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

Hubert Kario <hkario@redhat.com> Mon, 25 March 2019 18:11 UTC

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From: Hubert Kario <hkario@redhat.com>
To: David Schinazi <dschinazi.ietf@gmail.com>
Cc: tls@ietf.org
Date: Mon, 25 Mar 2019 19:11:41 +0100
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Subject: Re: [TLS] comment on draft-kinnear-tls-client-net-address
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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

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