Conditional entitlement processing for obtaining a control word

A receiver for enabling descrambling of scrambled content, the receiver comprising:

• at least one processor;
• and
• at least one memory operatively coupled to the at least one processor and storing instructions which, when executed by the at least one processor, cause the at least one processor to:
• receive a positive entitlement message and a negative entitlement message from a head-end system;
• obtain a first subkey using first entitlement data received in the positive entitlement message, the first subkey being under control of the first entitlement data;
• obtain a second subkey using second entitlement data received in the negative entitlement message, the second subkey being under control of the second entitlement data, wherein the negative entitlement message instructs the receiver to revoke an entitlement to use a particular key;
• and
• derive a control word operable to descramble the scrambled content by forming a combination of the subkeys.