Patent ID: 6839840

Claim:
An authenticating method between a memory chip card having at least one counter and a terminal, comprising the following steps: (a) inserting the memory chip card into the terminal, (b) calculating, in the terminal, a secret code CSC 1 , according to a cryptographic function F of a number of variables comprising at least a code CSN identifying the memory chip card and the value of said counter, (c) authenticating the terminal by the card when the calculated secret code CSC 1 is identical to a code CSC 0 recorded in a memory of the card at the end of a previous authentication operation, (d) carrying out a desired transaction and modifying the value of said counter, (e) calculating, in the terminal, a new secret code CSC 2 according to the cryptographic function F of the code CSN identifying the memory chip card and the new value of said counter, (f) updating the memory chip card for the next transaction by recording, in said memory, the new secret code CSC 2 calculated by the operation (e).