5 ms·
With my car the fob has to be within 2 feet to unlock the door. At first I thought this was due to using low power transmitters, now I see it as an unintended
by cwilkes 7y ago
With my car the fob has to be within 2 feet to unlock the door.
At first I thought this was due to using low power transmitters, now I see it as an unintended security feature.
- zaroth 7y agoThe attack uses a directional antenna and a signal booster / relay, so it works against short-range fobs.
- tinus_hn 7y agoThey could use timing to limit the distance due to the laws of physics but it’s difficult.
- ryacko 7y agoThey could use rangefinding to limit the distance without dealing with precise timers.
- tinus_hn 7y agoHow does rangefinding work?
- ryacko 7y agoTrigonometric rangefinding using multiple sensors is simpler.
- foxyv 7y agoMost short distance rangefinders use an interferometer. You send a radar/laser/sound wave at a target and compare it against a reference. You measure the displacement in the phase angle of the beam bounced off the target to determine distance. You can get insane precision using short wavelengths. The most common long range rangefinders use nanosecond timers to measure the delay between a pulse and a response. At 100 meters, a laser beam will take 666ns to bounce off a target, 200 meters will take 1300ns etc... The precision of this method is a lot less because of confounding factors like the precision of your timing device, refraction, etc... Data will be encoded into the laser pulses similar to a GPS signal to reduce issues with cross talk between rangefinders and jamming. These measurements are confounded by the huge speed of light. A 1 nanosecond mis-timing will result in 0.3 meters loss of precision. A triangulating range finder (Usually a LIDAR) will further refine the above measurement by positioning sensors a distance apart to make medium distance sensing more accurate. This allows LIDAR scanners to increase their precision down into the millimeter range.
- matt-attack 7y agoBe careful. The attack uses a directional RF booster to allow that fob (while in your house!) to communicate with your car while in the driveway.