Re:FBI agrees to unlock iPhone for Arkansas prosecutor
by mikeash on Thursday March 31, 2016 @12:41PM
(#11398496)
There is no indication that the Secure Enclave has its own flash. I've looked everywhere, and while there are lots of hopeful people who think it should, there's no evidence that it does.
If you read through Apple's security document, you'll see that the Secure Enclave achieves separation from the rest of the system by encrypting everything with keys that can't be replicated on the outside, and by having its own secure boot verification. It's possible that there's some internal storage that they just don't mention, but it doesn't look like the way to bet.
This means that even devices with the Secure Enclave are still vulnerable to flash cloning. You can't understand the contents of the Secure Enclave's stuff, but you can still save and restore them once you desolder the flash.
The attack described in the comment you're replying to won't work, of course. The counter is stored in the flash, so cutting power won't do anything. There was a bug where the OS would report an unlock failure before updating the flash memory, so if you were quick to cut the power you could bypass the counter, but that's been fixed.
What does work (in theory) is to desolder the flash and hook it up so you can save and restore its contents. Then you turn on the phone, try a few passcodes, shut down, restore flash to original state, repeat until success.
Of course, this only works if the passcode is simple enough that a brute force is feasible. You can attack a four-digit passcode in a few days this way. A six-digit passcode would take maybe a year, and proper passphrase would still be completely infeasible.
If you read through Apple's security document, you'll see that the Secure Enclave achieves separation from the rest of the system by encrypting everything with keys that can't be replicated on the outside, and by having its own secure boot verification. It's possible that there's some internal storage that they just don't mention, but it doesn't look like the way to bet.
This means that even devices with the Secure Enclave are still vulnerable to flash cloning. You can't understand the contents of the Secure Enclave's stuff, but you can still save and restore them once you desolder the flash.
The attack described in the comment you're replying to won't work, of course. The counter is stored in the flash, so cutting power won't do anything. There was a bug where the OS would report an unlock failure before updating the flash memory, so if you were quick to cut the power you could bypass the counter, but that's been fixed.
What does work (in theory) is to desolder the flash and hook it up so you can save and restore its contents. Then you turn on the phone, try a few passcodes, shut down, restore flash to original state, repeat until success.
Of course, this only works if the passcode is simple enough that a brute force is feasible. You can attack a four-digit passcode in a few days this way. A six-digit passcode would take maybe a year, and proper passphrase would still be completely infeasible.