[Skunkleton]

> generate the list of pseudonyms from a single short “seed” that both Timmy and Ruth will keep a copy of. This is nice because the data stored by each party will be very small. However, to find Timmy, Ruth must still send all of the pseudonyms — or her “seed” — up to Apple, who will have to search its database for each one.

I would imagine something along the lines of TOTP would provide a better mechanism here. There would be no need to scan a whole list of pseudonyms, and the BLE would rotate the identifier it transmits frequently. The lassie device can include GPS timestamps when it reports the device to apple.