Re: [TLS] No more GMT exposure in the handshake

Viktor Dukhovni <viktor1dane@dukhovni.org> Sun, 08 June 2014 15:40 UTC

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Date: Sun, 8 Jun 2014 15:39:36 +0000
From: Viktor Dukhovni <viktor1dane@dukhovni.org>
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Subject: Re: [TLS] No more GMT exposure in the handshake
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On Sun, Jun 08, 2014 at 03:10:46PM +0000, Jacob Appelbaum wrote:

> That sounds fine to me, sure. I admit, I haven't put a lot of thought
> into the format because it seems that most of the momentum is in
> removing anything meaningful from that field.

A good thing.  If the client wants a server time-stamp, it can ask
for it via an extension.

> In any case, having 64bits of timing information from a server would
> allow for a parasitic network time protocol that is as accurate as NTP
> to be built on top of TLS. I haven't checked but I believe Google
> still uses this to set clocks on ChromeOS.

"As accurate as NTP" is a bold claim.  NTP "accuracy" (as opposed
to precision which is a different beast entirely) comes from using
multiple sourcs a PLL to estimate round-trip delay and smooth out
noise, and when possible multiple sources, ...

NTP runs over UDP which is less likely to be delayed, re-transmitted, ...

Attaining NTP "accuracy" over TLS, seems rather implausible.

-- 
	Viktor.