Patent ID: 8090104

Claim:
A method of descrambling a scrambled content data object, comprising: establishing each channel key with a first key, obtaining at least one content descrambling key from a message received from a conditional access sub-system over a data communication channel, decrypting under an associated channel key at least one cryptogram of data obtainable from the at least one content descrambling key in the message with each of cryptogram being carried in the message, applying at least one decryption operation under a key at least partly derivable from the at least one content descrambling key to descramble at least a section of the scrambled content data object, and applying a decryption operation under a key at least partly derivable from the first key to descramble at least the section of the scrambled content data object, wherein the first key comprises a public key of an asymmetric key pair, and the method further comprises applying a cryptographic operation including an asymmetric cipher under the first key on data exchanged with the conditional access sub-system.