Robust Group Key Agreement Using Short Broadcasts

A Group Key Agreement protocol (GKA) allows a set of players to establish a shared secret key which can be used to se-cure a subsequent communication. Several efficient constant-round GKAs have been proposed. However, their performance degrades if some players fail during protocol execution. This is a problem in practice, e.g. for mobile nodes communicating over wireless media, which can lose connectivity during the protocol execution. Current constant-round GKA protocols are either efficient and non-robust or robust but not efficient: assuming a reliable broadcast communication medium, the standard encryption-based group key agreement protocol can be robust against arbitrary number of node faults, but the size of the messages broadcast by every player is proportional to the number of players.