KEY ALLOCATION SCHEMES FOR RESTRICTED MULTICAST

Abstract

This thesis addresses the problem of communicating securely with a set of users (the target set) over an insecure broadcast channel. This problem occurs in two application domains: satellite/cable pay TV and the Internet MBone. In these systems, the parameters of major concern are the number of key transmissions and the number of keys held by each receiver. In the Internet domain, existing schemes maintain a single tree key structure that requires each receiver to keep a logarithmic number of keys (establishment keys) for its entire lifetime. In this thesis I propose a scheme that organizes the receivers in a two dimensional array. Each receiver keeps only seven establishment keys for its entire life time regardless of number of receivers. At the same time the scheme also reduces the average number of transmissions. To achieve this, the scheme allows a controlled number of users outside the target set to occasionally receive a multicast. This is being called f- redundant establishment key allocations, which guaranteesthat the total number of recipients is no more thanf times the number of intended recipients. The performance measures used to compare the scheme with the existing schemes are the number of transmissions required and the probability that a user outside the target set (a free-rider) will be able to decrypt the multicast. I also extended this scheme for the dynamic environment where users can join and leave the target set during a specific program broadcast.