Paper 2003/259

Attack on Two ID-based Authenticated Group Key Agreement Schemes

Fangguo Zhang and Xiaofeng Chen

Abstract

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 \cite{CHL04} scheme, the other is Du $et\ al.$'s \cite{Du03} scheme. They are all constructed from bilinear pairings based on Burmester and Desmedt scheme \cite{BD94}. 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.