The iOS device keeps seeing a random AirTag in close proximity. Even as the ID rotates, it's still about 2m away, and continues to be 2m away as you move. It doesn't know who it belongs to, but it's probably the same physical device, because it keeps going to wherever you're going.
That's a different scenario than the evil store owner who wants to track their customers. In that case, it's just a random procession of tags roaming about the store. A tag arriving at the store on repeated days has nothing to indicate that it's the same one.
So if it's being used as a malicious tracker (hidden in someone's car or purse), then the constant proximity is a clue. But if someone is trying to guess which tag belongs to a specific person, they can't unless they maintain constant contact with that tag over a long timeline. At that point, they can just see you :)
how long is the suffix? I can't see it being effective for both anti-stalking (ie. someone placing a tag on you without your consent) and anti-tracking (ie. shops/malls using your tag to follow you around).
I don't know the answer to that, but thinking about it generally: If the suffix was just a single hex digit, it would work to detect a persistent tag. After, say 5 key rotations, if the last digit is still "E", then it's highly likely that the tag that's constantly in range is the same physical thing.
Meanwhile, if you're trying to use these things to track visitors to your store, you're only getting 16 bins of people. My "E" tag will be the same as 50 other people who've visited last week with the same "E" suffix.
I'm having a hard time finding the actual whitepaper on this. Hopefully someone links it in this thread.
Unfortunately, the spec is currently only available to partners in the MFi program. That is probably where parameters like the one you are asking about are defined: https://developer.apple.com/find-my/. I’m sure there will be a paper published that reverse engineers the spec once these devices are out in the wild.
Finally, the static part of the broadcast doesn’t need to be permanently static. It simply needs to rotate at a period that’s longer than the rest of the public key.
The iOS device keeps seeing a random AirTag in close proximity. Even as the ID rotates, it's still about 2m away, and continues to be 2m away as you move. It doesn't know who it belongs to, but it's probably the same physical device, because it keeps going to wherever you're going.
That's a different scenario than the evil store owner who wants to track their customers. In that case, it's just a random procession of tags roaming about the store. A tag arriving at the store on repeated days has nothing to indicate that it's the same one.
So if it's being used as a malicious tracker (hidden in someone's car or purse), then the constant proximity is a clue. But if someone is trying to guess which tag belongs to a specific person, they can't unless they maintain constant contact with that tag over a long timeline. At that point, they can just see you :)