# A Data Sharing Scheme for GDPR-Compliance Based on Consortium Blockchain
## 6 Conclusions and Future Work  
When applying blockchain to GDPR compliance, how to ensure as much as possible the security and privacy protection in data sharing is a challenging issue. Our research designed the first data sharing solution using ZK-proof in the combination of technologies such as consortium blockchain, CEM-PoA, and zk-SNARK. The analysis shows that confidentiality, availability, and other indicators are met in the proposed scheme. Compared with the existing GDPR blockchain solution, the proposed solution has an efficiency advantage in block generation speed while achieving ideal privacy protection. Precisely, by automatically verifying the ZK-proof, the smart contract can determine whether the user's data meets the service provider's established requirements or not, without revealing the user's privacy. After verification, the transaction is recorded in the blockchain through CEM-POA, and the reputation incentive mechanism can ensure the honesty of the node. Any violations of regulations will be immutably recorded in the blockchain, and can be easily detected by regulatory agencies.  
The proposed scheme can be applied to various data transactions or sharing scenes with privacy protection and compliance requirements. For example, in the medical area, this solution can share medical data among patients, hospitals, and research institutions while protecting patient data from being leaked. Additionally, it can provide a privacy-preserving solution from technical design for contact tracing for the COVID-19 pandemic. In the Internet of Vehicles (IoV) area, our scheme can solve the anonymity and authentication problems, such as traffic services or location services in vehicular social networks.  
In addition to the technology used in our scheme, there are numerous technologies that can ensure the security and privacy of the blockchain. For instance, Differential Privacy (DP) [26] technology can be used to scramble data before sharing it or adding noise in  
\begin{table}
\begin{tabular}{l l l} \hline \hline
**Inputs** & \(\textbf{EK}_{c}\) **Size** & \(\textbf{VK}_{c}\) **Size** & **Proof Size** \\ \hline
200 & 14.7 MB & 8.6 KB & 33.5 KB \\
400 & 14.7 MB & 17.2 KB & 66.7 KB \\
600 & 14.7 MB & 24.1 KB & 92.3 KB \\
800 & 14.7 MB & 32.5 KB & 127.1 KB \\
1000 & 14.7 MB & 40.9 KB & 160.5 KB \\ \hline \hline \end{tabular}
\end{table}
Table 2: The size of \(EK_{c}\), \(VK_{c}\), and the proof.  
the calculation process. Fully Homomorphic Encryption (FHE) [27] technology is a major breakthrough in cryptography, which implements various operations requested by users without decrypting data. However, the overhead must be considered.  
The contribution of this article explores how the blockchain-based solution can better comply with the GDPR regulations. Our new GDPR-compliance consortium blockchain scheme supports many features, such as regulatory-traceability, mutual authentication, and others, all defects that exist in previous works are eliminated. Our experimental results show the practicality of our scheme. To put it in a nutshell, we leave the following questions for future research:  
* Further optimizing the security and privacy of the proposed scheme based on the above technologies.
* Adding more functions to better comply with GDPR requirements.
* Exploring how to improve the efficiency of generation and verification of zero- knowledge proof.  
Writing--review and editing, Y.P.; visualization, K.Y.; supervision, X.C.; project administration, Y.P. All authors have read and agreed to the published version of the manuscript.  
This research was funded by National Key Research and Development Program of China (grant no. 2018 YFC1604000) and Fundamental Research Funds for the Central Universities (grant no. 2042017 gf0035).  
The data presented in this study are available on request from the corresponding author.  
The authors declare no conflict of interest.