Blockchainbased fair payment smart contract for public cloud storage auditing Abstract   Cloud storage plays an important role in todayxe2x80x99s cloud ecosystem. Increasingly clients tend to outsource their data to the cloud. In spite of its copious advantages, integrity has always been a significant issue. The audit method is commonly used to ensure integrity in cloud scenarios. However, traditional auditing schemes expect a thirdparty auditor (TPA), which is not always available in the real world. Also, the former scheme implies a limited payasyougo service, as it requires the client to pay for the service in advance.  In this paper, we aim to address the aforementioned drawback by adopting blockchain to replace TPA and designing a blockchainbased fair payment smart contract for public cloud storage auditing. In our system, data owner and cloud service provider (CSP) will run a blockchainbased smart contract. The contract ensures that the CSP is required to submit data possession proof regularly. The CSP gets paid only if the verification is passed; otherwise, it gets no remuneration but has to pay the penalties. To reduce the number of interactions in the execution of contract, we present the notion of noninteractive public provable data possession and design a blockchainbased smart contract for public cloud storage auditing based on this primitive.

New group user based privacy preserving cloud auditing protocol Abstract   Cloud storage is now a very popular service for many enterprises and their users. However, ensuring the integrity of the outsourced data is a very challenging problem. The concept of provable data possession is very effective for solving this problem. Based on this concept, in this paper we propose a new groupuserbased privacypreserving secure cloud auditing protocol for enterprise users and analyse its security. This protocol is also constructed on a recently proposed lightweight and privacypreserving secure cloud auditing scheme for group users via a thirdparty medium. We point out that scheme is not secure and that the authenticators corresponding to the outsourced data blocks can be easily forged, that means the cloud servers can delete all the outsourced data but can still give correct proof for the possession of outsourced data, while our protocol has no such shortcoming. The performance analysis results demonstrate that our proposal is very practical and can have largescale applications.