PTAD:Provable and Traceable Assured Deletion in Cloud Storage As an efficient deletion method, unlinking is widely used in cloud storage. While unlinking is a kind of incomplete deletion, xe2x80x98deleted dataxe2x80x99 remains on cloud and can be recovered. To make xe2x80x98deleted dataxe2x80x99 unrecoverable, overwriting is an effective method on cloud. Users lose control over their data on cloud once deleted, so it is difficult for them to confirm overwriting. In face of such a crucial problem, we propose a Provable and Traceable Assured Deletion (PTAD) scheme in cloud storage based on blockchain. PTAD scheme relies on overwriting to achieve assured deletion. We reference the idea of data integrity checking and design algorithms to verify if cloud overwrites original blocks properly as specific patterns. We utilize technique of smart contract in blockchain to automatically execute verification and keep transaction in ledger for tracking. The whole scheme can be divided into three stagesunlinking, overwriting and verificationand we design one specific algorithm for each stage. For evaluation, we implement PTAD scheme on cloud and construct a consortium chain with Hyperledger Fabric. The performance shows that PTAD scheme is effective and feasible.

A Novel Exploration for Blockchain in Distributed File Storage Distributed file storage provides reliable access to data through redundancy spread on distributed nodes. Various application scenarios emerge, such as include data centers, storage in wireless networks and peertopeer storage systems. Storing data by using code, such as an erasure code, calls for less redundancy compared with simple replication in terms of reliability. Nevertheless, since data fragments are periodically replaced when some nodes fail, a key acute question is how to generate encoded data fragments in a distributed way when transferring as little data as possible over the network. For a coded system, a new node to repair from a node failure is to download subsets of data from some surviving nodes, reconstructs some lost coded blocks by using the downloaded fragments, and stores them at the new node. This procedure is not optimal. In this paper, we introduce blockchain to protect distributed data in terms of node failure and etc. We show that blockchain can significantly improve the integrity and credibility in distributed file storage systems. Furthermore, we harvest theory discovery of blockchain in distributed file storage system.