通过推理阶段的可证鲁棒性保护用户隐私,防止模型输出泄露敏感信息。
Robust Privacy: Inference-Stage Privacy through Certified Robustness
- 在输入邻域内预测不变时,可证明用户隐私得到保障。
- 使属性推断精度下降,黑盒攻击成功率从73%降至4%。
- 适合关注推理阶段隐私安全的研究者与应用开发者。
观察模型输出的攻击者可能推断查询输入的敏感属性,甚至重建训练数据。我们提出鲁棒隐私(RP),一种受可证鲁棒性启发的推理阶段隐私概念:若模型在输入x的半径R邻域内以至少1−α的置信度保持预测不变,则x享有(R,α)−鲁棒隐私,此时任何观测预测的攻击者区分x与其距离R内的输入的最优优势不超过α/2。基于RP,我们定义鲁棒属性隐私(RAP),刻画与释放预测兼容的敏感属性取值集合。在分类任务中,RP将RAP兼容推断区间的中位长度从23.50提升至29.96,降低属性推断精度。模型反演攻击常被视为训练阶段威胁,实则依赖推理接口泄露的细粒度输入-输出依赖信号;RP在推理阶段屏蔽这些信号,使黑盒反演攻击成功率从73%降至4%。直接针对泄漏通道,使RP在隐私-效用权衡上优于DP-SGD和随机响应:在21%攻击成功率下,RP保持98.4%准确率,而DP-SGD需降至61.7%。增加平滑样本数N,在固定噪声尺度下同时增强隐私并提升性能。最后,通过模型蒸馏分析边界,表明RP可缓解属性级与实例级推理阶段隐私泄露。
原文摘要 · Abstract (English)
An adversary observing a model's released prediction can infer sensitive attributes of the queried input, or even reconstruct representatives of the model's training data. The inference interface thus acts as a side channel for privacy leakage. We introduce Robust Privacy (RP), an inference-stage privacy notion inspired by certified robustness: if a model's prediction is provably invariant within a radius-$R$ neighborhood around an input $x$ with confidence at least $1-α$, then $x$ enjoys $(R,α)$-Robust Privacy, under which we prove that any adversary observing the released prediction has at most $α/2$ advantage in distinguishing $x$ from any input within distance $R$ of $x$. Building on RP, we formalize Robust Attribute Privacy (RAP), an attribute-level privacy notion that characterizes the set of sensitive-attribute values that remain compatible with a released prediction. On a classification task, RP increases the median length of the RAP-compatible inference interval from $23.50$ to $29.96$, reducing attribute-inference precision. Model inversion attacks, often treated as a training-stage threat, in fact rely on fine-grained input-output dependence signals leaked through the inference interface; RP masks these signals at the inference stage, reducing attack success rate (ASR) from $73\%$ to $4\%$ on a black-box inversion attack. This direct targeting of the leakage channel enables RP to dominate DP-SGD and randomized response in the privacy-utility tradeoff space: RP retains $98.4\%$ accuracy at $21\%$ ASR, whereas DP-SGD must drop accuracy to $61.7\%$ to reach a comparable ASR. Across both experiments, increasing the smoothing sample size $N$ at fixed noise scale strengthens privacy and improves utility together. Finally, we examine model distillation as a scope boundary and show that RP mitigates attribute-level and instance-level inference-stage privacy leakage.
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