Patent ID: 7933414

Claim:
A method of transmitting data to a plurality of client devices from a service provider, comprising: encrypting the data with a scrambling key Ks at the service provider; calculating a set of partial keys comprising a respective partial key for each respective one of the plurality of client devices at the service provider, the respective partial key being calculated by applying a predetermined associative function to unique identifiers of all client devices except for the unique identifier of the respective one of the plurality of client devices; transmitting the set of partial keys to a master device; and retransmitting to each client device, by the master device, the respective calculated partial key; wherein each client device can derive the scrambling key from the respective partial key received from the master device by reference to its own unique identifier, and can use the derived scrambling key to decrypt the encrypted data; and wherein the predetermined associative function satisfies for n unique identifiers X: Fct ⁡ ( ⋃ i = 0 i = n ⁢ X i ) = Fct ( Fct ( ( ⋃ i = 0 , i ≠ j i = n ⁢ X i ) ⋃ X j ) ) .