Outsourcing scheme of ABE encryption secure against malicious adversary

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.