UDID is an acronym for Unique Device Identifier. The UDID is a feature of
Apple's devices running
iOS
iOS (formerly iPhone OS) is a mobile operating system created and developed by Apple Inc. exclusively for its hardware. It is the operating system that powers many of the company's mobile devices, including the iPhone; the term also include ...
,
tvOS
tvOS (formerly known as Apple TV Software) is an operating system developed by Apple Inc. for the Apple TV, a digital media player. In the first-generation Apple TV, Apple TV Software was based on Mac OS X. Starting with the second-generation, ...
,
watchOS
watchOS is the operating system of the Apple Watch, developed by Apple Inc. It is based on iOS, the operating system used by the iPhone, and has many similar features. It was released on April 24, 2015, along with the Apple Watch, the only d ...
, and
macOS
macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and lapt ...
. 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.
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
The International Mobile Equipment Identity (IMEI) is a numeric identifier, usually unique, for 3GPP and iDEN mobile phones, as well as some satellite phones. It is usually found printed inside the battery compartment of the phone but can al ...
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
Apple ID is an authentication method used by Apple for iPhone, iPad, Mac and other Apple devices. Apple IDs contain the user's personal information and settings. When an Apple ID is used to log in to an Apple device, the device will automat ...
and iCloud. This also holds the
Find My
Find My is an asset tracking app and service provided by Apple Inc. that enables users to track the location of iOS, iPadOS, macOS, watchOS devices, AirPods, AirTags and a number of supported third-party accessories through a connected iCloud acc ...
Activation Lock status.
Starting from
iOS 11, 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
*
IMEI
The International Mobile Equipment Identity (IMEI) is a numeric identifier, usually unique, for 3GPP and iDEN mobile phones, as well as some satellite phones. It is usually found printed inside the battery compartment of the phone but can al ...
*
Product code
References
{{Apple
IOS