The onerous media sharing task prompts resource-constrained media owners to seek help from a cloud platform, i.e., storing media contents in the cloud and letting the cloud do the sharing. There are three key security/privacy problems that need to be solved in the cloud media sharing scenario, including data privacy leakage and access control in the cloud, infringement on the owner's copyright, and infringement on the user's rights. In view of the fact that no single technique can solve the above three problems simultaneously, two cloud media sharing schemes are proposed in this paper, named FairCMS-I and FairCMS-II. By cleverly utilizing the proxy re-encryption technique and the asymmetric fingerprinting technique, FairCMS-I and FairCMS-II solve the above three problems with different privacy/efficiency trade-offs. Among them, FairCMS-I focuses more on cloud-side efficiency while FairCMS-II focuses more on the security of the media content, which provides owners with flexibility of choice. In addition, FairCMS-I and FairCMS-II also have advantages over existing cloud media sharing efforts in terms of optional IND-CPA (indistinguishability under chosen-plaintext attack) security and high cloud-side efficiency, as well as exemption from needing a trusted third party. Furthermore, FairCMS-I and FairCMS-II allow owners to reap significant local resource savings and thus can be seen as the privacy-preserving outsourcing of asymmetric fingerprinting. Finally, the feasibility and efficiency of FairCMS-I and FairCMS-II are demonstrated by experiments.

翻译：繁重的媒体共享任务促使资源受限的媒体所有者向云平台寻求帮助，即将媒体内容存储在云端并让云平台负责共享。在云媒体共享场景中，需要解决三个关键的安全/隐私问题，包括云中的数据隐私泄露与访问控制、对所有者版权的侵犯以及对用户权利的侵犯。鉴于没有任何单一技术能够同时解决上述三个问题，本文提出了两种云媒体共享方案，分别命名为FairCMS-I和FairCMS-II。通过巧妙利用代理重加密技术和非对称指纹技术，FairCMS-I和FairCMS-II以不同的隐私/效率权衡解决了上述三个问题。其中，FairCMS-I更侧重于云端效率，而FairCMS-II更侧重于媒体内容的安全性，为所有者提供了灵活性选择。此外，与现有的云媒体共享工作相比，FairCMS-I和FairCMS-II在可选的IND-CPA（选择明文攻击下的不可区分性）安全性、高云端效率以及无需可信第三方方面也具有优势。此外，FairCMS-I和FairCMS-II允许所有者大幅节省本地资源，因此可被视为非对称指纹技术的隐私保护外包。最后，通过实验验证了FairCMS-I和FairCMS-II的可行性和效率。