Abstract
A conditional access system (CAS) is essential for controlling digital content usage in narrow-band broadcasting such as terrestrial 1-segment broadcasting and digital audio broadcasting.We assume that 'broadcasting receivers' refers not only to mobile phones but also to mobile receivers that do not have two-way communication functions.This would include mobile receivers for use in motor vehicles and portable receivers used in combination with personal digital assistants (PDAs) and portable game stations.A CAS provides a way of restricting broadcasting reception and content playback services to subscribers.To distinguish between subscribers and non-subscribers,contract information needs to be distributed to each receiver,and this needs to be done by broadcasting to mobile receivers.Conventional CASs,i.e.,those used for digital satellite broadcasting,broadcast contract information in this way.Doing this,however,requires a wide transmission band of about 300 kbps because contract information is transmitted to individual receivers.The current technology for distributing contract information on conventional CASs cannot therefore be applied to narrow-band broadcasting.In order to resolve this problem,we have developed a new CAS that is capable of transmitting contract information even in narrow-band broadcasting.We describe the scheme used to calculate the transmission rate of contract information.Furthermore,we have evaluated both the security and the implementation of the proposed CAS and determined that the proposed CAS can be applied to existing services.
