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Secure dynamic conferencing (SDC) is a scenario where given a group of participants, any subset of participants can form a privileged subgroup, called a conference, and communicate securely among themselves. The existing SDC schemes belong to two classes: centralized and distributed. The former incurs the single-point of failure, the central point of attack and performance bottleneck. The two existing distributed dynamic conferencing schemes, which are based on public key cryptosystems, are inefficient and imply that anyone, as long as having a pair of public and private keys, can be in the group, thus, lacking the concept of group and the group membership management. In this paper, we first introduce two new concepts based on the well-known key tree scheme: sponsors and co-distributors and then, propose a new distributed dynamic conferencing scheme by designing an efficient algorithm for finding a sponsor or co-distributors. The new scheme enforces group/conference membership management and surpasses all the existing SDC schemes in terms of simplicity, efficiency and scalability.