A Method to Prevent CW Sharing in DTV CAS

This paper discusses the security of Conditional Access System and proposed several attack methods. It analyzes fundamentals of CW sharing and points out the security hole during the communication between the IC and STB. It proposes several existent traditional solutions to the CW sharing. Because there are security problems or cost problems accompanied with the traditional solutions this paper proposes a new technical method to prevent the CW sharing with low cost and high security. The method is based on a practical authentication and key agreement algorithm. The communication between STB and smart card is encrypted by the agreement key to protect the CW, which prevented effectively CW sharing based on plaintext.