Answers 'how do you get keys to login elsewhere' — both mechanisms, Signal/WhatsApp style:
Server:
- migration 0002: key_backups (recovery blobs) + provisions (QR relay), ciphertext only
- routes/backup.js: POST/GET /api/backup, /backup/exists; provision new/get/complete
- routes/keys.js: POST /api/keys/reset — atomically wipe stale prekeys + install fresh
(fixes Bad MAC: restore regenerates prekey IDs that INSERT-OR-IGNORE kept stale)
Crypto (crypto.js):
- exportIdentityBlob/importIdentityBlob (identity travels only encrypted)
- generateRecoveryCode (120-bit Crockford base32) + encrypt/decryptWithCode (PBKDF2 250k)
- ephemeral ECDH (P-256) encrypt/decrypt for QR transfer
Client (app.js): account-menu 'Set up recovery code' + 'Link a device' (camera scan
via BarcodeDetector or paste); auth-screen 'Restore with recovery code' + 'Link from
another device' (shows QR + code, polls, restores). Vendored qrcode-generator.
All verified live end-to-end (3-process isolated-store integration tests):
restore-from-code and QR-link both let a fresh device receive + decrypt messages.
SW cache v3->v4.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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