Conditional access system and method for prevention of replay attacks
View Patent ↗In a conditional access system, a headend transmits content to one or more receivers in encrypted transport streams. The system provides a multi-layer security architecture, rendering the system resistant to key replay attacks; if one layer is circumvented, subsequent layers remain intact. A first layer prevents unencrypted keys from being recorded by shielding the unencrypted keys from users and encrypting the path from the receiver's conditional access module to the transport decryption module; a second layer prevents a key recorded on one receiver from being played back to the transport decryption module on a second receiver; a third layer prevents a user from decrypting transport streams without the encryption module by encrypting the stream a second time prior to being passed through any user-accessible memory or processor. Event tables are transmitted with the transport stream, either unencrypted for immediate use or encrypted, to prevent unauthorized use.
1. A method, comprising:
creating, at a headend, an event table for a corresponding transport stream, the event table comprising a location of one or more start codes within the transport stream;
transmitting the transport stream from the headend to at least one receiver among a plurality of receivers;
transmitting the event table from the headend to the at least one receiver among a plurality of receivers.
2. The method of claim 1 , wherein the event table further comprises a type of at least one start code of the one or more start codes.
3. The method of claim 1 , further comprising:
encrypting the event table prior to transmission with the transport stream.
4. The method of claim 1 , wherein the transport stream is an encrypted transport stream, and further comprising:
storing the encrypted transport stream transmitted at the at least one receiver; and
encrypting, at the at least one receiver, the transport stream to obtain a doubly encrypted transport stream;
storing the doubly encrypted transport stream on a storage medium accessible to the at least one receiver.
5. The method of claim 1 , wherein at least one start code of the one or more start codes indicates a start of an element in an MPEG stream.
6. The method of claim 1 , wherein the transport stream is an encrypted transport stream.
7. A system comprising:
a subsystem, at a headend, implemented at least partially in hardware, that creates an event table for a corresponding transport stream, the event table comprising a location of one or more start codes within the transport stream;
a subsystem, implemented at least partially in hardware, that transmits the transport stream from the headend to at least one receiver among a plurality of receivers;
a subsystem, implemented at least partially in hardware, that transmits the event table from the headend to the at least one receiver among a plurality of receivers.
8. The system of claim 7 , wherein the event table further comprises a type of at least one start code of the one or more start codes.
9. The system of claim 7 , further comprising:
a subsystem, implemented at least partially in hardware, that encrypts the event table prior to transmission with the transport stream.
10. The system of claim 7 , wherein the transport stream is an encrypted transport stream, and further comprising:
a subsystem, implemented at least partially in hardware, that stores the encrypted transport stream transmitted at the at least one receiver; and
a subsystem, implemented at least partially in hardware, that encrypts, at the at least one receiver, the transport stream to obtain a doubly encrypted transport stream;
a subsystem, implemented at least partially in hardware, that stores the doubly encrypted transport stream on a storage medium accessible to the at least one receiver.
11. The system of claim 7 , wherein at least one start code of the one or more start codes indicates a start of an element in an MPEG stream.
12. The system of claim 7 , wherein the transport stream is an encrypted transport stream.
13. A non-transitory computer readable medium storing instructions which, when executed by one or more processors cause performance of steps comprising:
creating, at a headend, an event table for a corresponding transport stream, the event table comprising a location of one or more start codes within the transport stream;
transmitting the transport stream from the headend to at least one receiver among a plurality of receivers;
transmitting the event table from the headend to the at least one receiver among a plurality of receivers.
14. The computer readable medium of claim 13 , wherein the event table further comprises a type of at least one start code of the one or more start codes.
15. The computer readable medium of claim 13 , further comprising:
encrypting the event table prior to transmission with the transport stream.
16. The computer readable medium of claim 13 , wherein the transport stream is an encrypted transport stream, and further comprising:
storing the encrypted transport stream transmitted at the at least one receiver; and
encrypting, at the at least one receiver, the transport stream to obtain a doubly encrypted transport stream;
storing the doubly encrypted transport stream on a storage medium accessible to the at least one receiver.
17. The computer readable medium of claim 13 , wherein at least one start code of the one or more start codes indicates a start of an element in an MPEG stream.
18. The computer readable medium of claim 13 , wherein the transport stream is an encrypted transport stream.