Re: [Gen-art] Gen-ART LC Review of draft-ietf-dhc-forcerenew-nonce-03

Maglione Roberta <roberta.maglione@telecomitalia.it> Tue, 14 February 2012 10:23 UTC

Return-Path: <roberta.maglione@telecomitalia.it>
X-Original-To: gen-art@ietfa.amsl.com
Delivered-To: gen-art@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 31FBD21F86EA; Tue, 14 Feb 2012 02:23:04 -0800 (PST)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: 0.248
X-Spam-Level:
X-Spam-Status: No, score=0.248 tagged_above=-999 required=5 tests=[AWL=0.967, BAYES_00=-2.599, HELO_EQ_IT=0.635, HOST_EQ_IT=1.245]
Received: from mail.ietf.org ([12.22.58.30]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id ytzIAoNR8B2n; Tue, 14 Feb 2012 02:23:03 -0800 (PST)
Received: from GRFEDG702BA020.telecomitalia.it (grfedg702ba020.telecomitalia.it [156.54.233.201]) by ietfa.amsl.com (Postfix) with ESMTP id 19EB321F85B8; Tue, 14 Feb 2012 02:23:03 -0800 (PST)
Received: from GRFHUB702BA020.griffon.local (10.188.101.112) by GRFEDG702BA020.telecomitalia.it (10.188.45.101) with Microsoft SMTP Server (TLS) id 8.2.254.0; Tue, 14 Feb 2012 11:23:01 +0100
Received: from GRFMBX704BA020.griffon.local ([10.188.101.15]) by GRFHUB702BA020.griffon.local ([10.188.101.112]) with mapi; Tue, 14 Feb 2012 11:23:01 +0100
From: Maglione Roberta <roberta.maglione@telecomitalia.it>
To: 'Ben Campbell' <ben@nostrum.com>, Ted Lemon <Ted.Lemon@nominum.com>
Date: Tue, 14 Feb 2012 11:23:00 +0100
Thread-Topic: Gen-ART LC Review of draft-ietf-dhc-forcerenew-nonce-03
Thread-Index: Aczqk08e6IUgLj+qQM2pFobKJW9qmwAbyLQw
Message-ID: <282BBE8A501E1F4DA9C775F964BB21FE3EC1467FC5@GRFMBX704BA020.griffon.local>
References: <A57C4722-5E13-451E-ACB4-CAA8064FA68B@nostrum.com> <282BBE8A501E1F4DA9C775F964BB21FE3EC1467FB2@GRFMBX704BA020.griffon.local> <CEA6CD8F-7DCD-448C-8C31-EC64FD9902A3@nominum.com> <F184B794-3D1D-4A5A-860E-288DF2600DD6@nostrum.com>
In-Reply-To: <F184B794-3D1D-4A5A-860E-288DF2600DD6@nostrum.com>
Accept-Language: en-US, it-IT
Content-Language: en-US
X-MS-Has-Attach:
X-MS-TNEF-Correlator:
acceptlanguage: en-US, it-IT
Content-Type: text/plain; charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
Cc: "Henderickx, Wim \(Wim\)" <wim.henderickx@alcatel-lucent.com>, "gen-art@ietf.org Review Team" <gen-art@ietf.org>, Ullio Mario <mario.ullio@telecomitalia.it>, "draft-ietf-dhc-forcerenew-nonce.all@tools.ietf.org" <draft-ietf-dhc-forcerenew-nonce.all@tools.ietf.org>, The IETF <ietf@ietf.org>
Subject: Re: [Gen-art] Gen-ART LC Review of draft-ietf-dhc-forcerenew-nonce-03
X-BeenThere: gen-art@ietf.org
X-Mailman-Version: 2.1.12
Precedence: list
List-Id: "GEN-ART: General Area Review Team" <gen-art.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/gen-art>, <mailto:gen-art-request@ietf.org?subject=unsubscribe>
List-Archive: <http://www.ietf.org/mail-archive/web/gen-art>
List-Post: <mailto:gen-art@ietf.org>
List-Help: <mailto:gen-art-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/gen-art>, <mailto:gen-art-request@ietf.org?subject=subscribe>
X-List-Received-Date: Tue, 14 Feb 2012 10:23:04 -0000

Hello Ted and Bell,
 I tried to address both your comments by combining your proposals:
Basically I added the text suggested by Ted in the security considerations section and then I slightly modified the introduction in order to clarify the applicability.
I've just posted version -04 that includes these changes together with the resolutions of some other comments we received during the review.
Please let me know if you have additional comments.
Thanks,
Regards,
Roberta

-----Original Message-----
From: Ben Campbell [mailto:ben@nostrum.com]
Sent: lunedì 13 febbraio 2012 22.06
To: Ted Lemon
Cc: Maglione Roberta; draft-ietf-dhc-forcerenew-nonce.all@tools.ietf.org; gen-art@ietf.org Review Team; The IETF; Henderickx, Wim (Wim); Ullio Mario
Subject: Re: Gen-ART LC Review of draft-ietf-dhc-forcerenew-nonce-03

On Feb 11, 2012, at 10:24 AM, Ted Lemon wrote:

>> [RM] The intention is to use this method only for environments with native security mechanisms, such as the Broadband Access network. You are right it is not clearly said in the document I can add the following sentence at the end of the introduction in order to clarify this point:
>>
>> "This   mechanism is intended to be use in networks that already have native security mechanisms that provide sufficient protection against
>> spoofing of DHCP traffic."
>
> It's probably worth revisiting the purpose of this mechanism.   The problem that we are trying to solve is that people are reluctant to implement DHCPFORCERENEW because it's possible that an off-link attacker could more accurately guess the timing of DHCP renewal messages by first sending a DHCPFORCERENEW.   The mechanism in RFC3315 (DHCPv6), which this document mirrors for DHCPv4, uses a nonce to prevent an off-link attacker from successfully triggering a renewal on a client by sending DHCPFORCERENEW; since the attacker is off-link, it doesn't have the nonce, and can't force a renewal.
>
> An on-link attacker can always simply watch the DHCP renewal message go out and respond to it, so this mechanism is useless for preventing on-link attacks, and hence the security of the nonce in the case of on-link attacks isn't relevant.  So the above text isn't needed.   It's possible that the document doesn't clearly document the use case for this functionality; if so, you are free to take the above paragraph, Roberta, and modify it to suit your purposes.   But I am against adding the text you proposed, because it excludes the bulk of use cases for the DHCPFORCERENEW nonce mechanism.

This is good information, and it would help to include it in the security considerations. I meant (but failed) to  comment in my original review that the security considerations would benefit from a more detailed discussion about the properties of the mechanism, and what attacks or vulnerabilities it is intended to mitigate. Your text above seems to do that.

>
>> [RM] This is because this mechanism relays on the authentication protocol defined in section 21.5 of RFC 3315 for DHCPv6 Reconfigure and there HMAC-MD5 is used.
>
> Essentially HMAC-MD5 is being used here to package a secret into a chunk of predictable size, and the fact that there are hacks for the mechanism isn't terribly important because the only attacker we are attempting to foil is one that doesn't have access to the cleartext or the ciphertext.

Do I infer correctly from your comment that the security properties of the mechanism don't really matter? That is, if the attacker we care about can't eavesdrop in the first place, does this really need to be an HMAC?

Questo messaggio e i suoi allegati sono indirizzati esclusivamente alle persone indicate. La diffusione, copia o qualsiasi altra azione derivante dalla conoscenza di queste informazioni sono rigorosamente vietate. Qualora abbiate ricevuto questo documento per errore siete cortesemente pregati di darne immediata comunicazione al mittente e di provvedere alla sua distruzione, Grazie.

This e-mail and any attachments is confidential and may contain privileged information intended for the addressee(s) only. Dissemination, copying, printing or use by anybody else is unauthorised. If you are not the intended recipient, please delete this message and any attachments and advise the sender by return e-mail, Thanks.