UDID is an acronym for Unique Device Identifier. The UDID is a feature of
Apple's devices running
iOS,
tvOS,
watchOS, and
macOS. It is a unique identifier that is calculated from different hardware values, such as the
ECID. It is sent to Apple servers when a user tries to activate the device during Setup. This ID is also used to detect the phone or to communicate with it while restoring the
IPSW firmware
In computing, firmware is a specific class of computer software that provides the low-level control for a device's specific hardware. Firmware, such as the BIOS of a personal computer, may contain basic functions of a device, and may provide h ...
.
Formats
This unique ID has been formatted in two ways: for devices introduced between 2007 and 2018 it was represented as a 40-digit lowercase hex code, and for device models introduced after 2018, as a 25-digit uppercase hex code. It is not written on the device cover as the
IMEI is, but it can be retrieved by iTunes in normal mode.
Usage
Apple mostly uses this ID to identify the device on their services, such as
Apple ID and iCloud. This also holds the
Find My Activation Lock status.
Starting from
iOS 11
iOS 11 is the iOS version history, eleventh major release of the iOS mobile operating system developed by Apple Inc., being the successor to iOS 10. It was announced at the company's Apple Worldwide Developers Conference, Worldwide Developers C ...
, Apple's verification server will check the device's UDID before it could be set up. If the device's UDID is malformed or not present in Apple's database, the device cannot be activated and will be denied access to the verification server. If said device is connected to iTunes, an error message will appear stating that the iPhone could not be activated because "the activation information could not be obtained from the device."
Calculation of 2007 format
The UDID is calculated as follows for the
Verizon iPhone 4:
UDID = SHA1(serial + ECID + wifiMac + bluetoothMac)
All other devices use:
UDID = SHA1(serial + IMEI + wifiMac + bluetoothMac)
See also
*
Identifier
An identifier is a name that identifies (that is, labels the identity of) either a unique object or a unique ''class'' of objects, where the "object" or class may be an idea, physical countable object (or class thereof), or physical noncountable ...
*
IMEI
*
Product code
References
{{Apple
IOS