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

[FUSTE Emmanuel <[e-mail]>]

Le 19/01/2021 à 10:42, Miroslav Lichvar a écrit :
> On Mon, Jan 18, 2021 at 10:28:41PM +0100, Magnus Danielson wrote:
>> On 2021-01-18 22:15, Kurt Roeckx wrote:
>>> In case keys are compromised, an attacker can send you an invalid
>>> initial time. That same attacker can create DNSSEC records, which
>>> you're happy to validate with the wrong time. So now you think DNS
>>> is working properly and ask for the time again, and still get the
>>> wrong time.
>> The DNSSEC records need to validate data-wise for the time-attack to do
>> any good. The design goal was just to enable the DNSSEC validation to
>> have good enough time for time-validation for bootstrap.
> I think the point is that you cannot bootstrap secure time out of
> nothing. You either do full validation using some trusted time source
> (e.g. RTC), or you don't. It doesn't matter if multiple systems are
> involved and their data seem consistent with each other.
I do not agree. Because :
>
> 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.
And even in this case, you could cross enough sources to get better time 
than most RTC ones.
When time matter, you will have RTC and other out of band validation 
process to ensure correct time.

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.

Emmanuel.