NSUUID /CFUUIDRef /UIDevice -uniqueIdentifier /-identifierForVendor

Just as privacy and piracy have phonetic and conceptual similarities, device identifiers, whether UUID / GUID, UDID, or otherwise can be rather confusing:

• UUID (Universally Unique Identifier): A sequence of 128 bits that can guarantee uniqueness across space and time, defined by RFC 4122.
• GUID (Globally Unique Identifier): Microsoft’s implementation of the UUID specification; often used interchangeably with UUID.
• UDID (Unique Device Identifier): A sequence of 40 hexadecimal characters that uniquely identify an iOS device (the device’s Social Security Number, if you will). This value can be retrieved through iTunes, or found using UIDevice -uniqueIdentifier. Derived from hardware details like MAC address.

→ nshipster.com/uuid-udid-unique-identifier/

Apple stopped letting apps use the unique device identifier, called UDID, from iOS 5 onwards. Apple blocked new apps using it after May 2013.

The vendor identifier stays the same for all apps from one maker on a device. It changes if the user removes all those apps and adds one back. The advertising identifier lets ad networks track users across apps. Users can turn off ad tracking in settings. Apps can make their own unique identifier with NSUUID or CFUUIDRef. Create it once and save it in user defaults to keep it between launches.

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