Method for authenticating a central unit connected to peripheral units using a secure server

A method for authenticating rights of a central unit of a user device for communicating bidirectionally at radio frequency with one or more peripheral units fixed to wheels of a motor vehicle which transmit raw measurement data consisting of measurements performed on tires of the vehicle which the one or more peripheral units acquire, each of the central unit and each of the one or more peripheral units possessing a specific identifier, this method using, over the Internet, an external server device comprising at least one secure server, comprising a secure connection between a plurality of the at least one secure server, and possessing, in a database, the identifier of the peripheral units, the method comprising the following successive steps:

• the central unit uses its identifier and a password to get itself recognized by each peripheral unit, each peripheral unit generates a symmetric shared random encryption key, and in parallel, the central unit establishes a secure connection with the server device, authenticating so that the server recognizes, in the server database, the specific identifier of the peripheral unit;
• the server device generates a dynamic temporary session key;
• the server device generates an encryption key which is the same as the symmetric shared encryption key on the basis of the identifier of the peripheral unit, then performs a first encryption with this shared encryption key and with the dynamic temporary session key in order to form a first shared dynamic encryption key, then performs a second encryption using the identifier of the central unit, and the symmetric shared encryption key or the dynamic temporary session key, in order to give an encrypted central-unit information item which is a proof of authentication;
• the shared dynamic encryption key and the encrypted central-unit information item are transmitted to the central unit, which transmits them, in its turn, to the peripheral units;
• the one or more peripheral unit perform a decryption which is the reverse of the first encryption, performed by the server device in its third step, with the shared encryption key and the shared dynamic encryption key, in order to obtain the dynamic temporary session key;
• and
• the one or more peripheral unit perform, in parallel, an encryption with its shared encryption key and the central-unit identifier in order to give a second encrypted information item, then compares this second encrypted information item with the received encrypted central-unit information item in order, if they coincide, to grant its authentication to this central unit.