In wireless sensor networks, sensor nodes generally cooperate with each other in collecting sensing data and in-network processing according to the group communication model. Key distribution is at the heart of secure group communications. In this paper, we present a scalable, efficient and authenticated scheme for group key distribution. The proposed scheme is based on a combinatorial exclusion basis system (EBS) for efficiency and one-way hash chains for authentication. It guarantees an authenticated group rekeying procedure and is efficient in terms of storage, communication and computation overheads.