Re: NTP Sync Issue Across Tata (Europe)

[Mel Beckman <mel () beckman org>]

Forrest,

GPS spoofing may work with a primitive Raspberry Pi-based NTP server, but commercial industrial NTP servers have 
specific anti-spoofing mitigations. There are also antenna diversity strategies that vendors support to ensure the 
signal being relied upon is coming from the right direction. It’s a problem that has received a lot of attention in 
both NTP and aviation navigation circles. What is hard to defend against is total signal suppression via high powered 
jamming. But that you can do with a geographically diverse GPS NTP network.

 -mel

On Aug 7, 2023, at 1:39 AM, Forrest Christian (List Account) <lists () packetflux com> wrote:


The problem with relying exclusively on GPS to do time distribution is the ease with which one can spoof the GPS 
signals.

With a budget of around $1K, not including a laptop, anyone with decent technical skills could convince a typical GPS 
receiver it was at any position and was at any time in the world.   All it takes is a decent directional antenna, some 
SDR hardware, and depending on the location and directivity of your antenna maybe a smallish amplifier.   There is much 
discussion right now in the PNT (Position, Navigation and Timing) community as to how best to secure the GNSS network, 
but right now one should consider the data from GPS to be no more trustworthy than some random NTP server on the 
internet.

In order to build a resilient NTP server infrastructure you need multiple sources of time distributed by multiple 
methods - typically both via satellite (GPS) and by terrestrial (NTP) methods.   NTP does a pretty good job of sorting 
out multiple time servers and discarding sources that are lying.  But to do this you need multiple time sources.  A 
common recommendation is to run a couple/few NTP servers which only get time from a GPS receiver and only serve time to 
a second tier of servers that pull from both those in-house GPS-timed-NTP servers and other trusted NTP servers.   I'd 
recommend selecting the time servers to gain geographic diversity, i.e. poll NIST servers in Maryland and Colorado, and 
possibly both.

Note that NIST will exchange (via mail) a set of keys with you to talk encrypted NTP with you.   See 
https://www.nist.gov/pml/time-and-frequency-division/time-services/nist-authenticated-ntp-service .



On Sun, Aug 6, 2023 at 8:36 PM Mel Beckman <mel () beckman org<mailto:mel () beckman org>> wrote:
GPS Selective Availability did not disrupt the timing chain of GPS, only the ephemeris (position information).  But a 
government-disrupted timebase scenario has never occurred, while hackers are a documented threat.

DNS has DNSSec, which while not deployed as broadly as we might like, at least lets us know which servers we can trust.

Your own atomic clocks still have to be synced to a common standard to be useful. To what are they sync’d? GPS, I’ll 
wager.

I sense hand-waving :)

-mel via cell

On Aug 6, 2023, at 7:04 PM, Rubens Kuhl <rubensk () gmail com<mailto:rubensk () gmail com>> wrote:




On Sun, Aug 6, 2023 at 8:20 PM Mel Beckman <mel () beckman org<mailto:mel () beckman org>> wrote:
Or one can read recent research papers that thoroughly document the incredible fragility of the existing NTP hierarchy 
and soberly consider their recommendations for remediation:

The paper suggests the compromise of critical infrastructure. So, besides not using NTP, why not stop using DNS ? Just 
populate a hosts file with all you need.

BTW, the stratum-0 source you suggested is known to have been manipulated in the past 
(https://www.gps.gov/systems/gps/modernization/sa/), so you need to bet on that specific state actor not returning to 
old habits.

OTOH, 4 of the 5 servers I suggested have their own atomic clock, and you can keep using GPS as well. If GPS goes 
bananas on timing, that source will just be disregarded (one of the features of the NTP architecture that has been 
pointed out over and over in this thread and you keep ignoring it).

Rubens


--
- Forrest