STR multicast key management protocol has an optimal cost in computation

communication and storage.But on security property

STR cannot resist active attacks without providing key authentication.By introducing the bilinear pairing cryptosystem and the 3-ary key tree

the improved STR protocol which is called PSTR（bilinear pairing-based STR） was proposed.The key generation process and six basic sub-protocols were included in the protocol.Through proving the bilinear form of PSTR key tree

the security of the PSTR in computation was proved.Finally PSTR were compared with STR through performance analysis

the results of which show that: PSTR is more efficient than STR in the communication cost and the computation cost as well as the storage requirement.Therefore

PSTR is a novel

reliable group key management protocol

and is well-suited for Ad hoc networks.