EHBT: An efficient protocol for group key management. Several protocols have been proposed to deal with the group key management problem. The most promising are those based on hierarchical binary trees. A hierarchical binary tree of keys reduces the size of the rekey messages, reducing also the storage and processing requirements. In this paper, we describe a new efficient hierarchical binary tree (EHBT) protocol. Using EHBT, a group manager can use keys already in the tree to derive new keys. Using previously known keys saves information to be transmitted to members when a membership change occurs and new keys have to be created or updated. EHBT can achieve I·log 2 n message size (I is the size of a key index) for join operations and K·log 2 n message size (K is the size of a key) for leave operations. We also show that the EHBT protocol does not increase the storage and processing requirements when compared to other HBT schemes.