Patent ID: 7447315

Claim:
In a system where a scrambled message is scrambled in accordance with a scrambling key and is capable of being descrambled in accordance with a descrambling key, descrambling key generating information for generating the descrambling key being comprised within a control message (ECM) associated with the scrambled message, an unmodified ECM comprising descrambling key generating information for generating a descrambling key for descrambling the scrambled message being generated by the system, a first derived value based on the scrambled message using a first value derivation function being generated by the system, a first modification function being applied to the unmodified ECM thereby producing a modified ECM, the first modification function being based, at least in part, on the first derived value, the scrambled message and the modified ECM being transmitted to a receiver, a method comprising, at the receiver: receiving the scrambled message and the modified ECM; generating a second derived value based on the received scrambled message using a second value derivation function; applying a second modification function to the modified ECM thereby producing the unmodified ECM, the second modification function being based, at least in part, on the second derived value; and employing the unmodified ECM to determine that all of the message has been successfully received.