fix: rebuild block 0 from the scanned UID when it can't be read

chameleonultragui/lib/gui/component/mifare/classic.dart

@@ -66,6 +66,35 @@ class CardReaderState extends State<MifareClassicHelper> {
       );
     } else {
       var tags = appState.sharedPreferencesProvider.getCards();
+      var dumpData = widget.mfcInfo.recovery!.cardData;
+      // Block 0 (the UID block) can't always be read. If it wasn't, ask before
+      // rebuilding it from the scanned UID so data is never changed silently.
+      if (!skipDump && !widget.mfcInfo.recovery!.block0Read) {
+        final rebuild = await showDialog<bool>(
+          context: context,
+          builder: (context) => AlertDialog(
+            title: Text(localizations.block0_read_failed_title),
+            content: Text(localizations.block0_read_failed_text),
+            actions: [
+              TextButton(
+                onPressed: () => Navigator.of(context).pop(false),
+                child: Text(localizations.cancel),
+              ),
+              TextButton(
+                onPressed: () => Navigator.of(context).pop(true),
+                child: Text(localizations.rebuild_uid),
+              ),
+            ],
+          ),
+        );
+        if (rebuild == true) {
+          dumpData = List<Uint8List>.of(dumpData);
+          dumpData[0] = mfClassicGenerateFirstBlock(
+              hexToBytes(widget.hfInfo.uid),
+              hexToBytes(widget.hfInfo.sak)[0],
+              hexToBytes(widget.hfInfo.atqa));
+        }
+      }
       tags.add(CardSave(
           uid: widget.hfInfo.uid,
           sak: hexToBytes(widget.hfInfo.sak)[0],
@@ -74,7 +103,7 @@ class CardReaderState extends State<MifareClassicHelper> {
           tag: (skipDump)
               ? TagType.mifare1K
               : mfClassicGetChameleonTagType(widget.mfcInfo.type),
-          data: widget.mfcInfo.recovery!.cardData,
+          data: dumpData,
           ats: (widget.hfInfo.ats != localizations.no)
               ? hexToBytes(widget.hfInfo.ats)
               : Uint8List(0)));

chameleonultragui/lib/helpers/mifare_classic/general.dart

@@ -577,13 +577,13 @@ Uint8List mfClassicGenerateFirstBlock(Uint8List uid, int sak, Uint8List atqa) {
   if (uid.length == 4) {
     block0.setAll(0, uid);
     block0[4] = calculateBcc(uid);
-    block0[5] = sak + 0x80;
-    block0.setAll(6, atqa);
+    block0[5] = sak;
+    block0.setAll(6, atqa.reversed);
     block0.setAll(8, [0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69]);
   } else if (uid.length == 7) {
     block0.setAll(0, uid);
-    block0[7] = sak + 0x80;
-    block0.setAll(8, atqa);
+    block0[7] = sak;
+    block0.setAll(8, atqa.reversed);
     block0.setAll(10, [0x00, 0x00, 0x00, 0x00, 0x00, 0x00]);
   }
   return block0;

chameleonultragui/lib/helpers/mifare_classic/recovery.dart

@@ -43,6 +43,7 @@ class MifareClassicRecovery {
   void Function() update;
   MifareClassicType mifareClassicType;
   bool isMifareClassicEV1;
+  bool block0Read = false;
 
   MifareClassicRecovery(
       {required this.appState,
@@ -570,6 +571,7 @@ class MifareClassicRecovery {
 
   Future<void> dumpData() async {
     cardData = List.generate(256, (_) => Uint8List(0));
+    block0Read = false;
 
     for (var sector = 0;
         sector <
@@ -601,6 +603,8 @@ class MifareClassicRecovery {
             } else {
               continue;
             }
+          } else if (sector == 0 && block == 0) {
+            block0Read = true;
           }
 
           if (mfClassicGetSectorTrailerBlockBySector(sector) ==

chameleonultragui/lib/l10n/app_en.arb

@@ -570,5 +570,8 @@
   "lf_sniff_load_file": "Load .bin file",
   "lf_sniff_load_failed": "Failed to load file: {error}",
   "lf_sniff_loaded": "Loaded {count} sample(s) from file.",
-  "sniff_device_required_hint": "No device connected. Connect a Chameleon to capture, or load a saved file."
+  "sniff_device_required_hint": "No device connected. Connect a Chameleon to capture, or load a saved file.",
+  "block0_read_failed_title": "Couldn't read block 0",
+  "block0_read_failed_text": "The UID block couldn't be read. Rebuild it from the scan so the clone keeps its UID? Cancel keeps the dump unchanged.",
+  "rebuild_uid": "Rebuild UID"
 }

chameleonultragui/test/mifare_classic_block0_test.dart

@@ -0,0 +1,29 @@
+import 'dart:typed_data';
+
+import 'package:chameleonultragui/helpers/mifare_classic/general.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  group('mfClassicGenerateFirstBlock', () {
+    test('keeps SAK as-is and stores ATQA reversed (4-byte UID)', () {
+      // SAK 08 / ATQA 0004 must land as SAK 08 and ATQA bytes 04 00,
+      // matching the write-side block 0, not 88 00 04.
+      final block0 = mfClassicGenerateFirstBlock(
+          Uint8List.fromList([0x82, 0xB9, 0x4F, 0x4B]),
+          0x08,
+          Uint8List.fromList([0x00, 0x04]));
+      expect(block0.length, 16);
+      expect(block0.sublist(0, 4), [0x82, 0xB9, 0x4F, 0x4B]); // UID
+      expect(block0[4], 0x3F); // BCC = 0x82 ^ 0xB9 ^ 0x4F ^ 0x4B
+      expect(block0[5], 0x08); // SAK, not 0x88
+      expect(block0.sublist(6, 8), [0x04, 0x00]); // ATQA reversed
+    });
+
+    test('a genuine zero UID rebuilds to a zero UID', () {
+      final block0 = mfClassicGenerateFirstBlock(
+          Uint8List(4), 0x08, Uint8List.fromList([0x00, 0x04]));
+      expect(block0.sublist(0, 4), [0, 0, 0, 0]);
+      expect(block0[4], 0x00); // BCC of an all-zero UID
+    });
+  });
+}