Differentially private (DP) training methods like DP-SGD can protect
sensitive training data by ensuring that ML models will not reveal private
information. An alternative approach, which this paper studies, is to use a
sensitive dataset to generate a new synthetic dataset which is differentially
private with respect to the original data. Doing so has several advantages:
synthetic data can be reused for other tasks (including for hyper parameter
tuning), retained indefinitely, or shared with third parties without
sacrificing privacy.
However, obtaining DP data is much harder than introducing DP during
training. To make it feasible for text, recent work has utilized public data by
starting with a pre-trained generative language model and privately finetuning
it on sensitive data. This model can be used to sample a DP synthetic dataset.
While this strategy seems straightforward, executing it has proven problematic.
Previous approaches either show significant performance loss, or have, as we
show, critical design flaws.
In this paper we demonstrate that a proper training objective along with
tuning fewer parameters results in excellent DP synthetic data quality. Our
approach is competitive with direct DP-training of downstream classifiers in
terms of performance on downstream tasks. We also demonstrate that our DP
synthetic data is not only useful for downstream classifier training, but also
to tune those same models.

本文研究了使用敏感数据集生成新的差分隐私数据集作为替代方法，通过使用预先训练好的生成式语言模型并在敏感数据上进行私有调优，然后利用该模型可以产生差分隐私合成数据集，同时展示了训练目标及少调参数可提高合成数据的质量并与直接使用差分隐私训练下游分类器性能竞争力几乎相同，还可用于调整同一模型等级的分类器。