Private badges for geosocial networks

Geosocial networks (GSNs) extend classic online social networks with the concept of location. Users can report their presence at venues through 'check-ins' and, when certain check-in sequences are satisfied, users acquire special status in the form of 'badges'. We first show that this innovative functionality is popular in Foursquare, a prominent GSN. Furthermore, we address the apparent tension between privacy and correctness, where users are unable to prove having satisfied badge conditions without revealing the corresponding time and location of their check-in sequences. To this end, we propose several privacy preserving protocols that enable users to prove having satisfied the conditions of several badge types. Specifically, we introduce (i) GeoBadge and T-Badge, solutions for acquiring location badges, (ii) FreqBadge, for mayorship badges, (iii) e-Badge, for proving various expertise levels and (iv) MPBadge, for accumulating multi-player badges. We show that a Google Nexus One smartphone is able to perform tens of badge proofs per minute while a provider can support hundreds of million of check-ins and badge verifications per day.