The present invention relates to a method of protecting an electronic chip (1) of a user against fraud in transactions between an application (2) and the electronic chip (1).The method consists in: both the electronic chip (1) and the application (2) computing (16, 17) a certificate (Sp, S) which is the result of applying the logic function g to a list of arguments (e1, e2) comprising at least the seed R and the secret key K, allocating to the electronic chip (1) a second secret key K′ known only to the electronic chip (1) and to the application (2) and kept secret (13) in the electronic chip (1), on each authentication of the electronic chip (1), determining (18, 19) a mask M computed by applying a non-linear function f to at least a portion of the secret key K′, masking (20) the value of the certificate (Sp) by means of the mask M to make available to the application (2) only the masked value of the certificate (Spm), and using the application (2) to verify the masked value of the certificate (Spm) computed by the electronic chip (1).