Revision with unchanged content. Current market analysis indicates that the most challenging issue in IPTV relates to content security. To achieve high access control a sophisticated group key management is required. This key must be updated and distributed each time a new member joins the group or a current one leaves it. Because of its dependency on time-consuming cryptographic operations this rekeying process can become a bottleneck in the Pay-TV system over Internet. This book tackles this problem by providing novel high-performance architectures, called rekeying processors, which act as coprocessors in the server environment to accelerate group rekeying. The direct effect thereof is higher quality of service regarding joining members and higher access control concerning leaving ones. In addition, a benchmarking framework is presented to evaluate the performance of different rekeying algorithms. The book is intended for Internet Pay-TV providers who plan to scale up their service without loss of access control or QoS. Designers of new rekeying solutions will find a reliable benchmark framework to evaluate their algorithms. Non-specialists will gain an insight into a serious challenge in the emerging IPTV.