Patent attributes
Data encrypted with a scrambling key Ks are transmitted from a service provider via a master device to a plurality of client devices having unique identifiers, administered by the master device. A set of partial keys comprising a respective partial key for each respective one of the plurality of clients is calculated at the service provider, by applying a predetermined function to the unique identifiers of all clients but for the identifier of the respective one of the plurality of clients. This set of partial keys is transmitted to the master device, which transmits to each respective clients the respective partial key calculated therefore. Each client can then derive the scrambling key from the respective partial key received from the master device by reference to its own unique identifier, and use the result to decrypt the data.
