Convolutional neural networks (CNN) have become one of the most popular
machine learning tools and are being applied in various tasks, however, CNN
models are vulnerable to universal perturbations, which are usually
human-imperceptible but can cause natural images to be misclassified with high
probability. One of the state-of-the-art algorithms to generate universal
perturbations is known as UAP. UAP only aggregates the minimal perturbations in
every iteration, which will lead to generated universal perturbation whose
magnitude cannot rise up efficiently and cause a slow generation. In this
paper, we proposed an optimized algorithm to improve the performance of
crafting universal perturbations based on orientation of perturbation vectors.
At each iteration, instead of choosing minimal perturbation vector with respect
to each image, we aggregate the current instance of universal perturbation with
the perturbation which has similar orientation to the former so that the
magnitude of the aggregation will rise up as large as possible at every
iteration. The experiment results show that we get universal perturbations in a
shorter time and with a smaller number of training images. Furthermore, we
observe in experiments that universal perturbations generated by our proposed
algorithm have an average increment of fooling rate by 9% in white-box attacks
and black-box attacks comparing with universal perturbations generated by UAP.