The rest of the paper is organized as follows. Section 2 re- views the literature to discuss the pros and cons of the existing authentication protocols for WSNs. In Section 3 , we present the attacker model that describes the capabilities of an adversary to get into the system. In this section, we also present the notations used in our proposed protocol and properties of the one-way hash function. Section 4 presents the proposed authentication and key agreement protocol in WSNs to authenticate the colliary profes- sionals and the sensors. Section 5 provides the detailed security analysis of the proposed protocol to justify the claim that it is very safe against all the known attacks. Section 6 provides the proof of authentication and key agreement in our protocol using BAN logic. In Section 7 , we simulate and formally analyze our protocol using the AVISPA tool. Section 8 presents the performance evaluation of our protocol to prove its fruitfulness over the existing protocols. Finally, in Section 9 , we draw our conclusion and also the future work.