Disparate Impact on Group Accuracy of Linearization for Private
  Inference
Saswat Das Marco Romanelli Ferdinando Fioretto
Ensuring privacy-preserving inference on cryptographically secure data is a
well-known computational challenge. To alleviate the bottleneck of costly
cryptographic computations in non-linear activations, recent methods have
suggested linearizing a targeted portion of these activations in neural
networks. This technique results in significantly reduced runtimes with often
negligible impacts on accuracy. In this paper, we demonstrate that such
computational benefits may lead to increased fairness costs. Specifically, we
find that reducing the number of ReLU activations disproportionately decreases
the accuracy for minority groups compared to majority groups. To explain these
observations, we provide a mathematical interpretation under restricted
assumptions about the nature of the decision boundary, while also showing the
prevalence of this problem across widely used datasets and architectures.
Finally, we show how a simple procedure altering the fine-tuning step for
linearized models can serve as an effective mitigation strategy.