Fast and Effective Robustness Certification for Recurrent Neural Networks

We present a precise and scalable verifier for recurrent neural networks, called R2. The verifier is based on two key ideas: (i) a method to compute tight linear convex relaxations of a recurrent update function via sampling and optimization, and (ii) a technique to optimize convex combinations of multiple bounds for each neuron instead of a single bound as previously done. Using R2, we present the first study of certifying a non-trivial use case of recurrent neural networks, namely speech classification. This required us to also develop custom convex relaxations for the general operations that make up speech preprocessing. Our evaluation across a number of recurrent architectures in computer vision and speech domains shows that these networks are out of reach for existing methods as these are an order of magnitude slower than R2, while R2 successfully verified robustness in many cases.