The wide adoption of cloud greatly facilitates the sharing of explosively generated media content today, yet deprives content providers' direct control over the outsourced media content. Thus, it is pivotal to build an encrypted cloud media center where only authorized access is allowed. Enforcing access control alone, however, cannot fully protect content providers' interests, as authorized users may later become traitors that illegally redistribute media content to the public. Such realistic threat should have been seriously treated yet is largely overlooked in the literature. In this paper, we initiate the first study on secure media sharing with fair traitor tracing in the encrypted cloud media center, through a new marriage of proxy re-encryption (for secure media sharing) and fair watermarking (for fair traitor tracing). Our key insight is to fully leverage the homomorphic properties residing in proxy re-encryption to embrace operations in fair watermarking. Two protocols are proposed for different application scenarios. We also provide complexity analysis for performance, showing that our work can also be treated as secure outsourcing of fair watermarking, and thus kills two birds with one stone. We thoroughly analyze the security strengths and conduct extensive experiments to validate the effectiveness of our design.

Magnetic Resonance Imaging (MRI) is a widely used technique to help form images of internal body structures for medical diagnosis. Recently, the Simultaneous Auto-calibrating and K-space Estimation (SAKE) becomes one of the most popular rapid imaging reconstruction methods to restore key information from scanned MRI data. This technique intrinsically requires a fair amount of high-resolution MRI data to accommodate the need of accurate diagnosis and imposes vast computational overhead onto resource-constrained clinics. To solve this problem, the practitioners start seeking the help of cloud computing platform to utilize its robust and economical computation power. However, the privacy concerns with outsourcing patients' private data to public cloud servers are ignited and hinder those practitioners from enjoying the benefits of cloud computing