Advanced Generative Adversarial Defense Model using Instance Sparsity Mapping Network

Ⅰ. Introduction

Adversarial networks are applying to diverse areas to solve complex vision tasks. Recently, deep learning bases supervised, and unsupervised learning models are used to understand human mids to improve the humanoid robot and autonomous applications. Due to the popularity of adversarial models in many real-world applications, mainly for security-sensitive applications, this advances an essential issue as to their strength against adversarial attacks. Adversarial models are vulnerable to quasi-imperceptible perturbations. For example, adversarial examples produced noise or perturbations that can cause inaccurate prediction[1][2].

Moreover, a small perturbation on inputs can mislead the model. More clearly, considering Fig. 1, the deep learning model unable to segment a specific portion of the image that included adversarial perturbations.

Fig. 1.

The source image is perturbed with universal adversarial noise, and the resulting prediction is misclassified due to the noise and unable to segment all the information[3].

Different strategies are adopted to defend against adversarial examples. First, to assure that networks are strong against adversarial examples, second is to transform adversarial examples, and the last one is to distinguish adversarial examples. One of the most effective strategies is to train the adversarial model with adversarial examples to obtain an adversarially trained targeted network concerning the first type. Nevertheless, all of these approaches have particular limitations. The first method is unable to effectively defend against adversarial attacks if it has not been trained about attacks. The second one inescapably has an impact on certain attacks as they would also be reformed. Finally, the third approach may decline the detected adversarial examples, which might be unacceptable in specific scenarios.

To overcome the drawbacks mentioned above, the proposed model introduces a defense framework to fuse the attacks and prevent misclassification.

Ⅱ. Related Theories

The robustness of adversarial networks against adversarial attacks has achieved notable attention in the recent deep learning applications[4]-[8]. As a result, adversarial networks became the core attention in this field to prevent and eliminate attacks.

2.1 Adversarial Attack

Adversarial attacks are two types: first, engineered attacks outlined by hackers, and self-generated attacks occurred during training time. Both attacks are vulnerable for deep learning models, mainly for the adversarial network, because adversarial networks are constructed with complex architecture to achieve their predefined goal. The network uses latent noise to generate images, and in most cases, adversarial examples are originated during adversarial training time. Furthermore, recently, adversarial models apply in a wide range of social and security applications, and this model is targeted to mislead by adversarial attacks. In Fig. 2 an example of adversarial attacked shown that fooled by adversarial attack.

Fig. 2.

Adversarial attack to fool neural network

Adversarial attacks that generate adversarial examples in linear models can be explained due to high-dimensional dot products or noise.

$\[ x^{adv}=x+ϵ•sign\left({\text{∇}}_x{j}_{\theta }\left(x,y\right)\right. \]$

(1)

In Eq. (1), (∇_xj_θ(x,y) is the gradient of the loss function j_θ of the learning model parameterize by θ in x, and true label is y.

When a perturbed image is input, the output will be the sum of the dot product of the weights and the unperturbed information and the dot product of the weights and specific perturbation. Each weight vector holds average magnitude m, and the input is n-dimensional. Therefore, the activation of the classifier will grow by mn(where is the magnitude of the perturbation). This does not result in a significant difference in classification between the original and attacked data for low-dimensional problems. Despite, if the input has a large dimension n, even weak perturbations can cause large errors in the classifier[9].

Rely on the adversary knowledge attacks can be classified into three categories such as white-box attacks, black-box attacks, and gray-box attacks. These attacks directly access the deep learning model to harm the target task[10].

In this category, the white-box attack[11] conducts on the model architecture and parameter, while in black-box attacks has no access to model parameters. Instead, it utilizes a different model to generate adversarial images assuming that influence on the target model. Finally, the gray-box attack can take over full access to model parameters but unaware of the model defense system.

The proposed network is constructed with an instance sparsity mapping network that is associated with a classifier to fuse the adversarial attacks. The instance sparsity mapping network prevents the attacks and leads the base network to generate a perfect image with exact order.

Ⅲ. Proposed Algorithm

The proposed network applies a defense strategy to eliminate adversarial attacks. The defense model is constructed with the combination of a classifier and mapping network.

The architecture of the proposed network is shown in Fig. 3. The defense network adopts two core techniques to fuse the internal and external attacks, i.e., Adversarial training and defensive distillation. These techniques are directed to balance the network and improve the robustness against adversarial attacks.

Fig. 3.

Network architecture of instance sparsity mapping network

In the initial stage, the model is constructed by considering the adversarial training. In this block, the network is incorporated with the approach of a conventional adversarial network. The adversarial network conducts the operation by balancing the adversarial distribution between the generator block and discriminator block.

The adversarial training method includes adversarial examples from the attacks during the training phase, so the discriminator is trained either on a mix of both clean and adversarial examples.

However, despite the adversarial examples generated with a specific type of attack, the discriminator remains weak to other types of attacks. Therefore, to eliminate the issue and improve the defense method, the proposed network included a defense distillation technique.

From Eq. (2), φ is the noise factor and $$ \widehat{x}$$ is a random vector.

The model combined with a mapping network and a classifier to improve the robustness of the proposed network. In this part, the classifier examines the generated samples to justifies the sample is attacked or not. It assumes a probabilistic classifier that maintains the network to develop a defense against adversarial attacks.

The instance sparse mapping network trained with both clean and attacked image samples that to ensure that the adversarial attacks do not bias the change learned by the network.

In Eq. (3), n is the number of samples and x′is the perturbed version of x.

The proposed instance sparsity mapping network detects the classifier noise and sends the generator network to feedback to regenerate the sample again along with association with the network. This process continues until the generated sample completely matches the source data.

Ⅳ. Experiments

4.1 Baseline Architecture

The proposed network is constructed with an adversarial network and a defense block known as the instance sparsity mapping network. Improved MagNet [12] architecture use to construct the instance sparsity mapping network. In addition, the network adopts adversarial learning and defense distillation model to fuse the adversarial attacks the defense model constructed with the combination of classification block and autoencoder. Eventually, both of model combines to generate image samples by easing influence of adversarial attacks. The architecture of the classifier is shown in Table 1, and the architecture of the instance sparsity mapping network is shown in Table 2.

Table 1.

Neural network architectures used for classifiers

Table 2.

Neural network architectures of instance sparsity mapping network

Ⅴ. Results

The evaluation of the proposed defense network is conducted by varying the attacking levels. The adversarial model is aware of the defense framework and incorporates them in generating attack-free examples. We consider two types of dataset to test the defense performance for the multi-resolution image generation task. The evaluation result on the result on CIFAR-10 is shown in Fig. 4, and the result the CelebA dataset is shown in Fig. 5.

Fig. 4.

Evaluation results on CIFAR-10 dataset

Fig. 5.

Evaluation results on CelebA dataset

In terms of the proposed adversarial model defense itself, the success rate of a fusing attack is higher than the robust defense model. Low-resolution images are vulnerable to attack, and it is tough to generate images by fusing adversarial attacks. On the other hand, fusing attacks in the high-resolution image is also tricky because if the classifier network and discriminator network are unable to trace the difference between the original image and adversarial examples, then the quality of generation examples will be decreased.

In CelebA dataset evaluation task, 2000 images were used in the test dataset, with the perturbation σ= 0.2 to 0.4. Analogously, the proposed model tested to fuse adversarial examples with perturbations [0.1, 0.2, 0.3, 0.4] to attack methods with full access to the adversarial model. The defense performance of the proposed method is shown in Tables 3, and 4. The conventional defence models are only specified for low or high resolution dataset. Hence, the proposed model trained and evaluated in multi-resolution images to fuse the adversarial attacks and the successive rate is higher than the conventional defence model.

Table 3.

Classification accuracy based on different attack level on CIFAR-10 dataset

Table 4.

Classification accuracy based on different attack level on CelebA dataset

As shown in Table 4, the proposed model showed an enormous rate to fuse the attacks on σ = 0.4 from 86.02% to 89.04% and on σ = 0.3 from 92.7% to 93.6%. Moreover, the success rate is showed more prominent in low-level attacks for both dataset.

Ⅵ. Conclusions

We introduce a defense framework containing three modules: adversarial example identification, adversarial perturbation fusing, and adversarially trained targeted network. Specifically, if an input sample is detected to be adversarial, the sample is cleaned by an instance sparsity mapping network and then analyzed by the adversarially targeted network. As a result, the proposed model achieved successive scores to protect the target model against adversarial attacks. In future work, the proposed adversarial defense framework extends to apply real-world applications, such as face recognition.

Acknowledgments

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (NO.2017R1D1A1B04030870)

This paper is an extension of the "Adversarial Sparsity Mapping Network to Defense Against Adversarial Attacks" published at the Proceedings of Korean Institute of Information Technology Comprehensive Academic Conference in 2021.

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