[szc]

The handling of biometric data is designed to be secure between the sensors and the secure enclave. For example, data from the fingerprint sensor is encrypted when it is sent over the wires inside the device. The secure enclave does not store images of the fingerprint, but a representation of it which is not enough to reverse back into a fingerprint.

This is covered in the Apple Platform Security Guide.

https://manuals.info.apple.com/MANUALS/1000/MA1902/en_US/app... (I believe this link can change when the guide gets updated)