SDDR: Light-Weight, Secure Mobile Encounters

Emerging mobile social apps use short-range radios to discover nearby devices and users. The device discovery protocol used by these apps must be highly energy-efficient since it runs frequently in the background. Also, a good protocol must enable secure communication (both during and after a period of device co-location), preserve user privacy (users must not be tracked by unauthorized third parties), while providing selective linkability (users can recognize friends when strangers cannot) and efficient silent revocation (users can permanently or temporarily cloak themselves from certain friends, unilaterally and without re-keying their entire friend set). We introduce SDDR (Secure Device Discovery and Recognition), a protocol that provides secure encounters and satisfies all of the privacy requirements while remaining highly energyefficient. We formally prove the correctness of SDDR, present a prototype implementation over Bluetooth, and show how existing frameworks, such as Haggle, can directly use SDDR. Our results show that the SDDR implementation, run continuously over a day, uses only ∼10% of the battery capacity of a typical smartphone. This level of energy consumption is four orders of magnitude more efficient than prior cryptographic protocols with proven security, and one order of magnitude more efficient than prior (unproven) protocols designed specifically for energy-constrained devices.