Method for downloading conditional access system for digital broadcasting

A method of downloading a conditional access system (CAS) for digital broadcasting in a digital broadcasting system comprising a broadcasting system as a transmitter, which includes a DCAS authentication proxy (AP), a personalization server, a DCAS provisioning server, and a head-end, and a set-top box as a receiver, which includes a DCAS host, the method comprising:

• (A) mutual authentication between the DCAS AP and the DCAS host and key distribution comprising a step of generating a shared key from a license number inputted to the set-top box, a step in which the DCAS AP and the DCAS host mutually authenticate each other using the shared key, and a step in which the DCAS AP generates a temporary key (TK) and distributes the TK to the DCAS host and the personalization server upon completion of the mutual authentication;
• (B) mutual authentication between the personalization server and the DCAS host and key distribution comprising a step in which the personalization server and the DCAS host mutually authenticate each other using the TK and a step in which the personalization server generates a session key (SK) and distributes the SK to the DCAS host and the DCAS provisioning server upon completion of the mutual authentication;
• and
• (C) mutual authentication between the DCAS provisioning server and the DCAS host and key distribution comprising a step in which the DCAS provisioning server encrypts CAS software by using the SK and transmits the encrypted CAS software to the DCAS host and a step in which the DCAS host decrypts the encrypted CAS software by using the SK and installs the CAS software.