setup() encrypted BOTH the wrapped private key AND the key_check under the same
wrapKey with the SAME wrapIv — a GCM nonce-reuse bug (leaks keystream + enables
GHASH/tag forgery, which matters under E2EE's malicious-server threat model).
Fixes:
- setup() gives key_check its own independent nonce (checkIv).
- unlock() no longer decrypts key_check to verify the passphrase — that was
redundant (a wrong passphrase already fails the wrapped_private_key GCM auth
tag) AND was the second consumer of the reused nonce.
Backward-compatible: the uploaded bundle shape is unchanged, and existing users'
bundles still unlock (unlock only presence-checks key_check now; the private-key
decrypt path with wrap_iv is untouched). Also removed the unused, architecturally
ineffective lock() export (re-unlocks from IndexedDB on next mount; the meaningful
primitive is clearDevice). Re-review clean; tsc green.
peter
52197b28fb