Use secure random number generator for document ID generation

@@ -9,6 +9,7 @@
 - Add support for creating PDF/A 3b [ilaurillard]
 - Add support for creating PDF/A 3b [ilaurillard]
 - Add helper functions to replace text styles and cell content [Brian Kayfitz]
 - Add helper functions to replace text styles and cell content [Brian Kayfitz]
 - Fix TextStyle merge decoration [AtlasAutocode]
 - Fix TextStyle merge decoration [AtlasAutocode]
+- Use secure random number generator for document ID generation
 
 
 ## 3.11.1
 ## 3.11.1
 
 

@@ -177,7 +177,7 @@ class PdfDocument {
   /// Generates the document ID
   /// Generates the document ID
   Uint8List get documentID {
   Uint8List get documentID {
     if (_documentID == null) {
     if (_documentID == null) {
-      final rnd = math.Random();
+      final rnd = math.Random.secure();
       _documentID = Uint8List.fromList(sha256
       _documentID = Uint8List.fromList(sha256
           .convert(DateTime.now().toIso8601String().codeUnits +
           .convert(DateTime.now().toIso8601String().codeUnits +
               List<int>.generate(32, (_) => rnd.nextInt(256)))
               List<int>.generate(32, (_) => rnd.nextInt(256)))