Time Is Running Out for NTP • Hacker News Board

Re: Time Is Running Out for NTP

#31

Post by privong » Tue, Nov 29, 2016, 3:53 PM UTC

toomuchtodo wrote: post #16

privong wrote: post #15

Earlier quoted context omitted.

> IMHO, too much of NTP relies on GPS, but that's a separate matter. I'm curious to know more. Can you please elaborate or point to some articles discussing this?

https://ntpserver.wordpress.com/2008/09/10/ntp-server-stratu... http://www.ntp.org/ntpfaq/NTP-s-refclk.htm TL;DR Most NTP networks are relying on GPS versus a high precision on-site time keeping device. Break GPS, and you break timekeeping for a wide swath of the worldwide NTP pool. But thems the breaks when you can get access to atomic clocks in space (each GPS satellite carries an atomic clock on board) just by sti…

Thanks, but the articles you link don't really describe what I was asking about (and the "TL;DR" doesn't appear to be actually derived from those in an obvious way). I know about the strata and the use of GPS as stratum 0 clocks.

I was interested in more details about why GPS is dangerous (i.e., more about "breaking GPS"). I get that a cheap jamming attack can disrupt a single NTP server/location. But it isn't obvious that that leads to widespread use of GPS being a bad thing for NTP pools. Because it would require a widespread (near-simultaneous?) jamming for several hundred physical locations to bring down a large chunk of the pool in that way. Of course, somehow corrupting the global GPS signal would be an issue, but how would that happen?

Re: Time Is Running Out for NTP

#32

Post by privong » Tue, Nov 29, 2016, 7:46 PM UTC

jevinskie wrote: post #24

toomuchtodo wrote: post #16

Earlier quoted context omitted.

https://ntpserver.wordpress.com/2008/09/10/ntp-server-stratu... http://www.ntp.org/ntpfaq/NTP-s-refclk.htm TL;DR Most NTP networks are relying on GPS versus a high precision on-site time keeping device. Break GPS, and you break timekeeping for a wide swath of the worldwide NTP pool. But thems the breaks when you can get access to atomic clocks in space (each GPS satellite carries an atomic clock on board) just by sti…

If anyone is wondering: yes, you can own your very own atomic clock for a "reasonable" price! I encourage everyone to read [0] where a father takes his kids and a few atomic clocks up a mountain and back down. By looking at the clock drift due to changes in gravity, he was able to observe relativity! [0]: http://leapsecond.com/great2005/

> If anyone is wondering: yes, you can own your very own atomic clock for a "reasonable" price!

Just to clarify, the clocks used to demonstrate gravitational time dilation were on the order of $10,000 (or more, e.g., [0]). But one can find rubidium standards online for a few hundred dollars.

[0] http://www.ebay.com/itm/HP-5061B-Cesium-Beam-Frequency-Stand...

Re: Time Is Running Out for NTP

#33

Post by sliken » Wed, Nov 30, 2016, 7:08 AM UTC

frio wrote: post #26

toomuchtodo wrote: post #16

Earlier quoted context omitted.

https://ntpserver.wordpress.com/2008/09/10/ntp-server-stratu... http://www.ntp.org/ntpfaq/NTP-s-refclk.htm TL;DR Most NTP networks are relying on GPS versus a high precision on-site time keeping device. Break GPS, and you break timekeeping for a wide swath of the worldwide NTP pool. But thems the breaks when you can get access to atomic clocks in space (each GPS satellite carries an atomic clock on board) just by sti…

There was an interesting presentation at Kiwicon (a New Zealand security conference) the other day; someone demonstrated mimicing a GPS radio to trigger NTP drift in servers. The upshot was that it wasn't difficult, and gave you an avenue to replaying TOTP/2fa tokens...

Were they properly setup? Generally you want a local time source (GPS), the local CPU clock, and of course anyone you peer with (ideally 2 other peers on site) and of course your servers (ideally 3 as separate as possible from each other).

So the way it's supposed to work is that NTP models the error in all the above services and noticed when a source deviates. So if someone screws with the local GPS you should ignore it, and do the best you can with the remaining sources.

If you trigger NTP drift with a single source something is wrong with the setup.

Re: Time Is Running Out for NTP

#34

Post by sliken » Wed, Nov 30, 2016, 7:13 AM UTC

throwbsidbdk wrote: post #19

hga wrote: post #7

Classic NTP is hardly the only game in town. For example, see the NTPsec work in progress: https://www.ntpsec.org/ which I'll probably transition to someday, maybe even get an el-cheapo GPS receiver now that I'm not effectively living in a basement. And I've personally be using chrony for a while, although my needs are significantly less than whatever level of accuracy it provides. There are some other clients out th…

My biggest issue with NTP is little control over who runs the servers. Unlike the CA system that has checks in place against bad actors, practically anyone can run an NTP pool. It was discovered a while ago for example that some part of the Linux default NTP servers are run by shodan. So when your machine gets the time it lets shodan know you've got a server running so they can port scan you. It would be stupid not t…

NTP is hierarchical. If you run a large organization generally you run a few NTP servers that talk to the internet. Then you setup your local nodes to talk to your NTP servers.

So it's hardly "a list of every running linux server".