Security properties of two provably secure conference key agreement protocols.

Wen-Guey Tzeng, Zhi-Jia Tzeng

Qiang Tang, Chris J. Mitchell

Wen-Guey Tzeng

Lei Zhang

Yuh‐Min Tseng

Recently, Tzeng proposed a provably secure and fault-tolerant conference-key agreement protocol. It requires only a constant number of rounds to establish a conference key among all honest participants. This article will show that Tzeng’s protocol does not offer forward secrecy. We say that a conference-key agreement protocol offers forward secrecy if the long-term secret key of any participant is compromised and will not result in the compromise of the previously established conference keys. This property is important and has been included in most key agreement protocols and standards. In this paper, an improvement based on Tzeng’s protocol is proposed and it achieves forward secrecy. Under the Diffie–Hellman decision problem assumption and the random oracle model, we show that the proposed protocol can withstand passive attacks and is secure against impersonator’s attacks. The improved protocol requires a constant number of rounds to compute a conference key. The improved protocol provides fault-tolerance.

Xinglan Zhang, Quanmin Wang

A conference-key protocol is used to establish a common conference key K such that a group of people can communicate securely over a public network. To improve the implementation efficiency of Tzeng¿s conference-key agreement protocol, an efficient conference-key agreement protocol is proposed under the authenticated broadcast channel. First, the improved protocol is round-efficient, and relaxes the waiting time for fault-check. Second, it reduces the computational complexity by revoking the signature procedure in the Tzeng¿s protocol. It is provably secure in the standard model under the DDH assumption.