Patent ID: 8850518

Claim:
User authentication device, provided with an encryption function of variables K, t, x, in which: K is a secret shared with a server; t is a time-dependent element; and x is a variable that may take on at least first and second predetermined and distinct values known by said user device and said server, the device comprising: means of calculation of encryption function results for one or other of said at least two values of x; instructions to perform a first calculation of an encryption function, with said parameter x being assigned said first value, with the means of calculation; means for requesting an authentication of the user by the server, said requesting comprising a first result being the result of said first calculation and said first value of said parameter x; instructions to perform a second calculation of said encryption function, with said parameter x being assigned a second value, with the means of calculation, obtaining a second result; instructions to receive, between the first calculation and the second calculation, a challenge for said device to provide to said server at least a part of said second result, the at least part of said second result having been chosen randomly, for verification of the authentication of the user by the server; and means for transmitting to said server a response to said challenge, said response comprising the at least part of the second result.