Cloud storage services allow users to outsource their data remotely to save their local storage space and enable them to manage resources on demand. However, once users outsourced their data to the remote cloud platform, they lose the physical control of the data. How to ensure the integrity of outsourced data is the major concern of cloud users and also is the main challenge in the cloud service deployment. Limited by the communication and computation overheads, traditional hash-based integrity verification solutions in the stand-alone systems cannot be directly adopted in remote cloud storing environment. In this paper, we improve the previous privacy preserving model and propose an effective integrity verification scheme of cloud data based on BLS signature (EoCo), which ensures public audition and data privacy preserving. In addition, EoCo also supports batch auditing operations. We conducted theoretical analysis of our scheme, demonstrated its correctness and security properties, and evaluated the system performance as well.

Recently, optimistic fair exchange in electronic commerce (e-commerce) or mobile commerce (m-commerce) has made great progress. However, new technologies create large amounts of data and it is difficult to handle them. Fortunately, with the assistance of cloud computing and big data, optimistic fair exchange of digital items in cyber-physical systems (CPSes) can be efficiently managed. Optimistic fair exchange in cloud-assisted CPSes mainly focuses on online data exchange in e-commerce or online contracts signing. However, there exist new forms of risks in the uncertain network environment. To solve the above problems, we use a new technique called verifiably encrypted identity-based signature (VEIS) to construct optimistic fair exchange in cloud-assisted CPSes. VEIS is an encrypted signature, and we can check the validity of the underlying signature without decrypting it. We introduce a robust arbitration mechanism to guarantee fairness of the exchange, and even the trusted third party (TTP) cannot get the original signatures of the exchange parties. And the TTP in our protocol is offline, which greatly improves the efficiency. Besides, we show that our protocol is secure, fair, and practical.

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Ensuring the integrity of remote data is the prerequisite for implementing cloud-edge computing. Traditional data integrity verification schemes make users spend a lot of time regularly checking their data, which is not suitable for large-scale IoT (Internet of Things) data. On the other hand, the introduction of a third-party auditor (TPA) may bring about greater privacy and security issues. We use blockchain to address the problem of TPA. However, implementing dynamic integrity verification with blockchain is a bigger challenge due to the low throughput and poor scalability of blockchain. More importantly, whether there is a security problem with blockchain-based integrity verification is not yet known. In this paper, we propose a scalable blockchain-based integrity verification scheme that implements fully dynamic operations and blockless verification. The scheme builds scalable homomorphic verification tags based on ZSS (Zhang-Safavi-Susilo) short signatures. We exploit smart contract technology to replace TPA for integrity verification tasks, which not only eliminates the risk of privacy leakage but also resists collusion attacks. Furthermore, we formally define a blockchain-based security model and prove that our scheme is secure under the security assumption of cryptographic primitives. Finally, the mathematical analysis of our scheme shows that both the communication complexity and the communication complexity of an audit are O c , in which c is the number of challenge blocks. We compare our scheme with other schemes, and the results show that our scheme has the lowest time consumption to complete an audit.

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