Conditional access system
AssigneeScientific-Atlanta, Inc.
InventorsAnthony J. Wasilewski, Howard G. Pinder, Glendon L. Akins, III, Michael S. Palgon
Life of this patent
Estimating the term…
Abstract
A cable television system provides conditional access to services. The cable television system includes a headend from which service "instances", or programs, are broadcast and a plurality of set top units for receiving the instances and selectively decrypting the instances for display to system subscribers. The service instances are encrypted using public and/or private keys provided by service providers or central authorization agents. Keys used by the set tops for selective decryption may also be public or private in nature, and such keys may be reassigned at different times to provide a cable television system in which piracy concerns are minimized.
Claims46
A method of decrypting an instance of a service that has been encrypted with a short-term key, the method being carried out in a receiver that has a public key-private key pair and the method comprising the steps of:
- receiving a first message in the receiver whose contents include a long-term key, the contents having been encrypted using the public key for the receiver;
- using the private key to decrypt the contents;
- storing the long-term key;
- receiving a second message in the receiver together with the instance of the service, the second message including a key derivation value;
- using the key derivation value and the long-term key to obtain the short-term key;
- and
- using the short-term key to decrypt the instance of the service.
A method of enabling a receiver that has a public key to decrypt an instance of a service that has been encrypted with a short-term key, the method comprising the steps of:
- using the public key to encrypt contents of a first message, the contents including a long-term key;
- sending the first message to the receiver;
- sending a second message to the receiver together with the encrypted instance of the service, the second message including a key derivation value;
- and
- the receiver responding to the first message by decrypting the contents and storing the long-term key and responding to the second message by using the key derivation value and the long-term key to obtain the short-term key and using the short-term key to decrypt the instance of the service.
A receiver for receiving and decrypting an instance of a service that has been encrypted with a short-term key, the receiver having a public key, and the receiver comprising:
- a memory that contains the private key corresponding to the receiver's public key;
- a service decryptor that uses the short-term key to decrypt the instance of the service;
- a first message interpreter that responds to a first message received in the receiver, the first message's contents, including a long-term key, having been encrypted using the receiver's public key and the first message interpreter responding to the first message by decrypting the contents and storing the long-term key in the memory;
- and
- a second message interpreter that responds to a second message received in the receiver together with the instance of the service, the second message's contents including a key derivation value and the second message interpreter responding to the second message by using the key derivation value and the long-term key to obtain the short-term key and providing the short-term key to the service decryptor.
Dependencies are inferred from the claim text.