In a typical server-client business model, a server should be in charge of both the authentication of the paid customer and the distribution of the contents. The drawback of it is that if the customers' requests go on growing rapidly for the specific contents, the quality of service is degraded due to the server overload or bandwidth restriction. On the contrary, in a P2P network, if more and more users participate in the service, the quality of service is improved, because a peer (a customer) that has same contents can act as a seeder (a server). But, the drawback of the P2P is that there are too many servers to manage, thus it’s more prone to occur illegal distribution of contents. In this paper, we propose the dynamic group authentication scheme suited to P2P based contents streaming. The proposed scheme consists of group key generation, key update, signature generation, and verification protocols. It can control the seeder's state whether the seeder is joining or leaving the network. The proposed scheme can be applied to hybrid P2P based business model where the index server covers sales transactions and the contents are distributed by the P2P protocol.