Building a recommendation system involves analyzing user data, which can
potentially leak sensitive information about users. Anonymizing user data is
often not sufficient for preserving user privacy. Motivated by this, we propose
a privacy-preserving recommendation system based on the differential privacy
framework and matrix factorization, which is one of the most popular algorithms
for recommendation systems. As differential privacy is a powerful and robust
mathematical framework for designing privacy-preserving machine learning
algorithms, it is possible to prevent adversaries from extracting sensitive
user information even if the adversary possesses their publicly available
(auxiliary) information. We implement differential privacy via the Gaussian
mechanism in the form of output perturbation and release user profiles that
satisfy privacy definitions. We employ R\'enyi Differential Privacy for a tight
characterization of the overall privacy loss. We perform extensive experiments
on real data to demonstrate that our proposed algorithm can offer excellent
utility for some parameter choices, while guaranteeing strict privacy.