Notes on the CRTDH Group Key Agreement Protocol

Group key management (GKM) is one of the primary issues for secure group communication (SGC). Contributory group key agreement is crucial for SGC over wireless and mobile ad hoc networks (MANETs) when there is lack of a fixed infrastructure and it is difficult to have a central trusted entity. Recently, Balachandran et al. proposed a contributory key agreement protocol for MANETs, called CRTDH (R. Balachandran et al. 2005). This protocol is based upon both the Chinese Remainder Theorem and the Diffie-Hellman key exchange scheme. CRTDH exhibits a very nice idea, but contains some problems that make it not very practical in terms of efficiency and security. We point out these problems and propose a solution to them. Analysis and experiments are also presented which show our improved protocol outperforms the original CRTDH protocol in terms of both efficiency and security.