A METHOD FOR COMMUNICATING ENTITLEMENT DATA FROM A SERVER, RELATED SERVER, CLIENT SYSTEMS AND COMPUTER PROGRAM PRODUCT

摘要

A server (RI) communicates a set of entitlement data (P) representative of the entitlement of a client (U) to access corresponding contents data by using a set of keys (K) and a non-invertible cryptographic function (f). The cryptographic function (f) is applied to a set of candidate bit strings (S) using the set of keys (K) to find a selected bit string that produces the set of entitlement data (P) as a result of the application of the non-invertible cryptographic function by using the keys in the set. The server (RI) and the client (U) share the cryptographic function (f) as well as the set of keys (or the selected bit string) . The server transmits to the client (U) the selected bit string (or the set of keys) . In either case, the client (U) is thus in a position to apply the cryptographic function (f) to the selected string of bits (S) by using the set of keys (K), thereby reconstructing the set of entitlement data (P).