Abstract. Wireless Sensor Networks are edging closer to widespread feasibility with recent research showing promising results in developing and adapting new mechanisms to suit their environment. Secure communication between these distributed wireless devices is a desired characteristic, especially in scenarios where these sensors will be exploited for military and other mission-critical operations. This paper highlights some of the research challenges for extending secure communications over these resource-constrained devices and points out why current protocols do not scale well in this unique application realm. Then, a storage-optimal key sharing scheme with authentication is proposed in this paper. This scheme requires each sensor node to hold one secret key and hash functions only, and is optimal in terms of memory consumption which is more rigorous constraint factor than computation and communication resources limit.