This work assumes an environment in which users are already authenticated. The key distribution plays a very important role in manipulating the communication, the storage and the computation costs. Two popular key management protocols today are GKMP (Group Key Management Protocol)--a heavily centralized one, and LTKP (Logical Tree Key Protocol). In what follows, we develop their functionality principles, their advantages and disadvantages. Then, we do the same for more popular protocols like OFT, ELK, GDH.1, GDH.2, GDH.3, 2D-Octopus and hybrid extensions, etc.

In this work we will attempt to combine these protocols with all the possible combinations into a two-layered hybrid scheme that exploits adavantages of both protocols and reduces possibly their overhead. We will develop models of these combinations, redefine their function principles and we will do a mathematical analysis to derive all costs. The analytical formulae of these models will provide us with the tools for comparisons among them, and push the research towards the best behaving models.