We present a Dynamic Provable Data Possession (PDP) system with Public Verifiability and Data Privacy. Three entities are involved: a client who is the owner of the data to be stored, a server that stores the data and a Third Party Auditor (TPA) who may be required when the client wants to check the integrity of its data stored on the server. The system is publicly verifiable with the possible help of the TPA who acts on behalf of the client. The system exhibits data dynamicity at block level allowing data insertion, deletion and modification to be performed. Finally, the system is secure at the untrusted server and data private. We present a practical PDP system by adopting asymmetric pairings to gain efficiency and reduce the group exponentiation and pairing operations. In our scheme, no exponentiation and only three pairings are required during the proof of data possession check, which clearly outperforms all the existing schemes in the literature. Furthermore, our protocol supports proof of data possession on as many data blocks as possible at no extra cost. Abstract. We present a Dynamic Provable Data Possession (PDP) system with Public Verifiability and Data Privacy. Three entities are involved: a client who is the owner of the data to be stored, a server that stores the data and a Third Party Auditor (TPA) who may be required when the client wants to check the integrity of its data stored on the server. The system is publicly verifiable with the possible help of the TPA who acts on behalf of the client. The system exhibits data dynamicity at block level allowing data insertion, deletion and modification to be performed. Finally, the system is secure at the untrusted server and data private. We present a practical PDP system by adopting asymmetric pairings to gain efficiency and reduce the group exponentiation and pairing operations. In our scheme, no exponentiation and only three pairings are required during the proof of data possession check, which clearly outperforms all the existing schemes in the literature. Furthermore, our protocol supports proof of data possession on as many data blocks as possible at no extra cost.

Blockchain is the revolutionary invention of the twentieth century that offers a distributed and decentralized setting to communicate among nodes in a list of networks without a central authority. On the other hand, an electronic health records (EHRs) is the electronically stored health information in a digital format.EHRs are normally shared among healthcare stakeholders and facing power failure, data misuse, lack of privacy and security, and audit trail. Blockchain is a leading technology among others to address the limitations related to EHRs. It can provide a safer and secured decentralized environment for exchanging EHRs data. There are three categories of blockchain-based potential solutions have been proposed to handle EHRs: conceptual, prototype, and implemented. This study focused on a Systematic Literature Review (SLR) to find and analyze articles proposed either conceptual or implemented to manage EHRs using blockchain. The study analyzed 99 papers that were described from various publication categories. The deep technical analysis focused on evaluating articles based on privacy, security, scalability, accessibility, cost, consensus algorithms, and type of blockchain used. The SLR found that the blockchain technology is promising to provide decentralization, security, and privacy that traditional EHRs often lack. Moreover, results obtained from the detailed studies would provide potential researchers with a reference as to which type of blockchain to choose for future development. Finally, future research directions, in the end, would direct enthusiasm to combine new blockchain-based systems to properly manage EHRs.

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.Correctness. We require that a DPDP with PV and DP is correct if for (pk, sk) ← KeyGen(λ), T m ← TagGen(pk, sk, m), (F ′ , E ′ , ν ′ ) ← PerfOp (pk, F, E, inf o), ν ← GenProof(pk, F, chal, Σ), then 1 ← CheckOp(pk, ν ′ ) and 1 ← CheckProof (pk, chal, ν). N.B. The set of ranks is [1, n] at the first upload; it then becomes (0, n + 1) ∩ Q after operations as in the construction in [12]. Security and Privacy ModelsSecurity Model against the Server This model against the server is given in [12], and follows the one proposed in [1,7].We consider a DPDP with PV and DP as defined above. Let a data possession game between a challenger B and an adversary A (acting as the server) be as follows: ⋄ Setup. B runs (pk, sk) ← KeyGen(λ) such that pk is given to A while sk is kept secret. ⋄ Adaptive Queries. First, A is given access to a tag generation oracle O T G . A chooses blocks m i and gives them to B, for i ∈ [1, n]. B runs TagGen(pk, sk, m i ) → T m i and gives them to

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