Securing communications in wireless sensor networks is increasingly important, as the diversity of applications increases. In this paper, we analyze the performance and power efficiency of bulk user data communications in a simple, secure PKI-based communication scheme employing a hybrid cryptographic approach. Detailed benchmarks of the involved cryptographic primitives are performed. The results are used to determine how the necessary computing ressources can be reduced from the current implementation, without compromising and even increasing security. At the same time, the special circumstances of the PKI-based framework on memory constrained sensor motes, such as IRIS or MICA2 motes, are considered. An improved set of cryptographic primitives is determined and implemented, improving execution speed and thus energy efficiency. © 2013 IEEE.