# A Security-Oriented Data-Sharing Scheme Based on Blockchain
## 1 Introduction  
Data sharing facilitates knowledge dissemination, enhances collaborative research endeavors, and advances the public interest. Data sharing can make full use of data resources by sharing one's data for others to use [1], reduce the cost of data collection, maximize the social benefits of similar data, and also help to improve the reproducibility and verifiability of data and enhance the credibility and scientific value of research results. However, in practice, data are often segmented and stored by different organizations and individuals and shared only within a specific scope, forming many independent datasets, which forms \"data silos\" [2], leading to inefficient utilization of data resources and limiting the release of their potential value. Investigating secure data-sharing mechanisms is of utmost importance, as it helps prevent the formation of data silos and privacy breaches. Despite its advantages, data sharing faces numerous practical challenges and obstacles. Traditional data-sharing models usually rely on a single third-party platform to facilitate data exchange and sharing [3]. Owners of data upload their data to third-party platforms, and data demanders pay these third-party platforms to access the data [4]. This data-sharing model simplifies management and maintenance but requires reliance on a third-party platform responsible for overseeing data-sharing records. Therefore, there are several shortcomings of traditional data-sharing models, such as absence of transparency in data transaction, data ownership may get lost, and data security cannot be guaranteed [5]. In recent years, cloud services have facilitated the storage and sharing of multimedia data [6], but they also bring some security problems, such as attackers tampering with the data and users being unable to ensure the integrity and authenticity of the data. There are also other problems, including poor reliability, poor scalability, high cost, and poor compatibility [7]. Blockchain-based solutions for data sharing are extensively utilized across specialized fields, including healthcare, energy management, and the Internet of Things. Blockchainis the core support technology of the digital cryptocurrency system represented by Bitcoin, which can provide a technical basis for building trusted peer-to-peer data security sharing [8], being open and transparent, tamper-proof, and leaving traces throughout the process. Blockchain technology adopts the structure of a \"chain\" to store data, which consists of individual blocks connected by a hash function, where each block contains the hash value of the previous block, timestamps, transaction data, etc. [9], and any attempt to tamper with the data will lead to the collapse of the blockchain. In addition, the data stored on the blockchain are jointly maintained by all parties, and any operation information related to the data can be stored on the blockchain to realize the whole trace management of the data [10]. Therefore, blockchain provides a new solution for solving the existing problems in secure data sharing. However, it is difficult to guarantee the security of data because of the open and transparent nature of the data stored in blockchains [10]. The open and transparent nature of the system allows unrestricted data access, thereby increasing exposure risks. Consequently, ensuring data integrity and confidentiality becomes more challenging, necessitating robust security measures to mitigate potential threats and attacks. In addition, each client of the blockchain system must maintain a complete copy of the block data [11], and the increasing size of the data to be shared on the blockchain will lead to increasing storage pressure on the blockchain, which will also result in high overhead for the clients. The immutability of blockchain data, coupled with increasing data volumes, substantially affects querying and storage efficiency.