Untargeted, Targeted and Universal Adversarial Attacks and Defenses on Time Series

Deep learning based models are vulnerable to adversarial attacks. These attacks can be much more harmful in case of targeted attacks, where an attacker tries not only to fool the deep learning model, but also to misguide the model to predict a specific class. Such targeted and untargeted attacks are specifically tailored for an individual sample and require addition of an imperceptible noise to the sample. In contrast, universal adversarial attack calculates a special imperceptible noise which can be added to any sample of the given dataset so that, the deep learning model is forced to predict a wrong class. To the best of our knowledge these targeted and universal attacks on time series data have not been studied in any of the previous works. In this work, we have performed untargeted, targeted and universal adversarial attacks on UCR time series datasets. Our results show that deep learning based time series classification models are vulnerable to these attacks. We also show that universal adversarial attacks have good generalization property as it need only a fraction of the training data. We have also performed adversarial training based adversarial defense. Our results show that models trained adversarially using Fast gradient sign method (FGSM), a single step attack, are able to defend against FGSM as well as Basic iterative method (BIM), a popular iterative attack.