Improved pairing-free constant round certificateless authenticated group key agreement protocol

Current certificateless group key agreement protocols are not secure when adversaries can replace the participants' public keys or the key generation center (KGC) master secret key is known. An improved protocol appends a signature in the second round to eliminate this weakness. The signature is related to the group identity, the broadcast messages in the first round and the computed message in the second round, to ensure the protocol freshness and the entity authenticity. The message in the second round guarantees that the adversary cannot attack the protocol by corrupting neighboring entities. The improved protocol is resilient to these two attacks and is more efficient other certificateless group protocols.