Re: [TLS] comment on draft-kinnear-tls-client-net-address

We don't trust that the key share or certificate is good either, but once we have a Finished message, that is retroactively authenticated and can be used.  We rely on this property for a bunch of things.

On Mon, Mar 25, 2019, at 19:12, Hubert Kario wrote:
> On Monday, 25 March 2019 17:02:34 CET David Schinazi wrote:
> > Ah, I see - thanks. In other words, the proposal requires trusting the
> > server and the reply comes before the identity of the server has been
> > authenticated.
> 
> exactly
> 
> > David
> > 
> > On Mon, Mar 25, 2019 at 4:54 PM Hubert Kario <hkario@redhat.com> wrote:
> > > On Monday, 25 March 2019 15:09:21 CET David Schinazi wrote:
> > > > Hi Hubert,
> > > > 
> > > > Can you elaborate on how "TLS is a providing integrity and authenticity
> > > 
> > > to
> > > 
> > > > the IP address information"? In my understanding, TLS only provides
> > > > integrity and authenticity to a byte stream, not to how your byte stream
> > > 
> > > is
> > > 
> > > > being transported over the network.
> > > 
> > > my point is that EncryptedExtensions, while encrypted and integrity
> > > protected
> > > on record layer level, are _not yet_ bound to any identity, so an attacker
> > > can
> > > trivially reply to any non-PSK ClientHello with a ServerHello of its own
> > > and
> > > then he'll be able to generate arbitrary encrypted EncryptedExtensions
> > > message
> > > 
> > > the forgery will be noticed only after the CertificateVerify is processed
> > > 
> > > > Thanks,
> > > > David
> > > > 
> > > > On Mon, Mar 25, 2019 at 12:31 PM Hubert Kario <hkario@redhat.com> wrote:
> > > > > I wanted to rise one comment on the IETF session, but we ran out of
> > > 
> > > time:
> > > > > given that TLS is a providing integrity and authenticity to the IP
> > > 
> > > address
> > > 
> > > > > information, shouldn't the protocol require the client to perform the
> > > 
> > > full
> > > 
> > > > > handshake and only then request information from the server? I.e. make
> > > 
> > > it
> > > 
> > > > > a
> > > > > post-handshake messages, like KeyUpdate, rather than an extension.
> > > > > 
> > > > > I worry that some clients may short-circuit processing and do the
> > > > > handshake
> > > > > only up to EncryptedExtensions, without processing CertificateVerify
> > > > > or
> > > > > Finished (in case of PSK), and in result expose themselves to MitM
> > > > > attacks.
> > > > > --
> > > > > 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_______________________________________________
> > > > > TLS mailing list
> > > > > TLS@ietf.org
> > > > > https://www.ietf.org/mailman/listinfo/tls
> > > 
> > > --
> > > 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
> 
> 
> -- 
> 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
> _______________________________________________
> TLS mailing list
> TLS@ietf.org
> https://www.ietf.org/mailman/listinfo/tls
> 
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