I blogged a lot of words → 0pointer.net/blog/authentic
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There's a nice description of how disk encryption works on modern Android devices at grapheneos.org/faq#encryption. Not intended to cover the verified boot system used to fully verify all firmware and OS images with downgrade protection support for all of it but mentions it in passing.
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TPM compare very poorly to the modern secure elements heavily used by Pixels and Apple devices. API is very flawed and lacks a lot of capabilities.
Common approach of wiping data on firmware upgrade instead of a proper insider attack resistance API like AOSP is also quite awful.
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Secure elements aren't just heavily used by the OS but also by lots of apps via the hardware keystore APIs available to every sandboxed app.
developer.android.com/training/artic is the stripped down newer version of this for secure elements as opposed to the traditional TEE (TrustZone) one.
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Among other things, they can be used as FIDO2 security keys including secure physical confirmation and optionally requiring that the user profile is unlocked.
The hardware attestation support is also drastically nicer and more usable. It doesn't break on upgrades for one thing.
Auditor app (attestation.app/about) is a nice example of those attestation capabilities. Worth trying out.
Screenshots show output from local verification and automated monitoring service.
Main section is hardware signed. 2nd based on chaining verification to app through OS.
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