The Cost of Push Notifications for Smartphones Using Tor Hidden Services

Push notification services provide reliable, energy efficient, store-and-forward messaging between servers and clients. This mode of communication is widely used, and sufficiently compelling for mobile devices that push notification services are integrated into operating systems. Unfortunately, push notification services today allow the service provider to practice censorship, surveillance, and location tracking. We explore whether running a Tor hidden service from a smartphone offers a viable, privacy-aware alternative. We conduct empirical measurements in the lab as well as modelling using data from 2 014 handsets in the Device Analyzer dataset. We estimate the monthly median cost of cellular data required to support a Tor hidden service from a smartphone at 198 MiB. We further estimate that the network activity would cost at least 9.6% of total battery on a Nexus One device with a daily charging cycle and connected to the Internet via 3G. We explore four strategies for reducing cellular data costs which, when combined, could potentially reduce the total monthly median cost to 61 MiB.