The invention is related to a system which allows a user to authenticate unknown terminals. The invention uses a first authentication step wherein the terminal authenticates itself to a server. Depending on whether the personal device has its own output means, such as a loudspeaker or a screen, the final message, whether the terminal can be trusted or not, can be output on the personal device or on the terminal itself. In the case where the device has no output means of its own, this message can originate in the device and be transmitted from there to the terminal. The user can input authentication information into his personal device, which can then be fully or partially transmitted to the terminal. In the end, the terminal may use the transmitted information to give out the authenticity output message. After the first authentication step follows a second authentication step, wherein the server authenticates itself to the personal device, if there is one. Upon success of both authentication steps, the authenticity output message can be given to the user.