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Due to the sensitivity of the collected data in Ubiquitous Sensor Networks, security becomes the top priority issue for the USNs to be widely deployed. To enhance the security, various key management schemes have been proposed so that the messages among the sensor nodes can be encrypted. Especially, the Polynomial based key management scheme is famous because it guarantees to establish a secure session key between two sensor nodes if the number of nodes in the system is below a threshold. In this paper, we extend the polynomial based key management scheme so that the secure transmission can be achieved in a large network. Basically, we partition the sensor nodes into multiple groups in such a way that the number of nodes in a group is less than the threshold, which guarantees secure session key establishment inside each group. We also propose to exploit structural properties such as the topology and location of the sensor networks to secure the inter-group communications. Furthermore, we introduce a session key computation scheme called Enhanced Direct Key Establishment Option to enhance the robustness against node compromise attacks. Through extensive simulations, we show that the proposed scheme can reduce the number of the compromised links by 10-30% against the node compromise attacks.