  This paper presents a DNN bottleneck reinforcement scheme to alleviate the
vulnerability of Deep Neural Networks (DNN) against adversarial attacks.
Typical DNN classifiers encode the input image into a compressed latent
representation more suitable for inference. This information bottleneck makes a
trade-off between the image-specific structure and class-specific information
in an image. By reinforcing the former while maintaining the latter, any
redundant information, be it adversarial or not, should be removed from the
latent representation. Hence, this paper proposes to jointly train an
auto-encoder (AE) sharing the same encoding weights with the visual classifier.
In order to reinforce the information bottleneck, we introduce the multi-scale
low-pass objective and multi-scale high-frequency communication for better
frequency steering in the network. Unlike existing approaches, our scheme is
the first reforming defense per se which keeps the classifier structure
untouched without appending any pre-processing head and is trained with clean
images only. Extensive experiments on MNIST, CIFAR-10 and ImageNet demonstrate
the strong defense of our method against various adversarial attacks.
