[IETF-PKIX] digitalSignature vs. nonRepudiation

[John Garner <john@xxxxxxxxxxxxx>]

Simonetti David wrote:
>
> David,
>
> You state that an application that is validating S/MIME signatures only
> wants to know if the cert is valid for NR (it only checks the NR bit and
> ignores the DS bit).  Do you mean a cert that is used to provide
> non-repudiation for S/MIME signatures may not be used to provide
> authentication and integrity?
>
> Again, all that I am saying is that when non-repudiation is claimed,
> authentication and integrity are by-products.  I have yet to see an
> example that contradicts this.  Of the (few) responses I have received
> (which you have also received, Dave), they all agree with this
> statement.
>
> I would very much like to hear the opinions of others.
>
> Dave Simonetti
>

David,

I am also currently attempting to implement the key usages as defined in
the X.509 KeyUsage extension, and I am also similarly  confused about
the use of the digitalSignature and nonRepudiation bits. I am also very
new to the certificate processing arena, and was glad to see the
responses generated by your message.

For me, nonRepudiation implies that at sometime in the future, one of
the parties involved in a transactions is attempting to prove that the
transaction in question took place, and the other party was involved.
Therfore providing a nonrepudiation service would require verifying that
the other parties signature was properly validated in the past. This
would require a "snapshot" of the environment at the exact time of
validation be saved somewhere. Therefore as mention in the response by
Charles Blauner the nonRepudiation bit implies much more than the
digitalSignture bit.

The digitalSignature and the nonRepudiation bits are extremely
interconnected. Part of me believes that nonRepudiation implies
digitalSignature, while the other part like the idea of the KeyUsage
bits having distinct and seperate purposes. I also agree with your
assetion that authentication and integrity are by-products on
non-repudiation, but only at a future time. So if it is authentication
and integrity you are after, digitalSignature should be set, and if you
are after some more envolved non-repudiation service (archiving of all
pertinent data, by a trusted third party for future use), set the
nonRepudiation bit.

Not much help I imagine, but hey, worst case I could be wrong.

John Garner

======================================================================
      //_/_/               John R. Garner
   _/      _/
  _/       _/              Chromatix, Inc.
 _/           _/  _/       10451 Twin Rivers Road, Suite 265
_/            _/_/         Columbia, MD 21044
 _/     _/   _/_/  Phone:  (301) 596-8466  |  http://www.chromatix.com
  _/_/_/   _/   _/ Fax:    (410) 997-4306  |  john@chromatix.com