Boosting Adversarial Transferability via Relative Feature Importance-Aware Attacks

Modern deep neural networks are known highly vulnerable to adversarial examples. As a pioneering work, the fast gradient sign method (FGSM) is proved more transferable in black-box attacks than its multi-small-step extension, i.e., iterative-FGSM, particularly being restricted by a limited number of iterations. This paper revisits their early, representative successor MI-FGSM as a baseline, i.e., iterative-FGSM with momentum, and introduces an innovative boosting idea different from either FGSM-inspired algorithms or other mainstream methods. For one thing, during gradient backpropogation of MI-FGSM, the proposed approach merely requires amending the chain rule with respect to adversarial images using the counterpart original images. For another, a credible analysis has revealed that such a naively boosted MI-FGSM essentially performs a special kind of intermediate-layer attacks. In specific, the notable finding in the paper is a new principle of adversarial transferability guided by the relative feature importance, emphasizing the significance of semantically non-critical information for the first time in the literature, although originally thought to be weak in large. Experimental results on various leading victim models, both undefended and defended, demonstrate that the new approach incorporating robust gradients has indeed attained stronger adversarial transferability than state-of-the-art works. The code is available at:https://github.com/ljwooo/RFIA-main.