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Re: [TLS] Server time

Jeffrey Walton <noloader@gmail.com> Wed, 08 April 2015 10:27 UTC

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Date: Wed, 08 Apr 2015 06:27:27 -0400
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From: Jeffrey Walton <noloader@gmail.com>
To: Kurt Roeckx <kurt@roeckx.be>, "tls@ietf.org" <tls@ietf.org>
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Subject: Re: [TLS] Server time
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On Wed, Apr 8, 2015 at 6:15 AM, Kurt Roeckx <kurt@roeckx.be> wrote:
> On Wed, Apr 08, 2015 at 10:11:50AM +0200, Florian Weimer wrote:
>> On 04/06/2015 01:44 PM, Kurt Roeckx wrote:
>>
>> > There is work being done to make NTP more secure.  But if you
>> > don't know what time it is there is no way that we know how to
>> > get the correct time in a secure way.  About the best you can do
>> > is assume that not everybody is compromised.
>>
>> What about hard-coded (CA) certificates?
>
> That might have expired, been revoked, whatever.  If you go and
> check a CRL the attacker might give you an old copy.  If you use
> OCSP it might give you an old reply.  You probably at least want
> an OCSP server that supports a nonce.
>
Gossip protocols.

As the density of networked devices increases (especially with mobile
clients), I think it makes sense to look at it as a partial solution
or a way to reduce the problem. The mobile clients bring in time from
outside channels, so its a nice cross check.

A device still probably needs to contact an NTP server on occasion for
sanity checking. But there won't be a need to hammer a secure time
server every 30 minutes or every hour.

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