Keyword-Based Delegable Proofs of Storage

Cloud users (clients) with limited storage capacity at their end can outsource bulk data to the cloud storage server. A client can later access her data by downloading the required data files. However, a large fraction of the data files the client outsources to the server is often archival in nature that the client uses for backup purposes and accesses less frequently. An untrusted server can thus delete some of these archival data files in order to save some space (and allocate the same to other clients) without being detected by the client (data owner). Proofs of storage enable the client to audit her data files uploaded to the server in order to ensure the integrity of those files. In this work, we introduce one type of (selective) proofs of storage that we call keyword-based delegable proofs of storage, where the client wants to audit all her data files containing a specific keyword (e.g., "important"). Moreover, it satisfies the notion of public verifiability where the client can delegate the auditing task to a third-party auditor who audits the set of files corresponding to the keyword on behalf of the client. We formally define the security of a keyword-based delegable proof-of-storage protocol. We construct such a protocol based on an existing proof-of-storage scheme and analyze the security of our protocol. We argue that the techniques we use can be applied atop any existing publicly verifiable proof-of-storage scheme for static data. Finally, we discuss the efficiency of our construction.Comment: A preliminary version of this work has been published in International Conference on Information Security Practice and Experience (ISPEC 2018

Dynamic Provable Data Possession Protocols with Public Verifiability and Data Privacy

Cloud storage services have become accessible and used by everyone. Nevertheless, stored data are dependable on the behavior of the cloud servers, and losses and damages often occur. One solution is to regularly audit the cloud servers in order to check the integrity of the stored data. The Dynamic Provable Data Possession scheme with Public Verifiability and Data Privacy presented in ACISP'15 is a straightforward design of such solution. However, this scheme is threatened by several attacks. In this paper, we carefully recall the definition of this scheme as well as explain how its security is dramatically menaced. Moreover, we proposed two new constructions for Dynamic Provable Data Possession scheme with Public Verifiability and Data Privacy based on the scheme presented in ACISP'15, one using Index Hash Tables and one based on Merkle Hash Trees. We show that the two schemes are secure and privacy-preserving in the random oracle model.Comment: ISPEC 201

Cloud Data Auditing Using Proofs of Retrievability

Cloud servers offer data outsourcing facility to their clients. A client outsources her data without having any copy at her end. Therefore, she needs a guarantee that her data are not modified by the server which may be malicious. Data auditing is performed on the outsourced data to resolve this issue. Moreover, the client may want all her data to be stored untampered. In this chapter, we describe proofs of retrievability (POR) that convince the client about the integrity of all her data.Comment: A version has been published as a book chapter in Guide to Security Assurance for Cloud Computing (Springer International Publishing Switzerland 2015

Smarter Data Availability Checks in the Cloud: Proof of Storage via Blockchain

Cloud computing offers clients flexible and cost-effective resources. Nevertheless, past incidents indicate that the cloud may misbehave by exposing or tampering with clients' data. Therefore, it is vital for clients to protect the confidentiality and integrity of their outsourced data. To address these issues, researchers proposed cryptographic protocols called “proof of storage” that let a client efficiently verify the integrity or availability of its data stored in a remote cloud server. However, in these schemes, the client either has to be online to perform the verification itself or has to delegate the verification to a fully trusted auditor. In this chapter, a new scheme is proposed that lets the client distribute its data replicas among multiple cloud servers to achieve high availability without the need for the client to be online for the verification and without a trusted auditor's involvement. The new scheme is mainly based on blockchain smart contracts. It illustrates how a combination of cloud computing and blockchain technology can resolve real-world problems

Identity-based remote data integrity checking with perfect data privacy preserving for cloud storage

This is the author accepted manuscript. The final version is available from the publisher via the DOI in this record.Remote data integrity checking (RDIC) enables a data storage server, such as a cloud server, to prove to a verifier that it is actually storing a data owner’s data honestly. To date, a number of RDIC protocols have been proposed in the literature, but almost all the constructions suffer from the issue of a complex key management, that is, they rely on the expensive public key infrastructure (PKI), which might hinder the deployment of RDIC in practice. In this paper, we propose a new construction of identity-based (ID-based) RDIC protocol by making use of key-homomorphic cryptographic primitive to reduce the system complexity and the cost for establishing and managing the public key authentication framework in PKI based RDIC schemes. We formalize ID-based RDIC and its security model including security against a malicious cloud server and zero knowledge privacy against a third party verifier. We then provide a concrete construction of ID-based RDIC scheme which leaks no information of the stored files to the verifier during the RDIC process. The new construction is proven secure against the malicious server in the generic group model and achieves zero knowledge privacy against a verifier. Extensive security analysis and implementation results demonstrate that the proposed new protocol is provably secure and practical in the real-world applications.This work is supported by the National Natural Science Foundation of China (61501333,61300213,61272436,61472083), Fok Ying Tung Education Foundation (141065), Program for New Century Excellent Talents in Fujian University (JA1406

Public cloud data auditing with practical key update and zero knowledge privacy

Data integrity is extremely important for cloud based storage services, where cloud users no longer have physical possession of their outsourced files. A number of data auditing mechanisms have been proposed to solve this problem. However, how to update a cloud user\u27s private auditing key (as well as the authenticators those keys are associated with) without the user\u27s re-possession of the data remains an open problem. In this paper, we propose a key-updating and authenticator-evolving mechanism with zero-knowledge privacy of the stored files for secure cloud data auditing, which incorporates zero knowledge proof systems, proxy re-signatures and homomorphic linear authenticators. We instantiate our proposal with the state-of-the-art Shacham-Waters auditing scheme. When the cloud user needs to update his key, instead of downloading the entire file and re-generating all the authenticators, the user can just download and update the authenticators. This approach dramatically reduces the communication and computation cost while maintaining the desirable security. We formalize the security model of zero knowledge data privacy for auditing schemes in the key-updating context and prove the soundness and zero-knowledge privacy of the proposed construction. Finally, we analyze the complexity of communication, computation and storage costs of the improved protocol which demonstrates the practicality of the proposal

Efficient Method Based on Blockchain Ensuring Data Integrity Auditing with Deduplication in Cloud

With the rapid development of cloud storage, more and more cloud clients can store and access their data anytime, from anywhere and using any device. Data deduplication may be considered an excellent choice to ensure data storage efficiency. Although cloud technology offers many advantages for storage service, it also introduces security challenges, especially with regards to data integrity, which is one of the most critical elements in any system. A data owner should thus enable data integrity auditing mechanisms. Much research has recently been undertaken to deal with these issues. In this paper, we propose a novel blockchain-based method, which can preserve cloud data integrity checking with data deduplication. In our method, a mediator performs data deduplication on the client side, which permits a reduction in the amount of outsourced data and a decrease in the computation time and the bandwidth used between the enterprise and the cloud service provider. This method supports private and public auditability. Our method also ensures the confidentiality of a client's data against auditors during the auditing process

Multi-instance publicly verifiable time-lock puzzle and its applications

Time-lock puzzles are elegant protocols that enable a party to lock a message such that no one else can unlock it until a certain time elapses. Nevertheless, existing schemes are not suitable for the case where a server is given multiple instances of a puzzle scheme at once and it must unlock them at different points in time. If the schemes are naively used in this setting, then the server has to start solving all puzzles as soon as it receives them, that ultimately imposes significant computation cost and demands a high level of parallelisation. We put forth and formally define a primitive called “multi-instance time-lock puzzle” which allows composing a puzzle’s instances. We propose a candidate construction: “chained time-lock puzzle” (C-TLP). It allows the server, given instances’ composition, to solve puzzles sequentially, without having to run parallel computations on them. C-TLP makes black-box use of a standard time-lock puzzle scheme and is accompanied by a lightweight publicly verifiable algorithm. It is the first time-lock puzzle that offers a combination of the above features. We use C-TLP to build the first “outsourced proofs of retrievability” that can support real-time detection and fair payment while having lower overhead than the state of the art. As another application of C-TLP, we illustrate in certain cases, one can substitute a “verifiabledelay function” with C-TLP, to gain much better efficiency

Blockchain & Multi-Agent System: A New Promising Approach for Cloud Data Integrity Auditing with Deduplication

Recently, data storage represents one of the most important services in Cloud Computing. The cloud provider should ensure two major requirements which are data integrity and storage efficiency. Blockchain data structure and the efficient data deduplication represent possible solutions to address these exigencies. Several approaches have been proposed, some of them implement deduplication in Cloud server side, which involves a lot of computation to eliminate the redundant data and it becomes more and more complex. Therefore, this paper proposed an efficient, reliable and secure approach, in which the authors propose a Multi-Agent System in order to manipulate deduplication technique that permits to reduce data volumes thereby reduce storage overhead. On the other side, the loss of physical control over data introduces security challenges such as data loss, data tampering and data modification. To solve similar problems, the authors also propose Blockchain as a database for storing metadata of client files. This database serves as logging database that ensures data integrity auditing function