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

Mobile Edge Computing, Fog et al.: A Survey and Analysis of Security Threats and Challenges

This paper shows a generic and simple conversion from weak asymmetric and symmetric encryption schemes into an asymmetric encryption scheme which is secure in a very strong sense- indistinguishability against adaptive chosen-ciphertext attacks in the random oracle model. In particular, this conversion can be applied efficiently to an asymmetric encryption scheme that provides a large enough coin space and, for every message, many enough variants of the encryption, like the ElGamal encryption scheme.

Secure integration of asymmetric and symmetric encryption schemes

With cloud storage services, it is commonplace for data to be not only stored in the cloud, but also shared across multiple users. However, public auditing for such shared data --- while preserving identity privacy --- remains to be an open challenge. In this paper, we propose the first privacy-preserving mechanism that allows public auditing on shared data stored in the cloud. In particular, we exploit ring signatures to compute the verification information needed to audit the integrity of shared data. With our mechanism, the identity of the signer on each block in shared data is kept private from a third party auditor (TPA), who is still able to verify the integrity of shared data without retrieving the entire file. Our experimental results demonstrate the effectiveness and efficiency of our proposed mechanism when auditing shared data.

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Oruta: Privacy-Preserving Public Auditing for Shared Data in the Cloud

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VABKS: Verifiable attribute-based keyword search over outsourced encrypted data

Cloud computing is getting increasingly popular, but has yet to be widely adopted arguably because there are many security and privacy problems that have not been adequately addressed. A specific problem encountered in the context of cloud storage, where clients outsource their data (files) to untrusted cloud storage servers, is to convince the clients that their data are kept intact at the storage servers. An important approach to achieve this goal is called Proof of Retrievability (POR), by which a storage server can convince a client --- via a concise proof --- that its data can be recovered. However, existing POR solutions can only deal with static data (i.e., data items must be fixed), and actually are not secure when used to deal with dynamic data (i.e., data items need be inserted, deleted, and modified). Motivated by the need to securely deal with dynamic data, we propose the first dynamic POR scheme for this purpose. Moreover, we introduce a new property, called fairness, which is necessary and also inherent to the setting of dynamic data because, without ensuring it, a dishonest client could legitimately accuse an honest cloud storage server of manipulating its data. Our solution is based on two new tools, one is an authenticated data structure we call range-based 2-3 trees (rb23Tree for short), and the other is an incremental signature scheme we call hash-compress-and-sign (HCS for short). These tools might be of independent value as well.

Fair and dynamic proofs of retrievability

Both security and efficiency are crucial to the success of cloud storage. So far, security and efficiency of cloud storage have been separately investigated as follows: On one hand, security notions such as Proof of Data Possession (PDP) and Proof of Retrievability (POR) have been introduced for detecting that the data stored in the cloud has been tampered with. On the other hand, the notion of Proof of Ownership (POW) has also been proposed to alleviate the cloud server from storing multiple copies of the same data, which could substantially reduce the consumption of both network bandwidth and server storage space. These two aspects are seemingly quite to the opposite of each other. In this paper, we show, somewhat surprisingly, that the two aspects can actually co-exist within the same framework. This is possible fundamentally because of the following insight: The public verifiability offered by PDP/POR schemes can be naturally exploited to achieve POW. This "one stone, two birds" phenomenon not only inspired us to propose the novel notion of Proof of Storage with Deduplication (POSD), but also guided us to design a concrete scheme that is provably secure in the Random Oracle model based on the Computational Diffie-Hellman (CDH) assumption.

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Secure and efficient proof of storage with deduplication

Named data networking (NDN) is a new paradigm for the future Internet wherein interest and data packets carry content names rather than the current IP paradigm of source and destination addresses. Security is built into NDN by embedding a public key signature in each data packet to enable verification of authenticity and integrity of the content. However, existing heavyweight signature generation and verification algorithms prevent universal integrity verification among NDN nodes, which may result in content pollution and denial of service attacks. Furthermore, caching and location-independent content access disables the capability of a content provider to control content access, e.g., who can cache a content and which end user or device can access it. We propose a lightweight integrity verification (LIVE) architecture, an extension to the NDN protocol, to address these two issues seamlessly. LIVE enables universal content signature verification in NDN with lightweight signature generation and verification algorithms. Furthermore, it allows a content provider to control content access in NDN nodes by selectively distributing integrity verification tokens to authorized nodes. We evaluate the effectiveness of LIVE with open source CCNx project. Our paper shows that LIVE only incurs average 10% delay in accessing contents. Compared with traditional public key signature schemes, the verification delay is reduced by over 20 times in LIVE.

LIVE: Lightweight Integrity Verification and Content Access Control for Named Data Networking

It is common nowadays for data owners to outsource their data to the cloud. Since the cloud cannot be fully trusted, the outsourced data should be encrypted. This however brings a range of problems, such as: How should a data owner grant search capabilities to the data users? How can the authorized data users search over a data owner's outsourced encrypted data? How can the data users be assured that the cloud faithfully executed the search operations on their behalf? Motivated by these questions, we propose a novel cryptographic solution, called verifiable attribute-based keyword search (VABKS). The solution allows a data user, whose credentials satisfy a data owner's access control policy, to (i) search over the data owner's outsourced encrypted data, (ii) outsource the tedious search operations to the cloud, and (iii) verify whether the cloud has faithfully executed the search operations. We formally define the security requirements of VA B K S and describe a construction that satisfies them. Performance evaluation shows that the proposed schemes are practical and deployable.

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Qingji Zheng

Papers

VABKS: Verifiable attribute-based keyword search over outsourced encrypted data

Fair and dynamic proofs of retrievability

Secure and efficient proof of storage with deduplication

LIVE: Lightweight Integrity Verification and Content Access Control for Named Data Networking

VABKS: Verifiable Attribute-based Keyword Search over Outsourced Encrypted Data.