Authenticated Multi-Party Key Agreement

We examine multi-party key agreement protocols that provide (i) key authentica-tion, (ii) key connrmation and (iii) forward secrecy. Several minor (repairable) attacks are presented against previous two-party key agreement schemes and a model for key agreement is presented that provably provides the properties listed above. A generalization of the Burmester-Desmedt model (Eurocrypt '94) for multi-party key agreement is given, allowing a transformation of any two-party key agreement scheme into a multi-party scheme. Multi-party schemes (based on the general model and two speciic 2-party schemes) are presented that reduce the number of rounds required for key computation compared to the speciic Burmester-Desmedt scheme. It is also shown how the speciic Burmester-Desmedt scheme fails to provide key authenti-cation.