Finding minimum distortion of adversarial examples and thus certifying robustness in neural network classifiers for given data points is known to be a challenging problem. Nevertheless, recently it has been shown to be possible to give a non-trivial certified lower bound of minimum adversarial distortion, and some recent progress has been made towards this direction by exploiting the piece-wise linear nature of ReLU activations. However, a generic robustness certification for general activation functions still remains largely unexplored. To address this issue, in this paper we introduce CROWN, a general framework to certify robustness of neural networks with general activation functions for given input data points. The novelty in our algorithm consists of bounding a given activation function with linear and quadratic functions, hence allowing it to tackle general activation functions including but not limited to four popular choices: ReLU, tanh, sigmoid and arctan. In addition, we facilitate the search for a tighter certified lower bound by adaptively selecting appropriate surrogates for each neuron activation. Experimental results show that CROWN on ReLU networks can notably improve the certified lower bounds compared to the current state-of-the-art algorithm Fast-Lin, while having comparable computational efficiency. Furthermore, CROWN also demonstrates its effectiveness and flexibility on networks with general activation functions, including tanh, sigmoid and arctan.

该论文介绍了一种名为CROWN的通用框架，可以证明具有一般激活函数的神经网络分类器对于给定的输入数据点是健壮的，通过绑定给定激活函数的线性和二次函数，从而可以处理包括但不限于ReLU、tanh、sigmoid和arctan在内的一般激活函数，同时在可比的计算效率下，在ReLU网络上CROWN可以显着提高认证下限，同时CROWN能够展示其对包括tanh、sigmoid和arctan在内的具有一般激活函数的网络的有效性和灵活性。

具有通用激活函数的高效神经网络鲁棒性认证