Re: Consensus Text for key usage?

[Ed Gerck <egerck@xxxxxxx>]

Denis Pinkas wrote:

> Ed Gerck wrote:
> > No comments.  The key usage text looks fine.
>
> Good ! (pending a small change requested by Aram which seems quite
> reasonable).

Yes.

> > > When such a
> > >     certificate is delivered, it implies that the owner of the
> > >     corresponding private key should be warned that, in the event of a
> > >     dispute, he may be held responsible of the data signed with this
> > >     key.
>
> > I am not in favor of this entire sentence.
> ....
> > Suggestion: delete the sentence.
>
>  If I re-use the example I
> used during my presenation at the last PKIX session in Washington,
> the user should really be warned, e.g. not to insert his key in an
> unknown door lock so that instead of getting the door opened he
> unknowingly signs a check of 5.000 $.

Or not. It depends on the CA's CPS, on what is disclaimed by the user
in the signed data, etc.  My objection to that text segment is that PKIX
is not the party that should "warn" the user of anything, or mandate that
the user "should be warned" -- such "warning" is outside the scope of
PKIX in the same way that the CPS is outside the scope of PKIX.

> There may be alternatives to
> the proposed wording, but the warning should be kept. Do not forget
> that this belongs to the security considerations section, where
> warnings are fully appropriate.

But not for warnings that lie outside the scope of PKIX. For example, the
user  is not warned to set the date correctly in his computer -- and yet,
setting a wrong date may make an expired certificate, valid.  The
justification/negation of user actions, or lack of actions,  lie outside the
scope of PKIX in the same way that justification of CA's actions are not
the concern of PKIX.

>
> > >     If a certificate has both the digitalSignature and the
> > >     nonRepudiation bit set, the owner of the private key should make
> > >     sure that all the environments and applications where the
> > >     corresponding private key is being used do not allow a misuse of
> > >     that private key.
> >
> > I am not in favor of this entire sequence.
> >....
> > Suggestion: A toned-down statement might be useful, such as:
> >
> >     If a certificate has both the digitalSignature and the
> >     nonRepudiation bit set, the private key owner should take
> >     justified measures to prevent a misuse of that private key.
>
> I think your sentence creates more problems than the original one.
> Some people might argument: what means a "justified measure" ? The
> original sentence should be kept.

Your point is well taken. Perhaps an even more toned-down note would
be useful, for example:

     If a certificate has both the digitalSignature and the
     nonRepudiation bit set, the private key owner should take
     measures to prevent a misuse of that private key.

where not even justification is predicated -- leaving the user
responsible for deciding "how", while PKIX clearly warns
about "what" should be protected when the NR and DS bits
are set.

> > >  If that confidence can only be obtained in some
> > >     environments, two different certificates, one with one public
> > >     key and the digitalSignature bit set and another one with a
> > >     different public key and the nonRepudiation bit set, should be used,
> > >     so that the private key corresponding to the certificate with the
> > >     nonRepudiation bit set is only used in secure environments.
> >
> > I am not in favor of this addition, which seems obvious
> ....
> > If one thinks though that saying something is necessary, I suggest, in
> > agreement with the change proposed above:
> >...
>
> Your proposed text is much more complicated to follow (and longer)
> than the original one.

Your point is well taken. I go back to my first suggestion to simply delete
the addition. Seems less confusing at this time.

Cheers,

Ed Gerck