add method to export vault encryption key

Author: matthiasgeihs

packages/keyring-controller/src/KeyringController.ts

@@ -527,6 +527,20 @@ function assertIsExportableKeyEncryptor(
   }
 }
 
+/**
+ * Assert that the encryption key is set.
+ *
+ * @param encryptionKey - The encryption key to check.
+ * @throws If the encryption key is not set.
+ */
+function assertIsEncryptionKeySet(
+  encryptionKey: string | undefined,
+): asserts encryptionKey is string {
+  if (!encryptionKey) {
+    throw new Error(KeyringControllerError.EncryptionKeyNotSet);
+  }
+}
+
 /**
  * Assert that the provided password is a valid non-empty string.
  *
@@ -1471,6 +1485,16 @@ export class KeyringController extends BaseController<
     }
   }
 
+  /**
+   * Exports the vault encryption key.
+   *
+   * @returns The vault encryption key.
+   */
+  async exportEncryptionKey(): Promise<string> {
+    assertIsEncryptionKeySet(this.state.encryptionKey);
+    return this.state.encryptionKey;
+  }
+
   /**
    * Attempts to decrypt the current vault and load its keyrings,
    * using the given password.

packages/keyring-controller/src/constants.ts

@@ -4,6 +4,7 @@ export enum KeyringControllerError {
   UnsafeDirectKeyringAccess = 'KeyringController - Returning keyring instances is unsafe',
   WrongPasswordType = 'KeyringController - Password must be of type string.',
   InvalidEmptyPassword = 'KeyringController - Password cannot be empty.',
+  EncryptionKeyNotSet = 'KeyringController - Encryption key not set.',
   NoFirstAccount = 'KeyringController - First Account not found.',
   DuplicatedAccount = 'KeyringController - The account you are trying to import is a duplicate',
   VaultError = 'KeyringController - Cannot unlock without a previous vault.',