Security weakness of Tseng's fault-tolerant conference-key agreement protocola

Abstract

A fault-tolerant conference-key agreement protocol establishes a shared key among participants of a conference even when some malicious participants disrupt key agreement processes. Recently, Tseng proposed a new fault-tolerant conference-key agreement protocol that only requires a constant message size and a small number of rounds. In this paper, we show that the Tseng's protocol cannot provide forward and backward confidentiality during a conference session for the proposed attack method. We also show that a simple countermeasure-re-randomizing short-term keys of some participants-to avoid the proposed attack can be broken by extending the proposed attack method. (C) 2009 Elsevier Inc. All rights reserved.