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Re: Notary signatures

2002-04-28 07:39:18

At 11:21 PM -0400 4/25/02, Derek Atkins wrote:
Jon Callas <jon(_at_)callas(_dot_)org> writes:

On 4/25/2002 5:54 PM, "Len Sassaman" <rabbi(_at_)quickie(_dot_)net> wrote:

I'd like to be able to run a service wherein a user submits a signed
document, and the service signs the signature. This is done to allow for
verification that the signature was made prior to the timestamp provided
by my service (the trusted notary).

Not the document, only the signature packet? I'm trying to envision what one
would do with this mechanically, as well as syntactically and semantically.

Yes.  The notary verifies the signature, and then signs the
_signature_, not the document.  This is why it's a signature on a
signature.  The notary is trusted to have verified the contents before
it actually creates the new signature.

The notary doesn't need to verify the original signature.  Operationally,
the notary doesn't need to ever see the document, only the signature on the
document.  This lack of "need to know" seems to me to be an advantage for
confidential documents.

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.

Which is what happens if the original signature doesn't match the document.

Cheers - Bill

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