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Re: Non-repudiation

From: Denis Pinkas <Denis.Pinkas@bull.net>
Date: Tue, 12 Oct 1999 11:35:36 +0100
Message-ID: <38030EF8.57FB0913@bull.net>
To: "Donald E. Eastlake 3rd" <dee3@torque.pothole.com>
CC: w3c-ietf-xmldsig@w3.org
> I don't have much disagreement with anything you say.  I've also heard
> support for the idea the "non-repudiation" can be considered a
> contractual item.  So, for some purposes, it can be obtained even with
> shared secret key technology for a class of disputes by a party
> contractually agreeing that they can not dispute the signature.

The term "non repudiation" must be used with great care. The ISO
10181-4 document (called non repudiation Framework) starts with:
"The goal of the non-repudiation service is to collect, maintain,
make available and validate irrefutable evidence concerning a
claimed event or action in order to solve disputes about the
occurrence of the event or action".

When public key technology and when no mandatory tamper resistant
hardware token are used, this must remain true even if the signer's
private key is compromised or declared compromised (and thus
revoked) after a digital signature has been given. In practice,
unless time stamping is used, the non repudiation property cannot be

At the last meeting in Oslo I raised the question whether the coming
document will address non repudiation and, at that time, the answer
was no. Is the answer to that question still the same today ?


> In any case, I think it is easiest for use to continue to use the term
> and include a definition if we think it necessary for clarity.
> Thanks,
> Donald
> From:  "Milton M. Anderson" <miltonma@gte.net>
> Resent-Date:  Wed, 6 Oct 1999 10:30:42 -0400 (EDT)
> Resent-Message-Id:  <199910061430.KAA17800@www19.w3.org>
> Message-ID:  <010701bf1006$c11b4020$8c3bbfd1@computer>
> To:  "Donald E. Eastlake 3rd" <dee3@torque.pothole.com>
> Cc:  <w3c-ietf-xmldsig@w3.org>
> Date:  Wed, 6 Oct 1999 10:15:30 -0400
> >What the public key security model actually provides is
> >that the signer can fairly successfully claim that other recipients
> >of the document could not have forged the signer's signature.
> >The signer can offer evidence that the keys were created under
> >proper conditions using trusted key generation software, that
> >the private signing key has been in hardware of an appropriate
> >tamper resistance, that the hardware has been connected to
> >a host which has been well-secured,
> >that administrative controls over signing priviledges
> >have been properly implemented and enforced, etc.
> >
> >What the public key security model doesn't
> >provide very adequately is for the recipients of the
> >document to prove against the signer's will that only the
> >signer could have created the signature, since the signer
> >can reasonably claim that the keys were generated improperly, that the
> >private key was stored in an encrypted file under a guessable
> >password, that hackers might have invaded the host and planted
> >a trojan horse that created the signature, and that the
> >whole system was haphazardly administered, etc.
> >
> >So the second property of non-repudiation can only be
> >claimed in closed systems where there is an overall
> >security system design and adminstrative framework
> >that supports it.  It's not a property of public key cryptography
> >per se.
> >
> >Unfortunately, the first property, which is more nearly a
> >property of public key signatures, doesn't have a
> >single-word name that I know of.
> >
> >Milt
> >
> >
> >-----Original Message-----
> >From: Donald E. Eastlake 3rd <dee3@torque.pothole.com>
> >To: w3c-ietf-xmldsig@w3.org <w3c-ietf-xmldsig@w3.org>
> >Date: Wednesday, October 06, 1999 8:55 AM
> >Subject: Re: Non-repudiation
> >
> >
> >>
> >>Well, other people think it very important to distinguish the security
> >>model provided by, for example, public key versus keyed hash.  One
> >>difference in these models is normally called non-repudiation and in
> >>technical documents such as this, that refers to the fact that you
> >>either need the private key or need to have broken the cryptography to
> >>forge a signture.   Having small glossary at the end of the document
> >>and defining the term is fine.  But if you want it replaced, I think
> >>you should provide a single word substitute that people could agreee
> >>on as a replacement.
> >>
> >>Saying '"non-repudiation" is actually a marketing term!' doesn't
> >>persuade me since marketers use and screw up essentially every word in
> >>the language.
> >>
> >>Donald
> >>
> >>From:  "Chris Smithies" <Chris_Smithies@penop.com>
> >>Resent-Date:  Wed, 6 Oct 1999 08:27:14 -0400 (EDT)
> >>Resent-Message-Id:  <199910061227.IAA12816@www19.w3.org>
> >>X-Lotus-FromDomain:  PENOP
> >>To:  w3c-ietf-xmldsig@w3.org
> >>Message-ID:  <85256802.0044BD01.00@penop.com>
> >>Date:  Wed, 6 Oct 1999 13:35:15 +0100
> >>
> >>>I would strongly recommend that the term "non-repudiation" and its
> >>>derivatives not appear in the draft. From a legal perspective it is seen as
> >>>a hollow boast. The only thing that can't be _denied_ is that if a hash can
> >>>be decrypted by K1, then it was encrypted by K2. But even allowing that the
> >>>surrounding system is completely secure in all respects, it remains
> >>>possible for the "appropriate user" of K2 to _repudiate_ a signature
> >>>demonstrably signed by K2. Duress... mistake... deception...
> >>>"non-repudiation" is actually a marketing term!
> >>
> >
Received on Tuesday, 12 October 1999 05:36:54 UTC

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