Abstract
In Pay-TV broadcasting systems, only the authorized subscribers are allowed to precisely access the TV programs/channels subscribed by them. In order to achieve this requirement, several key management mechanisms are proposed to provide the channel protection. Two kinds of key management mechanisms, time-bound hierarchical key management and conditional access systems, are widely discussed in Pay-TV broadcasting systems. A time-bound hierarchical key management scheme is a method to assign time-dependent encryption keys to a set of classes which have partially ordered hierarchy. On the other hand, conditional access systems provide the channel protection according to distinct business models. In this thesis, these two mechanisms are discussed. In the first part of this thesis, we focus on time-bound hierarchical key management schemes. We first demonstrate that a new scheme proposed by Betrino et al. is insecure against the collusion attack even their scheme has adopted tamper-resistant devices. We also provide some possible amendments to this scheme. Besides, we propose a new time-bound hierarchical key management scheme which can effectively defeat the collusion attacks without adopting a tamper-resistant device. Compared with the previous schemes, our design requires less public parameters. In the second part of this thesis, we put emphasis on the conditional access system. Since the existing business models, pay-per-view and pay-per-channel, have some constraints and drawbacks, we define a new business model which is more flexible for subscribers. In order to fulfill the requirements and assumptions of this business model, we also propose a new conditional access system. Besides, we also describe two methods to reduce the size of the access control matrix which is used for recording the subscription of all subscribers.