Propagating authentication between terminals connected to a server having identification information and user information for the terminals. The terminal receives identification information, user information, location information and a login status from a first terminal and a second terminal in response to a predetermined impact between the terminals, or the terminals coming within a predetermined distance of each other, the login status of the terminals being either authenticated or unauthenticated. The server then authenticates the second terminal in response to the users of the first terminal matching some or all of the users of the second terminal based on the identification and user information, in response to the terminals being located within a predetermined distance of each other, and in response to the first terminal being authenticated and the second terminal being unauthenticated on the basis of the login status.