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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When, in 2008, Satoshi Nakamoto envisioned the first distributed database management system that relied on cryptographically secured chain of blocks to store data in an immutable and tamper-resistant manner, his primary use case was the introduction of a digital currency. Owing to this use case, the blockchain system was geared towards efficient storage of data, whereas the processing of complex queries, such as provenance analyses of data history, is out of focus. The increasing use of Internet of Things technologies and the resulting digitization in many domains, however, have led to a plethora of novel use cases for a secure digital ledger. For instance, in the healthcare sector, blockchain systems are used for the secure storage and sharing of electronic health records, while the food industry applies such systems to enable a reliable food-chain traceability, e.g., to prove compliance with cold chains. In these application domains, however, querying the current state is not sufficient—comprehensive history queries are required instead. Due to these altered usage modes involving more complex query types, it is questionable whether today’s blockchain systems are prepared for this type of usage and whether such queries can be processed efficiently by them. In our paper, we therefore investigate novel use cases for blockchain systems and elicit their requirements towards a data store in terms of query capabilities. We reflect the state of the art in terms of query support in blockchain systems and assess whether it is capable of meeting the requirements of such more sophisticated use cases. As a result, we identify future research challenges with regard to query processing in blockchain systems.

The ability to capture and quantify any aspect of daily life via sensors, enabled by the Internet of Things ( IoT ), data have become one of the most important resources of the 21 st century. However, the high value of data also renders data an appealing target for criminals. Two key protection goals when dealing with data are therefore to maintain their permanent availability and to ensure their integrity. Blockchain technology provides a means of data protection that addresses both of these objectives. On that account, blockchains are becoming increasingly popular for the management of critical data. As blockchains are operated in a decentralized manner, they are not only protected against failures, but it is also ensured that neither party has sole control over the managed data. Furthermore, blockchains are immutable and tamper-proof data stores, whereby data integrity is guaranteed. While these properties are preferable from a data security perspective, they also pose a threat to privacy and confidentiality, as data cannot be concealed, rectified, or deleted once they are added to the blockchain. In this paper, we therefore investigate which features of the blockchain pose an inherent privacy threat when dealing with personal or confidential data. To this end, we consider to what extent blockchains are in compliance with applicable data protection laws, namely the European General Data Protection Regulation ( GDPR ). Based on our identified key issues, we assess which concepts and technical measures can be leveraged to address these issues in order to create a privacy-by-design blockchain system.