Efficient Secure Building Blocks With Application to Privacy Preserving Machine Learning Algorithms

Nowadays different entities (such as hospitals, cyber security companies, banks, etc.) collect data of the same nature but often with different statistical properties. It has been shown that if these entities combine their privately collected datasets to train a machine learning model, they would end up with a trained model that often outperforms the human experts of the corresponding field(s) in terms of classification accuracy. However, due to judicial, privacy and cost reasons, no entity is willing to share their data with others. We have the same problem during the classification (inference) stage. Namely, the user doesn't want to reveal any information about his query or its' final classification, while the owner of the trained model wants to keep this model private. In this article we overcome these drawbacks by firstly introducing novel efficient secure building blocks for general purpose, which can also be used to build privacy preserving machine learning algorithms for both training and classification (inference) purposes under strict privacy and security requirements. Our theoretical analysis and experimentation results show that our building blocks (hence also our privacy preserving algorithms which are built on top of them) are more efficient than most (if not all) of the state-of-the-art schemes in terms of computation and communication cost, as well as security characteristics in the semi-honest model. Furthermore, and to the best of our knowledge, for the Naïve Bayes model we extend this efficiency for the first time to also deal with active malicious users, which arbitrarily deviate from the protocol.