Maximizing service availability for secure satellite broadcasting

Cryptography is the most suitable technique to protect the access to subscribed value-added services for mobile applications provided through satellite broadcasting (e.g. localization and mobile TV). However, if a temporary loss of signal is experienced by receivers, not only the data streaming is compromised, but also the key management-related messages. Hence, when the signal is received again, it is impossible for the receivers to decrypt it. One way to overcome this issue is the re-transmission of keys to guarantee that the largest set of legitimate receivers has the updated (set of) keys. In this paper we analyze the problem of key update in a mobile user context in order to maximize the service availability. In particular, we provide the following contributions: we propose a mathematical model that captures all the relevant features of mobile users. Then, we formally prove a few novel results on the structure of the admissible rekeying sequence. These results are used to design a scheduling algorithm for key broadcasting that, according to our model, minimizes the number of mobile users that are prevented from updating their crypto keys, hence continuing accessing the service. Finally, simulation results support our theoretical findings. Copyright r 2008 John Wiley & Sons, Ltd.