  Machine Learning (ML) architectures have been applied to several applications
that involve sensitive data, where a guarantee of users' data privacy is
required. Differentially Private Stochastic Gradient Descent (DPSGD) is the
state-of-the-art method to train privacy-preserving models. However, DPSGD
comes at a considerable accuracy loss leading to sub-optimal privacy/utility
trade-offs. Towards investigating new ground for better privacy-utility
trade-off, this work questions; (i) if models' hyperparameters have any
inherent impact on ML models' privacy-preserving properties, and (ii) if
models' hyperparameters have any impact on the privacy/utility trade-off of
differentially private models. We propose a comprehensive design space
exploration of different hyperparameters such as the choice of activation
functions, the learning rate and the use of batch normalization. Interestingly,
we found that utility can be improved by using Bounded RELU as activation
functions with the same privacy-preserving characteristics. With a drop-in
replacement of the activation function, we achieve new state-of-the-art
accuracy on MNIST (96.02\%), FashionMnist (84.76\%), and CIFAR-10 (44.42\%)
without any modification of the learning procedure fundamentals of DPSGD.

Machine Learning;Cryptography and Security;Computer Vision and Pattern Recognition