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