3 ms·

The normal defence against replay attacks is to use a framecounter rather than a timestamp. Either way, there are normal crypto techniques to resolve this issu

The normal defence against replay attacks is to use a framecounter rather than a timestamp. Either way, there are normal crypto techniques to resolve this issue.

krisoft 7y ago
Out of curiosity: airplane receives the broadcasted properly signed packets with frame counter included. How does it know if the antenna broadcasting is the official one or one replaying the official at 2 miles south of the normal glideslope?
- TickleSteve 7y ago
  this does not solve the original issue of signal strength being faked.... but... Authentication provides this, not encryption. The receivers would need a valid certficate to authenticate the transmission.
- throw0101a 7y ago
  > * How does it know if the antenna broadcasting is the official one or one replaying the official at 2 miles south of the normal glideslope?* With multipole antennas, one can use MLat to determine where the signal came from: * http://www.multilateration.com/surveillance/multilateration.html http://www.multilateration.com/surveillance/multilateration.... * http://www.navcanada.ca/EN/products-and-services/Pages/on-board-operational-initiatives-mlat.aspx http://www.navcanada.ca/EN/products-and-services/Pages/on-bo... * https://en.wikipedia.org/wiki/Multilateration https://en.wikipedia.org/wiki/Multilateration If the signal was received on the antenna pointing forward, then the signal probably came from where you're headed; if it came from an antenna off to the side, then someone may be spoofing.
michaelt 7y ago
GPS replay attacks only need to delay a signal by a very small amount - after all, a radio signal travels 300 meters in a microsecond. And the GPS C/A code has a bandwidth of 1 MHz - 1 microsecond per bit. Neither frame counters nor timestamps are sufficient to robustly detect a replay attack that delays the signal by a fraction of a single bit.

The normal defence against replay attacks is to use a framecounter rather than a timestamp. Either way, there are normal crypto techniques to resolve this issue.

krisoft 7y ago

Out of curiosity: airplane receives the broadcasted properly signed packets with frame counter included. How does it know if the antenna broadcasting is the official one or one replaying the official at 2 miles south of the normal glideslope?

TickleSteve 7y ago
this does not solve the original issue of signal strength being faked.... but... Authentication provides this, not encryption. The receivers would need a valid certficate to authenticate the transmission.
throw0101a 7y ago
> * How does it know if the antenna broadcasting is the official one or one replaying the official at 2 miles south of the normal glideslope?* With multipole antennas, one can use MLat to determine where the signal came from: * http://www.multilateration.com/surveillance/multilateration.html http://www.multilateration.com/surveillance/multilateration.... * http://www.navcanada.ca/EN/products-and-services/Pages/on-board-operational-initiatives-mlat.aspx http://www.navcanada.ca/EN/products-and-services/Pages/on-bo... * https://en.wikipedia.org/wiki/Multilateration https://en.wikipedia.org/wiki/Multilateration If the signal was received on the antenna pointing forward, then the signal probably came from where you're headed; if it came from an antenna off to the side, then someone may be spoofing.

michaelt 7y ago

GPS replay attacks only need to delay a signal by a very small amount - after all, a radio signal travels 300 meters in a microsecond. And the GPS C/A code has a bandwidth of 1 MHz - 1 microsecond per bit. Neither frame counters nor timestamps are sufficient to robustly detect a replay attack that delays the signal by a fraction of a single bit.