Network protocol for contents protection in digital cable broadcasting service and conditional access system using the protocol

A method for renewing conditional access client software (CACS) by a headend in a renewable conditional access system (RCAS), the method comprising:

• transmitting an RCAS announcement message for announcing that renewal of the CACS is required to a conditional access module (CAM) included in a digital cable broadcast receiver;
• receiving a key registration request message for requesting an authorization key for renewing the CACS from the digital cable broadcast receiver;
• generating the authorization key and security factors based on the key registration request message;
• and
• transmitting to the CAM a key registration response message including the authorization key and transmitting renewal information for downloading the CACS.

A digital cable broadcast receiver of a renewable conditional access system (RCAS), comprising:

• at least one memory;
• at least one processor;
• and
• a conditional access module (CAM),
• wherein the conditional access module
• receives an RCAS announcement message for announcing that renewal of conditional access client software (CACS) is required from a headend,
• transmits to the headend a key registration request message for requesting an authorization key for renewing the CACS when the RCAS announcement message is authenticated,
• receives a key registration response message including the authorization key from the headend, and
• generates security factors based on the authorization key and renewing the CACS by using the security factors.