Privacy-preserving machine learning algorithms are crucial for the
increasingly common setting in which personal data, such as medical or
financial records, are analyzed. We provide general techniques to produce
privacy-preserving approximations of classifiers learned via (regularized)
empirical risk minimization (ERM). These algorithms are private under the
ϵ-differential privacy definition due to Dwork et al. (2006). First we
apply the output perturbation ideas of Dwork et al. (2006), to ERM
classification. Then we propose a new method, objective perturbation, for
privacy-preserving machine learning algorithm design. This method entails
perturbing the objective function before optimizing over classifiers. If the
loss and regularizer satisfy certain convexity and differentiability criteria,
we prove theoretical results showing that our algorithms preserve privacy, and
provide generalization bounds for linear and nonlinear kernels. We further
present a privacy-preserving technique for tuning the parameters in general
machine learning algorithms, thereby providing end-to-end privacy guarantees
for the training process. We apply these results to produce privacy-preserving
analogues of regularized logistic regression and support vector machines. We
obtain encouraging results from evaluating their performance on real
demographic and benchmark data sets. Our results show that both theoretically
and empirically, objective perturbation is superior to the previous
state-of-the-art, output perturbation, in managing the inherent tradeoff
between privacy and learning performance.Comment: 40 pages, 7 figures, accepted to the Journal of Machine Learning
Researc