Re: [Ntp] NTP Security (was NTPv5: big picture)

[Miroslav Lichvar <[e-mail]>]

On Tue, Jan 19, 2021 at 10:20:31AM +0000, FUSTE Emmanuel wrote:
> Le 19/01/2021 à 10:42, Miroslav Lichvar a écrit :
> > Even if we assume the attacker didn't manipulate the DNS(SEC) records,
> > there is a possibility the name or address is no longer under the
> > control of the original owner when those records were valid. In the
> > pool that happens frequently.
> This is a completely different and non technical problem, specific to 
> the pool.

It's not specific to the pool. IP addresses and domains are sold,
lost, hijacked, etc.

> And even in this case, you could cross enough sources to get better time 
> than most RTC ones.

Having multiple sources doesn't protect you against a focused MITM
attack.

> The main point is that if I have a very simple device without RTC, which 
> point to my own Internet NTP servers, I could bootstrap it with perfect 
> confidence only by ensuring that the root DNS key are up to date. If I 
> do not trust the root servers, this is another out of topic problem.

I'd say it's just shifting the responsibility. "Not my problem"
doesn't make that problem disappear.

If an attacker hijacks your domain and makes their own records, how
will your simple device know they shouldn't be trusted later when you
get it back? You will need to make some modification on the device.

When using NTS with your own servers, it might be easier to use a
self-signed certificate or your own CA. You can disable the time
validation, or make the certificate valid even in the initial boot
date (e.g. 1970). Of course, if the key is compromised, you will need
to update the device.

-- 
Miroslav Lichvar