US Patent 7434070 Secret code security access to data processing means

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.