fix(security): require passphrases for local backups

Derive every MDD2 key from a non-empty user passphrase and the per-backup scrypt salt while keeping the embedded application material isolated to read-only MDD1 migration imports. Normalize missing, wrong, and authentication-failure results to the same controlled decryption error.

Add the modal-based export confirmation and format-aware import flow across renderer, preload, IPC, and controller boundaries. Clear transient passphrase state on completion or cancellation, retain pending import data only until consumption, and keep passphrases out of results, snapshots, payloads, and logs.

Cover mismatch and cancellation paths, MDD1 passphrase-free migration, preload forwarding, successful UI/crypto round-trips, one-byte-short ciphertext, authenticated empty ciphertext, and truncated legacy envelopes.

src/renderer/App.tsx

@@ -45,6 +45,7 @@ import type { AccountEditState, AccountEditTarget, AccountKind, AccountService,
 import { ACCOUNT_SERVICE_ICONS } from "./account-service-icons";
 import { DOWNLOAD_SPEED_MAX_SAMPLES, updateDownloadSpeedHistory } from "./download-speed-state";
 import { createUiLocalizer, normalizeLanguage } from "./i18n";
+import { runLocalBackupExport, runLocalBackupImport, type BackupPassphraseMode } from "./backup-flow";
 import type { DownloadSpeedHistoryState } from "./download-speed-state";
 import { extractHoster, formatDateTime, formatSpeedMbps, humanSize, providerLabels } from "./download-format";
 import { AppShell } from "./shell/AppShell";
@@ -53,6 +54,7 @@ import { OverlayHost } from "./shell/OverlayHost";
 import { UpdateExperience } from "./shell/UpdateExperience";
 import type { MainView } from "./shell/shell-model";
 import { ContextMenu } from "./ui/ContextMenu";
+import { BackupPassphraseDialog } from "./ui/BackupPassphraseDialog";
 import { Dialog } from "./ui/Dialog";
 import { Icon } from "./ui/Icon";
 import { Toast } from "./ui/Toast";
@@ -1865,6 +1867,7 @@ export function App(): ReactElement {
   const [startConflictPrompt, setStartConflictPrompt] = useState<StartConflictPromptState | null>(null);
   const startConflictResolverRef = useRef<((result: { policy: Extract<DuplicatePolicy, "skip" | "overwrite">; applyToAll: boolean } | null) => void) | null>(null);
   const [confirmPrompt, setConfirmPrompt] = useState<ConfirmPromptState | null>(null);
+  const [backupPassphraseMode, setBackupPassphraseMode] = useState<BackupPassphraseMode | null>(null);
   const [onlineBackupDialog, setOnlineBackupDialog] = useState<OnlineBackupDialogState | null>(null);
   const [remoteDiag, setRemoteDiag] = useState<RemoteDiagnosticsInfo | null>(null);
   const [remoteDiagOpen, setRemoteDiagOpen] = useState(false);
@@ -1874,7 +1877,8 @@ export function App(): ReactElement {
   const [rdPort, setRdPort] = useState("9868");
   const [rdAllowlist, setRdAllowlist] = useState("");
   const [rdName, setRdName] = useState("");
-  const confirmResolverRef = useRef<((confirmed: boolean) => void) | null>(null);
+  const confirmResolverRef = useRef<((confirmed: boolean) => void) | null>(null);
+  const backupPassphraseResolverRef = useRef<((passphrase: string | null) => void) | null>(null);
   const confirmQueueRef = useRef<Array<{ prompt: ConfirmPromptState; resolve: (confirmed: boolean) => void }>>([]);
   const importQueueFocusHandlerRef = useRef<(() => void) | null>(null);
   const [contextMenu, setContextMenu] = useState<ContextMenuState | null>(null);
@@ -2262,11 +2266,16 @@ export function App(): ReactElement {
         startConflictResolverRef.current = null;
         resolver(null);
       }
-      if (confirmResolverRef.current) {
+      if (confirmResolverRef.current) {
         const resolver = confirmResolverRef.current;
         confirmResolverRef.current = null;
-        resolver(false);
-      }
+        resolver(false);
+      }
+      if (backupPassphraseResolverRef.current) {
+        const resolver = backupPassphraseResolverRef.current;
+        backupPassphraseResolverRef.current = null;
+        resolver(null);
+      }
       while (confirmQueueRef.current.length > 0) {
         const request = confirmQueueRef.current.shift();
         request?.resolve(false);
@@ -3422,6 +3431,20 @@ export function App(): ReactElement {
     });
   }, [pumpConfirmQueue]);
 
+  const closeBackupPassphraseDialog = useCallback((passphrase: string | null): void => {
+    const resolver = backupPassphraseResolverRef.current;
+    backupPassphraseResolverRef.current = null;
+    setBackupPassphraseMode(null);
+    resolver?.(passphrase);
+  }, []);
+
+  const askBackupPassphrase = useCallback((mode: BackupPassphraseMode): Promise<string | null> => {
+    return new Promise((resolve) => {
+      backupPassphraseResolverRef.current = resolve;
+      setBackupPassphraseMode(mode);
+    });
+  }, []);
+
   const restoreHistoryEntries = useCallback(async (entryIds: string[]): Promise<void> => {
     const requested = new Set(entryIds);
     const entries = historyEntriesRef.current.filter((entry) => requested.has(entry.id));
@@ -4519,7 +4542,7 @@ export function App(): ReactElement {
   const onExportBackup = async (): Promise<void> => {
     closeMenus();
     await performQuickAction(async () => {
-      const result = await window.rd.exportBackup();
+      const result = await runLocalBackupExport(window.rd, askBackupPassphrase);
       if (result.saved) {
         showToast("Sicherung exportiert");
       }
@@ -4531,7 +4554,7 @@ export function App(): ReactElement {
   const onImportBackup = async (): Promise<void> => {
     closeMenus();
     await performQuickAction(async () => {
-      const result = await window.rd.importBackup();
+      const result = await runLocalBackupImport(window.rd, askBackupPassphrase);
       if (result.restored) {
         showToast(result.message, 4000);
         // A settings-only import applies live without a relaunch, so the editable
@@ -5987,6 +6010,13 @@ export function App(): ReactElement {
       </AppShell>
 
       <OverlayHost
+        backupPassphrase={backupPassphraseMode ? (
+          <BackupPassphraseDialog
+            mode={backupPassphraseMode}
+            onCancel={() => closeBackupPassphraseDialog(null)}
+            onSubmit={(passphrase) => closeBackupPassphraseDialog(passphrase)}
+          />
+        ) : null}
         confirm={confirmPrompt ? (
           <Dialog actions={null} danger={confirmPrompt.danger} onClose={() => closeConfirmPrompt(false)} open title={confirmPrompt.title}>
             <p style={{ whiteSpace: "pre-line" }}>{confirmPrompt.message}</p>