提出新方法检测对抗样本,通过捕捉特征不确定性的全局与局部差异提升精度。
USAD: Uncertainty-aware Statistical Adversarial Detection

- 设计两种新统计量:特征方差差和扰动协方差差,分别捕捉全局与局部不确定性。
- 在多种攻击下检测性能优于基线方法,误报率可控。
- 适合关注对抗样本检测鲁棒性与统计检验的开发者与研究人员。
统计对抗检测(SAD)将检测任务视为双样本检验:给定干净样本参考集与待测批量样本(可能混合干净样本与对抗样本),判断查询分布是否偏离参考分布,同时控制误报率。现有方法多用最大均值差异(MMD)衡量分布差异,但其分布特性难以捕捉对抗样本的关键不确定性特征——即异常特征扩散(全局不确定性)与扰动下的不稳定性(局部不确定性)。为此,我们提出不确定性感知的统计对抗检测(USAD),引入两个新统计量:(1) 方差差异(VD),衡量对抗样本与干净样本间特征扩散的差异,捕获全局不确定性;(2) 扰动协方差差异(PCD),通过高斯扰动下特征协方差对比,捕获局部不确定性。融合VD与PCD后,USAD在多种对抗攻击下表现显著优于基线方法,凸显考虑对抗样本典型行为对有效检测的重要性。代码已公开于https://anonymous.4open.science/r/USAD。
原文摘要 · Abstract (English)
Statistical adversarial detection (SAD) treats detection as a two-sample test. Given a reference set of clean examples (CEs) and a batch of queries, potentially containing an unknown mixture of CEs and adversarial examples (AEs), SAD decides whether the query distribution drifts away from the CE distribution while controlling the false-alarm rate. Existing SAD-based methods mainly use maximum mean discrepancy (MMD) to measure the distributional discrepancy. However, MMD's distributional properties limit its ability to capture characteristic uncertainty patterns of AEs that are crucial for detection: AEs typically exhibit abnormal feature spread (i.e., global uncertainty) and instability under perturbations (i.e., local uncertainty). To close the gap, we propose Uncertainty-aware Statistical Adversarial Detection (USAD), which explicitly captures these uncertainty patterns with two new statistics: (1) Variance Discrepancy (VD), which measures the difference in feature spread between AEs and CEs to capture global uncertainty differences. (2) Perturbation-based Covariance Discrepancy (PCD), which compares feature covariance under Gaussian perturbations to capture local uncertainty differences. By aggregating VD and PCD, USAD achieves superior detection performances over baseline methods against various adversarial attacks, highlighting the importance of considering characteristic behaviors of AEs for effective SAD. Our code is available at: https://anonymous.4open.science/r/USAD.
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