**1.3. Secure routing goals**

Security problems in WSN at the network layer can be related to router identity or router behavior. These two issues highlight two main tasks when we would like to design a secure routing solution [1,10].

	- Data Confidentiality: In this service, only the destination node should be able to access the packet content initiated from the source node. Any intermediate router must not have any access to such information. As we can see here, the access of the packet is restricted to the destination node. Thus, if a node other than the destination accesses the packet, it means that the destination identity has been compromised.
	- Data Integrity: When a destination node receives a message from a source, the destination should be able to detect any change that could occur in the message.

Securing packet content is obtained usually based on the idea of identity trust in which a routing decision is made after verifying that the selected node is authorized and has an acceptable identity according to certain criteria. This is achieved in literature by using crypto-based systems. However, any solution must obey WSN constraints of processing capacity, memory limits and energy consumption.

 Securing Packet Delivery: This task deals mainly with behavior related security problems. Its objective is to guarantee that any packet transmitted will be ultimately received at the target destination. Thus, a misbehaving router node should not be able to drop a packet, misroute a packet or deny the ability of routing of other nodes by denial of service attacks. This task can be interpreted in terms of a security service called data availability.

236 Wireless Sensor Networks – Technology and Protocols

Routing is a fundamental operation in almost all types of networks because of the introduction of inter-domain communication. Ensuring routing security is a necessary requirement to guarantee the success of routing operation. When we talk about secure routing, we are concerned with security problems that may occur due to improper actions from an assumed router. These undesired actions can be related either to the router identity or the router behavior. If the router has an undesirable identity or authorization, it is considered as an intruder who might perform serious attacks. Such attacks can be avoided by providing security services that validate the routers' identities. On the other hand, a router that misbehaves in the network by performing undesirable routing operations also contributes to the routing security problem. However, the attacks caused by misbehaving routers can be avoided by mechanisms that validate and evaluate the router behavior in the

In WSN, secure routing is more demanding due to the nature of the routing operation in WSN. Since WSN lacks an infrastructure, nodes depend on the cooperation among each other to route their packets. Thus, a router in WSN is simply any node that offers a routing service. This "any node" should be selected such that it will be the most secure choice to route the packet. To come up with a proper routing decision we need to understand first

Security problems in WSN at the network layer can be related to router identity or router behavior. These two issues highlight two main tasks when we would like to design a secure

 Securing Packet Content: This task is concerned with identity related security problems. The goal of this task is to assure that the packet is not accessed by unauthorized nodes as it travels from the source to the destination. This task can be achieved if we can

 Data Confidentiality: In this service, only the destination node should be able to access the packet content initiated from the source node. Any intermediate router must not have any access to such information. As we can see here, the access of the packet is restricted to the destination node. Thus, if a node other than the destination accesses the packet, it means that the destination identity has been

 Data Integrity: When a destination node receives a message from a source, the destination should be able to detect any change that could occur in the message.

Securing packet content is obtained usually based on the idea of identity trust in which a routing decision is made after verifying that the selected node is authorized and has an acceptable identity according to certain criteria. This is achieved in literature by using crypto-based systems. However, any solution must obey WSN constraints of processing

**1.2. Secure routing problem** 

what security goals we are targeting.

provide the following services:

capacity, memory limits and energy consumption.

compromised.

**1.3. Secure routing goals** 

routing solution [1,10].

network.

 Data Availability: If a node A is authorized to get information from another node B, then node A should acquire this information at any time and without unreasonable delay.

There are different approaches to achieve this second task. However, as the first task, the designer should be aware of the suitability of the solution with WSN tight constraints such as energy scarcity. In this work, we are proposing a solution for securing packet delivery task with an account for energy efficiency. Our solution is based on the concept of behavior trust where nodes should trust the behavior of another node in order to select it as a router. This approach is well-known in literature as trust aware routing.

The rest of the chapter is organized as follows. Section 2 of the chapter provides the relevant background material covering an overview of WSN that includes WSN definition, sensor node structure, applications, etc. As WSN is a class of MANET, the main differences between WSN and MANET will be presented. These differences are explained in a way that emphasizes to the reader how they make WSN an independent research target as compared with MANET. Then we introduce the notion of trust and reputation in social networks, how these concepts can be applied smoothly to Wireless Sensor Networks to mitigate node misbehaviors, illustrate the issues in Modeling and Management of Trust & reputation, highlighting the importance of Trust-Aware Routing, and general concept of reputation systems. This will be followed by a detailed discussion on some of the important related work carried out in the area of Reputation system based trust-enabled routing for WSNs.

Section 3, being the Reputation System Overview section, will provide an overview of the proposed reputation system. The section will start by discussing the general reputation system framework clearly introducing the readers to various components of the Reputation system highlighting the functions to be performed by each component. This is followed by description of our customized reputation system- SNARE (Sensor Node Attached Reputation Evaluator)[82] that fits into the framework guidelines. Reputation-based solution will be discussed as a detection approach by presenting the general concept of reputation systems, followed by suggestions and approaches in reputation system solutions that can fit WSN secure routing requirements. In this section, we briefly describe our proposed monitoring component called Efficient Monitoring Procedure in Reputation Systems (EMPIRE)[84], a new rating approach for reputation systems in WSN called CRATER(Cautious RAting for Trust Enabled Routing)[85] and a simple but strong, independent and representative scale to evaluate reputation systems called *REputaion Systems-Independent Scale for Trust On Routing* (RESISTOR)[85].

In section 4, our enhanced routing protocol that aims to provide a secure packet delivery service guarantee by incorporating the trust awareness concept into the routing decision is presented. Our proposed protocol is called Geographic, Energy and Trust Aware Routing (GETAR) which is an enhanced version of the Geographic and Energy Aware Routing (GEAR) protocol[9]. GEAR is basically a geographic routing protocol in which the next hop is selected based on two metrics: the distance between the next hop and the destination and the remaining energy level the next hop owns. The new contribution in GETAR is to add a third metric in the next-hop selection process, i.e. the risk value of a node that is computed by the rating component, CRATER[85] in our case. In section 5, we present a comparison of our approaches with previous reported work and highlight our main contributions. The chapter finally concludes with a summary and future research directions in this field.
