Privacy Preservation for Versatile Pay-TV Services

In pay-TV services, content is encrypted and transmitted to subscribers. Each subscriber has a security module that holds a decryption key(s) for the encrypted content. A set-top box or a smart card is often used as the security module. When a subscriber wants to obtain the same services outside the home, the subscriber has to bring the security module. However, even if the security module is a card, it is not easy to take it out because of the structure of TV sets and set-top boxes. As a way of improving current pay-TV services, Ogawa, Tamura, and Hanaoka (OTH17) proposed a system using an attribute-based encryption scheme (ABE). ABE is used to restrict the time and location at which a subscriber can obtain the service. However, OTH17 requires a third trusted party (TTP) for key and ciphertext generation; thus, the TTP knows the time and location of the subscriber. This means that the subscriber’s private information is disclosed to the party. Here, we propose a system that avoids disclosure of private data by adding a multi-party computation (MPC). In addition, MPC makes the TTP unnecessary.