Multiparty authentication services and key agreement protocols with semi-trusted third party

This paper introduces a new family of group key establishment protocols suitable for small or medium-sized groups. Five protocols are presented, using a semi-trusted server, with varying security service. The first one is a non-authenticated key agreement protocol suitable for applications with low security requirements. The second protocol adds an authenticated key agreement to provide collaborative authentication. The third and the fourth protocols provide key establishment with integrity and confirmation services, and the fifth protocol is the member adding protocol. A major advantage of the protocols is that they reduce the numbers of rounds fromn to 5.