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.

Enabling Cloud Storage Auditing with KeyExposure Resilience under Continual KeyLeakage Abstract   Cloud storage auditing is a service that is usually provided to enable clients to verify the integrity of their data stored in the cloud. However, clients risk exposing their secret key. To address the problem of key exposure, researchers have provided xe2x80x9cForward Securityxe2x80x9d by dividing the entire lifetime of the secret key into several periods and updating the secret key within each of these periods. Forward security can ensure the validity of authenticators before the period in which the secret key is fully exposed. However, the security of these protocols can be broken by launching sidechannel attacks to leak the secret key partially rather than fully. In this study, we focus on implementing measures in cloud storage auditing to protect against sidechannel attacks in practice. We formalize the definition and security model of a cloud storage auditing protocol, which supports forward security under continual keyleakage, and construct the first protocol. Our protocol remains secure even if an adversary obtains partial leakage of the secret key during a period. In addition, if the secret key were to be fully disclosed in a certain period, our protocol would maintain forward security. Therefore, the proposed protocol provides stronger security compared with existing protocols.