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These can help against GPS spoofing / jamming by identifying false signals and allowing rapid resynchronization: https://www.army.mil/article/88361/Miniaturize

by geenew 5y ago

These can help against GPS spoofing / jamming by identifying false signals and allowing rapid resynchronization: https://www.army.mil/article/88361/Miniaturized_atomic_clock_to_support_Soldiers_in_absence_of_GPS/ https://www.army.mil/article/88361/Miniaturized_atomic_clock... Also related, NASA has a spaceborne atomic clock in testing that, if it works, will make space navigation much more efficient: https://www.nasa.gov/mission_pages/tdm/clock/index.html https://www.nasa.gov/mission_pages/tdm/clock/index.html

KirillPanov 5y ago
> These can help against GPS spoofing / jamming by identifying false signals Hrm, it would definitely stop a spoofer from misleading you about what time it is. If you care about your position: given the fact that GPS satellites are so far away and the signal is so weak, I don't see how it provides any defense against jamming specifically. If you can't hear the satellites, you can't hear them. Regarding spoofing, it really only defends against spoofed signals emanating from other satellites. This is a big concern for the military. For everybody else "spoofing" means spoofed signals from other land-based or atmospheric transmitters, which once again are close enough to easily drown out the true signal completely. TL;DR: useful if threat model includes attacker-controlled satellites.
- geenew 5y ago
  I'm not sure how much you know about GPS, but position in GPS is intrinsically linked to time. You know a satellite's orbit from its orbital elements, so, a given moment in time, you know where it is. The satellite emits signals with its internal time. You receive the signal sometime later. The difference between those times gives you the distance to the satellite at that frame[0]. When you have three or more measurements, you can triangulate your position in 3D. In terms of spoofing, one method is to emit signals from ground based transmitters that match the signal from the actual satellite, but with offset times, and at higher power levels than the actual satellite[1]. This gives the receiver a false location.[2] If you have a source of time-truth, you can reject these signals. In terms of jamming, you'll note that it allows rapid resynchronization after jamming. During jamming, you don't know where you are. After jamming, without a highly precise clock, you need to solve for the actual time by integrating signals from >=4 satellites. With a highly precise clock, this step is removed. [0] There are confounding factors, like refraction in the ionosphere, but a rough approximation is that the signal is travelling at c [1] Higher power is trivial because the signals from the satellites are very weak [2] This is a classic example: https://en.wikipedia.org/wiki/Iran%E2%80%93U.S._RQ-170_incident https://en.wikipedia.org/wiki/Iran%E2%80%93U.S._RQ-170_incid... TL;DR: useful for existing ground/air based threats.
  - sudosysgen 5y ago
    This is not quite how GPS works. Because of relativity, there is a difference between local time and remote time for all GPS satellites relative to the drone. Jamming nowadays does not work by simply throwing off random numbers. This is trivially defeated by gyroscope. It works by feeding time data that initially is exactly the same as the satellite, and slowly changes that as if it was in some other plausible direction, ultimately giving total control. Against primitive forms of jamming, sure this might work. Against modern spoofing attacks, no there is no fix. Overall, what worked works and what doesn't work won't.
    - geenew 5y ago
      Relativity doesn't really factor into this issue; the core of the issue is false timing signals. Any introduction of a false timing signal whose time offset from the true signal is greater than the local clock's uncertainty can be flagged as false. Higher-accuracy local clocks reduce the amount of error that can be introduced without detection. CSACs don't solve the issue, but they do allow for detection of more spoofing signals, and they reduce the amount of error that any successful spoofing signal can introduce.
      - sudosysgen 5y ago
        No, relativity absolutely does factor. The timing signal from the GPS satellites is warped by relativity as you move relative to them. Without a source of location truth, you have no way of knowing if the change in the time signal is because of your movement relative to the GPS satellites, or because of spoofing. As I said, the false GPS signal will start with a time offset of zero. They will then progressively offset the time signal of each satellite as if, for example, the GPS receiver was deviating slightly right, after which the drone will turn left.
        geenew 5y ago
        Relativity matters in GNSS in general, but it doesn't really matter for the issue of spoof detection; relativistic effects would be solved for by both the attacker and receiver. There's no uncertainty in them.
sudosysgen 5y ago
Hmm, no, I don't think it will. GPS spoofers start off feeding you exactly the same data as the GPS satellites, then start diverging exactly as if you were slowly turning in a different direction. Ergo, this will not work at all.
- geenew 5y ago
  [Reposting a response written above] Any introduction of a false timing signal whose time offset from the true signal is greater than the local clock's uncertainty can be flagged as false. Higher-accuracy local clocks reduce the amount of error that can be introduced without detection. CSACs don't solve the issue, but they do allow for detection of more spoofing signals, and they reduce the amount of error that any successful spoofing signal can introduce.
  - geenew 5y ago
    Reading this again I wasn't as complete as I should have been. Any introduction of a false timing signal whose time offset from the existing measurements is greater than the local clock's uncertainty can be flagged as false. If your previous reported satellite time is Sp, previous local time is Lp, local time uncertainty is U, current local time is Lc = Lp + Ld±U, and current reported satellite time is Sc = Sp + Sd, then, roughly speaking, if Sd > (Ld + U) or Sd < (Ld - U), the reported signal is a spoof. So the original spoof signal as well as any subsequent spoof signals are subject to the stricter constraints offered by your higher-accuracy local time source.
    - sudosysgen 5y ago
      Again I don't think you understand what I meant. The spoofed signal will start with an offset of exactly 0. This offset will progressively increase in a way that is undistinguishable from an offset caused by receiver moving slightly left, for example. That being said, the main source of error in GPS signals isn't the time-keeping of the receiver, but rather atmospheric interference and rounding errors in computations.

by geenew 5y ago

KirillPanov 5y ago

> These can help against GPS spoofing / jamming by identifying false signals Hrm, it would definitely stop a spoofer from misleading you about what time it is. If you care about your position: given the fact that GPS satellites are so far away and the signal is so weak, I don't see how it provides any defense against jamming specifically. If you can't hear the satellites, you can't hear them. Regarding spoofing, it really only defends against spoofed signals emanating from other satellites. This is a big concern for the military. For everybody else "spoofing" means spoofed signals from other land-based or atmospheric transmitters, which once again are close enough to easily drown out the true signal completely. TL;DR: useful if threat model includes attacker-controlled satellites.

geenew 5y ago
I'm not sure how much you know about GPS, but position in GPS is intrinsically linked to time. You know a satellite's orbit from its orbital elements, so, a given moment in time, you know where it is. The satellite emits signals with its internal time. You receive the signal sometime later. The difference between those times gives you the distance to the satellite at that frame[0]. When you have three or more measurements, you can triangulate your position in 3D. In terms of spoofing, one method is to emit signals from ground based transmitters that match the signal from the actual satellite, but with offset times, and at higher power levels than the actual satellite[1]. This gives the receiver a false location.[2] If you have a source of time-truth, you can reject these signals. In terms of jamming, you'll note that it allows rapid resynchronization after jamming. During jamming, you don't know where you are. After jamming, without a highly precise clock, you need to solve for the actual time by integrating signals from >=4 satellites. With a highly precise clock, this step is removed. [0] There are confounding factors, like refraction in the ionosphere, but a rough approximation is that the signal is travelling at c [1] Higher power is trivial because the signals from the satellites are very weak [2] This is a classic example: https://en.wikipedia.org/wiki/Iran%E2%80%93U.S._RQ-170_incident https://en.wikipedia.org/wiki/Iran%E2%80%93U.S._RQ-170_incid... TL;DR: useful for existing ground/air based threats.
- sudosysgen 5y ago
  This is not quite how GPS works. Because of relativity, there is a difference between local time and remote time for all GPS satellites relative to the drone. Jamming nowadays does not work by simply throwing off random numbers. This is trivially defeated by gyroscope. It works by feeding time data that initially is exactly the same as the satellite, and slowly changes that as if it was in some other plausible direction, ultimately giving total control. Against primitive forms of jamming, sure this might work. Against modern spoofing attacks, no there is no fix. Overall, what worked works and what doesn't work won't.
  - geenew 5y ago
    Relativity doesn't really factor into this issue; the core of the issue is false timing signals. Any introduction of a false timing signal whose time offset from the true signal is greater than the local clock's uncertainty can be flagged as false. Higher-accuracy local clocks reduce the amount of error that can be introduced without detection. CSACs don't solve the issue, but they do allow for detection of more spoofing signals, and they reduce the amount of error that any successful spoofing signal can introduce.
    - sudosysgen 5y ago
      No, relativity absolutely does factor. The timing signal from the GPS satellites is warped by relativity as you move relative to them. Without a source of location truth, you have no way of knowing if the change in the time signal is because of your movement relative to the GPS satellites, or because of spoofing. As I said, the false GPS signal will start with a time offset of zero. They will then progressively offset the time signal of each satellite as if, for example, the GPS receiver was deviating slightly right, after which the drone will turn left.
      - geenew 5y ago
        Relativity matters in GNSS in general, but it doesn't really matter for the issue of spoof detection; relativistic effects would be solved for by both the attacker and receiver. There's no uncertainty in them.

sudosysgen 5y ago

Hmm, no, I don't think it will. GPS spoofers start off feeding you exactly the same data as the GPS satellites, then start diverging exactly as if you were slowly turning in a different direction. Ergo, this will not work at all.

geenew 5y ago
[Reposting a response written above] Any introduction of a false timing signal whose time offset from the true signal is greater than the local clock's uncertainty can be flagged as false. Higher-accuracy local clocks reduce the amount of error that can be introduced without detection. CSACs don't solve the issue, but they do allow for detection of more spoofing signals, and they reduce the amount of error that any successful spoofing signal can introduce.
- geenew 5y ago
  Reading this again I wasn't as complete as I should have been. Any introduction of a false timing signal whose time offset from the existing measurements is greater than the local clock's uncertainty can be flagged as false. If your previous reported satellite time is Sp, previous local time is Lp, local time uncertainty is U, current local time is Lc = Lp + Ld±U, and current reported satellite time is Sc = Sp + Sd, then, roughly speaking, if Sd > (Ld + U) or Sd < (Ld - U), the reported signal is a spoof. So the original spoof signal as well as any subsequent spoof signals are subject to the stricter constraints offered by your higher-accuracy local time source.
  - sudosysgen 5y ago
    Again I don't think you understand what I meant. The spoofed signal will start with an offset of exactly 0. This offset will progressively increase in a way that is undistinguishable from an offset caused by receiver moving slightly left, for example. That being said, the main source of error in GPS signals isn't the time-keeping of the receiver, but rather atmospheric interference and rounding errors in computations.