  Wireless Sensor Networks (WSNs) are rapidly emerging as an important new area
in wireless and mobile computing research. Applications of WSNs are numerous
and growing, and range from indoor deployment scenarios in the home and office
to outdoor deployment scenarios in adversary's territory in a tactical
battleground (Akyildiz et al., 2002). For military environment, dispersal of
WSNs into an adversary's territory enables the detection and tracking of enemy
soldiers and vehicles. For home/office environments, indoor sensor networks
offer the ability to monitor the health of the elderly and to detect intruders
via a wireless home security system. In each of these scenarios, lives and
livelihoods may depend on the timeliness and correctness of the sensor data
obtained from dispersed sensor nodes. As a result, such WSNs must be secured to
prevent an intruder from obstructing the delivery of correct sensor data and
from forging sensor data. To address the latter problem, end-to-end data
integrity checksums and post-processing of senor data can be used to identify
forged sensor data (Estrin et al., 1999; Hu et al., 2003a; Ye et al., 2004).
The focus of this chapter is on routing security in WSNs. Most of the currently
existing routing protocols for WSNs make an optimization on the limited
capabilities of the nodes and the application-specific nature of the network,
but do not any the security aspects of the protocols. Although these protocols
have not been designed with security as a goal, it is extremely important to
analyze their security properties. When the defender has the liabilities of
insecure wireless communication, limited node capabilities, and possible
insider threats, and the adversaries can use powerful laptops with high energy
and long range communication to attack the network, designing a secure routing
protocol for WSNs is obviously a non-trivial task.
