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Re: [TLS] Proposed text for removing renegotiation

Andrei Popov <Andrei.Popov@microsoft.com> Wed, 11 June 2014 19:41 UTC

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From: Andrei Popov <Andrei.Popov@microsoft.com>
To: Nikos Mavrogiannopoulos <nmav@redhat.com>, "Salz, Rich" <rsalz@akamai.com>
Thread-Topic: [TLS] Proposed text for removing renegotiation
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Date: Wed, 11 Jun 2014 19:41:53 +0000
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Subject: Re: [TLS] Proposed text for removing renegotiation
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In any case, the triple handshake vulnerability has to be fixed, at least in TLS1.2 and below. The same fix would likely apply to TLS1.3, so IMHO triple handshake does not necessitate the removal of renegotiation from TLS1.3.

Cheers,

Andrei

-----Original Message-----
From: TLS [mailto:tls-bounces@ietf.org] On Behalf Of Nikos Mavrogiannopoulos
Sent: Tuesday, June 10, 2014 9:04 AM
To: Salz, Rich
Cc: tls@ietf.org
Subject: Re: [TLS] Proposed text for removing renegotiation

On Tue, 2014-06-10 at 10:53 -0400, Salz, Rich wrote:
> > Could you please cite these security issues. In the 17 years of the protocol I have only seen one.
> 
> Which one are you omitting -- Marsh's  or triple-handshake?

The triple handshake identified many issues in TLS but no issue in the renegotiation. Renegotiation cannot solve the protocol's vulnerability the triple handshake exploits.

Nevertheless, you can see the importance of renegotiation in the triple handshake attack  by checking the preconditions for the attack. The authors on their website clarify on the vulnerabilities they identified and quoting them for renegotiation: "During renegotiation, both the server and client certificates can change. This is allowed by TLS (and supported in its main implementations) but no definitive guidance is given to applications on how to deal with such changes".

Mentioning the lack of application level guidance (for applications that need and make use of it) as a reason to drop renegotiation, is a bit far fetched.

regards,
Nikos


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