Practical Pay TV Schemes

We propose an efficient and robust Pay TV scheme for the case when there are a number of streams, as opposed to just one. In our model, the broadcast is divided into billing periods; during each billing period the entitlement of the users does not change. We achieve full flexibility with only a constant factor data redundancy. Our scheme has very little secure memory requirements and does not require the users' secure keys to be changed once they have been written into the secure memory. There is also no upper limit on the number of subscribers. We extend this scheme to have the cracker identification property: If a collusion of less than t users crack their set-top terminals and produce a new decryption key, the exact set of crackers can be efficiently identified with high probability. This property is similar to but different from the traitor tracing schemes of Chor et al [5].