A Cross-Border Data Privacy Protection Approach Based on Smart Contracts and Ring Fully Homomorphic Encryption

This paper aims to address the technical challenges in cross-border data privacy protection by proposing a decentralized privacy governance solution based on smart contracts. Through the design of a blockchain network architecture, the development of privacy protection algorithms, and the construction of a verification environment, the potential applications of smart contracts in data privacy governance are systematically explored. An experimental testing approach is employed to comprehensively evaluate algorithm performance and protocol security, followed by the optimization of key technical parameters. Experimental results show that the proposed framework achieves a Sybil attack detection accuracy of 96.3 %, a 1.8 -second cross-chain transaction latency, and reduces homomorphic encryption delay from 218 ms to 47 ms. Furthermore, the semantic compliance mapping model achieves <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{9 2. 4 \%}$</tex> accuracy, and the average gas cost per verification is <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{0. 0 0 3 2}$</tex> ETH, demonstrating a 43 % cost reduction compared to traditional schemes. These results confirm the effectiveness and efficiency of our decentralized privacy governance framework for cross-border data flows.