Towards Transferable Unrestricted Adversarial Examples with Minimum Changes

Fangcheng Liu, Chao Zhang, Hongyang Zhang

Keywords: Transfer-based Black-box Attack, Unrestricted Adversarial Examples

Abstract: Transfer-based adversarial example is one of the most important classes of black-box attacks. However, there is a trade-off between transferability and imperceptibility of the adversarial perturbation. Prior work in this direction often requires a fixed but large $\ell_p$-norm perturbation budget to reach a good transfer success rate, leading to perceptible adversarial perturbations. On the other hand, most of the current unrestricted adversarial attacks that aim to generate semantic-preserving perturbations suffer from weaker transferability to the target model. In this work, we propose a \emph{geometry-aware framework} to generate transferable adversarial examples with minimum changes. Analogous to model selection in statistical machine learning, we leverage a validation model to select the best perturbation budget for each image under both the $\ell_{\infty}$-norm and unrestricted threat models. Extensive experiments verify the effectiveness of our framework on {balancing} imperceptibility and transferability of the crafted adversarial examples. The methodology is the foundation of our entry to the adversarial competition of a 2021 conference, in which we ranked 1st place out of 1,559 teams and surpassed the runner-up submissions by 4.59\% and 23.91\% in terms of final score and average image quality level, respectively.

Community Implementations: [ 2 code implementations](https://www.catalyzex.com/paper/towards-transferable-unrestricted-adversarial/code)