It's interesting to me that other trackers have end-to-end encryption. I wouldn't have expected it but makes sense for the threat model.
> Providerslike Apple and Google achieve location indistinguishability by end-to-end encrypting location information using a public key embedded in BLE advertisements emitted by a tag
Though it makes me wonder... What's the private key? If the public key is attached to the tag, how is the device getting it? I'm guessing it gets shared during pairing.
In general, yes! We did some follow on work explaining how all of this works, depending on the provider: https://petsymposium.org/popets/2026/popets-2026-0113.pdf
Very cool! I only skimmed Section 4 a bit, but that's really cool!
I was going to ask how the web UIs possibly work if the location is indistinguishable, but I went to the Google Find Hub, and it appears you can't view the location for tags unless you enter your phone's pin code / pattern lock. This must either communicate with the phone or the keys are stored on Google's end.
EDIT: I turned my phone off, and I can still get the location of my keys... surely this doesn't mean the key is stored on their end? Wouldn't be very good E2EE in that case :)
The encryption key is derived from your PIN, it doesn't need to access the phone to do a new derivation.
AFAIK, there's a pre-shared key exchanged during pairing, and you then calculate keypairs based on (key, timestamp).
Rotating your keypairs in that way prevents attackers from identifying you across time. E.G. if they link a particular keypair to you — let's say at an Airport security gate — that doesn't let them know you've entered a lawyer's office a week later, because that's done under a different, unrelated public key.