Metric Differential Privacy is a generalization of differential privacy tailored to address the unique challenges of text-to-text privatization. By adding noise to the representation of words in the geometric space of embeddings, words are replaced with words located in the proximity of the noisy representation. Since embeddings are trained based on word co-occurrences, this mechanism ensures that substitutions stem from a common semantic context. Without considering the grammatical category of words, however, this mechanism cannot guarantee that substitutions play similar syntactic roles. We analyze the capability of text-to-text privatization to preserve the grammatical category of words after substitution and find that surrogate texts consist almost exclusively of nouns. Lacking the capability to produce surrogate texts that correlate with the structure of the sensitive texts, we encompass our analysis by transforming the privatization step into a candidate selection problem in which substitutions are directed to words with matching grammatical properties. We demonstrate a substantial improvement in the performance of downstream tasks by up to $4.66\%$ while retaining comparative privacy guarantees.

本文旨在解决基于文本的隐私保护问题，提出了一种基于度量的差分隐私方法，利用词向量在向量空间的表示来添加噪声并完成替换。分析表明现有方法替换后语法上存在局限性，提出用候选选择解决替换方向的问题。实验结果表明，该方法在保证隐私的同时，提升了下游任务的表现。

通过语法指导文本到文本的隐私保护