Tuning a two-round group key agreement

Offline Assisted Group Key Exchange

“…We therefore desire non-interactive solutions that allow the initiator to complete their actions before any recipients come online, and do not require any interaction between the recipients. This rules out traditional group key exchange protocols [5,2,18,3,13].…”

“…We need a group key exchange protocol that is non-interactive with respect to the initiator and the responders, and that at the same time provides forward secrecy. [14,16,12] b 2 GKE [5,2,18,3,13] N Mona [22], Tresorit [20,21] N Chu et al We overcome these obstacles by noting that the cloud server is online at all times, and use ephemeral values provided by the cloud server to give us forward secrecy. This allows us to achieve the best possible level of forward secrecy in our collaboration scenario, without trusting the cloud server.…”

“…An example of a modern optimised protocol is that of Gao et al [13] which adds signatures to all messages and requires users to verify the signature on broadcast messages from all other users. In comparison our requirements are relatively modest.…”