On 5/7/2011 7:54 AM, Hauke Laging wrote: > Am Samstag, 7. Mai 2011, 04:33:17 schrieb Grant Olson: > >> 1) I digitally sign a document saying I owe you money. The signing key >> has an expiration date. >> >> 2) Key expires. I do nothing. >> >> 3) The original document is invalidated. I no longer owe you money? > > Whether you owe me money does not depend on signing any documents in general. > :-) Documents are usually just a proof. > > You can still claim that somebody owes you money but the document does not > have the same legal value. What courts decide is another question... >
Yes, of course. > But the fiscal authorities don't accept digital bills (probably the most > frequent use of legally qualified signatures here) which are signed by > expired > keys only. You need a chain of signatures which prove that there was a non- > expired signature at any point in time. > > For the same reason it makes sense to have digitally signed documents signed > by another key (not just the document but the document together with the > signature) at once when you get them. Because you cannot know whether and if > a > key will be revoked in the future. The moment it is revoked and you cannot > prove the signatures being older than the revoke all signatures are dead. > Okay, now I understand. It sounds like you're talking something like a digital notarization. That makes sense now. -- Grant
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