# 4.3 Key Custody & Biometrics
Key custody is the most critical security property of PTERI.
It is enforced at the **hardware level**.
***
#### Where keys live
* iOS: Secure Enclave
* Android: Hardware-backed Keystore
These environments ensure:
* Keys cannot be exported
* Keys cannot be read by apps
* Keys can only be used via approved operations
***
#### Role of biometrics
Biometrics in PTERI:
* Do **not** identify the user
* Do **not** leave the device
* Do **not** replace cryptography
They serve one purpose only:
> **Gating key usage.**
Biometrics answer:
> “Is the legitimate device holder present right now?”
They do **not** answer:
> “Who is this person globally?”
***
#### What Kakr never receives
* Biometric data
* Biometric hashes
* Biometric signals
All biometric enforcement happens locally.
***
#### No recovery, no override
Because Kakr never has keys:
* Kakr cannot recover identities
* Kakr cannot reset wallets
* Kakr cannot bypass biometrics
* Kakr cannot sign on behalf of users
This is an explicit tradeoff:
* Slightly more responsibility for users
* Vastly stronger security guarantees
> Authority that cannot be stolen is authority worth protecting.
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