Encryption alone is not enough to protect data privacy, because access pattern leaks some sensitive information. Oblivious RAM (ORAM), the solution to this problem, is still far from practical deployment for heavy storage and communication/ computation overhead. To reduce them, an insightful idea was proposed to utilize non-colluding clouds to shift client computation and client-cloud communication to the clouds. The proposed multi-cloud ORAM achieved $O$O(1) client-cloud bandwidth cost and removed most of client computation. In this paper, we exploit “disconnected ORAM operation” and design “two-layer encryption” to further reduce these overheads. Experiments show that our proposed scheme, NewMCOS, significantly reduces evict cache size from GB/MB to KB level with about 2-3 times lower response time and 20 percent savings in bandwidth for clouds, compared to other schemes. Theoretically speaking, we reduce evict cache size from $O(\sqrt{N})$O(N) to $O(ZK)$O(ZK), where $N$N is the number of real data blocks, $K$K is the number of clouds ($22<K<<N), and $Z$Z is the number of real blocks uploaded from the client for eviction. By employing “lazy eviction operation”, the write frequency is reduced by $O(Z)$O(Z), the shuffling bandwidth cost is reduced by $\Omega (Z\; \log Z)$Ω(ZlogZ). Meanwhile, NewMCOS is proved to be secure.

中文翻译：

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NewMCOS：迈向实用的多云遗忘存储方案

仅靠加密不足以保护数据隐私，因为访问模式会泄露一些敏感信息。Oblivious RAM（ORAM），这个问题的解决方案，对于大量存储和通信/计算开销来说，离实际部署还很远。为了减少它们，提出了一个有见地的想法，即利用非共谋云将客户端计算和客户端-云通信转移到云上。提出的多云 ORAM 实现$O$哦(1) 客户端-云带宽成本并消除了大部分客户端计算。在本文中，我们利用“断开的 ORAM 操作”和设计“两层加密”以进一步减少这些开销。实验表明，与其他方案相比，我们提出的方案 NewMCOS 将 evict 缓存大小从 GB/MB 显着减少到 KB 级别，响应时间缩短约 2-3 倍，云带宽节省 20%。从理论上讲，我们将 evict 缓存大小从$O(\sqrt{N})$哦(N) 至 $O(ZK)$哦(Z钾)， 在哪里 $N$N 是真实数据块的数量， $K$钾 是云的数量（2 美元2<钾<<N）， 和 $Z$Z是从客户端上传的用于驱逐的实际块数。通过采用“懒惰驱逐操作”，写入频率降低了 $O(Z)$哦(Z)，洗牌带宽成本减少了 $\Omega (Z\; \log Z)$Ω(Z日志Z). 同时，NewMCOS被证明是安全的。