A position-aware Merkle tree for dynamic cloud data integrity verification

In the cloud storage framework, once clients remotely store their data on cloud storage providers, they will lose the physical control over their outsourced data. The risk of unauthorized access to the data increases dramatically. One of the most serious problems in cloud storage is to ensure the correctness of the outsourced data. Specifically, we need to protect these data from unauthorized operations; we also need to detect and recover users' data after unexpected changes. In this paper, we propose a publicly verifiable scheme to protect the integrity of cloud data and support dynamic maintenance, which is based on a position-aware Merkle tree. We adopt a 3-tuple to define the node of the new Merkle tree, which records the position of the corresponding node, so that users can verify the consistency of the challenge-response blocks by computing the root value directly without retrieving the whole Merkle tree. In our scheme, the storage complexity at the client side is O(1); the computation complexity at the client side is O(log n); the computation cost at the server side is O(log n) and the communication overhead is O(log n). Our method supports unlimited verification challenges as well.