6 ms·

I mean ... That's what's cryptography is for. Making sure that what you receive is from the sender you expect it from. Ie sign the current data package plus th

• j16sdiz 5y ago
  GPS spoofing is the same signal, emitted at different time and space.
  • zelphirkalt 5y ago
    Which is why the GP mentioned encoding the timestamp and mentioned data packages (ergo package based one-directional communication). If by same signal you mean looking similar, but not containing the same data, then the problem is already solved. If you mean containing the same data, then there is no problem.
    • sobriquet9 5y ago
      This requires a precise internal clock that is always correct. If that clock drifts or is reset because the battery dies, GPS receiver would stop working.
      • JanisErdmanis 5y ago
        Wouldn't it suffice to have a rather imprecise time + counter in the GPS message? So if multiple messages arrives the one with the largest count is kept. I wonder if the problem lies in a different aspect of needing to authenticate messages quickly enough and thus requiring more processing power.
        • tialaramex 5y ago
          This is not a packet switched network and you are not receiving nice neat little messages to decode, you've got a radio receiver, the real transmissions are from a satellite in space, while unfortunately your adversary is transmitting from radio towers or even a portable transmitter, much closer and able to be supplied with energy easily so more powerful, but on the same frequencies. Also, be careful with assuming that late = imposter. The whole point of GPS is that signals take time to travel over distance, so, maybe the signal is late because you're further from that satellite instead, which is what you were trying to measure when you got distracted trying to prevent spoofing.
          • JanisErdmanis 5y ago
            I agree that there is an issue with overwhelming the satellite transmission frequencies. However, the signal can never be delivered earlier by adversary as signal travelling in air is about the physical limit. Perhaps only a stalking satellite could intercept and deliver the message faster, but that seems like a sci-fi. > got distracted trying to prevent spoofing Indeed overwhelming the processing power with junk seems the important issue if crypto is added.
• tialaramex 5y ago
  But these signals are from the real GPS birds, and they are really the ones for Las Vegas three weeks ago. They are completely authentic.
  • brandmeyer 5y ago
    It sounds like you are referring to a replay attack. Mental model tweak: The signals aren't for a specific location, they are world-wide. So the "for Las Vegas" part doesn't work. Replay attacks are just a kind of denial of service. In that case, you may as well just use jamming. Spoofing attacks are far more dangerous, and cryptographic signing defeats them effectively.
    • tialaramex 5y ago
      > The signals aren't for a specific location, they are world-wide. So the "for Las Vegas" part doesn't work. The whole point of GPS is that the differential in signal timing between the signals from the transmitters on different satellites tells you how far you are from those satellites, and thus if you know where the satellites are supposed to be, that tells you where you must be. As a result, recording the signals in a desert outside Las Vegas three weeks ago is by far the easiest way to get... drum roll... the signals which when received by your GPS receiver right now will convince it that right now it's three weeks ago and it is just outside Las Vegas. > Replay attacks are just a kind of denial of service Nope, as explained they're actually a very common and effective spoofing tactic. The receiver doesn't say "No service" it will tell you that you're outside Las Vegas three weeks ago. > Spoofing attacks are far more dangerous, and cryptographic signing defeats them effectively. Spoofing attacks use the same principle (although of course they'll tell your receiver it's a few milli-seconds ago and it is somewhere nearby, not outside Las Vegas three weeks ago). Signatures make no major difference, this data is authentic it's just second hand. Everything checks out, that's why they do it.
  • fho 5y ago
    Yep ... and they (should) contain signed timestamps from three weeks ago ... so you ignore them. The thing with GPS is that it is also a time source, so you'd need a secondary source for your time to confirm that you are not off by three weeks.