Multicast security has been intensively studied in recent years. In all previous schemes a trusted group controller is essential. However this is a restrictive assumption in applications such as teleconferences among members of a dynamic group. This leads to the problem of constructing dynamic group controllers in the multicast environment. That is, after the initialisation of the system, each user in the group can establish a common key among a subset of users by broadcasting a message (or messages) such that only the users in the designated group are able to decrypt it. In this paper, we present two solutions, one based on key distribution patterns which can cater for both private key and public key settings, and the other using tree based key hierarchy structure by employing the Diffie-Hellman key exchange protocol. We assess security and efficiency of our proposed schemes.