Security for mobile wireless sensor networks has many unique challenges. Existing security protocols have serious drawbacks revoking compromised nodes from the network, replenishing the network with new nodes in secure manner and performing in network processing if nodes migrate from one cluster to another. In this paper, the authors propose a new energy-efficient protocol that provides security for a heterogeneous mobile WSN. The protocol is based on Identity Based Encryption (IBE) which facilitates communication-efficient key establishment among the nodes in a WSN as well as revocation of compromised nodes from or addition of new nodes to the network.