Security weakness in an authenticated group key agreement protocol in two rounds

Dutta and Barua recently proposed an efficient authenticated group key agreement protocol for dynamic membership. To reduce computation overhead, the protocol makes use of a simplified authentication mechanism such that only two neighbors of a participant check if a message is originated from the participant. In this paper, we show that the authenticated group key agreement protocol has some security breaches caused by the restrictive authentication. In addition, we present a simple method to fix the security breaches and prove its security under the standard assumptions.