Group Key Management: From a Non-hierarchical to a Hierarchical Structure
S. Canard and A. Jambert

Since the very beginnings of cryptography many centuries ago, key management has been one of the main challenges in cryptographic research. In case of a group of players wanting to share a common key, many schemes exist in the literature, managing groups where all players are equal or proposing solutions where the group is structured as a hierarchy. This paper presents the first key management scheme suitable for a hierarchy where no central authority is needed and permitting to manage a graph representing the hierarchical group with possibly several roots. This is achieved by using a HMAC and a non-hierarchical group key agreement scheme in an intricate manner and introducing the notion of virtual node.