With the development of Internet technology, the volume of data is increasing tremendously. To tackle with large-scale data, more and more applications choose to enlarge the storage capacity of users’ terminals with the help of cloud platforms. Before storing data to an untrusted cloud server, some measures should be adopted to guarantee the data security. However, the communication overhead will increase dramatically when users transmit files encrypted by a traditional encryption scheme. In this paper, we address the above problems by proposing a blockchain-based security architecture for distributed cloud storage, where users can divide their own files into encrypted data chunks, and upload those data chunks randomly into the P2P network nodes that provide free storage capacity. We customize a genetic algorithm to solve the file block replica placement problem between multiple users and multiple data centers in the distributed cloud storage environment. Numerical results show that the proposed architecture outperforms the traditional cloud storage architectures in terms of file security and network transmission delay. On average, the file loss rate based on the simulation assumptions utilized in this paper is close to 0% on our architecture while it’s nearly 100% and 71.66% on the architecture with single data center and the distributed architecture using genetic algorithm. Besides, with proposed scheme, the transmission delay on the proposed architecture is reduced by 39.28% and 76.47% on average on the user’s number and the number of file block replicas, respectively, in comparison to the architecture with single data center. Meanwhile, the transmission delay of file block replicas is also reduced by 41.36% on average than that on the distributed architecture using genetic algorithm.

Introduction

Cloud storage is a kind of system with distributed data centers that takes advantage of virtualization technology and provides interfaces for data storage. It also makes servers or data centers be able to work together for conveniently 5 sharing and accessing resources. Recently, cloud storage has received massive attractions in personal and business organizations because it’s convenient and efficient. In order to access application resources from anywhere and at any time, users have to move their data into the cloud. Cloud provides benefits like 10 flexibility, automatic software update, disaster tolerance, cost reduction and etc. For advantages, challenges and key technologies in different types of cloud storage one can refer to [40, 13]. It’s important to protect users’ privacy [46] and data security [47] because the data may leak when users store their data in the cloud. Meanwhile, the 15 influence of cloud storage security is widely and there is an increasing public concern about users’ privacy [36, 35]. However, there still exists weakness for the existing cloud storage architectures, such as centralized data storage that severely harms server physical security and the need for trusted third-party which are nightmares for the privacy of users’ data. 20 For the current distributed cloud storage, the data stored in several data centers are not fully distributed. The data are still stored in several data centers at high density, and a massive amount of data will be leaked even if one of the data centers was broken down. Public media all around the world have repeatedly reported security issues related to cloud storage in recent years, such 25 as users’ privacy file leakage on iCloud [25]. Unfortunately, there are still no effective solutions for the security of distributed cloud storage. Zyskind et al. propose an architecture and their architecture uses blockchain to protect personal data through distributed storing file access permissions in the blockchain, but its data storage still uses a centralized cloud and requires 30 a trusted third-party to support [50]. Blockchain is a distributed database system, it also can be regarded as a number of nodes jointly maintained by the Distributed Ledger Technology (DLT), which is difficult to tamper, forge and trace [29]. The blockchain records all the information of the transactions, and once the data enter the blockchain, almost nobody can change it. This 35 unchangeable feature is not derived from the use of a certain operation but from the blockchain system and the mechanism itself.