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CK42X PassVault FIDO2 progress

This is a clean-room, MIT-compatible experimental implementation. It is not a FIDO-certified or hardened security key.

Current increment

  • CTAPHID framing plus INIT, PING, CBOR, CANCEL, and ERROR dispatch.
  • Minimal CTAP2.0 getInfo, makeCredential, and allowList getAssertion core.
  • Non-resident ES256 credentials, self packed attestation, DER ECDSA, SHA-256, versioned records, deterministic test RNG seams, and zeroization.
  • BSD-2-Clause micro-ecc pinned to commit 541b3a78026420a3e369c4c9281c396b5e531113, configured for portable 32-bit secp256r1 with upstream fast modular reduction enabled.
  • Strict host tests. Test sources are excluded from the FAP manifest.
  • A bounded 1024-byte CTAPHID USB worker using the exported Flipper U2F HID interface. The USB callback only wakes the worker; CTAP and cryptography run in thread context, and the prior USB configuration is restored on stop.
  • Flipper RNG, interruptible local presence approval/denial with 100 ms polling, CTAPHID UPNEEDED keepalives and matching-channel cancellation, and a separate AES-GCM encrypted fido2.pv1 store holding up to 20 versioned credentials.
  • Store updates are synced to fido2.pv1.tmp, the prior valid target is moved to fido2.pv1.bak, and the temp is renamed into place. The SDK rename call overwrites a destination but does not document power-loss atomicity, so this sequence favors recoverability: a failed install restores the backup, a successful install removes it, and unreadable/authentication-failed targets are never treated as empty or overwritten. On startup, a missing target with a remaining backup restores that backup; stale temp files are then removed.
  • The Security Key screen now starts/stops the runtime and reports ready/waiting state.

Physical acceptance evidence

  • Oaspote enumerated as 0483:5741 in U2F HID mode and reported FIDO 2.0 GetInfo.
  • Native CTAP2 MakeCredential and GetAssertion completed after explicit physical approval. The assertion credential matched, its ES256 signature verified, and its counter advanced.
  • Chromium completed WebAuthn registration and authentication. Browser output reported matching credential IDs and valid assertion signatures.
  • A browser credential registered before a FIDO-mode restart authenticated after re-entry, proving encrypted credential persistence for the tested workflow.
  • Exiting FIDO2 restored Oaspote's 0483:5740 serial endpoint and removed the FIDO HID endpoint.
  • Enabling micro-ecc fast modular reduction reduced measured native registration time from 34.720 seconds to 3.003 seconds, below Chromium's HID timeout.

Final tested artifact:

  • Size: 44,544 bytes
  • SHA-256: 251790b4401e455d56cb84268898d7dd295eb9f168e473bec9fc14a9176bd417

Remaining limitations

  • No secure element and no FIDO certification or conformance-suite claim.
  • No client PIN, resident credentials, or user verification.
  • Interrupted-write recovery has strict source/host coverage, but deliberate physical power-loss testing at every rename boundary remains future work.
  • This must not be the user's only authenticator or recovery method.