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

Provable Data Possession (PDP) model provides an efficient means for people to audit the integrity of data stored in cloud storage. When sensitive data is shared among multiple users based on cloud storage, it is critical to preserve the anonymity of the data uploader against the auditor. That is, the auditor should not get data uploader’s identity through the data audition. To address this problem, many PDP schemes with user identity privacy-persevering are proposed. However, most proposed schemes are designed based on PKI technique which suffers from big burden of certificate management. Moreover, data auditors in most proposed schemes bear heavy computation cost which results to the lower efficiency of the scheme. To overcome the shortcomings, we present a novel identity-based PDP protocol to audit efficiently the integrity of group shared data with uploader’s privacy-preserving. Due to the inherent structural advantage of identity-based crypto mechanism, our PDP scheme is able to avoid the problem of certificate management. Different from previous works, our scheme ensures the relationship of the data and the data uploader in the phase of proof generation not the phase of integrity audition. Therefore, the data auditor does not know the relationship at all as well as the extract data uploader of the challenged data. At the same time, establishing the relationship by cloud server in proof generation step can reduce the computational cost of data auditor greatly. Furthermore, the relationship of data uploader and challenged data in the proof is randomized so as to strength the security of the scheme. All these efforts are made in our scheme to efficiently realize the anonymity protection of the data uploader. We give the detailed security proof of our scheme under the computational Diffie-Hellman assumption. Many experiments are performed to evaluate the efficiency of our scheme, the results show that our new scheme is efficient and feasible.

/pdf/efficient-identity-based-public-integrity-auditing-of-shared-4xrbi6ja0g.pdf

Efficient Identity-Based Public Integrity Auditing of Shared Data in Cloud Storage With User Privacy Preserving

Cloud auditing is one of the important processes to ensure the security and integrity of data in cloud storage. Implementing cloud auditing requires various cryptographic tools such as identity-based cryptography and its variant: certificateless cryptography which solves the inherent key escrow problem in identity-based cryptography. Applying certificateless cryptography to cloud auditing has shown many merits. However, in a multi-user setting, certificateless cloud auditing (CLCA) schemes require additional security requirements. For instance, the identity privacy becomes an important issue that should be taken into consideration in some applications. In this paper, we concentrate on the identity privacy of CLCA schemes. We define the security models of privacy-preserving CLCA schemes, namely the uncheatability and anonymity and propose an efficient CLCA scheme, which is secure in the security models. As a feature of our scheme, the tag of a message is compact, which consists of only one group element. The uncheatability is based on variants of bilinear Diffie–Hellman assumption in the random oracle model. The identity privacy of the user is information-theoretically guaranteed against the third party auditor.

Privacy-Preserving Certificateless Cloud Auditing with Multiple Users

Cloud computing is a burgeoning paradigm that offers reliable and adaptive infrastructure to the data owner who shares his data with the data user through the cloud server. In the data sharing process, the integrity of the data stored in the cloud faces serious threats. The provable data possession schemes ensure that a cloud server provider proves to a third party auditor that it is truthfully storing data from the data owner. However, the PKI-based provable data possession scheme suffers the management issue of the certificates and the identity-based provable data possession scheme causes an inherent key escrow problem. In this paper, we put forward an efficient privacy-preserving certificateless provable data possession scheme based on certificateless cryptography and elliptic curve cryptography, which has been proved to be unforgeable against adaptive chosen message attacks in the random oracle model. At the same time, the data integrity can be audited by the third party auditor without downloading the whole data. The proposed scheme gives away no information of the stored data to the third party auditor during the audit phase and the data owner's identity privacy is protected. The experiment results show that the proposed scheme is of efficiency and feasibility as far as computation and communication costs are concerned.

/pdf/efficient-privacy-preserving-certificateless-provable-data-5bh4k4jybn.pdf

Efficient Privacy-Preserving Certificateless Provable Data Possession Scheme for Cloud Storage

Cloud computing is a fast-growing technology which supplies scalable, innovative, and efficient business models. However, cloud computing is not fully trusted, and the security of the data outsourced in cloud storage needs to be guaranteed. One of the hottest issues is how to ensure the integrity of the data in cloud storage. Until now, many researchers have proposed lots of provable data possession (PDP) schemes to deal with the problem of data integrity audition. Nevertheless, very little effort has been devoted to preserve the data uploader’s privacy while auditing the integrity of data shared in a group. To overcome the shortcoming, we propose a novel certificateless PDP protocol to efficiently audit the integrity of data shared in a workgroup with user privacy preserving. Due to the inherent structural advantage of the certificateless crypto mechanism, our PDP scheme eliminates the key escrow problem and the certificate management problem simultaneously. Moreover, the audition process in our scheme does not need any user’s identity which helps to keep the anonymity of data uploader. We give for our scheme a detailed security proof and efficiency analysis. Experiment results of performance evaluation demonstrate that our new scheme is very efficient and feasible.

/pdf/efficient-privacy-preserving-certificateless-public-auditing-gunhq41t9h.pdf

Efficient Privacy-Preserving Certificateless Public Auditing of Data in Cloud Storage

Provable Data Possession (PDP) protocol makes it possible for cloud users to check whether the cloud servers possess their original data without downloading all the data. However, most of the existing PDP schemes are based on either public key infrastructure (PKI) or identity-based cryptography, which will suffer from issues of expensive certificate management or key escrow. In this paper, we propose a new construction of certificateless provable group shared data possession (CL-PGSDP) protocol by making use of certificateless cryptography, which will eliminate the above issues. Meanwhile, by taking advantage of zero-knowledge protocol and randomization method, the proposed CL-PGSDP protocol leaks no information of the stored data and the group user’s identity to the verifiers during the verifying process, which is of the property of comprehensive privacy preservation. In addition, our protocol also supports efficient user revocation from the group. Security analysis and experimental evaluation indicate that our CL-PGSDP protocol provides strong security with desirable efficiency.

/pdf/certificateless-provable-group-shared-data-possession-with-2fu5mg9q6r.pdf

Wenfeng Shen

Papers

Certificateless Provable Group Shared Data Possession with Comprehensive Privacy Preservation for Cloud Storage