Practical Privacy-Preserving Friend Recommendations on Social Networks.

Making friend recommendations is an important task for social networks, as having more friends typically leads to a better user experience. Most current friend recommendations systems grow the existing network at the cost of privacy. In particular, any given user's friend graph may be directly or indirectly leaked as a result of such recommendations. In many situations this is not desirable, as the friend list may reveal much about the user--from their identity to their sexual orientation and interests. In this work, we focus on the "cold start" problem of making friend recommendations for new users while raising the bar on protecting the privacy of the friend list of all users. We propose a practical friend recommendation framework, tested on the Snapchat social network, that preserves the privacy of users' friends lists with respect to brute-force attacks and scales to millions of users.