A method comprising: by one or more servers of a system providing an on-line service, sending a token to a first client computing device associated with a first user of the on-line service, the token being generated by the servers based at least in part on a user identifier of the first user; by the servers, receiving the token from a second client computing device associated with a second user of the on-line service, the token being sent to the second client computing device from the first client computing device through a wireless connection; by the servers, verifying the token based at least in part on the user identifier of the first user; by the servers, determining data accessible to the second user if the token is verified; and by the servers, sending to the second client computing device at least some of the data accessible to the second user, the system is a network-addressable computing system hosting an online social network storing one or more social graphs in one or more data stores the one or more social graphs comprising multiple user nodes and multiple edges connecting the nodes, the nodes and edges stored as data objects in a social-graph database, wherein at least a first node in the social graph corresponds to the first user and a second node in the social graph corresponds to the second user; and in that the verifying of the token comprises, by the servers, accessing the social graph, and verifying the token further based on a least number of edges traversed in the social graph from the first node and the second node; characterized in that the token is truncated and used as a media access control identifier within a physical wireless protocol. by one or more servers of a system providing an on-line service, sending a token to a first client computing device associated with a first user of the on-line service, the token being generated by the servers based at least in part on a user identifier of the first user; by the servers, receiving the token from a second client computing device associated with a second user of the on-line service, the token being sent to the second client computing device from the first client computing device through a wireless connection; by the servers, verifying the token based at least in part on the user identifier of the first user; by the servers, determining data accessible to the second user if the token is verified; and by the servers, sending to the second client computing device at least some of the data accessible to the second user, the system is a network-addressable computing system hosting an online social network storing one or more social graphs in one or more data stores the one or more social graphs comprising multiple user nodes and multiple edges connecting the nodes, the nodes and edges stored as data objects in a social-graph database, wherein at least a first node in the social graph corresponds to the first user and a second node in the social graph corresponds to the second user; and in that the verifying of the token comprises, by the servers, accessing the social graph, and verifying the token further based on a least number of edges traversed in the social graph from the first node and the second node; characterized in that the token is truncated and used as a media access control identifier within a physical wireless protocol.