Abstract
Secret group communication can be achieved by encryption messages with a group key. Dynamic groups face the problem of changing the group key whenever members join or leave. One of the solutions to this problem is to send updated group keys to members via rekey messages in a secure manner. The recovery of lost group keys consequently becomes important because a member cannot decrypt the group data if she loses the rekey messages. Also, any rekey messages lost while a member is logged off cannot be recovered in real-time. Saving recent rekey messages and resending them by the key distribution center not only requires large storage space, but also can cause unnecessary transmission and decryption of keys. Furthermore, the keys in the unsaved rekey messages cannot be recovered. This paper analyzes the problem of rekey message loss and proposes an efficient scheme for recovering group keys based on a logical key hierarchy. The group key generation method used in the scheme makes it possible to recover group keys without transmission and decryption of useless keys.