iOS & iCloud: ubiquityIdentityToken and password change or device restores

Question

My client recently got emails from customers reporting the following problems with an app that checks for the iCloud ubiquity token on each app launch ( [[NSFileManager defaultManager] ubiquityIdentityToken]; ):

• when a device was restored from backup, sometimes the app detects a mismatch of the current and the previous token. Does the ubiquityIdentityToken change when restoring from backup?
• in one case the user got a new device, changed the iCloud password and restored the device from backup. The app detects a mismatch of the token. Does the ubiquityIdentityToken change when the iCloud password is changed?

Answer 1

I am seeing that the ubiquityIdentityToken definitely changes when you restore a backup to a new device - such as when copying an old device backup across to a new device.

This behaviour does not seem to be documented - I'm guessing the fact it is reported in the documentation as returning an 'opaque token' means this is calculated on the combination of some kind of device UUID and an iCloud account UUID - hence the token changes when the device changes. Either that, or the device UUID is not preserved when a device is wiped and restored, and a new one is calculated.

Answer 2

I've been starting to look into this area and can't find much information, as it is described by Apple as an "opaque token", so I'll put down what I have observed in case it helps anyone,

The token is a series of 40 8-digit hexadecimal number groups. Most of those number groups don't change.

Asking for a token from a different app, on a different device, OR with a different iCloud account gives values that differ entirely for the 17th to 22nd number groups.

The rest of the numbers remain the same, even across unrelated users' devices.

I only found one exception- from a client's device where they are having a sync problem. In that case more than half of the numbers were different. I am investigating why this would be at the moment.