One strategy for distributing conference keys is for a chairman to one-way distribute the conference key to all participants. However, the chairman does not know whether the participants are present to receive the conference key or not. Thus, the number of attendees for the conference cannot be controlled, a drawback when a conference requires that the number of members exceed a certain threshold value. This paper will propose a new scheme such that only when t or more members out of m participants of the conference are on-line, they can derive the conference key. The scheme is also extended to a generalized case.
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