The clever cryptography behind Apple’s “Find My” feature
The Wired article is not detailed enough to definitively poo-poo this scheme, but I am pretty skeptical about some of the claims, given a) how easy it is to map an IP to a coarse location, b) how easy it is to map many IPs to a small number of already-known humans&#x2F;users.<p>That is to say: the asym crypto may strongly protect the precise (GPS or LTE triangulation) location from Apple and from others, but I do not see how a cloud-based system can ever hide coarse location <i>from Apple</i> and&#x2F;or from <i>governments</i> as, given the short range of BT, they can reliably infer that a device (and hence its owner) is&#x2F;was near whatever IP sends the encrypted precise location to their cloud. Then it&#x27;s just a matter of mapping the device&#x27;s &quot;randomized&quot; ID back to an actual user&#x2F;phone. That seems easy enough as soon as a second device accesses it from an IP that&#x27;s mappable to a specific residential address, Apple account, etc.<p>e.g.<p>A and B both log into iTunes or some other Apple service using a@apple.com and b@apple.com from HOMEIP at some point in the past. HOMEIP is never used by any other Apple accounts.<p>A(lice) and B(ob) exchange a secret and otherwise begin participating in this &quot;private&quot; tracking scheme.<p>A goes out shopping and while there it pushes its encrypted precise location to the Apple cloud, using random ID 424242, from MALLIP. Perhaps A&#x27;s device sends it directly, or perhaps it&#x27;s relayed from BT to Mall wifi to Cloud by C&#x27;s device if A has both LTE and wifi disabled.<p>A few minutes later S(omeone) requests encrypted location for random ID 424242, from HOMEIP.<p>Apple (and any government compelling it to share information) can reliably infer that &quot;Someone&quot; was A or B attempting to track either B or A, and that the tracked phone was at&#x2F;near the business address of MALLIP - their coarse location - even if they can&#x27;t decrypt the precise location without the secret key. If you know from public records that A and B are married, and assume that women are more likely to be at a mall on their own than men, you may further assume that A is at the Mall while B is at home.<p>Result: the &quot;private&quot;&#x2F;&quot;encrypted&quot; precise location beaconing has an unfixable metadata side channel that will leak coarse location data to Apple and to any governments that compell it.