State-of-the-art adversarial attacks on neural networks use expensive
iterative methods and numerous random restarts from different initial points.
Iterative FGSM-based methods without restarts trade off performance for
computational efficiency because they do not adequately explore the image space
and are highly sensitive to the choice of step size. We propose a variant of
Projected Gradient Descent (PGD) that uses a random step size to improve
performance without resorting to expensive random restarts. Our method, Wide
Iterative Stochastic crafting (WITCHcraft), achieves results superior to the
classical PGD attack on the CIFAR-10 and MNIST data sets but without additional
computational cost. This simple modification of PGD makes crafting attacks more
economical, which is important in situations like adversarial training where
attacks need to be crafted in real time.