Optimal key scheduling for secure satellite broadcasting to mobile users

Cryptography will be the most suitable technique to protect the access to subscribed added-value services for mobile applications provided through satellite broadcasting (e.g., localization and mobile TV). Although satellite broadcasting allows provision of the service even in remote locations, it may also prevent small mobile devices from sending feedback to the satellite when no special return link is provided. In specific locations, where the satellite signals cannot be received due to shadowing or interference, mobile users may also lose the key management data transmitted by the satellite, thus being impossible for them to decrypt the broadcasted data related to the service. A way to overcome these issues is the re-transmission of keys in order 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 and propose a scheduling algorithm for key broadcasting that minimizes the number of mobile users that are prevented from updating their crypto keys. Our results are supported by simulations