> This document introduces Timed Efficient Stream Loss-tolerant Authentication (TESLA). TESLA allows all receivers to check the integrity and authenticate the source of each packet in multicast or broadcast data streams. TESLA requires no trust between receivers, uses low-cost operations per packet at both sender and receiver, can tolerate any level of loss without retransmissions, and requires no per-receiver state at the sender. TESLA can protect receivers against denial of service attacks in certain circumstances. Each receiver must be loosely time-synchronized with the source in order to verify messages, but otherwise receivers do not have to send any messages. TESLA alone cannot support non-repudiation of the data source to third parties.
* https://tools.ietf.org/html/rfc4082
* A. Perrig, R. Canetti, J. Tygar and D. Song, “Efficient Authentication and Signing of Multicast Streams over Lossy Channels,” IEEE Symposium on Security and Privacy, pp. 56-73, May 2000.
The US Navy re-started celestial navigation a few years ago:
* https://www.npr.org/2016/02/22/467210492/u-s-navy-brings-bac...
This (1960s?) US government produced (45m) video video gives a pretty good overview:
* https://www.youtube.com/watch?v=UV1V9-nnaAs
For those wanting to invest (substantially) more time, the two videos by "Tippecanoe Boats" are slightly rambling at times, but he does lay things out pretty well by the end of it (second is largely examples):
> The US Navy re-started celestial navigation a few years ago:
Also, the SR-71, B-1, and B-2 and other aircraft have automated celestial navigation systems to provide corrections to their INSs:
https://www.thedrive.com/the-war-zone/17207/sr-71s-r2-d2-cou...
Honestly, for military applications, GPS seems to be mainly useful for bad weather and providing navigation to the smallest units (and I'd think a small unit would be able fall back to a map and compass).
https://en.wikipedia.org/wiki/Joint_Direct_Attack_Munition
The INS doesn't need to be terribly high performance because it only needs to work for the time it takes a bomb to fall from the sky.
Can I not just run two GNSS receivers 10 meters apart (on a ship), and if they report as having the same position, then I know someone is spoofing?
It should be really hard to beamform the spoofing to spoof two different locations, at least from a distance because of the precise angles needed.
Yes, this assumes that my real GNSS signal is good enough that they normally are 10M apart.
After the fact, why exactly can I not precalculate my spoofed data stream?
I just need to spend:
3*2^31*24*15*(spoof_seconds/30) ops (on average)?
Sure, not cheap, but hardly hard even for even a hobbyist.
So ~2^45 ops to spoof 10 minutes of data? That's doable.
Is my math off?
I have more faith in the direction finding aspects. Here's from the article, an understatement of the year:
> To beat these simple tricks, a spoofer will need to have multiple transmitters that actually show the same parallax as the actual satellites. However, you can only do this by placing your transmitters next to the satellites - in space. This raises the bar significantly.
I find the multiple antenna answers interesting.
For instance, one of the easier attack scenarios against an airplane is to have a directional antenna on the ground. Because airplanes broadcast their GPS position via ADS-B, you could also know that you'd succeeded.
In a case like that, however, the radio signal from the ground would be stronger than the signal from the sky and it would be obvious what was going on, unless the attacker managed to get the power level just right.
With multiple receivers you also will see very different results with spoofing than with a real signal. For instance if you had a receiver at the front of the airplane and one at the back of the airplane, the time delay for all the fake satellites would be the same (they all come from the same place) whereas the time delays (e.g. position) would be noticeably different from real sats.
Getting their exact locations is simplified by the fact the location is being transmitted by ADS-B...
That sounds tricky though. You need to be very precise. The attacker needs to provide different received signal to two antennas meters (at most!) apart, at a distance of maybe kilometers, on a moving target. That's a hair thin angle.
The aircraft just needs to TDoA "did it come from above or below (assuming an attack from the ground). That's 180 degrees.
Or am I missing something? Unless I am, this doesn't sound feasible to me.
If the GPS is integrated with inertial navigation systems, the effect of GPS spoofing on the computation of the position (that could be observed by ADS-B) might prove tricky to anticipate.
For instance, the Wiimote doesn't have the dynamic range to handle the highest accelerations you can generate waving your arms, which makes it hard to use that kind of thing for athletic training.
It's just extremely hard to make a pure INS navigation system.
Even if you could measure your acceleration accurate to 0.00001 m/s/s, because it gets integrated twice to give position even that tiny error is going to give you a position that's out by 100m after an hour.
And measuring acceleration precise to 0.00001 m/s/s is a demanding task - like weighing a car so precisely you could count the pages of a book on the back seat.
That level of precision simply isn't available in the affordable MEMS market segment.
You can buy RLGN off the shelf for a couple thousand bucks. You can buy gyrocompass-capable MEMS off of digi-key for dozens of dollars (Murata). Its just market forces and cost. You don't need super stable IMUs for game controllers.