XART

eXtendable Anti-Replay Tokens. Stylized as xART.

Introduction
https://en.wikipedia.org/wiki/Replay_attack https://papers.put.as/papers/ios/2019/blackhat-2019-crlmhg-v4.pdf

Use in Apple Processors

 * T2 (A10 base) has xART in sideband data
 * A11 and higher have on-package EEPROM for anti-replay
 * mART in iOS 12 and prior, xART in iOS 13 and up

Interfacing with xART
In recovery the xART can be reset with `xartutil`