Process for changing the authentication key

The invention relates to a method of generating an authentication key in a security module (10) which stores a first master key (K_root_A) shared with a first network entity (MNOA), the method comprising the steps of: - sending (E0, E0 ') at a second network entity (MNOB) of a transfer request, - receiving (E5, E10') of the second entity with a first secret (S_b1), - generation (E8, E11 ' ) of a generation of secret key (Kbl) from the first master key and the first secret, -receiving (E13, E10 ') of the second entity of a second secret (S_b2) and a message authentication of the second secret calculated from the generation of secret key transmitted to the second entity by the first entity, - verification (E14, E12 ') of authentication message using the secret key generation - generation (E15, E13 ') with a second master key (K_root_B) if the verifi tion is positive, said second master key is generated from the second secret (S_b2) and generation of secret key (Kbl), and used to generate an authentication key for accessing a network from the second network entity.