Re: [TLS] Fixing TLS

mrex@sap.com (Martin Rex) Thu, 14 January 2016 09:40 UTC

Return-Path: <mrex@sap.com>
X-Original-To: tls@ietfa.amsl.com
Delivered-To: tls@ietfa.amsl.com
Received: from localhost (ietfa.amsl.com [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 5CEA01B2DAE for <tls@ietfa.amsl.com>; Thu, 14 Jan 2016 01:40:49 -0800 (PST)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -6.551
X-Spam-Level:
X-Spam-Status: No, score=-6.551 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, HELO_EQ_DE=0.35, RCVD_IN_DNSWL_HI=-5, SPF_PASS=-0.001] autolearn=ham
Received: from mail.ietf.org ([4.31.198.44]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id xDaHmqVrp-iq for <tls@ietfa.amsl.com>; Thu, 14 Jan 2016 01:40:47 -0800 (PST)
Received: from smtpde02.smtp.sap-ag.de (smtpde02.smtp.sap-ag.de [155.56.68.140]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id 457C91B2DAD for <tls@ietf.org>; Thu, 14 Jan 2016 01:40:47 -0800 (PST)
Received: from mail05.wdf.sap.corp (mail05.sap.corp [194.39.131.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtpde02.smtp.sap-ag.de (Postfix) with ESMTPS id 62F2E4496D; Thu, 14 Jan 2016 10:40:45 +0100 (CET)
X-purgate-ID: 152705::1452764445-00006F99-8A62FCD9/0/0
X-purgate-size: 2282
X-purgate: clean
X-purgate: This mail is considered clean (visit http://www.eleven.de for further information)
X-purgate-Ad: Categorized by eleven eXpurgate (R) http://www.eleven.de
X-purgate-type: clean
X-SAP-SPAM-Status: clean
Received: from ld9781.wdf.sap.corp (ld9781.wdf.sap.corp [10.21.82.193]) by mail05.wdf.sap.corp (Postfix) with ESMTP id CD60240918; Thu, 14 Jan 2016 10:40:44 +0100 (CET)
Received: by ld9781.wdf.sap.corp (Postfix, from userid 10159) id 497531A3E9; Thu, 14 Jan 2016 10:40:44 +0100 (CET)
In-Reply-To: <20160114050629.GA23796@LK-Perkele-V2.elisa-laajakaista.fi>
To: Ilari Liusvaara <ilariliusvaara@welho.com>
Date: Thu, 14 Jan 2016 10:40:44 +0100 (CET)
X-Mailer: ELM [version 2.4ME+ PL125 (25)]
MIME-Version: 1.0
Content-Transfer-Encoding: 7bit
Content-Type: text/plain; charset="US-ASCII"
Message-Id: <20160114094044.497531A3E9@ld9781.wdf.sap.corp>
From: mrex@sap.com (Martin Rex)
Archived-At: <http://mailarchive.ietf.org/arch/msg/tls/-Ezk_TCVpdHSGytQvmgVYfByDW8>
Cc: "tls@ietf.org" <tls@ietf.org>
Subject: Re: [TLS] Fixing TLS
X-BeenThere: tls@ietf.org
X-Mailman-Version: 2.1.15
Precedence: list
Reply-To: mrex@sap.com
List-Id: "This is the mailing list for the Transport Layer Security working group of the IETF." <tls.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/tls>, <mailto:tls-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/tls/>
List-Post: <mailto:tls@ietf.org>
List-Help: <mailto:tls-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/tls>, <mailto:tls-request@ietf.org?subject=subscribe>
X-List-Received-Date: Thu, 14 Jan 2016 09:40:49 -0000

Ilari Liusvaara wrote:
>
> Peter Gutmann wrote:
>
>> Salz, Rich <rsalz@akamai.com>; writes:
>> 
>>>> TLS needs an LTS version that you can just push out and leave to its own
>>>> devices
>>>
>>>So don't you have that with TLS 1.1 and appropriate cipher and option
>>>choices?
>> 
>> Based on the feedback I've had, I'm kinda tempted to do a TLS 1.2 LTS draft
>> that specifices just a single boolean flag, "use this known-good
>> configuration and not the 6.023e23 other ones and you should be good
>> for the next decade or so".  That can then be baked into long-term
>> systems and devices and left alone while people get on with other things.
> 
> To actually fix the known problems with TLS 1.2, you would at minimum
> need a new extension, since there is currently no way to fix the broken
> server authentication.

One Boolean signaling is sufficent to fix all of the problems.
one SCSV in the Client->Server direction and a TLS extension Boolean
response in ServerHello.


> 
> Then there are the other security fix extensions (at least three already).
> Those all would need to be impiled.
> 
> And then there is the TLS 1.2 Diffie-Hellman issue...

TLS 1.2LTS should fix them all at once, including:

   - promise to support minimum DHE key lengths >= 2048 bits
     whenever ClientHello includes DHE cipher suites

   - promise to support a certain small subset of EC curves
     and uncompressed point format whenever ClientHello includes
     ECDHE cipher suites (but may omit TLS extensions).

   - new/improved ServerKeyExchange handshake message, which
     does not only contain the reasonable set of DHE parameters,
     but also uses a digititally signed covering all prior
     handshake messages, not just the two hello randoms.

   - overriding any TLS record layer protocol version and
     ClientHello.client_version that is less than TLSv1.2

   - promise that digital signatures using SHA-256 are supported

   - fix the misunderstood semantics of the signature_algorithm extension
     so that it is only used as a hint to certificate selection,
     but *NEVER* seen as a hard requirement (or reason for server to
     abort the TLS handshake based on the signature of the server cert).


-Martin