Comment by TazeTSchnitzel | Hacker News Reader

Comment by TazeTSchnitzel | Hacker News Reader

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AIUI your blog post was nonetheless wrong. As the OP explains, there are multiple layers of encryption.

The first is at the hardware level, performed by the SSD itself.[0] It encrypts all data on it with a key stored in rewriteable memory. By changing the key, you can "erase" the drive. The FBI could backup that key if they wanted to undo the "secure erase" feature.

However, this is not the only layer of encryption. The second is done in software, performed by iOS. It encrypts all user data with a key derived from the user's passcode and a unique key burned into the chip. The FBI cannot get past this layer, and this is what they wanted Apple's help for.

You were right in that the FBI could trivially get past the first layer of encryption, but it's not the one we care about. There's more than one layer.

[0] Or rather, by the flash controller. At least, I assume it is. It might actually be an iOS software feature too, but the OP's description reminds me very much of how some SSDs implement secure erase. Whether it's actually done in hardware or software is immaterial, anyway.

FBI didn't demand help with that layer, it demanded a way to bypass auto erase. They intended to perform the brute force of the 4 digit PIN themselves. Sure, they wanted to be able to enter PINs electronically, but they could just as easily have an intern sit there and enumerate the 1000 combinations once auto erase was disabled.

> FBI didn't demand help with that layer, it demanded a way to bypass auto erase.

...so that they could get past that layer of encryption by making lots of password attempts.

Seems like you could stick one of those stylus nubs on a 3d printer head and do the same thing but rapid fire. That would be pretty cool actually.

I've definitely seen a YouTube video of that.

That was a timing weakness in an older version of iOS that was patched in software. Previously you could just cut power at a precise monent and get unlimited attempts. It's no longer exploitable.

Does that mean that now if you cut power at the same moment the fail counter increments even if the entered code was correct?

Not that it's particularly useful for hackers, I'm just wondering if this can be done "perfectly" at all.

Yes you can, if you sync the commit to NVRAM before giving any external indication of success/failure, and don't leak through any side-channels. The CVE before demo'd by the famous youtube video was that you had a split second after failure was indicated where you could cut the power and keep the failure from being stored.

Milling machine might work better. You need Z as well as X and Y.

Most 3D printers also have a Z axis... Although, it's often the deck itself. But, point taken. Any 3-axis machine should do the trick pretty well.

Seems like if you were modifying the firmware you could just add a for loop in there that would enter the pins automatically.

Why do you assume it's a 4 digit PIN?

iDevices can have longer PINs and PINs with letters and symbols.

Many of the reports in the press were saying it was a 4-digit pin. But it's feasible even to brute force a six-digit PIN in the way I described, it would just take several weeks.

Is there any way to know the length of they pin before bruteforcing?

I'm not sure because I'm not running iOS 9, but from screenshots on the web it looks like the length of the passcode is displayed on the lock screen.

I use a larger than 8 digit pass code on my iphone. It looks different.

Using a default 4 digit code, you end up with a numeric pad and four boxes. If you use a longer than 4 digit code but stick with numbers, it gives a single box to enter the pass code in but presents a numeric pad. If you use letters at all, it switches to a qwerty-ish keyboard and a single box to enter the pass code.

10000

Plot twist, the PIN is 1234 and auto-erase isn't even enabled. I think there's no way to know without trying, and FBI is just too afraid to try it ;-)

> The FBI cannot get past this layer

Yes, it can, and I explained exactly how in the original post. It's true I got some of the technical details wrong, but the substance of the post was and is correct.

The technical details in this case really are everything, so it would make sense to get flagged out of existence if you got them wrong.

To be clear, I'm not one of the flaggers, but I can understand some potential motivation there. There is already a lot of noise on this topic.

One of the technical details is that disjunctive claims are true if any of their constituent elements are true. My claim was of the form, "The iPhone is vulnerable to attack. Here is one attack. If that doesn't work, here's a second attack." The first attack doesn't work, but the second one does. Hence the overall claim -- that the iPhone is vulnerable -- was (and remains) correct.

So should you be flagged to death because you got this wrong?

The second attack was added in an update after you were criticised, no? It hardly counts.

No, it was in the original post.

" 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. Lather, rinse, repeat. At worst this would take about a week or so."

>> Yes, it can, and I explained exactly how in the original post. It's true I got some of the technical details wrong, but the substance of the post was and is correct

No you were wrong. You claimed that if the FBI was competent they could retrieve the key from the flash. There were no technical details discussed at all. (you could trivially google this issue and find out what you suggested doesn't work)

The ACLU is describing an attack on the PIN not the key. You acknowledge this in another comment on this thread so I have no idea why you are claiming here that the FBI can get past the encryption in any way; which as others have said doesn't work.

> The ACLU is describing an attack on the PIN not the key

Yes. And so did I.

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