针对模型中间表示的成员推理风险,提出分层隐私保护方法。
Mitigating Membership Inference in Intermediate Representations with Differentially Private Training
- 根据各层成员推理风险动态分配隐私保护强度
- 相同隐私预算下,中间表示的成员推理攻击成功率显著降低
- 适合关注模型隐私泄露与实用性能平衡的研究者
在嵌入即接口(EaaI)场景中,预训练模型被用于查询中间表示(IRs)。IRs的分布特性可能泄露训练集成员信息,导致成员推理攻击(MIAs),且攻击强度在不同层间存在差异。尽管差分隐私随机梯度下降(DP-SGD)可缓解此类泄露,但现有方法采用逐样本梯度裁剪和统一的噪声倍数,忽视了层间MIA风险的异质性。本文提出分层MIA风险感知的DP-SGD(LM-DP-SGD),根据各层风险自适应分配隐私保护。具体地,通过在公开影子数据集上训练影子模型,提取其训练/测试集的每层IRs,拟合层级专属的MIA攻击者,并以攻击错误率作为层级MIA风险估计。利用成员推理攻击在不同数据集间的可迁移性,将这些风险估计用于重加权训练中各层对全局裁剪梯度的贡献,在固定噪声幅度下实现层级适配的隐私保护。我们进一步建立了LM-DP-SGD的隐私与收敛性理论保证。大量实验表明,在相同隐私预算下,LM-DP-SGD有效降低了峰值IR层级的MIA风险,同时保持良好模型性能,实现了更优的隐私-效用权衡。
原文摘要 · Abstract (English)
In Embedding-as-an-Interface (EaaI) settings, pre-trained models are queried for Intermediate Representations (IRs). The distributional properties of IRs can leak training-set membership signals, enabling Membership Inference Attacks (MIAs) whose strength varies across layers. Although Differentially Private Stochastic Gradient Descent (DP-SGD) mitigates such leakage, existing implementations employ per-example gradient clipping and a uniform, layer-agnostic noise multiplier, ignoring heterogeneous layer-wise MIA vulnerability. This paper introduces Layer-wise MIA-risk-aware DP-SGD (LM-DP-SGD), which adaptively allocates privacy protection across layers in proportion to their MIA risk. Specifically, LM-DP-SGD trains a shadow model on a public shadow dataset, extracts per-layer IRs from its train/test splits, and fits layer-specific MIA adversaries, using their attack error rates as MIA-risk estimates. Leveraging the cross-dataset transferability of MIAs, these estimates are then used to reweight each layer's contribution to the globally clipped gradient during private training, providing layer-appropriate protection under a fixed noise magnitude. We further establish theoretical guarantees on both privacy and convergence of LM-DP-SGD. Extensive experiments show that, under the same privacy budget, LM-DP-SGD reduces the peak IR-level MIA risk while preserving utility, yielding a superior privacy-utility trade-off.
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