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Comment by agwa | Hacker News Reader

No, there's an essential difference between your post and the ACLU's: you suggested that the FBI would be able to brute-force the key off-chip, which is not true because the encryption key is derived in part from the device ID, which can't be extracted. This is not what the ACLU/DKG is suggesting - they are suggesting making a backup of the flash storage and restoring it after the auto-erase kicks in. The decryption would still happen on the iPhone itself.

Granted, you updated your post to suggest what the ACLU is now suggesting, but that was after the commenters correctly criticized your post for being wrong.

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You must not have read my original post very carefully:

"they could use a copy of the chip to try five different PIN codes, and then replace the chip with a fresh copy of the original and try five more"

I don't know how I could have made it any clearer that I was proposing an attack on the PIN, not the key.

According to your post, the FBI would only need to do that if they were "completely incompetent." You wrote, "unless they are completely incompetent, having read out the contents of the chip they should be able to decrypt its contents in a matter of minutes if not seconds." Details matter, and it was fair to call you on your mistake. You shouldn't get all upset now that the ACLU has published a post which gets the details right.

You're right, I got that one detail wrong. Nonetheless, the substance of my post was correct. If every post that had a minor error like this was flagged to death the home page would be empty.

Security is just a collection of details; details matter.

The only detail that matters in this case is that one of the attacks I described does (almost certainly) work.

That isn't what you said:

>> It's encrypted, but here's the thing: the encryption key is also (almost certainly) stored in the same chip. So all the FBI needs to do is de-solder the chip, mount it in its own hardware, and read out the data.

This is not correct and was the main suggestion you made.

>> I don't know how I could have made it any clearer that I was proposing an attack on the PIN, not the key.

Because you just did. You are now claiming that an offhand comment you made that resembles what the ACLU suggests is the main point of your post and that is not the case.

That was one of two proposed attacks. At the time I wrote it, I was unaware that the A6 chip has a UID that is used in the KDF. That renders the first of my two proposed attacks ineffective, but not the second one.

He said mount on their own hardware but that doesn't preclude using the original chips as part of the setup.

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