identifier u this can be an encryption function f or a hashing function h 1 in this second case as the hashing operation carried out by the second server is not known by the first server it will be a function of a different hashing type this step is shown in fig2 in a second time the user connects to the first server s1 to access the desired service the first server s1 receives the current identifier u u2032 and the current password p u2032 the first server s1 transmits this information to the second server s2 in a secure manner once received by the second server the latter carries out the hash one way function on the current identifier u u2032 and the password p u2032 as well as the security parameter r for obtaining a second cryptogram h u2032 it returns this cryptogram h u2032 to the first server s1 the latter searches in its database if there is a first cryptogram equal to the second cryptogram and generates an error message if and only if there is no trace of this cryptogram h u2032 in the other case the first server s1 can authorize the access to the desired service if only the cryptograms h users having passed the enrolment phase are stored in the first server s1 this verification step of the existence of an entry in its database cannot be achieved before the transmission.