Personal data stores (PDSs) are gaining attention as an alternative to the current systems used by tech giants to manage users' data. PDSs centrally manage user logs and data across services and enable data to be passed on to service providers in accordance with the user's own intentions. Using cloud servers to manage personal information is a natural choice from the perspectives of convenience and cost. Therefore, security is highly important in the PDS model. However, to the best of our knowledge, not enough research on encrypting PDS data has been conducted. This is because merely using conventional encryption schemes could compromise the functionality of PDSs. In this study, we developed a key-aggregate identity-based proxy re-encryption (KA-IB-PRE) scheme combining a key-aggregate cryptosystem technique with an identity-based proxy re-encryption scheme. Our approach is highly compatible with PDSs, and a system using KA-IB-PRE called EncPDS can construct a privacy-preserving model that meets their requirements. In particular, it offers advantages in privacy protection compared with existing methods, allowing for selective re-encryption of any data through key aggregation while keeping information about which data to re-encrypt hidden from the cloud.

Subtitles and closed captions, which are prepared for hearing-impaired users, are now widely used by users without hearing concerns. In this paper, we focus on the adaptation of subtitles and captions for non-hearing-impaired users, particularly the adaptation of the kanji ruby. From our experiments on non-hearing-impaired adults, Welch’s t-test was used to clarify whether listening to audio with the same content affects the necessity of kanji ruby. In addition, we proposed and evaluated an adaptive model to predict whether ruby should be added to kanji captions based on the experimental results. The experimental results suggest that not only the difficulty of the kanji and the user’s kanji ability, but also the content of the audio is important for the optimization of kanji ruby.

Integrated broadcast-broadband services allow viewers to simultaneously receive broadcast content over the airwaves and additional information related to the content over the Internet. This integration provides opportunities for new services to be tailored and offered to individual viewers. Viewing histories provide a rich variety of data for service providers to learn the preferences of individual viewers and fine-tune their offerings. Each person’s viewing history, however, is privacy-sensitive data and may reveal information that the viewer does not want revealed. In this paper, we propose a system that allows viewers to specify a policy that they would like to be applied to their viewing history, when shared with service providers, by using attribute-based encryption (ABE). A ciphertext is associated with a policy, and it can be decrypted only by service providers who conform to the policy. To reduce the computations of the user terminal, we develop a system with provable security that allows the encryption to be outsourced to a cloud server, without the need to trust the cloud server. To the best of our knowledge, our construction gives the first outsourcing scheme of ABE encryption that is secure against a malicious cloud server. Although our solution is described for integrated broadcast-broadband services, the architecture and results could also be used for sharing viewing histories of OTT (Over-The-Top) services such as Netflix and location histories of mobile services. We implemented our scheme and showed that it significantly reduces the computation cost of a user terminal: about one third that of the Waters’ ABE scheme.

Integrated broadcast-broadband services allow viewers to simultaneously receive broadcast content over the airwaves and additional information related to the content over the Internet. This integration provides opportunities for new services to be tailored and offered to individual viewers. Viewing histories provide a rich variety of data for service providers to learn the preferences of individual viewers and fine-tune their offerings. Each person's viewing history, however, is privacy-sensitive data and may reveal information that the viewer does not want revealed. In this paper, we propose a system that allows viewers to specify a policy that they would like to be applied to their viewing history, when shared with service providers, by using attribute-based encryption (ABE). A ciphertext is associated with a policy, and it can be decrypted only by service providers who conform to the policy. To reduce the computations of the user terminal, we develop a system with provable security that allows the encryption to be outsourced to a cloud server, without the need to trust the cloud server. Although our solution is described for integrated broadcast-broadband services, the architecture and results could also be used for sharing viewing histories of services such as Netflix. We implemented our scheme and showed that it significantly reduces the computation cost of a user terminal.

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 viewer's 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.

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.