In this paper, we define and explore proofs of retrievability (PORs). A POR scheme enables an archive or back-up service (prover) to produce a concise proof that a user (verifier) can retrieve a target file F, that is, that the archive retains and reliably transmits file data sufficient for the user to recover F in its entirety.A POR may be viewed as a kind of cryptographic proof of knowledge (POK), but one specially designed to handle a large file (or bitstring) F. We explore POR protocols here in which the communication costs, number of memory accesses for the prover, and storage requirements of the user (verifier) are small parameters essentially independent of the length of F. In addition to proposing new, practical POR constructions, we explore implementation considerations and optimizations that bear on previously explored, related schemes.In a POR, unlike a POK, neither the prover nor the verifier need actually have knowledge of F. PORs give rise to a new and unusual security definition whose formulation is another contribution of our work.We view PORs as an important tool for semi-trusted online archives. Existing cryptographic techniques help users ensure the privacy and integrity of files they retrieve. It is also natural, however, for users to want to verify that archives do not delete or modify files prior to retrieval. The goal of a POR is to accomplish these checks without users having to download the files themselves. A POR can also provide quality-of-service guarantees, i.e., show that a file is retrievable within a certain time bound.

PORs: Proofs of Retrievability for Large Files

Remote data integrity checking (RDIC) enables a data storage server, say 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 most of 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. The proposed ID-based RDIC protocol leaks no information of the stored data 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 protocol is provably secure and practical in the real-world applications.

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Identity-Based Remote Data Integrity Checking With Perfect Data Privacy Preserving for Cloud Storage

With the rapid development of cloud computing, cloud storage has been accepted by an increasing number of organizations and individuals, therein serving as a convenient and on-demand outsourcing application However, upon losing local control of data, it becomes an urgent need for users to verify whether cloud service providers have stored their data securely Hence, many researchers have devoted themselves to the design of auditing protocols directed at outsourced data In this paper, we propose an efficient public auditing protocol with global and sampling blockless verification as well as batch auditing, where data dynamics are substantially more efficiently supported than is the case with the state of the art Note that, the novel dynamic structure in our protocol consists of a doubly linked info table and a location array  Moreover, with such a structure, computational and communication overheads can be reduced substantially Security analysis indicates that our protocol can achieve the desired properties Moreover, numerical analysis and real-world experimental results demonstrate that the proposed protocol achieves a given efficiency in practice

An Efficient Public Auditing Protocol With Novel Dynamic Structure for Cloud Data

Group data sharing in cloud environments has become a hot topic in recent decades. With the popularity of cloud computing, how to achieve secure and efficient data sharing in cloud environments is an urgent problem to be solved. In addition, how to achieve both anonymity and traceability is also a challenge in the cloud for data sharing. This paper focuses on enabling data sharing and storage for the same group in the cloud with high security and efficiency in an anonymous manner. By leveraging the key agreement and the group signature, a novel traceable group data sharing scheme is proposed to support anonymous multiple users in public clouds. On the one hand, group members can communicate anonymously with respect to the group signature, and the real identities of members can be traced if necessary. On the other hand, a common conference key is derived based on the key agreement to enable group members to share and store their data securely. Note that a symmetric balanced incomplete block design is utilized for key generation, which substantially reduces the burden on members to derive a common conference key. Both theoretical and experimental analyses demonstrate that the proposed scheme is secure and efficient for group data sharing in cloud computing.

Anonymous and Traceable Group Data Sharing in Cloud Computing

Enabling public auditing for shared data in cloud storage supporting identity privacy and traceability

Cloud storage auditing is viewed as an imperative service to corroborate the veracity of the data in public cloud. Existing auditing protocols are all based on the supposition that theClient’s secret key for auditing is completely protected. Such assumption may not always be held, due to the probably weak sense of security and/or low security settings at the client. In most of the current auditing protocols would inevitably become unable to work when a secret key for auditing is exposed. It is investigated on how to reduce the damage of the client’s key revelation in cloud storage auditing, and provide the first handy elucidation for this new problem setting. Formalized the definition and the security model of auditing protocol with key-exposure resilience and propose such a protocol. Utilized and developed a novel authenticator construction to support the forward security and the property of block less verifiability using the current design. The security proof and the performance analysis show that the projected protocol is protected and well-organized.

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P. Shiva Datta

Papers

Enabling Cloud Storage Auditing with Key Exposure Resistance