UDID is an acronym for Unique Device Identifier. The UDID is a feature of Apple's devices running

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tvOS tvOS (formerly Apple TV Software) is an operating system developed by Apple for the Apple TV, a digital media player. In the first-generation Apple TV, Apple TV Software was based on Mac OS X. The software for the second-generation and later ...

watchOS watchOS is the operating system of the Apple Watch, developed by Apple Inc., Apple. 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 o ...

, and

macOS macOS, previously OS X and originally Mac OS X, is a Unix, Unix-based operating system developed and marketed by Apple Inc., Apple since 2001. It is the current operating system for Apple's Mac (computer), Mac computers. With ...

. 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

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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 identifier, unique, for 3GPP and iDEN mobile phones, as well as some satellite phones. It is usually found printed inside the battery compartment of the ph ...

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 Account, formerly known as Apple ID, is a user account by Apple for their devices and software. Apple Accounts contain the user's personal data and settings, and when an Apple Account is used to log in to an Apple device, the device will ...

and iCloud. This also holds the

Find My Find My is an asset tracking service made by Apple Inc. that enables users to track the location of iOS, iPadOS, macOS, watchOS, visionOS devices, AirPods, AirTags, and a number of supported third-party accessories through a connected iC ...

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., Apple, being the successor to iOS 10. It was announced at the company's Worldwide Developers Conference on June 5, 2017, and w ...

, 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)

References

{{Apple IOS

Formats

Usage

Calculation of 2007 format

See also

References