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

Hubert Kario <hkario@redhat.com> Mon, 25 March 2019 15:54 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 16:54:37 +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 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

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