The ephemeral pairing problem requires two or more specific physical nodes in a wireless broadcast network, that do not yet know each other, to establish a short-term relationship between them. Such shortlived pairings occur, for example, when one pays at a check-out using a wireless wallet. This problem is equivalent to the ephemeral key exchange problem, where one needs to establish a high-entropy shared session key between two nodes given only a low bandwidth authentic (or private) communication channel between the pair, and a high bandwidth shared broadcast channel. We study this problem for truly anonymous broadcast networks, discuss certain impossible scenarios and present several protocols depending on the type of communication channel between the nodes.