用单次前向传播实现快速鲁棒性认证,比传统方法快上千倍。
RRISE: Robust Radius Inference via a Surrogate Estimator
- 训练一个代理模型替代多次采样,一次前向计算即可生成结果。
- 在图像分类任务中认证准确率与传统方法相差不到0.84个百分点。
- 适合需要频繁部署的实时系统,尤其适用于小样本或高复杂度数据集。
随机平滑(RS)通过平滑分类器为ℓ₂分类提供与架构无关的鲁棒性保证,但其依赖每输入的蒙特卡洛(MC)采样,限制了在实时系统中的应用。我们指出这种开销是结构性而非根本性的,可通过共享部署流中的信息显著降低。提出RRISE框架,将认证压缩为一次前向传播,通过学习代理模型实现。该代理模型基于预计算的MC类别计数目标,采用软标签交叉熵损失训练,并通过一次性置信校准步骤转化为可证明保守的认证半径。所得证书具备部署可验证性:只要校准半径为正,则代理预测必然匹配平滑分类器,且平滑分类器在输入周围半径为该值的球内保持不变。在图像分类基准上,RRISE在固定预算下与MC认证准确率相差不超过0.84个百分点,同时将每查询高达10⁴次的噪声基模型评估替换为一次代理前向传播,约10⁵次部署查询后即可回收训练成本。在CIFAR-100和Tiny ImageNet上,此前唯一离线代理方法失效,而RRISE实现1.23至1.91倍更高的认证准确率,确立了高效随机平滑在重复部署场景中实用化路径。
原文摘要 · Abstract (English)
Randomized smoothing (RS) uses a smoothed classifier to provide architecture-agnostic certificates of $\ell_2$ classification robustness, but its dependence on per-input Monte Carlo (MC) sampling undermines its use in real-time systems. We argue that this cost is structural rather than fundamental, such that it can be significantly reduced by sharing information across the deployment stream. We introduce RRISE, an RS framework that compresses certification into a single forward pass through a learned surrogate. RRISE trains the surrogate against precomputed MC class-count targets via a soft-label cross-entropy loss and converts surrogate predictions into provably conservative certified radii through a one-time conformal calibration step. The resulting certificate is deployment-verifiable: whenever the calibrated radius is positive, the surrogate's prediction provably matches the smoothed classifier's and the smoothed classifier is constant on a ball of that radius around the input. Across image classification benchmarks, RRISE matches fixed-budget MC certified accuracy within $0.84$ percentage points while replacing up to $10^4$ noisy base-model evaluations per query with a single surrogate forward pass, recouping MC training cost after $\approx 10^5$ deployment queries. On CIFAR-100 and Tiny ImageNet, where the only prior offline-surrogate method collapses, RRISE achieves $1.23$ to $1.91\times$ higher certified accuracy, establishing efficient randomized smoothing as a practical path to certified robustness in repeated-deployment settings.
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