retrieves the corresponding kn from a database and extrapolates the fn t f1 f8 using the time of the transaction u201c t u201d wherein replace f8 by dc4 in order to determine the exact time used by the small hand held device for the computation of the one time password in summary the decryption node can recuperate rebuild or re compute the true one time password one advantage of this methodology is to avoid the server impersonation fraud as described above another advantage of this method is the certification of the identity of the signor of any hand written signature stamped on any document after a person the signor activates his small hand held device and identities itself against the device by entering the correct pin and pressing the code button then the portable device will display the one time password and the signor should write the one time password on the document together with the time and date and identification information like the signor 39 s name login name or serial number of the small hand held device or any other info which will help the decryption node to query the database and proceed as described above thus checking the veracity and validity of such one time password at the presumed time of generation by the presumed small hand held device u s pat no 5 742 684 issued to the inventor of this invention describes a possible example of the portable device although the invention has been described herein using exemplary implementations it should be clear that any other implementation of the methodology presented here does not represent a departure from the spirit of the invention as set forth.