Key-Nets: Optical Transformation Convolutional Networks for Privacy Preserving Vision Sensors

Keynet

Abstract

Modern cameras are not designed with computer vision or machine learning as the target application. There is a need for a new class of vision sensors that are privacy preserving by design, that do not leak private information and collect only the information necessary for a target machine learning task. In this paper, we introduce key-nets, which are convolutional networks paired with a custom vision sensor which applies an optical/analog transform such that the key-net can perform exact encrypted inference on this transformed image, but the image is not interpretable by a human or any other key-net. We provide five sufficient conditions for an optical transformation suitable for a key-net, and show that generalized stochastic matrices (e.g. scale, bias and fractional pixel shuffling) satisfy these conditions. We motivate the key-net by showing that without it there is a utility/privacy tradeoff for a network fine-tuned directly on optically transformed images for face identification and object detection. Finally, we show that a key-net is equivalent to homomorphic encryption using a Hill cipher, with an upper bound on memory and runtime that scales with a user specified privacy parameter. Therefore, the key-net is the first practical, efficient and privacy preserving vision sensor based on optical homomorphic encryption.

[code] [paper]

Challenge Problem

Keynet

These images contain a secret message. We have released the first of these images with the paired keynet to challenge the research community to discover a weakness in semantic security of our proposed approach. Good luck!

Citation

Key-Nets: Optical Transformation Convolutional Networks for Privacy Preserving Vision Sensors
Jeffrey Byrne (Visym Labs), Brian Decann (STR), Scott Bloom (STR)
British Machine Vision Conference (BMVC) 2020, Best Paper - Runner up

@InProceedings{Byrne2020bmvc,
author = {J. Byrne and B. Decann and S. Bloom},
title = {Key-Nets: Optical Transformation Convolutional Networks for Privacy Preserving Vision Sensors},
booktitle = {British Machine Vision Conference (BMVC)},
year = {2020}
}

Acknowledgement

This material is based upon work supported by the Defense Advanced Research Projects Agency (DARPA) under Contract No. HR001119C0067.