Re: [Ntp] Antwort: Re: Antwort: Why Roughtime?

Watson Ladd <watsonbladd@gmail.com> Mon, 18 December 2023 17:24 UTC

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From: Watson Ladd <watsonbladd@gmail.com>
Date: Mon, 18 Dec 2023 09:24:00 -0800
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To: kristof.teichel=40ptb.de@dmarc.ietf.org
Cc: Ben Laurie <benl=40google.com@dmarc.ietf.org>, ntp@ietf.org
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Subject: Re: [Ntp] Antwort: Re: Antwort: Why Roughtime?
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On Mon, Dec 18, 2023 at 8:33 AM <kristof.teichel=40ptb.de@dmarc.ietf.org> wrote:
>
> Hey Ben, all,
>
> It's not, I think, so much that we missed it (Martin and I, can't speak for Hal - although he does mention the feature explicitly).
> I think it's more that we don't believe it's as useful as others seem to think (honestly, I think this is explicitly talked about in our mail from June, too):
>
> I've never heard a user express that they want to be able to get false time and then report it.
> I have heard users express that they want to get correct time.
> Those two goals are not the same, and the logical chain leading from the former to the latter (where I'm supposed to believe someone is trustworthy from the fact that I don't currently have a report at hand about misbehavior from them) just seems far-fetched to me.

I never heard users express that they wanted to catch misbhaving CAs:
they wanted properly behaving ones. But to make them behave properly
we created CT logs, so that instances of CA misbehavior couldn't be
hidden. And those CT logs get monitored to ensure trustworthiness via
similar mechanisms to Roughtime, even though most users of CT logs
don't directly interact with those mechanisms.

Likewise the possibility of detection raises the stakes for
misbehaving servers, even if most users won't.
>
> And this is just exacerbated by putting it next to Roughtime's other most-advertised feature: use in bootstrapping phase.
> If a device has just booted up and has close to zero knowledge, I think it extra unreasonable to rely on malfeasance reports that the device may simply never have gotten.

Devices don't rely directly on reports, just as in the WebPKI browsers
don't look at the contents of MDSP mechanically. However, without
reporting vendors have no way to reevaluate the trust relationships.
Even if this reevaluation is not instant it still limits the impact of
a compromise.

>
> Lastly, if malfeasance reporting IS deemed an important feature by someone, I again agree with Hal that it could be put into any protocol (e.g. NTP, with an extra extension field).
> It is definitely Roughtime's more complex feature, but it would also not be terribly much to ask of other protocols IMO.

How would you put it in? Signing the response takes significantly
longer than you want in NTS. Having a long term identity runs at cross
purposes to relying on the WebPKI. I'm not opposed to possible
integration but I think the security models and synchronization goals
are pretty opposed.

Sincerely,
Watson Ladd

-- 
Astra mortemque praestare gradatim