What is a SEFW file? An SEFW file contains firmware used by an iOS device's Secure Element. The Secure Element is a chip that stores a device's Apple Pay Device Account Number. Users should never encounter or have to manually install an SEFW file.

More Information When you add a payment option to Apple Pay, your bank creates an associated device-specific Device Account Number, encrypts it, and sends it to your iOS device. This Device Account Number is stored in your device's Secure Element, where it is isolated from your device's operating system and your iCloud backups. The Device Account Number is used only when you make a payment using Apple Pay. Just like other hardware, the Secure Element sometimes receives firmware updates, allowing it to function correctly when used with an updated version of iOS. These firmware updates are stored in SEFW files.