refactor(crypto): add areLocalSecretsAvailable method

src/utils/crypto/areLocalSecretsAvailable.ts

@@ -0,0 +1,30 @@
+/*
+ * Copyright 2025 New Vector Ltd.
+ *
+ * SPDX-License-Identifier: AGPL-3.0-only OR GPL-3.0-only OR LicenseRef-Element-Commercial
+ * Please see LICENSE files in the repository root for full details.
+ */
+
+import { MatrixClient } from "matrix-js-sdk/src/matrix";
+
+/**
+ * This function checks if:
+ * - the cross-signing private keys are cached locally
+ * - the backup decryption key is also available locally
+ *
+ * @param matrixClient
+ * @returns true if the secrets are cached and the backup decryption key is available, false otherwise
+ */
+export async function areLocalSecretsAvailable(matrixClient: MatrixClient): Promise<boolean> {
+    const crypto = matrixClient.getCrypto();
+    if (!crypto) return false;
+
+    // Check if the secrets are cached
+    const cachedSecrets = (await crypto.getCrossSigningStatus()).privateKeysCachedLocally;
+    const secretsOk = cachedSecrets.masterKey && cachedSecrets.selfSigningKey && cachedSecrets.userSigningKey;
+
+    // Check if the user has access to the backup decryption key
+    const backupDecryptionKeyOk = Boolean(await matrixClient.secretStorage.get("m.megolm_backup.v1"));
+
+    return secretsOk && backupDecryptionKeyOk;
+}