Effectively Improving Data Diversity of Substitute Training for Data-Free Black-Box Attack

Recent substitute training methods have utilized the concept of Generative Adversarial Networks (GANs) to implement data-free black-box attacks. Specifically, in designing the generators, the substitute training methods use a similar structure to the generators in GANs. However, this design approach ignores the potential situation that the generators in GANs operate under real data supervision, while the generators in substitute training methods lack such supervision. This difference in data-supervised conditions constrain the diversity of data generated by the substitute training methods, resulting in inadequate data to support effective training of the substitute model. This impacts the substitute model's ability to attack the target model further. Consequently, to solve the above issues, we propose three strategies to improve the attack success rates. For the generator, we first propose a dense projection space that projects the input noise into various latent feature spaces to diversify feature information. Then, we introduce a novel disguised natural color mode. This mode improves information exchange between the generator's output layer and previous layers, allowing for more diverse generated data. Besides, we present a regularization method for the substitute model, called noise-based balanced learning, to prevent the potential risk of overfitting due to the lack of diversity of the generated data. In the experimental analysis, extensive experiments are conducted to validate the effectiveness of these proposed strategies.