Method to prevent hidden communication on a channel during device authentication, corresponding VPLMN and HPLMN

A public land mobile network (PLMN) acting as a visited PLMN, said visited PLMN comprising processing means for:

• receiving a unique identifier from a telecommunication device cooperating with a secure element during an authentication phase,
• generating a required information and sending said unique identifier and said required information to a home PLMN identified by a Mobile Country Code/Mobile Network Code (MCC/MNC) comprised in said unique identifier, said visited PLMN:
• If said home PLMN has sent an authentication vector and a random value, computing a cryptographic value from said required information and said random value, verifying that said cryptographic value received in said authentication vector corresponds to the cryptographic value computed at said visited PLMN and, if yes, transmitting from said visited PLMN to a telecommunication terminal said cryptographic value and an authentication token retrieved from said authentication vector;
• If said home PLMN has sent only said authentication vector containing said random value instead of said cryptographic value, computing another cryptographic value from said required information and said random value, and transmitting from said visited PLMN to said telecommunication terminal said other cryptographic value and the authentication token retrieved from said authentication vector.

A public land mobile network, PLMN, acting as a home PLMN, said home PLMN comprising processing means for:

• receiving from a visited PLMN a required information and a unique identifier of a secure element cooperating with a telecommunication terminal;
• generating:
• a random value and computing a cryptographic value based on said random value and said required information, and
• an authentication vector based on said cryptographic value and a long-term key of said secure element, said long-term key being associated to said unique identifier, and sending said authentication vector and said random value or only said authentication vector containing said random value instead of said cryptographic value to said visited PLMN.