System for determining successful reception of a message

1. A method for determining that all of a scrambled message has been successfully received, the scrambled message being scrambled in accordance with a scrambling key and being 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, the method comprising:

providing a scrambled message scrambled in accordance with a scrambling key;

generating an unmodified ECM comprising descrambling key generating information for generating a descrambling key for descrambling the scrambled message;

generating a first derived value based on the scrambled message using a first value derivation function:

applying a first modification function to the unmodified ECM, the first modification function being based, at least in pan, on the first derived value, thereby producing a modified ECM;

transmitting the scrambled message and the modified ECM to a receiver; and

performing, at the receiver, the following steps:

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, the second modification function being based, at least in pan, on the second derived value and being an inverse of the first modification function, thereby producing the unmodified ECM; and

employing the unmodified ECM to determine that all of the message has been successfully received.

2. A method according to claim 1 and also comprising:

providing a first smart card, wherein at least one of the following is executed within the first smart card:

the step of generating an unmodified ECM; and

the step of applying a first modification function.

3. A method according to claim 1 and also comprising:

providing a second smart card, wherein at least one of the following is executed within the second smart card:

the step of applying a second modification function; and

at least a portion of the step of employing the unmodified ECM.

4. A method according to claim 1 and wherein the employing step comprises:

producing a descrambling key based, at least in part, on the descrambling key generating information; and

descrambling the scrambled message using the descrambling key.

5. A method according to claim 4 and also including:

determining that all of the scrambled message has been successfully received based on a result of the descrambling step.

6. A method according to claim 5 and wherein said determining step comprises examining the result of descrambling the scrambled message to determine that the descrambled message is valid.

7. A method according to claim 1 and wherein the first value derivation function and the second value derivation function each comprises a hash function.

8. A method according to claim 1 and wherein the first value derivation function and the second value derivation function are identical.

9. A method according to claim 1 and wherein the first modification function and the second modification function are complementary.

10. A method according to claim 1 and wherein the first modification function and the second modification function are identical.

11. A method according to claim 10 and wherein the first modification function and the second modification function each comprises an exclusive-or (XOR) function.

12. A method according to claim 1 and wherein the scrambled message comprises a plurality of scrambled sub-messages, and

the transmitting step comprises transmitting each of the plurality of scrambled sub-messages, and

the performing step comprises assembling the plurality of scrambled sub-messages, thereby producing the received scrambled message.

13. A method according to claim 1 and wherein the performing step comprises transmitting an indication that the scrambled message has been completely received.

14. A method according to claim 1 and wherein the performing step comprises recording an indication that the scrambled message has been completely received.

15. A method according to claim 13 and wherein the indication comprises an authorization to charge for receipt of the scrambled message.

16. A method according to claim 1 and wherein the unmodified ECM also comprises a signature of the contents of the unmodified ECM, the signature being produced according to a signature generating method.

17. A method according to claim 1 and also comprising sending a signature of the contents of the unmodified ECM to the receiver, the signature being produced according to a signature generating method, the signature being separate from the unmodified ECM.

18. A method according to claim 16 and wherein the signature generating method produces different signatures when applied to the contents of the unmodified ECM and when applied to the contents of the modified ECM.

19. A method according to any of claim 16 and wherein the employing step includes verifying the signature.

20. A system for determining that all of a scrambled message has been successfully received, the scrambled message being scrambled in accordance with a scrambling key and being 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, the system comprising:

a scrambler for scrambling a message in accordance with a scrambling key, thereby producing a scrambled message;

an ECM generator for generating an unmodified ECM comprising descrambling key generating information for generating a descrambling key for descrambling the scrambled message;

first value derivation apparatus for generating a first derived value based on the scrambled message using a first value derivation function;

first modifying apparatus for applying a first modification function to the unmodified ECM, the first modification function being based, at least in part, on the first derived value, thereby producing a modified ECM;

a transmitter for transmitting the scrambled message and the modified ECM to a receiver, the receiver comprising:

second value derivation apparatus for generating a second derived value based on the received scrambled message using a second value derivation function;

second modifying apparatus for applying a second modification function to the modified ECM, the second modification function being based, at least in part, on the second derived value and being an inverse of the first modification function, thereby producing the unmodified ECM; and

employing apparatus for employing the unmodified ECM to determine that all of the message has been successfully received.

21. Apparatus according to claim 20 and also comprising:

a first smart card, wherein the first smart card comprises at least one of the following:

the ECM generator; and

the first modifying apparatus.

22. Apparatus according to claim 20 and also comprising:

a second smart card, wherein the second smart card comprises at least one of the following:

the second modifying apparatus; and

at least a portion of the employing apparatus.