Use initial 128bit as loginKey

lib/utils/crypto_util.dart

@@ -462,8 +462,8 @@ class CryptoUtil {
   // `loginSubKeyLen` and `loginSubKeyContext` as context
   static Future<Uint8List> deriveLoginKey(
       Uint8List key,
-      ) {
-    return _computer.compute(
+      ) async {
+    final Uint8List derivedKey = await  _computer.compute(
       cryptoKdfDeriveFromKey,
       param: {
         "key": key,
@@ -473,6 +473,8 @@ class CryptoUtil {
       },
       taskName: "deriveLoginKey",
     );
+    // return the first 16 bytes of the derived key
+    return derivedKey.sublist(0, 16);
   }
 
   // Computes and returns the hash of the source file