Real-time Proof of Violation with Adaptive Huffman Coding Hash Tree for Cloud Storage Service

This paper proposes two adaptive Huffman coding hash tree algorithms to construct the hash tree of a file system. The algorithms are used to design the real-time proof of violation (PoV) scheme for the cloud storage service to achieve mutual non-repudiation between the user and the service provider. The PoV scheme can then generate cryptographic proofs once the service-level agreement (SLA) is violated. Based on adaptive Huffman coding, the proposed algorithms add hash tree nodes dynamically when a file is accessed for the first time. Every node keeps a count to reflect the frequency of occurrence of the associated file, and all nodes' counts and the tree structure are adjusted on-the-fly for every file access. This can significantly reduce the memory and computation overheads required by the PoV scheme. The file access patterns of the NCUCCWiki and the SNIA IOTTA datasets are used to evaluate the performance of the proposed algorithms. The algorithms are also compared with a related hash tree construction algorithm used in a PoV scheme, named ERA, to show their superiority in performance.