CAS key distribution model with revocation

To protect digital contents, CAS encrypts the contents with content encryption keys. Hence, it has been a main issue how to manage the content encryption keys efficiently as well as securely. To face this problem, CAS usually uses a hierarchical key structure and distributes the hierarchical keys to subscribers using smart cards. However, since the smart cards can be revoked so that the saved keys can also leak out, CAS should have a scheme to control the leak of the keys. In this paper, to control the revoked cards efficiently, we propose the key distribution model of CAS using a group key management scheme.