A collusion-free key assignment scheme for hierarchical access control using recursive hash chains

We propose an efficient key assignment scheme for flexible access control of scalable media consisting of multidimensional scalability. The proposed scheme manages one key composed of a single key segment and assigns keys for each entity through hash chains. This scheme is also resilient to collusion attacks by which malicious users illegally access many more portions than they can legally. We introduce recursive hash chains to decrease the number of key segments to one, whereas the conventional schemes that have the above mentioned features must use multiple key segments to compose each key. The managed key is not delivered to any user for security against key leakage. Moreover, our scheme inhibits the amount of hash calculation. Performance analysis validates the proposed scheme.