Key distribution for conditional access system in DTV broadcasting

In DTV broadcasting, key distribution is the essential part of the conditional access system (CAS), which is directly related with the security of CAS. In this paper, considering the inefficiency of the current CAS, a modified key distribution algorithm is put forward, in which the hierarchical access control technology is used to distribute the authorization keys of channels while the Chinese remainder theorem is adopted to distribute the group keys to the subscribers. The proposed algorithm is secure enough as well as greatly reducing the forward security problem. Moreover, the algorithm is flexible in dynamic management of subscriber. Most importantly, the algorithm is more efficient than the current CAS for fewer messages being transferred during key rekeying and system initializing, which greatly saves the bandwidth of the channel