Offering Data Confidentiality for Multimedia Overlay Multicast: Design and Analysis

Application layer multicast (ALM) has been proposed to overcome current limitations in IP multicast for large-group multimedia communication. We address offering data confidentiality tailored for ALM. To achieve confidentiality, a node may need to continuously re-encrypt packets before forwarding them downstream. Furthermore, keys have to be changed whenever there is a membership change, leading to rekey processing overhead at the nodes. For a large and dynamic group, these reencryption and rekeying operations incur high processing overhead at the nodes. We propose and analyze a scalable scheme called Secure Overlay Multicast (SOM) which clusters ALM peers so as to localize rekeying within a cluster and to limit re-encryption at cluster boundaries, thereby minimizing the total nodal processing overhead. We describe the operations of SOM and compare its nodal processing overhead with two other basic approaches, namely, host-to-host encryption and whole group encryption. We also present a simplified analytic model for SOM and show that there exists an optimal cluster size to minimize the total nodal processing overhead. By comparing with a recently proposed ALM scheme (DT protocol), SOM achieves a substantial reduction in nodal processing overhead with similar network performance in terms of network stress and delay