: Wireless Sensor Networks (WSN) pose a need for dynamically establishing a secret key joint to a group of nodes. Elliptic Curve Cryptography (ECC) has emerged as a suitable public key cryptographic foundation for WSN. This paper adopts an ECCbased Diffie-Hellman (DH) self-certified key establishment methodologies for securing ad hoc clusters of sensor nodes. The results pertain to a novel load-balancing technique accompanied by a detailed communication protocol. Pairwise DH self-certified key-establishment procedures are extended to online group key generation. Linear computational complexity is observed with respect to the network size, yielding a highly scalable framework. Moreover, authentication is introduced as an inherent component in all key generation processes. Implementation results are presented for the TelosB sensor node platform, clearly demonstrating the viability of the proposed approach.