station or it gives other nodes a notion that its routing metrics are good for further passing of the message. Hence, other motes will try to route their data through that node, causing immense traffic at that end.

HELLO Flood

In this type of attack, the attacker uses a powerful radio to send message across the network. The attacker will try to attract all the other motes by projecting itself as a parent mote and in turn they will try to send him the data which will be dropped later as it is far out of reach. [1]

Routing cycles

The path from the source to destination becomes a loop and the data keeps on travelling on and on.

Sybil attack

The affected mote in the Sybil attack exhibits multiple identities. It is usually don't to fool the neighboring mote and dump its memory with useless data. It may result in overwriting of useful data in the neighbors' memory.

Topics to be covered in future:

The primary concentration of my area of research is the security concern at the data link layer. In the above sections I have mentioned that the WSN is prone to attacks and provide a weak security aspect. I would like to study how more error correcting codes can be incorporated in the WSN's and how one can make it more secure in the near future. This will be done by studying how hamming code technique can be incorporated and what will be its overhead to the network.

Conclusion:

The WSN is still in its nascent stage and it will take time to launch it in a safe and secured way. The security comes to this technology as a challenge because of the limited resource, but the usefulness and the advantages of this system cannot be neglected. A lot of research has been going around in this field throughout the world and researchers are striving continuously to make it more secure and safe.

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