Wireless Sensor Network (WSN) is primarily designed for real-time collection and analysis of data in hostile environments. One of the major challenges of WSN is security. Network security is the most vital component in information security, because it is responsible for securing all information passed through the networks. The security of WSN poses challenges because of the criticality of the data sensed by a node and in turn the node meets severe constraints, such as minimal power, computational, and communicational capabilities.