Kee-Won Kim, Eun-Kyung Ryu, and Kee-Young Yoo
Department of Computer Engineering
yungpook National University
Taegu, Korea 702-701
e-mail : yook@knu.ac.kr
A number of two party key agreement protocols have been proposed ever since the famous Diffie-Hellman protocol was first proposed. The situation where three or more parties share a secrete key, which is often called multi-party keying or group keying, is getting more important as group communications grow up on open network. There have been many attempts to extend the well known Diffie-Hellman key exchange protocol to the multi-party setting.
The idea of ID-based Public Key Infrastructures(IDPKI) is that the identity information of an user functions as his public key. A key generation center which is trusted by all users is responsible for the generation of users' corresponding private keys.
Recently, Du et al.["An Improved ID-based Authenticated Group Key Agreement Scheme," Cryptology ePrint Archive, Report 2003/260, available at http://eprint.iacr.org/2003/260] proposed ID-based authenticated multi-party key agreement protocol.
However, we show that Du et al.'s protocol does not provide forward secrecy. In order to overcome this disadvantage, we propose a new enhanced ID-based authenticated multi-party key agreement protocol. The attacker cannot recover the session key, even though he has obtained the user's long-term private key. The authenticity of the protocol is assured by a special signature scheme, so the messages carrying the information of short-term public key can be broadcasted authentically by an entity. The security analysis of the proposed protocol are examined using heuristic methods.