In Android 8.0, Keymaster 3 transitioned from the old-style C-structure Hardware Abstraction Layer (HAL) to the C++ HAL interface generated from a definition in the new Hardware Interface Definition Language (HIDL). As part of the change, many of the argument types changed, though types and methods have a one-to-one correspondence with the old types and the HAL struct methods.[…]

https://source.android.com/security/keystore/

https://source.android.com/devices/architecture/

https://source.android.com/security/keystore/attestation

https://developer.android.com/training/articles/security-key-attestation.html

https://source.android.com/devices/architecture/hidl/

https://android.googlesource.com/platform/system/tools/hidl/