Research On Blockchain-based Reliable Storage And Secure Data-sharing Mechanism

Cloud-storage is a data-storage and data-accessing mechanism that is widely used in our day-to-day life.Applying blockchain technology into non-centralized data-storage and data-sharing system has become a newly emerged direction,as blockchain technology provides a decentralized storage service on key-data without relying on third-party vendors.However,how to ensure the reliability and security of data-storage and data-sharing process under such architecture still remains to be a major issue.In this dissertation,a blockchain-based data-sharing mechanism is proposed in a decentralized storage environment to ensure the secure access and efficient sharing for on-cloud encrypted data.This dissertation focuses on security and reliability of data-sharing protocol,where security is guaranteed by a series of cryptographic protocol whereas reliability is realized by a repairable redundancy mechanism.This data-sharing mechanism,where both security and reliability are ensured,works under the environment of blockchain storage where nodes are not trustworthy.On security,a data-sharing mechanism ‘Meta-key' is proposed,which enables users share their encrypted data under a blockchain-based decentralized storage architecture.All the data-encryption keys are encrypted by the owner's public key and put onto the blockchain for safe and secure storage and easy key-management.Encrypted data are stored in dedicated storage nodes and proxy re-encryption mechanism is used to ensure secure data-sharing in the untrusted environment.In the security analysis,the concept of cypher-text location security is proposed and it is further proved that the proxy re-encryption adopted in our system is naturally free from collusion-attack due to the specific architecture of Meta-key.On reliability,aiming at the feature of blockchain-based storage that data in off-chain nodes may be corrupted,lost or even the node itself may fail at any time,a secret-sharing-based redundancy strategy is proposed.Repairing locality is an appreciated feature for distributed storage,in which a damaged or lost data share can be repaired by accessing a subset of other shares much smaller than is required for decoding the complete data.However for Secret Sharing(SS)schemes,it has been proven theoretically that local repairing can not be achieved with perfect security for the majority of threshold SS schemes,where all the shares are equally regarded in both secret recovering and share repairing.In this dissertation we make an attempt on decoupling the two processes to make secure local repairing possible.Dedicated repairing redundancies only for the repairing process are generated,which are random numbers to the original secret.Through this manner a threshold SS scheme with improved repairing locality is achieved on the condition that security of repairing redundancies is ensured,or else our scheme degenerates into a perfect access structure that is equivalent to the best existing schemes can do.To maximize security of the repairing redundancies,a random placement mechanism is also proposed.