set the stage =

Setting the Stage

A couple of months ago the highly-publicised case of Apple vs. FBI brought attention to the topic of privacy - especially in the context of mobile devices. Following the 2015 San Bernardino terrorist attack, the FBI seized a mobile phone belonging to the shooter, Syed Farook, with the intent to search it for any additional evidence or leads related to the ongoing investigation. However, despite being in possession of the device, the FBI were unable to unlock the phone and access its contents.

This may sound puzzling at first. "Surely if the FBI has access to the phone, could they not extract the user data stored on it using forensic tools?". Well, the answer is not that simple. You see, the device in question was an iPhone 5c, running iOS 9.

As you may well know, starting with iOS 8, Apple has automatically enabled Full Disk Encryption (FDE) using an encryption key which is derived from the user's password. In order to access the data on the device, the FBI would have to crack that encryption. Barring any errors in cryptographic design, this would most probably be achieved by cracking the user's password.

"So why not just brute-force the password?". That sounds like a completely valid approach - especially since most users are notoriously bad at choosing strong passwords, even more so when it comes to mobile devices.

However, the engineers at Apple were not oblivious to this concern when designing their FDE scheme. In order to try and mitigate this kind of attack, they've designed the encryption scheme so that the generated encryption key is bound to the hardware of the device.

In short, each device has an immutable 256-bit unique key called the UID, which is randomly generated and fused into the device's hardware at the factory. The key is stored in a way which completely prevents access to it using software or firmware (it can only be set as a key for the AES Engine), meaning that even Apple cannot extract it from the device once it's been set. This device-specific key is then used in combination with the provided user's password in order to generate the resulting encryption key used to protect the data on the device. This effectively 'tangles' the password and the UID key.

from http://archive.fo/LGM8W

orig url on archive

baker set the stage

baker baker