If you think about it, your phone is almost always in the AFU state. You probably don't restart your smartphone for days or weeks at a time, and most people certainly don't power it down after each use. (For most, that would mean hundreds of times a day.) So how effective is AFU security? That's where the researchers started to have concerns.
The main difference between Complete Protection and AFU relates to how quick and easy it is for applications to access the keys to decrypt data. When data is in the Complete Protection state, the keys to decrypt it are stored deep within the operating system and encrypted themselves. But once you unlock your device the first time after reboot, lots of encryption keys start getting stored in quick access memory, even while the phone is locked. At this point an attacker could find and exploit certain types of security vulnerabilities in iOS to grab encryption keys that are accessible in memory and decrypt big chunks of data from the phone.
Based on available reports about smartphone access tools, like those from the Israeli law enforcement contractor Cellebrite and US-based forensic access firm Grayshift, the researchers realized that this is how almost all smartphone access tools likely work right now. It's true that you need a specific type of operating system vulnerability to grab the keys—and both Apple and Google patch as many of those flaws as possible—but if you can find it, the keys are available, too.
The researchers found that Android has a similar setup to iOS with one crucial difference. Android has a version of “Complete Protection” that applies before the first unlock. After that, the phone data is essentially in the AFU state. But where Apple provides the option for developers to keep some data under the more stringent Complete Protection locks all the time—something a banking app, say, might take them up on—Android doesn't have that mechanism after first unlock. Forensic tools exploiting the right vulnerability can grab even more decryption keys, and ultimately access even more data, on an Android phone.
Tushar Jois, another Johns Hopkins PhD candidate who led the analysis of Android, notes that the Android situation is even more complex because of the many device makers and Android implementations in the ecosystem. There are more versions and configurations to defend, and across the board users are less likely to be getting the latest security patches than iOS users.
“Google has done a lot of work on improving this, but the fact remains that a lot of devices out there aren’t receiving any updates,” Jois says. “Plus different vendors have different components that they put into their final product, so on Android you can not only attack the operating system level, but other different layers of software that can be vulnerable in different ways and incrementally give attackers more and more data access. It makes additional attack surface, which means there are more things that can be broken.”
The researchers shared their findings with the Android and iOS teams ahead of publication. An Apple spokesperson told WIRED that the company's security work is focused on protecting users from hackers, thieves, and criminals looking to steal personal information. The types of attacks the researchers are looking at are very costly to develop, the spokesperson pointed out; they require physical access to the target device and only work until Apple patches the vulnerabilities they exploit. Apple also stressed that its goal with iOS is to balance security and convenience.
“Apple devices are designed with multiple layers of security in order to protect against a wide range of potential threats, and we work constantly toadd new protections for our users’ data,” the spokesperson said in a statement. “As customers continue to increase the amount of sensitive information they store on their devices, we will continue todevelop additional protections in both hardware and software to protect their data.”
