Restrict secret keys to 128 or 256 bits

src/locales/en.json

@@ -35,6 +35,7 @@
 		"cancel": "@:invariants.controls.cancel",
 		"error": {
 			"invalidBase64": "The key must be a valid base64 string.",
+			"invalidKeyLength": "The key's length must be either 128 bits (16 bytes) or 256 bits (32 bytes).",
 			"invalidSeparator": "The separator must be a single character.",
 			"cameraNotAllowed": "Camera access permission was not granted.",
 			"cameraNotFound": "No camera detected.",