Authentication method between a reader and a radio tag

A radio tag suited to authenticating a radio reader and to authenticating itself to a radio reader, said tag comprising:

• reception means for receiving a ciphered piece of information and a data item and determining an index for identifying the authentication coupon of the reader, said piece of information being ciphered by applying a reversible operation to the authentication coupon of the reader and to the piece of information,
• calculation means for calculating a current authentication coupon for the reader as a function of the index,
• decipher means for deciphering the received piece of information ciphered by the reversible operation applied to the calculated current authentication coupon and to the ciphered received piece of information,
• checking means for checking the piece of information and verifying that the calculated current coupon corresponds to the authentication coupon used to cipher the piece of information.

A radio authentication system comprising:

• a radio tag, which comprises:
• reception means for receiving a ciphered piece of information and a data item and determining an index for identifying the authentication coupon of a radio reader, said piece of information being ciphered by applying a reversible operation to the authentication coupon of the radio reader and to the piece of information,
• calculation means for calculating a current authentication coupon for the radio reader as a function of the index,
• decipher means for deciphering the received piece of information ciphered by the reversible operation applied to the calculated current authentication coupon and to the ciphered received piece of information, and
• checking means for checking the piece of information and verifying that the calculated current coupon corresponds to the authentication coupon used to cipher the piece of information;
• and
• the radio reader, which comprises:
• selection means for selecting the authentication coupon for the radio reader,
• cipher means for ciphering the piece of information by applying the reversible operation to the authentication coupon of the radio reader and to the piece of information,
• sending means for sending the ciphered piece of information and the data item allowing determination of the index for identifying the authentication coupon of the radio reader.