Cryptographic method for protection against fraud

Cryptographic process for protecting against fraud in transactions between an application (1) and an electronic chip (2) of a user, comprising the following steps: - determining a f implanted nonlinear function known by the application (1) and in the electronic chip (2), - attributed to the electronic chip (2) a first secret key K, known only to the electronic chip (2) and the application (1) and stored in secret in the electronic chip (2 ), - generating in each authentication of the electronic chip (2) a word variable input, R, called random, - calculating (15) an SP certificate using the electronic chip (2) and calculating (16) an S by applying (1), each of the two certificates Sp, s the result of nonlinear function f applied to a list of arguments (e1, e2) comprising at least the random variable R and the secret key K characterized by that this procedure also has the following steps of: - attributed to the electronic chip (2) a second secret key kd known only to the electronic chip (2) and the application (1) and stored in secret ( 6) in the electronic chip (2), - on each authentication of the electronic chip (2) determine (17, 18) having a mask M computed from at least one part of the secret key kd, - masking (19 ) the value of the certificate Sp by the mask M to provide the application (1) only the value of the masked certificate (Spm) - see, through the application (1), the masked value (Spm) certificate calculated by the electronic chip (2).