Comment on Electronic devices or 'signal jammers' used in car thefts to be banned
KairuByte@lemmy.dbzer0.com 4 days agoTots only works when both source and recipient are synced pretty much identically in time. Meaning the car and fob would need to receive their time from an external source.
Not that hard in many places, just grab the time from a radio broadcast. But what happens when that broadcast isn’t available? You fall back on a known inaccurate time. I’ve seen cars with a bum RTC chip, which lost about a minute a day. That would be enough to kill off this kind of system.
Not to mention that an external time source would be larger, cost more, require more power, and would be vulnerable to brand new attacks.
There is no perfect system. Take your physical lock for instance, there is no unpickable lock. They just plum don’t exist.
sugar_in_your_tea@sh.itjust.works 4 days ago
Not the customer’s problem. If car manufacturers want to cheap out on components, they can pay the price when cars get stolen.
Even cheap watches keep the time really well, as in less than a second drift in a given month. I have a physical TOTP device that works for years, and that needs to be accurate to <30 seconds (realistically, <10 seconds drift). How much do those cost? $10-20, and they have way more features than a basic time crystal.
You don’t need an external time source, you just need non-crappy parts for your cars and fobs. That’s totally reasonable given the cost of those devices, so spending $1 more or whatever for a reliable time crystal isn’t an issue. Sync them periodically, such as when starting the car, and it won’t be an issue.
If you rely on an external time source, you have the same problem, but a little higher tech (e.g. blast your own network time), and you introduce privacy concerns (tracking).
My suggestion requires no privacy violations, prevents replay attacks, shield your time crystal in a Faraday cage), and keeping time synced with the car can be entirely done without the user noticing. It might fail in some crazy scenarios, like not driving the car for a year (possible if you never use one of your fobs), and it’ll need to be resynced after a battery swap, but you have the easy fallback of resyncing when you insert it into the car. The time doesn’t even need to be accurate, it just needs to tick the same way on both ends.