Re: [Ntp] Antwort: Why Roughtime?

Hello all,

But if I configure an NTS server in my client and the keys and 
certificates are valid, 
then I would expect the server not to intentionally send me false time 
information.
 ...and if I have multiple NTS-secured time servers, then the client can 
also protect 
itself against Byzantine errors.

I'm still not really convinced by the server malfeasance mechanism. Is 
this really
necessary for a "rough" time? What are the advantages over handling 
Byzantine
errors or using something like NTP pools?

In my humble opinion, Roughtime offers an advantage if I have weak 
hardware
that doesn't or can't do TLS, so you just digitally sign the time 
information directly.

I'd be happier if it didn't give the impression (as it does in some blogs 
and papers)
that Roughtime solves the chicken-and-egg problem. I also want Roughtime 
to be
minimalistic. ...why not just sign a Unix timestamp in seconds or max. 
milliseconds
with EC or ED25519 and send it from the server to the client?  ...or NTPv4 
with an
extension field containing a digital signature.  ...something like that as 
a suggestion.

but I may be seeing several things wrong. ...I'm always happy to be proven 
wrong.

kind regards,
Martin

__________________________________________

Dr.-Ing. Martin Langer
Physikalisch-Technische Bundesanstalt (PTB) 
Working Group 4.42 "Dissemination of Time"
Bundesallee 100,
38116 Braunschweig (Germany)
Tel.: +49 531 592-4470
E-Mail: martin.langer@ptb.de
__________________________________________

Von:    "Ben Laurie" <benl=40google.com@dmarc.ietf.org>
An:     kristof.teichel=40ptb.de@dmarc.ietf.org
Kopie:  "Hal Murray" <halmurray@sonic.net>, ntp@ietf.org
Datum:  18.12.2023 15:11
Betreff:        Re: [Ntp] Antwort: Why Roughtime?
Gesendet von:   "ntp" <ntp-bounces@ietf.org>

On Mon, 18 Dec 2023 at 08:09, <kristof.teichel=40ptb.de@dmarc.ietf.org> 
wrote:
Hey Hal, all,

I whole-heartedly agree with Hal's points.
In June, Martin and I sent a lengthy mail containing feedback on the 
Roughtime draft.
Perhaps there was too much in there for these points (malfeasance 
reporting is unclear what it would actually do; no malfeasance report 
doesn't mean good intentions; any security protocol could just ditch key 
lifetimes and go back to pre-shared keys [and thereby eliminate TLS] with 
little extra work, NTS too) to really come through succinctly, but all of 
them have been concerns of ours as well.

Further, I still think it is a bad idea to say 'We solve the 
chicken-and-egg problem of bootstrapping' with what seems like a mere 
reduction of a security feature (key lifetimes). It feels more like 
navigating around one of the operational ways in which the problem 
manifests rather than solving it (which makes sense, since the problem is 
probably fundamentally unsolvable). And to be clear: I'm not saying at all 
that it's bad to use long-term keys - I am just saying it's dangerous to 
imply that this is the bootstrapping solution the world has been waiting 
for

I think you've both missed an important point: if an NTS server gives me 
incorrect time and I point that out, there's no way for you to know, in 
general, whether my claim is true or not. With roughtime, I can present 
evidence.

Besten Gruß / Kind regards,
Kristof Teichel

__________________________________________

Dr.-Ing. Kurt Kristof Teichel
Physikalisch-Technische Bundesanstalt (PTB) 
Arbeitsgruppe 4.42 "Zeitübertragung"
Bundesallee 100
38116 Braunschweig (Germany)
Tel.: +49 531 592-4471
E-Mail: kristof.teichel@ptb.de
__________________________________________

-----"ntp" <ntp-bounces@ietf.org> schrieb: -----
An: ntp@ietf.org
Von: "Hal Murray" <halmurray@sonic.net>
Gesendet von: "ntp" <ntp-bounces@ietf.org>
Datum: 17.12.2023 05:35
Kopie: "Hal Murray" <halmurray@sonic.net>
Betreff: [Ntp] Why Roughtime?

I think Roughtime has 2 goals:

The first is:
  Furthermore clients may lack even a basic idea of the time, creating
  bootstrapping problems. Roughtime uses a list of keys and servers
  to resolve this issue.

The second is:
  Roughtime is a protocol for rough time synchronization that
  enables clients to provide cryptographic proof of server malfeasance.

Why do we need a separate protocol and separate servers?

For the bootstraping problem, the important idea is key lifetime.  NTS 
uses traditional web certificates and their root certificate bundle.  The 
root certificate bundle is distributed and maintained by OSes/distros so 
NTS doesn't have to operate a separate key distribution mechanism.  That 
path has a limited key lifetime policy.  If it isn't long enough, we will 
have to use self signed certificates and invent a new key distribution 
mechanism.  Roughtime has the same problem so whatever they are planning 
to use for key distribution can be used by NTS to distribute their 
self-signed root certificates.

Note that "lifetime" is a potentially ambiguous term.  Suppose you get a 
certificate with a 2 year lifetime.  That clock starts ticking when you 
purchase the certificate.  After a year, the useful lifetime is the time 
remaining, only 1 year.  The clock keeps ticking while the box and 
firmware are sitting on a retail shelf or the spares shelf.

We should issue a new key every year or so even if their lifetime is 10s 
of years.  There is no significant cost to a server to support 100s of 
keys.  The newer ones will have a longer useful life -- last year's key 
will expire a year before this year's key.

What is Roughtime's target market?  What sort of key lifetime does that 
need?
How about traffic volume?

On to server malfeasance.

I'm curious about the proof part.  Is Roughtime planning to take server 
operators to court?
Where else would you need a strong proof as compared to "Hey, your server 
is broken!"?

The NTP pool has a monitoring system that drops a server when it doesn't 
respond or returns time that is too far off.  It sends email to the 
operator.

NTS already signs NTP packets and that includes a nonce field.  The catch 
is that the key used for signing each packet is a client-server working 
key rather than a private key of a public/private pair.  We can fix that 
by adding a slot to NTS-KE which is the KE server signing the working key 
with it's private key.  (If the working key is exposed in a malfeasance 
report, the client needs to run NTS-KE again to get a new one.)

Wikipedia says;
  Malfeasance is the willful and intentional action that injures a party.

The proof scheme described by Roughtime doesn't prove the "willful and 
intentional" part.  Servers screwup because of bugs in software, firmware, 
or hardware as well as network troubles and bad luck and inadequate 
operational procedures.

There is another aspect to consider.  The lack of malfeasance reports 
doesn't prove correct operations.  If a bad guy takes over a server, he 
can respond correctly except to the system he is attacking.  You can't 
depend on monitoring by other sites.

In recent mail, Chris mentioned "consensus".  NTP already does that.  Does 
Roughtime have better heuristics for consensus than NTP is using?

Have I missed something that Roughtime does and NTP can't do with a simple 
extension?

-- 
These are my opinions.  I hate spam.

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