> please point me at the technology that lets you tell which key a message is signed with given only the signature and the verification key?
This is an honest question. this seems like it would be a breakthrough in non-reputiation if you can sign one message with a key and send it to person A, a second with the next key and send it to person B and a third with the next key and send it to person C and therefor prove that message B was send between message A and message C
As far as I know, all signing services currently boil down to "we include the timestamp in what we sign, and since you trust our signature, you trust the timestamp", with the trust in the signature being that you trust that nobody else is able to sign anything that can be verified with the verification key you have.
It's very possible that I am ignorant of some digital signing technology here, but this seems like such a useful combination of features that I would have expected to have heard that such things are at least possible, even without knowing the details.