Does two device will have the same 'UUID'

Question

In my iOS app, I have to restrict the user to use iOS app per device. To do this I found a solution that we can use the identifierForVendor method of UUID (Universally Unique Identifier) which will generate a unique ID to uniquely identify an app on a device. (Here, I am not using UDID (Unique Device Identifier) because Apple rejects apps if the app uses UDID).

So my question as is there any possibilities that the two devices will have the same UUID. any idea?

EDIT 1:

I have one more doubt as if I installed the same app on different two devices and save its UUID string into the device KeyChain. Both devices have same iCloud account. Now while doing iCloud sync for this two devices, is one my device KeyChain will gets overwritten?

EDIT 2:

I have found answer for EDIT 1 as 'Yes, through iCloud Keychain, the keychain would be synced to another one of my devices, and I’d get the same device identifier from here and from below answer too'

For the item to be synced with iCloud keychain, I’d need to explicitly set the kSecAttrSynchronizable attribute. Using the SecItem API, we can set this attribute while adding a keychain item.

Is there any tutorial how to add item in Keychain (Without third party libraries)?

Answer 1

No, Two device does not have the same UUID. I am 100% Sure about it. So go with identifierForVendor method.

But, The UUID may be changed when you reinstall the the application in your device (If there is not other application for the same vendor).

The value in this property remains the same while the app (or another app from the same vendor) is installed on the iOS device. The value changes when the user deletes all of that vendor’s apps from the device and subsequently reinstalls one or more of them. The value can also change when installing test builds using Xcode or when installing an app on a device using ad-hoc distribution. Therefore, if your app stores the value of this property anywhere, you should gracefully handle situations where the identifier changes.

EDIT

YOUR QUESTION

I have one more doubt as if I installed the same app on different two devices and save its UUID string into the device KeyChain. Both devices have same iCloud account. Now while doing iCloud sync for this two devices, is one my device KeyChain will gets overwritten?

ANSWER

YES. Your keychain will gets overwritten. So you have same UUID for both 2 devices.

Answer 2

I thought is NO!

The value of this property is the same for apps that come from the same vendor running on the same device. A different value is returned for apps on the same device that come from different vendors, and for apps on different devices regardless of vendor.

Normally, the vendor is determined by data provided by the App Store. If the app was not installed from the app store (such as enterprise apps and apps still in development), then a vendor identifier is calculated based on the app’s bundle ID. The bundle ID is assumed to be in reverse-DNS format.