Keyholm

Keyholm is all about single-device passkeys (i.e. client-side discoverable credentials) whose private key is protected by secure hardware.

You can never export or sync these passkeys. Think of Keyholm as a way to activate the built-in security key on your phone.

target devices: phones with secure hardware (including Pixels)

no INTERNET permission

no Google Play Services ever

takes advantage of latest Android version/APIs

allows extensive control over particulars of what credentials it creates and how

supports ES256: it's the only EC, StrongBox-backed algorithm

supports Ed25519: it's not NIST, it's fast and safe but TEE-only

supports ML-DSA: post-quantum! but Android 17 and TEE-only

supports android-key attestation

supports PRF extension

uses QUERY_ALL_PACKAGES in order to display icons for apps that were denied passkey usage

account list export/import for making it marginally easier to switch devices. All keys still need to be manually recreated on the new device!