Scalable group key management with partially trusted controllers

Scalable group key management solutions are crucial for supporting Internet applications that are based on a group communication model. Many solutions have been proposed and of these the most efficient and scalable ones are based on logical key hierarchies (LKH) with symmetric keys organized in a tree. However, these solutions centralize trust in the group controller and make it an attractive attack target for access to communication keys for all groups supported by the controller. In this paper we propose a novel group key management approach, which uses a partially trusted controller that does not have access to communication keys and yet provides the same level of efficiency and scalability as LKH schemes. For this we develop a new public-key encryption scheme, which is based on El Gamal, and we show that the scheme is as secure as El Gamal.