In the past, device makers have focused on safeguarding these keys
by storing the keys in secure locations and severely restricting
the number of people who have access to them. That’s good, but it
leaves those people open to attack by coercion or social
engineering. That’s risky for the employees personally, and we
believe it creates too much risk for user data.
To mitigate these risks, Google Pixel 2 devices implement insider
attack resistance in the tamper-resistant hardware security module
that guards the encryption keys for user data. This helps prevent
an attacker who manages to produce properly signed malicious
firmware from installing it on the security module in a lost or
stolen device without the user’s cooperation. Specifically, it is
not possible to upgrade the firmware that checks the user’s
password unless you present the correct user password. There is a
way to “force” an upgrade, for example when a returned device is
refurbished for resale, but forcing it wipes the secrets used to
decrypt the user’s data, effectively destroying it.
This seems like a good idea, and I think the iPhone has been doing this for years. But I’d love to see someone do a rundown of the low-level security across all popular Android phones.