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KeyStore: Block key attestation for Google Play Services #11

Closed ponces closed 3 years ago

ponces commented 3 years ago

All credits should go to @kdrag0n!

Based on his work in 7f7a9b1.

Original commit description:

In order to enforce SafetyNet security, Google Play Services is now using hardware attestation for ctsProfile validation in all cases, even when basic attestation is selected. The SafetyNet API response from GMS will report that basic attestation was used, but under the hood, hardware attestation is always used regardless of the reported state. This results in SafetyNet failing to pass due to TrustZone reporting an unlocked bootloader (and a partially invalidated root of trust) in the key attestation result.

We can still take advantage of the fact that this usage of hardware attestation is opportunistic - that is, it falls back to basic attestation if key attestation fails to run - and prevent GMS from using key attestation at the framework level. This causes it to gracefully fall back to basic attestation and pass SafetyNet with an unlocked bootloader.

Key attestation is still available for other apps, as there are valid uses for it that do not involve SafetyNet.

The "not implemented" error code from keymaster is used to simulate the most realistic failure condition to evade detection, i.e. an old device that lacks support for key attestation.

phhusson commented 3 years ago

F* it.

Please ping me when this breaks so I can remove this.

ponces commented 3 years ago

Ahaha Don't worry, I'll keep an eye on this 😉 Thanks!