Privacy-Preserving CNN Training with Transfer Learning: Two Hidden Layers

Fuente: arXiv
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Main Author: Chiang, John
Format: Preprint
Published: 2025
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author Chiang, John
author_facet Chiang, John
contents In this paper, we present the demonstration of training a four-layer neural network entirely using fully homomorphic encryption (FHE), supporting both single-output and multi-output classification tasks in a non-interactive setting. A key contribution of our work is identifying that replacing \textit{Softmax} with \textit{Sigmoid}, in conjunction with the Binary Cross-Entropy (BCE) loss function, provides an effective and scalable solution for homomorphic classification. Moreover, we show that the BCE loss function, originally designed for multi-output tasks, naturally extends to the multi-class setting, thereby enabling broader applicability. We also highlight the limitations of prior loss functions such as the SLE loss and the one proposed in the 2019 CVPR Workshop, both of which suffer from vanishing gradients as network depth increases. To address the challenges posed by large-scale encrypted data, we further introduce an improved version of the previously proposed data encoding scheme, \textit{Double Volley Revolver}, which achieves a better trade-off between computational and memory efficiency, making FHE-based neural network training more practical. The complete, runnable C++ code to implement our work can be found at: \href{https://github.com/petitioner/ML.NNtraining}{$\texttt{https://github.com/petitioner/ML.NNtraining}$}.
format Preprint
id arxiv_https___arxiv_org_abs_2504_12623
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Privacy-Preserving CNN Training with Transfer Learning: Two Hidden Layers
Chiang, John
Cryptography and Security
In this paper, we present the demonstration of training a four-layer neural network entirely using fully homomorphic encryption (FHE), supporting both single-output and multi-output classification tasks in a non-interactive setting. A key contribution of our work is identifying that replacing \textit{Softmax} with \textit{Sigmoid}, in conjunction with the Binary Cross-Entropy (BCE) loss function, provides an effective and scalable solution for homomorphic classification. Moreover, we show that the BCE loss function, originally designed for multi-output tasks, naturally extends to the multi-class setting, thereby enabling broader applicability. We also highlight the limitations of prior loss functions such as the SLE loss and the one proposed in the 2019 CVPR Workshop, both of which suffer from vanishing gradients as network depth increases. To address the challenges posed by large-scale encrypted data, we further introduce an improved version of the previously proposed data encoding scheme, \textit{Double Volley Revolver}, which achieves a better trade-off between computational and memory efficiency, making FHE-based neural network training more practical. The complete, runnable C++ code to implement our work can be found at: \href{https://github.com/petitioner/ML.NNtraining}{$\texttt{https://github.com/petitioner/ML.NNtraining}$}.
title Privacy-Preserving CNN Training with Transfer Learning: Two Hidden Layers
topic Cryptography and Security
url https://arxiv.org/abs/2504.12623