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Re: Notary signatures
>> Note that you still cannot change the document, because to change the
>> document you would need to change the signature (unless you break the
>> Hash function). If you change the signature, then the notary
>> signature fails. Therefore, transitively, the notary is verifying
>> the document.
I actually disagree with this. The notary is putting a signature on a chunk
of data. The signature means, "I saw this at time T." If that data, a
signature, verifies against a document, *we* may deduce certain things about
that document using the two signatures. But the notary says nothing about
the integrity of the document.
This is a subtle point, but one about the semantics of transitivity.
If Alice says, "A -> B" and Bob says "B -> C", then I might (modulo many
details) deduce that A -> C using both data from Alice and Bob.
However, this is something that *I* am doing, not something Alice nor Bob is
doing. Alice says nothing about C. Bob says nothing about A. I put them both
together. Not Alice, not Bob.