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This work concentrates on the design of an efficient and scalable group rekey method for P2P IPTV DRM system where the minimal division of right is a program. Our group rekey scheme is efficient in two aspects, less number of encryption and less individual transmission. We divide the members into three categories, namely, the fresh members, the rejoined members, and the remaining members, according to their knowledge to the current content encryption key (CEK) and watching behavior. Different rekey schemes are adopted for each of these categories. For the rejoined members, the number of encryption is reduced from Θ (Nrejoined) to Θ (k3 log Nrejoined), by using broadcast encryption algorithm where k is the collusion size. For the remaining members, a distributed key tree scheme is proposed to allow the remaining members to coordinate a common key. The number of keys encrypted in one rekey process is reduced to Θ (k log Nremaining). To achieve the second goal, we propose a multicast mechanism of P2P network to transmit the new content encryption key for the remaining members once the distributed key tree has been constructed. Individual transmission for the remaining members can be eliminated for the remaining members. This scheme is implemented in our Coolvideo P2P IPTV system. Real implementation suggests that our DRM solution adapts well in P2P IPTV system even when member size grows large.