add debugging to decryption.

lib/src/internal/crypto_utils.dart

@@ -1,7 +1,10 @@
 import 'dart:typed_data';
 
+import 'package:logging/logging.dart';
 import 'package:pointycastle/export.dart';
 
+final _logger = Logger('crypto_utils');
+
 /// https://gist.github.com/proteye/e54eef1713e1fe9123d1eb04c0a5cf9b
 class AesHelper {
   static const CBC_MODE = 'CBC';
@@ -84,10 +87,16 @@ class AesHelper {
   static Uint8List processBlocks(BlockCipher cipher, Uint8List inp) {
     final out = Uint8List(inp.lengthInBytes);
 
+    _logger.finest('Starting processBlocks. (${inp.lengthInBytes})');
+    var twoPercent = inp.lengthInBytes ~/ 100 * 2;
     for (var offset = 0; offset < inp.lengthInBytes;) {
-      final len = cipher.processBlock(inp, offset, out, offset);
+      offset += cipher.processBlock(inp, offset, out, offset);
-      offset += len;
+      if (offset > twoPercent) {
+        _logger.finest('> 2% done. ($offset)');
+        twoPercent = inp.lengthInBytes;
+      }
     }
+    _logger.finest('Done processBlocks.');
 
     return out;
   }