Re: [TLS] Negotiate only symmetric cipher via cipher suites (was: Ala Carte Cipher suites - was: DSA should die)

Dave Garrett <davemgarrett@gmail.com> Mon, 13 April 2015 17:45 UTC

Return-Path: <davemgarrett@gmail.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 6B4871AD0C5 for <tls@ietfa.amsl.com>; Mon, 13 Apr 2015 10:45:55 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -2
X-Spam-Level:
X-Spam-Status: No, score=-2 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, FREEMAIL_FROM=0.001, 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 I8G3HUJKJjQf for <tls@ietfa.amsl.com>; Mon, 13 Apr 2015 10:45:53 -0700 (PDT)
Received: from mail-qk0-x231.google.com (mail-qk0-x231.google.com [IPv6:2607:f8b0:400d:c09::231]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id B2C421AD0BC for <tls@ietf.org>; Mon, 13 Apr 2015 10:45:53 -0700 (PDT)
Received: by qkhg7 with SMTP id g7so191464287qkh.2 for <tls@ietf.org>; Mon, 13 Apr 2015 10:45:53 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=from:to:subject:date:user-agent:cc:references:in-reply-to :mime-version:content-type:content-transfer-encoding:message-id; bh=7J9lL0c7kU+lag4IVLw5R17121KFHmS6+KgeRJaY4kk=; b=hZxrF3B0t7mgqSW3hvyi7FsZh0fP6UFty/lZsvT0MIyDp1G7YzIEnqRFRQ2eCtvQMA KC0smm1tfUUdniEFjVr8yKDPHdgOzsr9TbauJg8ZSPP7lAhhyuvmghL4pHcsxwAQJWT3 hNCSh8yYw7e1tNY29HeL0brkUpcN1B5hXstEMcAAspBVhu7JtAo7MDAVHaNHzLFblOm9 FcvTTSA1vKopMH0jsMN11pdAz74UQPOvH7id7P6RvfYaZ7wkI0UVGbCT/Fn9el/Fl/Fp atoCsSUo3BwoBVzycs1rtd4gjVxXY16lBr+tyZpGDxLApBYLAVv8eBUHMaeiZKYIdmt9 FoIw==
X-Received: by 10.140.234.80 with SMTP id f77mr599842qhc.13.1428947152923; Mon, 13 Apr 2015 10:45:52 -0700 (PDT)
Received: from dave-laptop.localnet (pool-96-245-254-195.phlapa.fios.verizon.net. [96.245.254.195]) by mx.google.com with ESMTPSA id g80sm6266932qkh.18.2015.04.13.10.45.52 (version=TLSv1 cipher=RC4-SHA bits=128/128); Mon, 13 Apr 2015 10:45:52 -0700 (PDT)
From: Dave Garrett <davemgarrett@gmail.com>
To: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
Date: Mon, 13 Apr 2015 13:45:51 -0400
User-Agent: KMail/1.13.5 (Linux/2.6.32-73-generic-pae; KDE/4.4.5; i686; ; )
References: <CAK9dnSyKf7AY11h1i1h+SudRc-NmTZE5wC682YKhNsxnfV5ShQ@mail.gmail.com> <201504131325.20590.davemgarrett@gmail.com> <871tjoue8v.fsf@alice.fifthhorseman.net>
In-Reply-To: <871tjoue8v.fsf@alice.fifthhorseman.net>
MIME-Version: 1.0
Content-Type: Text/Plain; charset="utf-8"
Content-Transfer-Encoding: 7bit
Message-Id: <201504131345.51699.davemgarrett@gmail.com>
Archived-At: <http://mailarchive.ietf.org/arch/msg/tls/BgdHhOXOtU5af7iLnYzVCVBURKY>
Cc: tls@ietf.org
Subject: Re: [TLS] Negotiate only symmetric cipher via cipher suites (was: Ala Carte Cipher suites - was: DSA should die)
X-BeenThere: tls@ietf.org
X-Mailman-Version: 2.1.15
Precedence: list
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: <http://www.ietf.org/mail-archive/web/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: Mon, 13 Apr 2015 17:45:55 -0000

On Monday, April 13, 2015 01:31:12 pm Daniel Kahn Gillmor wrote:
> On Mon 2015-04-13 13:25:20 -0400, Dave Garrett wrote:
> >> So if we have to have non-(EC)DHE PSK, what would it mean if a TLS peer
> >> were to try to negotiate:
> >> 
> >>   key agreement: PSK
> >>  authentication: RSA-PSS
> >> 
> >> Do we just say "don't do that"?
> >
> > SGTM
> 
> This, i think, is one of the serious concerns about splitting the
> ciphersuite into orthogonal vectors.
> 
> Once the full cartesian explosion is available by multidimensional
> enumeration, we have to mark out which corners of the space are actually
> bad ideas, and we have to make sure our implementations don't stumble
> into those corners by accident.

Non-FS PSK adds some of those corners, which is one of the reasons why I think it should be prohibited.

> This isn't impossible to do, but it seems ripe for subtle implementation
> bugs.

The current situation is already ripe for subtle implementation bugs. These extensions already exist and can conflict with the cipher suite if not configured/used properly. I think this route reduces the risk here, and prohibiting/restricting the more problematic methods/algorithms would help more.


Dave