Re: [Ntp] The NTP WG has placed draft-schiff-ntp-chronos in state "Call For Adoption By WG Issued"

Neta R S <neta.r.schiff@gmail.com> Tue, 10 September 2019 09:54 UTC

Return-Path: <neta.r.schiff@gmail.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 CBAD31200A3 for <ntp@ietfa.amsl.com>; Tue, 10 Sep 2019 02:54:17 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -1.997
X-Spam-Level:
X-Spam-Status: No, score=-1.997 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, HTML_MESSAGE=0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001] autolearn=ham autolearn_force=no
Authentication-Results: ietfa.amsl.com (amavisd-new); dkim=pass (2048-bit key) header.d=gmail.com
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 XfP3rEGFEITI for <ntp@ietfa.amsl.com>; Tue, 10 Sep 2019 02:54:15 -0700 (PDT)
Received: from mail-lj1-x230.google.com (mail-lj1-x230.google.com [IPv6:2a00:1450:4864:20::230]) (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 81586120052 for <ntp@ietf.org>; Tue, 10 Sep 2019 02:54:14 -0700 (PDT)
Received: by mail-lj1-x230.google.com with SMTP id y23so15426340ljn.5 for <ntp@ietf.org>; Tue, 10 Sep 2019 02:54:14 -0700 (PDT)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=ka+itsnU3J9t8rdseoSGYAqcIrMp19s2NAbmBeJSzd0=; b=Z9sP8Qczyt016KbWecvMZaSOIKjTgsOPcWpo8ELv3ToD4g/HBFe1DSE4nvPeXQRYq1 rwnprKLicEB3LWK8Lo28/NWj6Sie85Cv5pASb2PyjVSHXZdiCGXajtsUFrZzD9n8l/lU s7rbT/OP7q+XBTDTAbNpc6aFZGcF/CPftdr3bXq/Fx87hTE5ALNIdK8HwL1zW+zoHmok n8UOv0IgW2V8U0wEmyr8pSrc80YoGJL+rYiXtx95VCzj0VO45QIZdTQ/RJC96T/Lc/XS xZdnhkoQ6fx/218HTfYhj0TX+atuYPA7a2zGZxJfVZoG4D4iYLSsPheMBLgEtumq7ynM 680w==
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=ka+itsnU3J9t8rdseoSGYAqcIrMp19s2NAbmBeJSzd0=; b=cSAYhfKu+QlczW1t3LRLA4s1H9PDV3kaDV4GXFyzFIFTesIkqVwGZw/4DVAqKbRLbW 5b9vOk2ujH4v+Y5eU7yRRjL94EyPH712ImbSxQW8hPbHWPcR1+iCsEfsiVZM9UfykrDD 12JbrbJzddzeB9qCfU67J0/4ih2Bf2g6fIjctnDttz9MTWus64uFXGG/6Nko8LvW+vaA L23e6XzwRgBLTAyrhCd4lPM0tkIqGHkCfj/N6Nu1To/R2ebG5uoNDig442RmzJyd1GHV MoyYNpH4FWAoxdFwTO3hJwLesr87iXmKQtL9ixrAQ/w4BKNpl6AQjDSKCT88MgVAJUE/ 7ajw==
X-Gm-Message-State: APjAAAXsfTYGL7vnInSphmlFNmdiGXsGK1WRV7/ZijFHql36XHnCZKzN ZBtEl1RX6XoFSAEItBD+/xDrYWNeg0SY/qiQa9M=
X-Google-Smtp-Source: APXvYqzgaCCKA2xC6m0XNjggp9MFSJqpZKDW5RTDAS6nfA4iDvHaX18LkDKjdOaFgUb1XBwXa5W1UeFiUY/myFHWU/k=
X-Received: by 2002:a2e:2953:: with SMTP id u80mr19275428lje.233.1568109251843; Tue, 10 Sep 2019 02:54:11 -0700 (PDT)
MIME-Version: 1.0
References: <156697054476.22343.803396183712486000.idtracker@ietfa.amsl.com> <36f6c676-7937-4876-3c38-e12d39be2666@nwtime.org> <CAM-HxCPGif77Nwj0gC4_paxczwyYTxo9tvgEFZ5V43AyUGLM7w@mail.gmail.com> <3bab5589-17c6-72d8-ac3e-5eb0f4df8a7c@nwtime.org>
In-Reply-To: <3bab5589-17c6-72d8-ac3e-5eb0f4df8a7c@nwtime.org>
From: Neta R S <neta.r.schiff@gmail.com>
Date: Tue, 10 Sep 2019 12:53:58 +0300
Message-ID: <CAM-HxCNRiei3OzZb0_=W9txtTPmbg+ZgAExVhksFRaXAMWuv5Q@mail.gmail.com>
To: Harlan Stenn <stenn@nwtime.org>
Cc: ntp@ietf.org
Content-Type: multipart/alternative; boundary="000000000000ecd8f605922fe269"
Archived-At: <https://mailarchive.ietf.org/arch/msg/ntp/25YuQqAa8whmtU1x-StErJriY9k>
Subject: Re: [Ntp] The NTP WG has placed draft-schiff-ntp-chronos in state "Call For Adoption By WG Issued"
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: Tue, 10 Sep 2019 09:54:18 -0000

Hi Harlan,

Please my comments inline.

On Tue, Sep 10, 2019 at 12:14 PM Harlan Stenn <stenn@nwtime.org>; wrote:

> Hi Neta,
>
> I want to see this sort of information either in the actual RFC or in
> related RFCs, even for Informational documents.
>
We will consider the best way to present this information.

I still have other issues with some of the core assumptions, and I'm not
> currently able to elaborate on those now.
>
Sure, we are currently working on extending Chronos and we will be glad to
hear you thoughts.
I understand you can't elaborate now. It can be done after the adoption.

Neta


> H
>
> On 9/10/2019 1:16 AM, Neta R S wrote:
> > Hi Harlan,
> >
> > Please see a brief description of Chronos threat model, Chronos
> > algorithm and security analysis below.
> >
> > *_Threat model:
> > _*Chronos considers a powerful form of man-in-the-middle (MitM)
> > Byzantine attacker, capable of determining precisely the values of the
> > time samples gathered by the Chronos client from
> > a subset of the NTP servers in its server pool (up to one-third of the
> > pool).
> >
> > *_A short reminder of Chronos' algorithm:
> > _*- Chronos client choose m servers at random, queries them, orders
> > their m samples according to their value, drop the d lowest and highest
> > samples.
> > - Then it tests the remaining set, and use its average as the new
> > client's clock only if the two conditions are satisfied:
> > 1 - All the samples are close (up to 2w)
> > 2 - Their average is close to the clients clock (up to ERR+2w)
> > Otherwise - the client resamples (choose again m servers at random,
> > queries them, orders them from low to high and drop the d lowest and the
> > d highest and tests the remaining set again).
> > After the client resamples (fails in the tests) K times, it moves to the
> > panic mode where all the servers are sampled.
> >
> > *_Security analysis
> > _*Chronos draft is based on the Chronos paper, which provide a security
> > analysis.
> > It was proved mathematically, that since Chronos use (slightly) more
> > servers to update, and choose them at random, the probability of
> > successful MitM attack decreases dramatically compares to NTPv4.
> > The improvement factor depends on the number of servers queries by
> > Chronos client at each update. For example, if the attacker controls 1/7
> > of the servers in the pool, while querying 14 servers per update,
> > Chronos client can reduce its probability for timeshifthimg by a factor
> > of approximately 1000.
> >
> > Moreover, we considered the spectrum of feasible attack scenarios in
> > order to evaluate the
> > effectiveness of Chronos in thwarting timeshifting attacks.
> > The scenarios depend on how many malicious servers were queried.
> > We considered two scenarios:
> >
> > _-  Scenario I: Less than m-d of the queried servers are under the
> > attacker’s control._
> > It means, that there are more than d ''good'' samples (defined as up to
> > w away from the UTC).
> > In this scenario, there are two options:
> >
> > 1. There is at least one ''good'' sample in the remaining set, and then
> > the others should be close to it (according to condition 1, otherwise
> > the client resamples).
> > Then, the average of the samples in the remaining set (which is used to
> > update the client's clock) is close to the UTC.
> >
> > 2. There are no ''good'' samples in the remaining set. Thus, since there
> > are more than d ''good'' samples, the values of remain set are bounded
> > by ''good'' samples.
> > Thus, the average of the remaining set is also close to the UTC
> >
> > Therefore, these attack strategies are ineffective.
> >
> > _- Scenario II:  More than m-d of the queried servers are under the
> > attacker’s control._
> > In the worst case of this scenario, all the samples in the remaining set
> > are ''bad'' (more than w away from the UTC).
> > However, we proved in the paper that the probability of this scenario is
> > extremely low (since it requires malicious servers to be randomly chosen
> > at a much higher ratio than their ratio in the population – the pool)..
> > Thus, the probability of repeated time shift is even exponentially lower
> > – negligible.
> > Consequently, a significant time shift is practically infeasible
> >
> >
> > Moreover, we examined the probability of DoS attack on the servers by an
> > attacker who cause many clients to resample and reach the panic mode
> > multiple times.
> > We found that the probability of this attack is extremely low, even if
> > the client moves to panic mode directly after 3 times of resampling.
> >
> > *_Next step:
> > _*We are continuing to evaluate Chronos's performance and security for
> > different attack strategies and at different locations.
> >
> > Detailed discussions (along with the parameters evaluation can be seen
> > in the full paper:
> >
> https://www.ndss-symposium.org/wp-content/uploads/2018/02/ndss2018_02A-2_Deutsch_paper.pdf
> )
> >
> >
> > Neta
> >
> > _______________________________________________
> > ntp mailing list
> > ntp@ietf.org
> > https://www.ietf.org/mailman/listinfo/ntp
> >
>
> --
> Harlan Stenn, Network Time Foundation
> http://nwtime.org - be a Member!
>
> _______________________________________________
> ntp mailing list
> ntp@ietf.org
> https://www.ietf.org/mailman/listinfo/ntp
>