Tuning a two-round group key agreement

In 2007, Bohli et al. (Int J Inf Secur 6:243–254, 2007) proposed a two-round group key agreement protocol in the random oracle model, which in addition to semantic security offers strong entity authentication and a security guarantee against malicious insiders. We suggest a modification of this protocol that preserves the security guarantees and the round complexity, but reduces the amount of data that has to be sent and also reduces the number of signature computations and verifications by 50 %. Moreover, we propose a variant of Bohli et al.’s protocol whose security analysis does not require a random oracle or other idealizing assumptions.