Cloud storage has been gaining popularity because its elasticity and pay-as-you-go manner. However, this new type of storage model also brings security challenges. This paper studies the problem of ensuring data integrity in cloud storage. In the Proof of Retrievability (PoR) model, after outsourcing the preprocessed data to the server, the client will delete its local copies and only store a small amount of meta data. Later the client will ask the server to provide a proof that its data can be retrieved correctly. However, most of the prior PoR works apply only to static data. The existing dynamic version of PoR scheme has an efficiency problem. In this paper, we extend the static PoR scheme to dynamic scenario. That is, the client can perform update operations, e.g., insertion, deletion and modification. After each update, the client can still detect the data losses even if the server tries to hide them. We develop a new version of authenticated data structure based on a B+ tree and a merkle hash tree. We call it Cloud Merkle B+ tree (CMBT). By combining the CMBT with the BLS signature, we propose a dynamic version of PoR scheme. Compared with the existing dynamic PoR scheme, our worst case communication complexity is O(logn) instead of O(n).
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机译：云存储因其弹性和即付即用方式而越来越受欢迎。但是，这种新型存储模型也带来了安全挑战。本文研究了确保云存储中数据完整性的问题。在可检索性（PoR）模型中，将预处理的数据外包给服务器后，客户端将删除其本地副本，仅存储少量的元数据。稍后，客户端将要求服务器提供可以正确检索其数据的证明。但是，大多数先前的PoR工作仅适用于静态数据。现有的动态版本的PoR方案存在效率问题。在本文中，我们将静态PoR方案扩展到动态方案。即，客户端可以执行更新操作，例如插入，删除和修改。每次更新后，即使服务器尝试隐藏数据丢失，客户端仍然可以检测到数据丢失。我们基于B +树和merkle哈希树开发了经过身份验证的数据结构的新版本。我们称其为Cloud Merkle B +树（CMBT）。通过结合CMBT和BLS签名，我们提出了PoR方案的动态版本。与现有的动态PoR方案相比，我们最差的通信复杂度是O（logn）而不是O（n）。
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