Constrained Gradient Descent: A Powerful and Principled Evasion Attack Against Neural Networks

We propose new, more efficient targeted whitebox attacks against deep neural networks. Our attacks better align with the attacker's goal: (1) tricking a model to assign higher probability to the target class than to any other class, while (2) staying within an -distance of the attacked input. First, we demonstrate a loss function that explicitly encodes (1) and show that Auto-PGD finds more attacks with it. Second, we propose a new attack method, Constrained Gradient Descent (CGD), using a refinement of our loss function that captures both (1) and (2). CGD seeks to satisfy both attacker objectives--misclassification and bounded `p-norm--in a principled manner, as part of the optimization, instead of via ad hoc postprocessing techniques (e.g., projection or clipping). We show that CGD is more successful on CIFAR10 (0.9-4.2%) and ImageNet (8.6-13.6%) than state-of-the-art attacks while consuming less time (11.4-18.8%). Statistical tests confirm that our attack outperforms others against leading defenses on different datasets and values of .