Towards Speeding up Adversarial Training in Latent Spaces.

Adversarial training is wildly considered as the most effective way to defend against adversarial examples. However, existing adversarial training methods consume unbearable time cost, since they need to generate adversarial examples in the input space, which accounts for the main part of total time-consuming. For speeding up the training process, we propose a novel adversarial training method that does not need to generate real adversarial examples. We notice that a clean example is closer to the decision boundary of the class with the second largest logit component than any other class besides its own class. Thus, by adding perturbations to logits to generate Endogenous Adversarial Examples(EAEs) -- adversarial examples in the latent space, it can avoid calculating gradients to speed up the training process. We further gain a deep insight into the existence of EAEs by the theory of manifold. To guarantee the added perturbation is within the range of constraint, we use statistical distributions to select seed examples to craft EAEs. Extensive experiments are conducted on CIFAR-10 and ImageNet, and the results show that compare with state-of-the-art "Free" and "Fast" methods, our EAE adversarial training not only shortens the training time, but also enhances the robustness of the model. Moreover, the EAE adversarial training has little impact on the accuracy of clean examples than the existing methods.