cs.LGOct 11, 2026

Adversarial Detection for Pre-trained Classifiers via Lipschitz-Margin Analysis with Certification

Authors: Rui Zhang, Xinle Cao, Huazhen Yu, Jian Liu, Youwen Zhu

Organizations: Nanjing University of Aeronautics and Astronautics · The State Key Laboratory of Blockchain and Data Security, Zhejiang University · Nanjing University of Information Science and Technology

Abstract

Deep classifiers deployed in safety-critical services like autonomous-driving perception remain vulnerable to small adversarial perturbations. Certified ℓ2\ell_2 defenses today face a costly trade-off: randomized smoothing (RS) requires hundreds of noisy queries per input, while Lipschitz networks (LN) constrain the architecture and sacrifice clean accuracy. We take a detection-oriented approach instead: rather than certifying that predictions are invariant inside an ℓ2\ell_2 ball, we certify that adversarial inputs within an ℓ2\ell_2 ball are detected --- a guarantee aligned with security-critical deployments where missing an attack is costlier than flagging a clean input. To realize this, we prove a Lipschitz-margin reduction from certified ℓ2\ell_2 robustness to certified detection, which reduces the problem to handling a single Lipschitz constant LL. We introduce two detector families: DAdv\mathbb{D}_{Adv}, which estimates LL from a single defender-side perturbed pair, and Dlc\mathbb{D}_{lc}, which augments that pair with a local margin centroid to keep the estimate above what the certificate requires. Both deploy on any pretrained classifier without retraining. With a valid global bound, the detector is fully certified at that radius; with a local estimate L′L', certification is sample-wise and applies only when our certified condition holds. Across MNIST, CIFAR-10, and ImageNet-1k on four backbones (LeNet-5, VGG16, ResNet-50, ViT-B/16), our detectors match or outperform five baselines (CTT, SortNet, CRM, ContraNet, A2^2D). For CIFAR-10 with 1-Lipschitz SortNet, our reduction delivers 100%100\% certified detection at the lowest FPR among compared certified detectors; on the standard CIFAR-10 VGG16, our detectors reject all evaluated in-budget adversarial examples, with 62-82% both rejected and formally certified.

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