**9. Security issues in wireless sensor network**

Security issues in sensor networks depend on the need to know what we are going to protect. In (Zia et al., 2006), the authors defined four security goals in sensor networks which are Confidentiality, Integrity, Authentication and Availability. Another security goal in sensor network is introduced in (Sharma et al., 2011).Confidentiality is the ability to conceal message from a passive attacker, where the message communicated on sensor networks remain confidential. Integrity refers to the ability to confirm the message has not been tampered, altered or changed while it was on the network. Authentication Need to know if the messages are from the node it claims to be from, determining the reliability of message's origin. Availability is to determine if a node has the ability to use the resources and the network is available for the messages to move on. Freshness implies that receiver receives the recent and fresh data and ensures that no adversary can replay the old data. This requirement is especially important when the WSN nodes use shared-keys for message communication, where a potential adversary can launch a replay attack using the old key as the new key is being refreshed and propagated to all the nodes in the WSN ( Sen, 2009). To achieve the freshness the mechanism like nonce or time stamp should add to each data packet.

18 Wireless Sensor Networks – Technology and Protocols

**Figure 10.** Chain-based data gathering and aggregation scheme

**9. Security issues in wireless sensor network** 

7. Geographic Adaptive Fidelity (GAF):

affecting the level of routing fidelity.

query or an interrogation that specifies what the inquirer wants.

The main elements of direct diffusion include interests, data messages, gradients, and reinforcements. Directed diffusion uses a publish-and-subscribe information model in which an inquirer expresses an interest using attribute–value pairs. An interest can be viewed as a

GAF (Xu et al., 2001) is an energy-aware location-based routing algorithm designed mainly for mobile ad hoc networks, but may be applicable to sensor networks as well. The network area is first divided into fixed zones and forms a virtual grid. Inside each zone, nodes collaborate with each other to play different roles. For example, nodes will elect one sensor node to stay awake for a certain period of time and then they go to sleep. This node is responsible for monitoring and reporting data to the BS on behalf of the nodes in the zone. Hence, GAF conserves energy by turning off unnecessary nodes in the network without

Security issues in sensor networks depend on the need to know what we are going to protect. In (Zia et al., 2006), the authors defined four security goals in sensor networks which are Confidentiality, Integrity, Authentication and Availability. Another security goal in sensor network is introduced in (Sharma et al., 2011).Confidentiality is the ability to conceal message from a passive attacker, where the message communicated on sensor networks remain confidential. Integrity refers to the ability to confirm the message has not been tampered, altered or changed while it was on the network. Authentication Need to know if the messages are from the node it claims to be from, determining the reliability of message's origin. Availability is to determine if a node has the ability to use the resources and the network is available for the messages to move on. Freshness implies that receiver receives the recent and fresh data and ensures that no adversary can replay the old data. This requirement is Having built a foundation of security goals in sensor network, the major possible security attacks in sensor networks are identified in (Undercoffer et al., 2002) . Routing loops attacks target the information exchanged between nodes. False error messages are generated when an attacker alters and replays the routing information. Routing loops attract or repel the network traffic and increases node to node latency. Selective forwarding attack influences the network traffic by believing that all the participating nodes in network are reliable to forward the message. In selective forwarding attack malicious nodes simply drop certain messages instead of forwarding every message. Once a malicious node cherry picks on the messages, it reduces the latency and deceives the neighboring nodes that they are on a shorter route. Effectiveness of this attack depends on two factors. First the location of the malicious node, the closer it is to the base stations the more traffic it will attract. Second is the percentage of messages it drops. When selective forwarder drops more messages and forwards less, it retains its energy level thus remaining powerful to trick the neighboring nodes. In sinkhole attacks, adversary attracts the traffic to a compromised node. The simplest way of creating sinkhole is to place a malicious node where it can attract most of the traffic, possibly closer to the base station or malicious node itself deceiving as a base station. One reason for sinkhole attacks is to make selective forwarding possible to attract the traffic towards a compromised node. The nature of sensor networks where all the traffic flows towards one base station makes this type of attacks more susceptible. Sybil attacks are a type of attacks where a node creates multiple illegitimate identities in sensor networks either by fabricating or stealing the identities of legitimate nodes. Sybil attacks can be used against routing algorithms and topology maintenance; it reduces the effectiveness of fault tolerant schemes such as distributed storage and disparity. Another malicious factor is geographic routing where a Sybil node can appear at more than one place simultaneously. In wormhole attacks an adversary positioned closer to the base station can completely disrupt the traffic by tunneling messages over a low latency link. Here an adversary convinces the nodes which are multi hop away that they are closer to the base station. This creates a sinkhole because adversary on the other side of the sinkhole provides a better route to the base station. In Hello flood attacks a Broadcasted message with stronger transmission power is pretending that the HELLO message is coming from the base station. Message receiving nodes assume that the HELLO message sending node is the closest one and they try to send all their messages through this node. In this type of attacks all nodes will be responding to HELLO floods and wasting the energies. The real base station will also be broadcasting the similar messages but will have only few nodes responding to it. Denial of service (DoS) attacks occur at physical level causing radio jamming, interfering with the network protocol, battery exhaustion etc. An specific type of DoS attack, Denial-of-service attack has been explored in (Raymond et al., 2009), in which a sensor node's power supply is targeted. Attacks of this type can reduce the sensor lifetime from years to days and have a devastating impact on a sensor network.


Data is collected and managed at application layer therefore it is important to ensure the reliability of data. Wagner (Wanger, 2004) has presented a resilient aggregation scheme which is applicable to a cluster based network where a cluster leader acts as an aggregator in sensor networks. However this technique is applicable if the aggregating node is in the range with all the source nodes and there is no intervening aggregator between the aggregator and source nodes. To prove the validity of the aggregation, cluster leaders use the cryptographic techniques to ensure the data reliability.

Network layer

Network layer is responsible for routing of messages from node to node, node to cluster leader, cluster leaders to cluster leaders, cluster leaders to the base station and vice versa.

Data link layer

Data link layer does the error detection and correction, and encoding of data. Link layer is vulnerable to jamming and DoS attacks. TinySec (Karlof et al., 2004) has introduced link layer encryption which depends on a key management scheme. However, an attacker having better energy efficiency can still rage an attack. Protocols like LMAC (Hoesel et al., 2004) have better anti-jamming properties which are viable countermeasure at this layer.

Physical Layer

The physical layer emphasizes on the transmission media between sending and receiving nodes, the data rate, signal strength, frequency types are also addressed in this layer. Ideally FHSS frequency hopping spread spectrum is used in sensor networks.
