Attack on Two ID-based Authenticated Group Key Agreement Schemes

Authenticated group key agreement problem is important in many modern collaborative and distributed applications. Recently, there are two ID-based authenticated group key agreement schemes have been proposed, one is Choi et al.’s [2] scheme, the other is Du et al.’s [3] scheme. They are all constructed from bilinear pairings based on Burmester and Desmedt scheme [1]. In this paper, we propose an impersonation attack on the two schemes. We show that any two malicious users can impersonate an entity to agree some session keys in a new group if these two malicious users have the previous authentication transcripts of this entity. So, the two ID-based authenticated group key agreement schemes can not provide the authenticity as claimed. We propose a proposal to repair these schemes.