Poison Frogs Neural Networks

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Presented by

Eric Anderson, Chengzhi Wang, YiJing Zhou, Kai Zhong

Introduction

Poison Frogs! Targeted Clean-Label Poisoning Attacks on Neural Networks from NeurIPS 2018 is written by Ali Shafahi, W. Ronny Huang, Mahyar Najibi, Octavian Suciu, Christoph Studer, Tudor Dumitras, and Tom Goldstein.

Data poisoning attacks are performed by an attacker by adding examples (poisons) to a training set to manipulate the model’s behavior on a test set. The ability for deep learning models to tolerate such poisons is necessary if they are to be deployed in high stakes, security-critical situations. Targeted attacks aim to only manipulate classifier behavior with respect to a specific test instance, and clean-label attacks do not require the attacker to have control over the poison’s labeling.

This paper presents a method to create poisons to effectively make targeted, clean-label poisoning attacks on neural networks, along with techniques to boost lethality. The proposed poisoning technique achieves an 100% success rate on a pretrained InceptionV3 network and sees up to 70% success rate on end-to-end trained scaled-down AlexNet architecture when using watermarks and multiple poison instances.

Previous Work

The current architecture is built on the network-in-network approach proposed by Lin et al.[1] for the purpose of increase the representation power of the neural networks. They added additional 1 X 1 convolutional layers, serving as dimension reduction modules to significantly reduce the number of parameters of the model. The paper also took inspiration from the Regions with Convolutional Neural Networks (R-CNN) proposed by Girshick et al. [2]. The overall detection problem is divided into two subproblems:

1. Utilize low-level cues for potential object proposals

2. Classify object categories with CNN

Motivation

The previous section shows that while there are studies related to poisoning attacks on SVMs and Bayesian classifiers, poisons for deep neural networks (DNNs) have rarely been studied, with the existing few studies indicating DNNs are extremely susceptible to poison attacks (Steinhardt et al. 2017).

Furthermore, poisons studied prior to this paper can be classified into at least one of the following:

  • Focus on classical attacks that degrade model accuracy indiscriminately
  • Require test-time instances to be manually modified
  • Require the attacker to have some degree of control over the labelling of the training set
  • Only achieve acceptable success rates with high poison doses

The proposal of targeted, clean-label poisons in this paper thus opens the door to more efficient, deadly poisons that future neural networks will have to find ways to tolerate.


Model Architecture

The Inception architecture consists of stacking blocks called the inception modules. The idea is that to increase the depth and width of model by finding local optimal sparse structure and repeating it spatially. Traditionally, in each layer of convolutional network pooling operation and convolution and its size (1 by 1, 3 by 3 or 5 by 5) should be decided while all of them are beneficial for the modeling power of the network. Whereas, in Inception module instead of choosing, all these various options are computed simultaneously (Fig. 1a). Inspired by layer-by-layer construction of Arora et al. [3], in Inception module statistics correlation of the last layer is analyzed and clustered into groups of units with high correlation. These clusters form units of next layer and are connected to the units of previous layer. Each unit from the earlier layer corresponds to some region of the input image and the outputs of them are concatenated into a filter bank. Additionally, because of the beneficial effect of pooling in the convolutional networks, a parallel path of pooling has been added in each module. The Inception module in its naïve form (Fig. 1a) suffers from high computation and power cost. In addition, as the concatenated output from the various convolutions and the pooling layer will be an extremely deep channel of output volume, the claim that this architecture has an improved memory and computation power use looks like counterintuitive. However, this issue has been addressed by adding a 1 by 1 convolution before costly 3 by 3 and 5 by 5 convolutions. The idea of 1 by 1 convolution was first introduced by Lin et al. and called network in network [1]. This 1x1 convolution mathematically is equivalent to a multilayer perceptron which reduces the dimension of filter space (the depth of the output volume) and on top of that they also act as a non-linear rectifying activation layer ReLu to add to the non-linearity immediately after each 1 by 1 convolution (Fig. 1b). This enables less over-fitting due to smaller Kernel size (1 by 1). This distinctive dimensionality reduction feature of the 1 by 1 convolution allows shielding of the large number of input filters of the previous stage to the next stage (Footnote 2).

Inception module, naıve version.JPG
Figure 1(a): Inception module, naïve version
Inception module with dimension reductions.JPG
Figure 1(b): Inception module with dimension reductions

The combination of various layers of convolution has some similarity with human eyes in interpreting the visual information in a sense that human eyes also process the visual information at various scale and combines to extract the features from different scale simultaneously. Similarly, in inception design network in network designs extract the fine grain details of input volume while medium- and large-sized filters cover a large receptive field of the inputs and extract their features and with pooling operations overfitting can be overcome by reducing the spatial sizes.

ILSVRC 2014 Challenge Results

The proposed architecture was implemented through a deep network called GoogLeNet as a submission for ILSVRC14’s Classification Challenge and Detection Challenge.

The classification challenge is to classify images into one of 1000 categories in the Imagenet hierarchy. The top-5 error rate - the percentage of test examples for which the correct class is not in the top 5 predicted classes - is used for measuring accuracy. The results of the classification challenge is shown in Table 1. The final submission of GoogLeNet obtains a top-5 error of 6.67% on both the validation and testing data, ranking first among all participants, significantly outperforming top teams in previous years, and not utilizing external data.

Image: 500 pixels
Table 1: Classification performance

The ILSVRC detection challenge asks to produce bounding boxes around objects in images among 200 classes. Detected objects count as correct if they match the class of the groundtruth and their bounding boxes overlap by at least 50%. Each image may contain multiple objects (with different scales) or none. The mean average precision (mAP) is used to report performance. The results of the detection challenge is listed in Table 2. Using the Inception model as a region classifier, combining Selective Search and using an ensemble of 6 CNNs, GoogLeNet gave top detection results, almost doubling accuracy of the the 2013 top model.

Image: 600 pixels
Table 2: Detection performance

Conclusion

This article studied targeted clean-label poisoning methods. These attacks are difficult to detect because they involve non-suspicious (correctly labeled) training data, and do not degrade the performance on non-targeted examples. Poison images collide with a target image in feature space, therefore the network will be very hard to distinguish them. Multiple poison images and a watermarking trick will make the attack more powerful. While our poisoned dataset training does indeed make the network more robust to base-class adversarial examples designed to be misclassified as the target, it also has the effect of causing the unaltered target instance to be misclassified as a base. Finally the paper hopes that it can raise attention for the important issue of data reliability and provenance.

Critiques

By using nearly 5 million parameters, GoogLeNet, compared to previous architectures like VGGNet and AlexNet, reduced the number of parameters in the network by almost 92%. This enabled Inception to be used for many big data applications where a huge amount of data was needed to be processed at a reasonable cost while the computational capacity was limited. However, the Inception network is still complex and susceptible to scaling. If the network is scaled up, large parts of the computational gains can be lost immediately. Also, there was no clear description about the various factors that lead to the design decision of this inception architecture, making it harder to adapt to other applications while maintaining the same computational efficiency.

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References

[1] Min Lin, Qiang Chen, and Shuicheng Yan. Network in network. CoRR, abs/1312.4400, 2013.

[2] Ross B. Girshick, Jeff Donahue, Trevor Darrell, and Jitendra Malik. Rich feature hierarchies for accurate object detection and semantic segmentation. In Computer Vision and Pattern Recognition, 2014. CVPR 2014. IEEE Conference on, 2014.

[3] Sanjeev Arora, Aditya Bhaskara, Rong Ge, and Tengyu Ma. Provable bounds for learning some deep representations. CoRR, abs/1310.6343, 2013.

[4] ¨Umit V. C¸ ataly¨urek, Cevdet Aykanat, and Bora Uc¸ar. On two-dimensional sparse matrix partitioning: Models, methods, and a recipe. SIAM J. Sci. Comput., 32(2):656–683, February 2010.

Footnote 1: Hebbian theory is a neuroscientific theory claiming that an increase in synaptic efficacy arises from a presynaptic cell's repeated and persistent stimulation of a postsynaptic cell. It is an attempt to explain synaptic plasticity, the adaptation of brain neurons during the learning process.

Footnote 2: For more explanation on 1 by 1 convolution refer to: https://iamaaditya.github.io/2016/03/one-by-one-convolution/