Method of descrambling a scrambled content data object

A device for descrambling a scrambled content data object, including an input for receiving the scrambled content data object and an input for receiving messages from a conditional access sub-system over a data communication channel, wherein the device is configured to execute a method comprising:

• 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 at least one content descrambling key in the message with each of cryptogram being carried in the message,
• establishing each channel key with a first key, 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

The method of providing conditional access to a content data object, including

• providing at least one content scrambling key to a scrambler, arranged to scramble at least a section of the data object by applying at least one encryption operation under a key at least partly derivable from the content scrambling key,
• providing an entitlement message to at least one conditional access sub-system for providing a message over a data communication channel to a descrambler of an authorised receiver, which message includes data enabling the descrambler to obtain at least one content descrambling key and which message to the descrambler carries at least one cryptogram,
• the conditional access sub-system being configured to generate the cryptogram by encrypting under a channel key data obtainable from at least one content descrambling key in the message,
• wherein the conditional access sub-system is configured to use a second key to establish the channel key,
• providing the conditional access sub-systems with key information representative of the second key and providing to the scrambler key information representative of a first key forming a key pair with the second key, wherein the scrambler is arranged to scramble at least the section of the content data object by applying an encryption operation under a key at least partly derivable from the first key.

A system for providing conditional access to a content data object, comprising

• a scrambler arranged to scramble at least a section of the content data object by applying at least one encryption operation under a key at least partly derivable from a content scrambling key,
• at least one conditional access sub-system for providing a message over a data communication channel to a descrambler of an authorized receiver, which message includes data enabling the descrambler to obtain at least one content descrambling key and which message carries at least one cryptogram,
• wherein the conditional access sub-system is configured to generate the cryptogram by encrypting under a channel key data obtainable from at least one content descrambling key in the message to the descrambler,
• wherein the conditional access sub-system is configured to use a second key to establish the channel key,
• wherein the scrambler is arranged to scramble at least the section of the content data object by applying an encryption operation under a key at least partly derivable from a first key forming a key pair with the second key.

Computer program, including a set of instructions capable, when incorporated in a machine readable medium, of causing a system having information processing capabilities to perform a method comprising:

• applying at least one decryption operation under a key at least partly derivable from a content descrambling key to descramble at least a section of the scrambled content data object,
• 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 at least one content descrambling key in the message with each of cryptogram being carried in the message,
• establishing each channel key with a first key, 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.