Constant Round Authenticated Group Key Agreement via Distributed Computation

A group key agreement protocol allows a set of users, communicating over a public network, to agree on a private session key. Most of the schemes proposed so far require a linear number (with respect to the number of participants) of communication rounds to securely achieve this goal. In this paper we propose a new constant-round group key exchange protocol that provides efficiency and privacy under the Decisional Diffie-Hellman assumption. Our construction is practical, conceptually simple and it is obtained by taking advantage of the properties of the El-Gamal encryption scheme combined with standard secret sharing techniques.