A method for coupling a first mobile device (102, 202) with a second mobile device (104, 204) in a 1:1 Proximity-based Services, ProSe, communication session, the method comprising: the first mobile device (102, 202) discovering the presence of the second mobile device (104, 204); negotiating between the first mobile device (102, 202) and the second mobile device (104, 204) to determine that the second mobile device (104, 204) is to become a group owner of the communication session and the first mobile device (102, 202) is to become a client of the communication session; and conducting a mutual authentication with the group owner; the first mobile device (102, 202) and the second mobile device (104, 204) communicate with each other via a device-to-device link; characterized in that conducting mutual authentication further comprises: the second mobile device (104, 204) verifying a first certificate owned by the first mobile device (102, 202); and the first mobile device (102, 202) verifying a second certificate owned by the second mobile device (104, 204); wherein, the first certificate includes a first link identifier that identifies the first mobile device (102, 202); the second certificate includes a second link identifier that identifies the second mobile device (104, 204); the first certificate is arranged to confirm that the first mobile device (102, 202) is authorized; and the second certificate is arranged to confirm that the second mobile device (104, 204) is authorized. the first mobile device (102, 202) discovering the presence of the second mobile device (104, 204); negotiating between the first mobile device (102, 202) and the second mobile device (104, 204) to determine that the second mobile device (104, 204) is to become a group owner of the communication session and the first mobile device (102, 202) is to become a client of the communication session; and conducting a mutual authentication with the group owner; the first mobile device (102, 202) and the second mobile device (104, 204) communicate with each other via a device-to-device link; characterized in that conducting mutual authentication further comprises: the second mobile device (104, 204) verifying a first certificate owned by the first mobile device (102, 202); and the first mobile device (102, 202) verifying a second certificate owned by the second mobile device (104, 204); wherein, the first certificate includes a first link identifier that identifies the first mobile device (102, 202); the second certificate includes a second link identifier that identifies the second mobile device (104, 204); the first certificate is arranged to confirm that the first mobile device (102, 202) is authorized; and the second certificate is arranged to confirm that the second mobile device (104, 204) is authorized. the second mobile device (104, 204) verifying a first certificate owned by the first mobile device (102, 202); and the first mobile device (102, 202) verifying a second certificate owned by the second mobile device (104, 204); wherein, the first certificate includes a first link identifier that identifies the first mobile device (102, 202); the second certificate includes a second link identifier that identifies the second mobile device (104, 204); the first certificate is arranged to confirm that the first mobile device (102, 202) is authorized; and the second certificate is arranged to confirm that the second mobile device (104, 204) is authorized.