4 ms·
Why aren't GPS signals signed?
by tlrobinson 9y ago
Why aren't GPS signals signed?
- 05 9y ago* Actual information is derived from phase shift between signals, not their contents * Signals are below noise level, you need to know their exact contents to be able to receive them * Military modification is encrypted, and it can help against some sorts of spoofing. * To spoof, you need to - receive signals from at least 4 sats (e.g. using a 2d phased array you can get pretty good directional sensitivity without knowing the contents of the signal). - retransmit the signals to the target, time-shifting each signal to achieve the required time+coordinate spoofing delta. - jam the original signals with a known noise source you can subtract from your own received signal to avoid jamming yourself ;)
- pjc50 9y agoThere used to be a separate encrypted channel for military use ("selective availability"). There's a replacement, secret system which is supposed to provide the same anti-spoofing for NATO military uses only. The data rate of GPS is surprisingly low. Furthermore, you can spoof someone's position by relaying genuine signals provided you alter their relative time delay.