Wireless Sensor Network is a collection of autonomous sensor nodes placed spatially. Unlike wired networks the sensor nodes here are subject to resource constraints such as memory, power and computation constraints. Key management and Security are the area of research in WSN. To ensure high level security encryption is necessary. The strength of any encryption algorithm depends upon the key used. So Key Management plays a significant role. The proposed KMS using LLT matrix achieves both Node-to-Node communication and Group communication. The main objective of the scheme is to strengthen the data transferring security mechanisms and also to ensure efficient key generation and management along with authentication. The main feature of this proposed system is 100% Local-connectivity; efficient node revocation methodology, perfect resilience; three-level authentication cum key generation and the most importantly reduced the storage. The scheme and its detailed performance analysis are discussed in this paper.