Re: [Ntp] Antw: Re: Antw: Re: New rev of the NTP port randomization I-D (Fwd: New Version Notification for draft-gont-ntp-port-randomization-01.txt)

Miroslav Lichvar <mlichvar@redhat.com> Wed, 29 May 2019 10:17 UTC

Return-Path: <mlichvar@redhat.com>
X-Original-To: ntp@ietfa.amsl.com
Delivered-To: ntp@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id 0E370120092 for <ntp@ietfa.amsl.com>; Wed, 29 May 2019 03:17:05 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -6.901
X-Spam-Level:
X-Spam-Status: No, score=-6.901 tagged_above=-999 required=5 tests=[BAYES_00=-1.9, RCVD_IN_DNSWL_HI=-5, SPF_PASS=-0.001] autolearn=ham autolearn_force=no
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 oUCiIwJg3MIT for <ntp@ietfa.amsl.com>; Wed, 29 May 2019 03:17:03 -0700 (PDT)
Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by ietfa.amsl.com (Postfix) with ESMTPS id B438E12006A for <ntp@ietf.org>; Wed, 29 May 2019 03:17:03 -0700 (PDT)
Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 5B33B30C31A1; Wed, 29 May 2019 10:16:58 +0000 (UTC)
Received: from localhost (holly.tpb.lab.eng.brq.redhat.com [10.43.134.11]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2C7269303; Wed, 29 May 2019 10:16:56 +0000 (UTC)
Date: Wed, 29 May 2019 12:16:54 +0200
From: Miroslav Lichvar <mlichvar@redhat.com>
To: Harlan Stenn <stenn@nwtime.org>
Cc: Ulrich Windl <Ulrich.Windl@rz.uni-regensburg.de>, "ntp@ietf.org" <ntp@ietf.org>
Message-ID: <20190529101654.GI11346@localhost>
References: <92e2c1f9-a745-c182-6194-c7ce819c8a3c@nwtime.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <92e2c1f9-a745-c182-6194-c7ce819c8a3c@nwtime.org>
User-Agent: Mutt/1.11.3 (2019-02-01)
X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23
X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.40]); Wed, 29 May 2019 10:17:03 +0000 (UTC)
Archived-At: <https://mailarchive.ietf.org/arch/msg/ntp/O2ilYnnxIJa8jtUk5bwiqOHufZA>
Subject: Re: [Ntp] Antw: Re: Antw: Re: New rev of the NTP port randomization I-D (Fwd: New Version Notification for draft-gont-ntp-port-randomization-01.txt)
X-BeenThere: ntp@ietf.org
X-Mailman-Version: 2.1.29
Precedence: list
List-Id: <ntp.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/ntp>, <mailto:ntp-request@ietf.org?subject=unsubscribe>
List-Archive: <https://mailarchive.ietf.org/arch/browse/ntp/>
List-Post: <mailto:ntp@ietf.org>
List-Help: <mailto:ntp-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/ntp>, <mailto:ntp-request@ietf.org?subject=subscribe>
X-List-Received-Date: Wed, 29 May 2019 10:17:05 -0000

On Wed, May 29, 2019 at 03:02:49AM -0700, Harlan Stenn wrote:
> On 5/29/2019 2:39 AM, Ulrich Windl wrote:
> >>>> Harlan Stenn <stenn@nwtime.org> schrieb am 29.05.2019 um 11:31 in
> > Nachricht
> >> - the window of time where an attack is possible starts when the client
> >>   sends its request, and ends when a valid response is received.

The attacker can prevent the valid responses from being received or
processed simply by sending the client more packets that it can
handle.

> OK, so what?  Low end normal machines might handle 2k packets/second,
> and low end slow machines are lucky to be able to handle 200 packets per
> second.

Your figures are off by several orders of magnitude.

I suspect the attack is practical, at least for clients using only one
server, but nobody has tried it (and published the results) yet.

-- 
Miroslav Lichvar