At WWDC 2019, Apple announced a new app called “Find My” which will be available on macOS and iOS. It allows users to find their missing Apple device — Mac, iPhone, iPad — by making use of nearby Apple devices to relay their location to the cloud and then to the owner.
It wasn’t that this feature was amazing — Tile already has a Bluetooth tracker that works in roughly the same way. What’s really remarkable is that Apple claims the whole process is end-to-end encrypted and anonymous, and that it uses existing network traffic so there’s no impact on battery life, data usage, or privacy. That sounds impressive, so how does it work?
1 According to Apple, who revealed a simplified version of how its “Find My” protocol operates, you need two Apple devices for this to work. When you first set up Find My, it generates two security keys: a private key that is shared on all your Apple devices via end-to-end encryption, and a public key that is used to encrypt data which can then only be decrypted using the private key.
2 The public key also serves as the signal that is being broadcasted via Bluetooth to other nearby Apple devices. To prevent users from being tracked, Apple periodically changes this public key. But thanks to advanced cryptography, the new public key retains its unique ability to encrypt data in such a way that only the private key — which is stored on your devices — can decrypt.
“Find My” allows users to find their missing Apple device — Mac, iPhone, iPad — by making use of nearby Apple devices to relay their location to the cloud and then to the owner.
3 When your Apple device goes missing. The public key that is being broadcast via Bluetooth will be picked up by a surrounding Apple device. The key is being broadcast even if the device is powered down and sleeping — crucial for MacBooks since they are often turned off when not in use. Since the public key does not carry any identifying information and because it frequently changes, the stranger cannot identify the missing device or link it to any of the device’s previous locations.
4 This stranger’s device will then take the public key that it has received, use it to encrypt its location, and upload that to Apple’s servers, along with a hash of the public key. This prevents Apple from knowing the location because it doesn’t have the private key — which, if you remember, is generated and only stored on your devices. The hash of the public key is important because it serves as an identifier in the later step.
5 When you want to locate your missing Apple device, you will launch Find My on your second Apple device. When you do that, your second Apple device sends a hash of its public key to Apple’s servers. Apple then searches through its library of encrypted locations and finds the matching hashed public key of your missing Apple device.
6 Once Apple finds a match, it will send the encrypted location information of your missing Apple device to your second Apple device, which will, in turn, use its private key to decrypt the location information and tell you where your missing location device is.