Extension of Broadcasting Service by Using Electronic Tokens

In the current broadcasting system or Internet content distribution system, content providers distribute decoders (STB) that contain secret keys for content decryption, prior to content distribution. A content provider sends encrypted content to each user, who then decodes it with his or her STB. While users can get the services at their houses if they have an STB, it is hard for them to get the services outside their houses. A system that allowed users to carry around their secret keys would improve usability, but it would require countermeasures against secret key exposure. In this paper, we propose such an extended broadcasting system using tokens and group signature. The content providers can control the number of keys that users can use outside their houses. The system enables the broadcasters to minimize the damage caused by group signature key exposures and the user to get services outside his or her home.