Methods and apparatus are provided that implement digital signing and/or encryption for the electronic transmission, storage, and retrieval of authenticated documents and that enable the establishment of the identity of the originator of an electronic document and of the integrity of the information...http://www.google.co.uk/patents/US5748738?utm_source=gb-gplus-sharePatent US5748738 - System and method for electronic transmission, storage and retrieval of authenticated documents 
