Cloud storage has been gaining in popularity as an on-line service for archiving, backup, and even primary storage of files. However, due to the data outsourcing, cloud storage also introduces new security challenges, which require a data audit and data repair service to ensure data availability and data integrity in the cloud. In this paper, we present the design and implementation of a network-coding-based Proof Of Retrievability scheme called ELAR, which achieves a lightweight data auditing and data repairing. In particular, we support  direct repair  mechanism in which the client can be free from the data repair process. Simultaneously, we also support the task of allowing a third party auditor ( TPA ), on behalf of the client, to verify the availability and integrity of the data stored in the cloud servers without the need of an asymmetric-key setting. The client is thus also free from the data audit process.  TPA  uses spot-checking which is a very efficient probabilistic method for checking a large amount of data. Extensive security and performance analysis show that the proposed scheme is highly efficient and provably secure.
['Tran Phuong Thao', 'Kazumasa Omote']
ELAR: extremely lightweight auditing and repairing for cloud security