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Comment by mrpippy | Hacker News Reader

This assumption is not correct. The (4-digit) passcode is entangled with the device's unique ID, which is burned into the A6 application processor (on the other side of the logic board). It's theoretically possible to extract the UID from the A6 at the silicon level, but not realistically possible.

I suggest you read the iOS Security Guide: https://www.apple.com/business/docs/iOS_Security_Guide.pdf

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It doesn't matter that the UID is incorporated into the key. If you have a copy of the flash then you can restore the device to its current state, at which point you can brute-force the PIN. The only way this could not work is if the A6 has some non-volatile storage on-chip and it is used to prevent this kind of replay attack, but AFAIK this is not the case.

I think it does have non-volatile on-chip storage, which is used to store a randomly generated key that is encrypted with the key derived from the PIN and UID. It is that randomly generated key that is used to encrypt flash data.

I cannot find documentation to verify this. I presume the people down voting you do, but unfortunately they've chosen to down vote instead of being useful and posting a link. (The only link I've seen is for A7 and later systems)

What you describe would not defeat a brute-force attack on the PIN using a duplicate flash. The only way NV-storage on the A6 chip would do that is if it stored the attempt counter there.

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