Privately Identifying Meeting Locations

Developed in collaboration by Stealth, Two Six Labs (now Two Six Technologies), and Raytheon BBN as part of our work on the DARPA Brandeis program, “Coffeebreak” is a novel mobile application that facilitates spontaneous meet-ups by finding good locations close to everyone, without actually revealing anyone’s current location.  Finding candidate meeting locations that are central to all participants is a straightforward task for any GPS-enabled mobile device, but doing so while preserving the privacy of each participant’s location requires advanced techniques from cryptography.  Coffeebreak does exactly this, allowing you to identify a meeting place that is convenient for everyone, without anyone actually learning where you are.

Why should you care?

Our digital footprint grows every day, as more and more information about us is stored on multiple devices and in myriad databases.  No device holds more of our personal information than our phone, and one of the most sensitive pieces of information is our current location.  While map apps and other on-device applications can take advantage of location data to make your life easier, sharing your location data with a remote server that you don’t trust or another mobile device creates a number of security concerns.  Maybe you’re at home and don’t want to reveal where you live, or maybe you’re at an appointment you don’t want anyone and everyone to know about, or maybe you’re just running late and aren’t exactly where you’re supposed to be.  There are any number of reasons you might want to hide your current location, even from people you’re about to meet up with.  Not to mention the fact that you’re not just sharing your location with the people you’ll be seeing—you’re also sharing it with their devices or a third-party server, any of which may be infected with malware or otherwise leak your location data to a much broader audience than you ever intended.

How it works

Using the participants’ current locations, Coffeebreak finds a place of interest – say a coffee shop – that will minimize everyone’s distance to get there.  However, instead of just sharing everyone’s location with each other or with a third-party server in order to identify the meeting location, Coffeebreak utilizes techniques from cryptography to calculate the optimal meeting place without requiring the users to share their location data with anyone.  Finding the closest spot to everyone without ever exposing anyone’s actual location may seem counterintuitive, even impossible.  But modern cryptography makes it not only possible but achievable in practice, with a mathematically proven guarantee of privacy.  Our technology is based on cryptographic techniques called Secure Multi-Party Computation, or “MPC” for short.  Coffeebreak’s underlying MPC engine, built by Stealth, is one of the first technologies to perform MPC entirely on users’ mobile devices, without requiring any other computing platform.  Our MPC engine has also been applied to a solution for secure scheduling, which enables you to find a common meeting time with your friends, coworkers, or collaborators without requiring anyone to reveal their personal schedules.

This work was supported by DARPA and NIWC Pacific under Contract No. N66001-15-C-4065, Distribution Statement A: “Approved for Public Release, Distribution Unlimited. If you have any questions, please contact the Public Release Center”. The views, opinions and/or findings expressed are those of the author and should not be interpreted as representing the official views or policies of the Department of Defense or the U.S. Government.