Improved authenticated multi-key agreement protocol

Zhou et al give an attack on Harn's modified authenticated multi-key agreement protocol, and give a protocol that can prevent the unknown key-share attack. The paper points out that the protocol is vulnerable to a concatenation attack. This paper proposes an improved authenticated multikey agreement protocol which shows how to make Harn's protocol more secure by modifying the signature and verification. And this prococol can escape the coneatenation attack.