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

[Magnus Danielson <[e-mail]>]

Hi,

On 2021-01-18 12:38, Hal Murray wrote:
> [e-mail] said:
>> And all bootstrapping problems could be solved with CD / DO flags  controls
>> and validation back checking with the first returned time of day. 
> How is that back checking going to work?  You don't know the time yet.
>
> Sure, it will say "OK" if you are talking to an honest server, but if you are talking to a bad guy, it can lie consistently.  Am I missing something?

So, you only need to have sufficiently accurate time that DNSSEC will
give thumbs up.

Also, it only really need to match of that handshake.

So, if you talk to server A, you can query which NTP server A say I
should be able to trust.

1) Query A for NTP server B for A.

2) Query B for NTP time to use in initial exchange.

3) Query A for DNSSEC verified answer, using the time as initiated from B.

4) With verified answer, now handshake B using verified DNS records. If
not verified, it fails.

5) Query B for NTP time.

6) If verified time matches that of the initial handshake request (as
updated using local time progess), then unauthenticated time in step 2
and 3 was valid, and thus the verification was valid and progress, else
fail.

So, we see how unauthenticated time can be used to bootstrap the
handshake. Notice that this is not used to initiate node time, but only
for that handshake. Only after things is secured, you accept time as
being secured.

This will work if the DNSSEC part and the consistency check in 6 leave
enough margin.

If it fails, it fails. This is why you want multiple sources for redundancy.

>
> ---------
>
> I know of 2 solutions for the 10 years on the shelf problem.
>
> 1) Have a battery that lasts long enough.  Watches are good for ballpark of 1 second per day so 10 years will be within an hour.  (worse if the device is stored in hot or cold)
>
> 2) Preload the box with whatever is needed to get off the ground without good time.  I think that is long lifetime certificates and long lifetime IP Addresses.
>
> Neither is easy, but I think both are possible.
Cheers,
Magnus