Arisa Fujii

On the Theoretical Gap between Group Signatures with and without Unlinkability

We investigate a theoretical gap between unlinkability of group signature schemes and their other requirements, and show that this gap is significantly large. Specifically, we clarify that if unlinkability is achieved from any other property of group signature schemes, then it becomes possible to construct a chosen-ciphertext secure cryptosystem from any one-way function . This result implies that it would be possible to drastically improve efficiency of group signature schemes if unlinkability is not taken into account. We also demonstrate to construct a significantly more efficient scheme (without unlinkability) than the best known full-fledged scheme.

Anonymous authentication scheme for subscription services

In bidirectional broadcasting services via networks, all user operations and actions are controlled with the user ID and are recorded by the service providers. This means the users personal information such as his/her payment method and preferences is disclosed to the providers possibly against the users will. Hence, to preserve privacy, an anonymous authentication scheme for subscription services would seem to be in order. In this paper, we introduce a subscription service model and its system requirements for preserving privacy. Moreover, we propose an efficient group signature scheme having a property of linkability, which is useful for anonymous authentication and a preference subscription service. We show that our authentication scheme is efficient in terms of signature size and that it is suited to subscription services having many members.

Network Broadcasting System Using Viewer Information

With the rapid spread of broadband internet networks, broadcasting services on television using IP networks will soon become a reality. The broadcasting services on television using IP networks will be available, providing variable services in response to individual demands using personal data. We carried out a questionnaire survey, and compiled technological requirements for implementing such services. One of the requirements is that the viewers personal data should be kept secure, and another is that viewers should be able to set their own disclosure rules. We created an experimental broadcasting system that satisfies these requirements and evaluated the transaction speed of the system.

A New Method for Management of Consumers' Private Information on Bidirectional Broadcasting Services

This paper proposes a new method for management of consumers private information on bidirectional broadcasting services using IP networks, based on secure distributed RDB (relational database). We also propose a new protocol for browsing user information that was registered in the database from user terminals securely. We compared the processing times to browse user information between the existing usual encryption method and the proposed method. As a result, we can confirm that the latter method is as practical as the former one.

Identified-Service Support System and Its Application to Network Broadcasting Services

Individualization of network services will be a key factor attracting users because customer satisfaction with identified services such as location-specific and time-specific news could increased by collecting and analyzing user information. Balancing the trade-off between privacy and individualization, however, will require the use of technical mechanisms we call identified-service support systems (ISSS). Here we describe the basic concept of an ISSS and describe its technical requirements. We propose an ISSS architecture combining user-information analysis for individualization, access control for privacy protection, shuffling data management for preventing the leakage of personal information, and digital signatures for authenticating the integrity of partially disclosed documents. We also describe the protocols, GUIs, and data management implementations of a prototype ISSS developed for personalized broadcasting services. An ISSS could protect user privacy against inside attacks as well as third-party attacks and could support various kinds of identified services.