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Comment by ayyghost | Hacker News Reader

I would like to see some clarification on point #5. The only other option I see for the FBI is to continue manually bruteforcing PINs, the arduousness of such a task being why they requested Apple's help in the first place. Is he talking about 0days?

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They can hack the chip hardware itself: https://www.technologyreview.com/s/519201/tamper-proof-chips...

(Thanks to tzs for posting this on another thread.)

Manually bruteforcing PINs is actually not a way to get in here, the phone will wipe the keys that the pin protects after 10 attempts.

I'm not sure what method Snowden has in mind for decrypting this device without going through Apple. It seems like it must be a 0day.

Depending on the device/iOS versions, you're able to bypass the count limits.

The FBI is asking that Apple provide them the ability to bypass the PIN timeout limits.

In modern iphones, those limits are handled by the secure enclave. However on the 5C in question, the limits are done in iOS and can be disabled by flashing a custom version of iOS. That's what the FBI is requesting.

The phone "may" wipe the keys after 10 failed attempts.

That is a configuration option. Can't that be changed by the remote configuration management software?

I was just going through Apple's Security White paper and according to it, there's no way to enter the passcode electronically.

Not that this fully addresses point #5, but automated mechanical means to enter the PIN do exist: http://www.blackhat.com/us-13/arsenal.html#Engler

As gpm pointed out in a sibling comment, the issue is that they can't brute force the PIN without wiping the phone.

Mechanical entry would take time as well if it is a alphanumeric code.

Is there's a way to connect a device to where the digitiser connects to the logic board that would mimic pressing the screen?

I am guessing the JTAG points are fused. FBI does not need Apple to try that.

Just one way I can think of would be to dump the contents of ROM chip, bruteforcing the encryption key by checking all possible PINs and comparing the decrypted data against some known plaintext that would be present on all iOS devices. (this would require the FBI to know what key derivation algorithm is used on pre-secure-enclave devices, but that's not outside the realm of possibility).

It's not that simple. The encryption key is not just the PIN. It's the PIN combined with a very strong unique key that is burned into the hardware, making hat particular brute force attack unfeasible.

That's true for devices with a Secure Enclave, which the iPhone 5C does not have. As far as I know the key derivation is done entirely in software on older iPhones, but even if there was device-specific keying material it would be possible to dump that as well.

The CPU contains both the UID and GID on all iPhones (old and new). The Secure Enclave, if available, contains it's own UID for it's own key derivation.

https://mikeash.com/pyblog/friday-qa-2016-02-19-what-is-the-...

The machine id of the phone appears to be already known:

https://www.eff.org/deeplinks/2016/02/technical-perspective-...

> From a technical standpoint, it would be possible to craft the cracking software to only run on Farook's phone by checking its hardware ID. The court order was actually quite specific that this is all that is being requested.

Note that the court's order presupposes that the hardware ID is already available through some means. The court's order was crafted after a period of inquiry regarding actually technically feasible work.

It's not certain how the machine id of a particular phone is known without being able to query it, but the case assumes it is known.

The keyphrase is combined with the machine id and a hash is generated and compared against the stored hash to allow access. The stored password hash is stored on the flash drive and is readable since it's ordinary flash memory that can be directly read if one has physical access.

So the hash and the machine id are available, and it is likely Apple uses a known and vetted secure hashing algorithm rather than roll their own. From this, one can do a brute force search using external computers to determine what the keyphrase is.

There are different hardware IDs. Your quote is probably referring to something readily available through software like the UDID. The IDs necessary to decrypt the NAND are not readily accessible.

It's a version of iOS without the trusted execution environment. It can be hacked.

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