LUKS disk encryption with FIDO2

This report examines using FIDO2 hmac-secret credentials to unlock LUKS-encrypted disks, demonstrating that some authenticators and CTAP implementations can allow disk decryption without requiring a PIN (or with inconsistent user verification), potentially enabling an attacker who obtains both the disk and the token to decrypt data. The authors show experimental results across devices, explain the CTAP 2.1 fix (separate CredRandom values for UV vs non-UV), and recommend using updated authenticators and proper credential creation to mitigate the risk.