Cold-start unlock wrapped the database key under the credential *public* key.
A public key is public: mavweb writes it verbatim to passkeys.json, normally in
the same state dir as db_key.wrapped, so anyone holding both files recovered the
database key offline with no authenticator involved. The wrapped blob was a
plaintext key with extra steps.
The secret is now the WebAuthn PRF extension output — 32 bytes the authenticator
computes over a fixed salt and never stores anywhere. The blob gains a version:
v2: "MVNKW2\x00" || salt || nonce || AES-256-GCM(key), magic as AAD
v1: salt || nonce || AES-256-GCM(key) (read-only)
v1 still opens so an existing deployment is not bricked, and reports itself so
the daemon can log a SECURITY line telling him to re-enroll. Nothing writes v1.
The magic is authenticated, so a v2 blob cannot be stripped and re-read as v1.
Four other defects on the same path:
- The locked-boot store was opened on an IPC goroutine inside UnlockFn and
never closed. Close is what re-encrypts the tmpfs working copy back over
the ciphertext, so every write of a cold-started session was lost silently
on the next boot. daemonLock now owns the store and seals it at shutdown.
- MethodUnlock was reachable by anything on the box; the socket is same-uid
and cannot authenticate its caller. It now requires a passkey assertion
that mavweb verified first.
- Concurrent unlocks would each open a store and wire a daemon. One at a
time, and never a second one.
- The hand-rolled HKDF keyed the expand step with the salt instead of the
PRK. Replaced with crypto/hkdf.
Key wrapping moves from enrolment to the first assertion, because create() does
not produce a PRF result on most authenticators — only a support flag. An
authenticator without PRF now writes no wrapped file at all rather than one
that looks protected and is not, and the page says so.
Verified: make build, make test. New tests cover the v2 round trip, a wrong
secret, every single-bit tamper, truncation, the v1 downgrade attempt, legacy
v1 reads, non-32-byte and all-zero secrets, the ipc wire field, locked-mode
default-deny, a forged assertion never reaching the unlock path, seal-on-
shutdown after a cold start, and that nothing in the state dir contains the
plaintext key. The PRF round trip against real hardware is a QA step.
Vikunja #14
kami