Content providers increasingly utilise Content Delivery Networks (CDNs) to enhance users' content download experience. However, this deployment scenario raises significant security concerns regarding content confidentiality and user privacy due to the involvement of third-party providers. Prior proposals using private information retrieval (PIR) and oblivious RAM (ORAM) have proven impractical due to high computation and communication costs, as well as integration challenges within distributed CDN architectures. In response, we present \textsf{OblivCDN}, a practical privacy-preserving system meticulously designed for seamless integration with the existing real-world Internet-CDN infrastructure. Our design strategically adapts Range ORAM primitives to optimise memory and disk seeks when accessing contiguous blocks of CDN content, both at the origin and edge servers, while preserving both content confidentiality and user access pattern hiding features. Also, we carefully customise several oblivious building blocks that integrate the distributed trust model into the ORAM client, thereby eliminating the computational bottleneck in the origin server and reducing communication costs between the origin server and edge servers. Moreover, the newly-designed ORAM client also eliminates the need for trusted hardware on edge servers, and thus significantly ameliorates the compatibility towards networks with massive legacy devices.In real-world streaming evaluations, OblivCDN} demonstrates remarkable performance, downloading a $256$ MB video in just $5.6$ seconds. This achievement represents a speedup of $90\times$ compared to a strawman approach (direct ORAM adoption) and a $366\times$ improvement over the prior art, OblivP2P.

翻译：内容提供商日益广泛地利用内容分发网络（CDN）来提升用户的内容下载体验。然而，由于第三方提供商的介入，这种部署场景引发了关于内容机密性和用户隐私的重大安全担忧。先前基于私有信息检索（PIR）和不经意随机存取存储器（ORAM）的方案，因其高昂的计算与通信开销以及在分布式CDN架构中的集成挑战，已被证明不切实际。为此，我们提出了 \textsf{OblivCDN}，这是一个实用的隐私保护系统，经过精心设计，可与现有的现实世界互联网-CDN基础设施实现无缝集成。我们的设计策略性地采用了范围ORAM原语，以优化在访问CDN连续内容块时（无论是在源服务器还是边缘服务器）的内存和磁盘寻道操作，同时保持内容机密性和用户访问模式隐藏特性。此外，我们精心定制了若干不经意构建模块，将分布式信任模型集成到ORAM客户端中，从而消除了源服务器的计算瓶颈，并降低了源服务器与边缘服务器之间的通信开销。而且，新设计的ORAM客户端还消除了在边缘服务器上使用可信硬件的需求，从而显著提升了对拥有大量遗留设备网络的兼容性。在实际流媒体评估中，OblivCDN 展现了卓越的性能，仅用 $5.6$ 秒即可下载一个 $256$ MB 的视频。这一成果相较于直接采用ORAM的简单方案（strawman approach）实现了 $90\times$ 的加速，相较于现有技术 OblivP2P 则实现了 $366\times$ 的提升。