Analysis and improvement on a contributory group key exchange protocol based on the Diffie-Hellman technique

In 2008, based on the two-party Diffie-Hellman technique, Biswas proposed a contributory group key exchange protocol called the Group-DH protocol. This contributory property is an important one of group key agreement. Unfortunately, in this paper we show that the proposed Group-DH protocol is not a contributory group key exchange protocol. Therefore, we propose an improved group key exchange protocol with verifiably contributory property based on the same Diffie-Hellman technique. When an identical group key is constructed, each participant can confirm that his/her contribution is actually included in the group key. We show that the improved protocol is provably secure against passive attacks under the decisional Diffie-Hellman assumption. As compared to the previously proposed group key exchange protocols, our protocol provides contributiveness and the required computational cost is suitable for low-power participants in a network environment.