Method for authentication between a portable telecommunication object and a public access terminal

A method of mutually authenticating, firstly, a portable telecommunications object (10) assigned a unique identifier (MSISDN) and including first wireless communications means and, secondly, a public access terminal (20) including second wireless communications means adapted to cooperate with said first wireless communications means and telecommunications means for communicating via a telecommunications network (1), which method is characterized in that it comprises the following operations:

• assigning said portable telecommunications object (10) a wireless communication key (Kme),
• installing on said telecommunications network (1) an authentication server (30) adapted to determine the wireless communication key (Kme) of the portable object (10) from said unique identifier (MSISDN),
• sending the unique identifier (MSISDN) of the portable object (10) from the portable object to the public access terminal (20) via said first and second wireless communications means,
• sending the unique identifier (MSISDN) of the portable object (10) from the public access terminal (20) to the authentication server (30) via said telecommunications means,
• the authentication server (30) determining the wireless communication key (Kme) of the portable object (10) from the unique identifier (MSISDN) sent,
• the authentication server (30) allocating said wireless communication key (Kme) to a calculation unit (20, 30),
• the calculation unit (20, 30) calculating a session key (Ksession) from said wireless communication key (Kme) of the portable object (10),
• allocating said session key (Ksession) to the public access terminal (20),
• the public access terminal (20) sending the portable object (10) a first message (mess1;
• mess11;
• mess12) signed using the session key (Ksession) via said first and second wireless communications means,
• the portable object (10) acquiring the session key (Ksession) from the first message (mess l;
• mess11;
• mess12) and the wireless communication key (Kme) and authenticating the public access terminal (20) by verifying the signature of said first signed message (mess1;
• mess11;
• mess12), and
• the portable object (10) sending the public access terminal (20) a second message (mess2) signed with the session key (Ksession) via said first and second wireless communications means and the public access terminal (20) authenticating the portable object (10) by verifying the signature of said second signed message (mess2).