On Mon, Sep 3, 2018 at 12:19 PM, Hubert Kario <hka...@redhat.com> wrote:
> On Monday, 3 September 2018 17:30:15 CEST Eric Rescorla wrote:
> > On Mon, Sep 3, 2018 at 8:20 AM, Hubert Kario <hka...@redhat.com> wrote:
> > > On Monday, 3 September 2018 17:15:24 CEST Eric Rescorla wrote:
> > > > On Mon, Sep 3, 2018 at 7:28 AM, Hubert Kario <hka...@redhat.com>
> wrote:
> > > > > On Monday, 3 September 2018 16:01:22 CEST Eric Rescorla wrote:
> > > > > > On Mon, Sep 3, 2018 at 4:18 AM, Hubert Kario <hka...@redhat.com>
> > > > > > wrote:
> > > > > not
> > > > > abort connection, so I still think it will create less confusion to
> > > > > re-allow
> > > > > them than to re-assign new codepoints
> > > >
> > > > The issue is that it's not possible to distinguish a non-compliant
> TLS
> > >
> > > 1.3
> > >
> > > > implementation which is inappropriately sending these code points
> from
> > > > one which actually supports Brainpool with TLS 1.3. Using new code
> > > > points makes this clear.
> > >
> > > and why having that distinction is that important?
> >
> > Because otherwise you are risking interop problems:
> >
> > 1. A stack which supports TLS 1.2 and TLS 1.3 but only supports Brainpool
> > for TLS 1.2 (the only kind you can write at this point), and
> inappropriately
> > advertises the Brainpool curves in violation of the MUST above.
> > 2. A stack which supports TLS 1.2 and TLS 1.3 and supports Brainpool for
> > both (assuming that we adopt your proposal and reactivate these code
> > points).
> >
> > If stack 2 receives a CH from stack 1 and responds by selecting a
> Brainpool
> > curve, then there will be an interop issue when it sends an HRR [0]
> > selecting
> > the Brainpool curve.
> >
> > -Ekr
> >
> > [0] I'm assuming that the client doesn't offer a Brainpool KeyShare.
>
> ah, yes, missed this case. That does taint all those codepoints for TLS 1..3
>
> but while the server may abort the connection upon receiving them in TLS
> 1.3
> CH (as it is violation of the MUST clause), I don't think it actually
> should
> abort it...
>
> For one, and I think we can agree on that, is the server MUST ignore them
> if
> it doesn't support them in TLS 1.2.
>
I don't think I agree with this. Why would that be the case?
Given that TLS 1.3 server usually implement both TLS 1.2 and TLS 1.3,
> having
> code that does ignore them in TLS 1.2 and doesn't ignore them in TLS 1.3
> is
> only inviting bugs.
>
We already have other special case code that enforces such rules. For
instance,
compression:
For every TLS 1.3 ClientHello, this vector
MUST contain exactly one byte, set to zero, which corresponds to
the "null" compression method in prior versions of TLS. If a
TLS 1.3 ClientHello is received with any other value in this
field, the server MUST abort the handshake with an
"illegal_parameter" alert. Note that TLS 1.3 servers might
receive TLS 1.2 or prior ClientHellos which contain other
compression methods and (if negotiating such a prior version) MUST
follow the procedures for the appropriate prior version of TLS.
-Ekr
--
> Regards,
> Hubert Kario
> Senior Quality Engineer, QE BaseOS Security team
> Web: www.cz.redhat.com
> Red Hat Czech s.r.o., Purkyňova 115, 612 00 Brno, Czech Republic
>
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