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Comment by okdood64 | Hacker News Reader

Do you know if I can emulate car keys with it? Say a relatively modern BMW? Or is there some safety mechanism.

(Not for nefarious purposes, but just in case I can’t find my keys.)

Not natively. There is other firmware out there, though, that allows such functionality. Depending on where you live, it may be illegal to even try, though, hence the native firmware locking out such use (you can record or visualize but not save/replay).

Just recording and replaying wouldn’t help you anyways, the code is rolling to prevent replay attacks.

I think if you have enough replays you can deconstruct the rolling code. Not sure.

Also there are ways to desync/resync your key so you might be able to “add a key” with the flipper with certain firmwares.

Cloning the current key and using it can desync it from your car. Super annoying. Be careful

I don’t know exactly how the rolling key works but wouldn’t it be kind of like having a secret stored in the key that’s needed to generate the next code? If it’s designed properly, recording a few thousand codes shouldn’t tell you anything about the next code, just like you can’t deduce private keys by looking at a few thousand encrypted files. I have no clue if that’s really how it works, so I would be happy to be corrected if my mental model is wrong here.

Basically yeah. You'd need millions of replays to even have a chance. Cracking basic wifi back in the day required a couple days worth of sniffed packets. I'd imagine this is similar, if there is in fact a way to do it.

Rolling code protocols like Keeloq can be broken pretty easily (apparently).

> If it’s designed properly,

That phrase is doing a lot of heave lifting there...

(This is only what I've read, but as i understand it many rolling code keys can be broken by recording three button presses while the keyfob is out of range of the car, then brute forcing the seed.)

Plenty of devices use the Keeloq protocol for rolling codes which is pretty straightforward to break in modern hardware.

Emulating the rolling code protocol would desync your keys.

What ever device you’d want to use as a backup would need to capture information sent from the vehicle during the last unlock.

I'd love to have this, mainly so that I could have a single dongle on my keychain for both my and my wife's car. I know others have said that there are issues around rolling codes. But it's possible to get official duplicate / replacement keys; how does that work?

IIRC it's somewhat possible but for some cars if you do it wrong it makes the car and key go out of sync which causes a lot of issues

Don't do it. The key can easily get messed up if the rolling code isn't handled appropriately.

The old Ford transponder keys don't do rolling codes.

So an attacker can cause your car keys not to work?

Yes, as well as gain access to your vehicle. This has been reported on quite a bit over the last couple of years.

So far I have not been able to emulate the keys on either of my cars, a 2001 Ford Ranger and a 2019 Subaru Outback. I think the Ranger is probably possible, but I haven't figured it out yet.

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