A Time Driven Methodology for Key Dimensioning in Multicast Communications

This work considers the key management for secure multicast in the Logical Key Hierarchy (LKH) model, and proposes a methodology to establish the minimal key length that guarantees a specified level of confidentiality. We reach such a result by analyzing and extending the threat model to the confidentiality of the multicast information. For this extended threat model, we present a methodology that takes into account the following parameters: (1) the required lifetime of the information confidentiality; (2) the level of the key in the LKH model; (3) the dynamics of the multicast group, that is the eviction rate of the users. From these rationales we develop an analytical model that, for each level, derives the appropriate key length, that is the minimal length that assures the desired degree of confidentiality under the hypotheses in the threat model. Finally, for a specific instance of the LKH model, we describe a numerical example that shows the saving that can be achieved in terms of the key lengths.