iPhone Forensics Experts Demonstrate Basic Proof Of Concept That The iPhone Hack The FBI Says 'Doesn't Work' Actually Does Work
from the the-fbi-lied-again? dept
When the DOJ announced that the FBI may have miraculously found a way in to Syed Farook’s work iPhone after swearing to a court that such a thing was impossible, many people zeroed in on the possibility of “NAND Mirroring” as the technique in question. After all, during a Congressional hearing, Rep. Darrell Issa had gone fairly deep technically (for a Congressperson, at least) in asking FBI Director James Comey if the FBI had tested such a method. Well-known iPhone forensics guru Jonathan Zdziarski wrote up a good blog post explaining why such a technique was the most likely. While recognizing that there are other possibilities, he does a good job breaking down why none of the other possibilities are all that likely, given a variety of facts related to the case (I won’t go through all of that — just go read his post). It’s worth a read. It also has a nice quick explanation of NAND mirroring:
This is where the NAND chip is typically desoldered, dumped into a file (likely by a chip reader/programmer, which is like a cd burner for chips), and then copied so that if the device begins to wipe or delay after five or ten tries, they can just re-write the original image back to the chip. This technique is kind of like cheating at Super Mario Bros. with a save-game, allowing you to play the same level over and over after you keep dying. Only instead of playing a game, they?re trying different pin combinations.
However, on Friday, we noted that FBI Director James Comey was already denying this was the method, saying that it “doesn’t work.” The FBI also “classified” the method in question which raised some additional eyebrows. Either way, Zdziarski was pretty sure that Comey’s claim that NAND mirroring doesn’t work was bogus:
FBI Director Comey, in a press conference, claims the NAND technique ?doesn?t work?; this says more about the credibility of this information than anything. Every expert I?ve consulted (including three hardware forensics firms) believe it works, and multiple firms are still in the process of validating the technique. The amount of time to prep and test this technique alone is proving greater than the month that we?ve been discussing it ? it?s very unlikely that any reputable source could have already discredited this method, given how much time and effort it is taking everyone else to fully flesh out and test it. When asked directly if the FBI tried this technique, Comey dodged the question and replied (on the topic of ?chip copying?), ?I don?t want to say beyond that?, indicating the FBI hadn?t tried it. This speaks volumes about how flippantly the FBI is willing to discount viable methods endorsed by numerous researchers.
And now, Zdziarski has cooked up a fairly straightforward proof of concept to show that NAND mirroring absolutely could work:
This is a simple ?concept? demonstration / simulation of a NAND mirroring attack on an iOS 9.0 device. I wanted to demonstrate how copying back disk content could allow for unlimited passcode attempts. Here, instead of using a chip programmer to copy certain contents of the NAND, I demonstrate it by copying the data using a jailbreak. For Farook?s phone, the FBI would remove the NAND chip, copy the contents into an image file, try passcodes, and then copy the original content back over onto the chip.
I did this here, only with a jailbreak: I made a copy of two property lists stored on the device, then copied them back and rebooted after five attempts. When doing this on a NAND level, actual blocks of encrypted disk content would be copied back and forth, whereas I?m working with files here. The concept is the same, and serves only to demonstrate that unlimited passcode attempts can be achieved by back-copying disk content. Again, NO JAILBREAK IS NEEDED to do this to Farook?s device, as the FBI would be physically removing the NAND to copy this data.
Elsewhere Zdziarski also points out that, despite the FBI insisting that it was reaching out to everyone who might be able to help, none of the top researchers in the space have been approached by the FBI (and apparently a few who reached out the other way were rebuffed). Once again, it looks like whatever the FBI is doing with the phone, it’s not being particularly upfront with the public (or, potentially, the courts).