INTEGRATED CIRCUIT CARDS AND DATA PROCESSING PROGRAMS FOR USE IN PRODUCTION, TRANSMISSION, VALIDATION AND ARCHIVING OF DIGITALLY SIGNED DOCUMENTS AND FOR VERIFICATION OF INFORMATION PERTAINING TO DIGITALLY SIGNED DOCUMENTS, SUCH AS THE IDENTITY OF SIGNATORIES, TIME OF SIGNING, AND CONTENTS OF DATA SIGNED, AND FOR INTERFACING WITH VARIOUS APPLICATION PROGRAMS WHICH MAY USE DIGITALLY SIGNED DOCUMENTS