USEr IdEntIfICatIon ChallEngES

I n this emerging era of pervasive computing, we interact with and rapidly switch among a diverse set of digital devices. We tend to transition from a smartphone to a notebook when arriving in the office, and when we return home, we often switch to a tablet. In between, we might use large wall-mounted displays, car navigation systems, selfcheckout kiosks at retail stores, and home security or smart home controls. Many of these devices—even if only used in the home—have multiple users. Over the next decade, this range of devices will likely increase, and our time with any single device will grow shorter. We argue that it’s time for touchbased personal tokens that let devices unobtrusively identify who is interacting with the device at any given time. This would let devices tailor services to users and apply authentication to control access to sensitive information and online services. Consider, for example, that a child reportedly spent more than $1,000 on in-app purchases while playing games on his mother’s iPhone.1 Devices that know their users could limit such spending from unauthorized users and serve age-appropriate content and media. Our approach is to use a wearable personal token to communicate an identification code through touch.