Abstract: Access control to data processing means, such as a smart card, is made secure by simulating a comparison block by block of part of a secret code with part of a presented code through a block-by-block comparison of part of the presented code and part of a determined number when the presented code is found to be erroneous. Each time the card is used, a constant number of operations are applied to the presented code and at least for part of the secret code, and at most for a complementary part to the determined number, thus avoiding different signatures of power consumption for different presented codes.

Abstract: The invention constitutes an improvement of access control security to data processing means, such as a smart card (MNV, MA), by simulating a comparison (E7) block by block (Si, Pi) of part of a secret code (S) with part of the presented code (P) through a block-by-block comparison (Pi, Aj) of part of the presented code and part of a number (A) when the presented code is found to be erroneous. Each time the card is used, a constant number of operations are applied to the presented code (P) and at least for part of the secret code (S) and at most for a complementary part relative to the number of operations, to the number (A), thus avoiding different signatures of power consumption for different presented codes.