In a terminal which received an electronic document with at leastone digital signature, when a user changes the contents of the received electronic document, a new digital signature is produced by enciphering signature data by using a secret key of the user, the signature data including a hash total...http://www.google.de/patents/US5465299?utm_source=gb-gplus-sharePatent US5465299 - Electronic document processing system and method of forming digital signature
