A method for secure and reliable authentication in a communication system. In an embodiment, the authentication method includes performing authentication of a user utilizing Extensible Authentication Protocol (EAP), and transmitting a result indication message to the user. The result indication message can include additional information for security and reliability. The method also includes receiving an acknowledgement message from the user. The acknowledgement message is sent by the user for confirming the reception of the result indication. In an embodiment, the method also includes retransmitting the result indication message if the acknowledgement message is not received within a predetermined time. The additional information for security and reliability can include Message Authentication Code (MAC) and time interval information. The additional information for security and reliability can also include a security/reliability flag.