Electronic authentication with a portable device such as a smart card has been receiving increasing attention. In an authentication, the portable device is regarded as the human user himself. However, in an open environment like authentication systems, it is necessary to have a way of secure communication between the portable device and the human user. This paper considers an authentication of a server computer of a service provider by a human with a portable device as a part of the authentication and an attack by a client computer which relays the communication between the portable device and the server computer. As a defense against the attack, we introduce a system with a portable device which has an interface to show information to a human.