—Security and liability issues set barriers to WiFi sharing, giving away opportunities to capitalize the unused capacity in WiFi networks and provide wider Internet access. Considering the lack of trust between WiFi sharers and potential guests, we leverage on the increasing penetration of online social networks to enable WiFi sharing with online friends. To this end, we present a WiFi sharing architecture, called Social WiFi, and the associated mechanisms for network discovery and authentication. Social WiFi couples Bloom Filter with extensions to existing authentication mechanisms for the discovery and authentication of guests to WiFi networks owned by their online friends. We assess the authentication in Social WiFi in terms of performance and efficiency. Furthermore, we discuss deployment issues and lay out a delegation framework for the migration of the existing WiFi network infrastructure to Social WiFi.