Patent ID: 7403618

Claim:
A transmission system for providing conditional access to transmitted data; the system including a transmitter and a plurality of receivers coupled via a network; the transmitter including means for transmitting: to all receivers the same data encrypted under control of a same authorization key; and to all receivers a same key block with a plurality of entries, wherein each entry is associated with a respective different device key, at least some of the entries containing a representation of the authorization key encrypted with the associated device key, and each of the receivers being associated with a corresponding set of a plurality of device keys, wherein at least two of the receivers are associated with sets that comprise at least one corresponding device key, each of the receivers including: means for receiving the key block and the encrypted data; a first decryptor for retrieving the authorization key by taking a single one of the device keys from the corresponding set of a plurality of device keys associated with the receiver and decrypting at least one entry of the key block that is associated with the single one device key; and a second decryptor for decrypting the encrypted data under control of the authorization key, wherein the transmitter is operative to renew a set of device keys of a specific receiver by transmitting to the receiver a new set of device keys encrypted under control of a fixed device key that is unique for the receiver, and wherein the receiver is operative to receive a set of encrypted device keys, and the receiver includes a third decryptor for decrypting the set of encrypted device keys under control of a fixed device key that is unique for the receiver.