The main challenge in WSNs is to provide strong security with low overhead to a sensor. In last few years, various authentica- tion protocols have been developed to provide security in a WSN environment. In a WSN, a remote authorized user is allowed to access a reliable sensor. Since the sensor nodes are equipped with the limited computing power, storage, and com- munication modules, it is important to design a secure, effective, and lightweight, authentication and key agreement protocol. The authentication protocols for WSNs have become a popular choice for the researchers due to their large applications