Multiparty Authentication Services and Key Agreement Protocols with Semi-Trusted Third Party

This paper introduces a new family of group keyestablishment protocols suitable for small or medium-sized groups.Five protocols are presented, using a semi-trusted server, with varyingsecurity service. The first one is a non-authenticated key agreementprotocol suitable for applications with low securityrequirements. The second protocol adds an authenticated key agreement toprovide collaborative authentication. The third and the fourthprotocols provide key establishment with integrity and confirmationservices, and the fifth protocol is the member adding protocol. A majoradvantage of the protocols is that they reduce the numbers of roundsfrom n to 5.