If it’s anything like TouchID, the sensor authenticates itself to the secure enclave with a unique private key burned into ROM. Any data not signed by this key

If it’s anything like TouchID, the sensor authenticates itself to the secure enclave with a unique private key burned into ROM. Any data not signed by this key (possibly even countersigned with a real-time code from the secure enclave to prevent replay attacks) will be rejected. Just ask anyone who replaced their home button on an iPhone with TouchID.