Depends on how synchronized you need to be. In the context of running airgapped: A rubidium oscillator or Chip Scale Atomic Clock is in the price range you quote. However, these can drift enough that you should occasionally synchronize with a reference time source. This is to ensure continued millisecond accuracy. Of course it all depends on how much drift you'll tolerate, and if you're OK with being within a second, then a rubidium might be ok. Caesium oscillators which have much lower drift are in the $30K-50K range. These would require significantly less frequent synchronization, but are definitely not a few thousand dollars. Note that these are both just oscillators and they need additional support hardware to be able to be queried by NTP. Or stated differently, they still need a NTP server. Yes, there are products out there which integrate everything in one box at an additional cost. On Mon, Aug 7, 2023, 11:02 PM Masataka Ohta < mohta@necom830.hpcl.titech.ac.jp> wrote:
Forrest Christian (List Account) wrote:
In the middle tends to be a more moderate solution which involves a mix of time transmission methods from a variety of geographically and/or network diverse sources. Taking time from the public trusted ntp servers and adding lower cost GPS receivers at diverse points in your network seems like a good compromise in the middle. That way, only coordinated attacks will be successful.
Instead, just rely on atomic clocks operated by you. They are not so expensive (several thousand dollars) and should be accurate enough without adjustment for hundreds of years. There can be no coordinated attacks. They may be remotely accessed through secured NTP.
Masataka Ohta