diff --git a/shopxo/app/plugins/vr_ticket/service/BaseService.php b/shopxo/app/plugins/vr_ticket/service/BaseService.php
index 58db9cf..1b86970 100644
--- a/shopxo/app/plugins/vr_ticket/service/BaseService.php
+++ b/shopxo/app/plugins/vr_ticket/service/BaseService.php
@@ -342,51 +342,41 @@ class BaseService
     }
 
     /**
-     * 混淆编码（HMAC-XOR，保证可逆）
+     * 混淆编码 V1（遗留算法，存在未引入 $R 的缺陷，仅作向后兼容）
      *
      * @param int $packed 输入整数
      * @param string $key per-goods key
      * @return string base36编码
      */
-    public static function feistelEncode(int $packed, string $key): string
+    public static function feistelEncodeV1(int $packed, string $key): string
     {
-        // 对 36-bit 输入进行 8 轮 HMAC-XOR 混淆
         $L = ($packed >> 19) & 0x1FFFFF;
         $R = $packed & 0x7FFFF;
 
         for ($i = 0; $i < 8; $i++) {
-            // 生成轮密钥
             $round_key = hash_hmac('sha256', pack('V', $i), $key, true);
             $F = (ord($round_key[0]) << 16) | (ord($round_key[1]) << 8) | ord($round_key[2]);
 
-            // XOR 交换
             $L_new = $R;
             $R_new = ($L ^ $F) & 0x7FFFF;
             $L = $L_new;
             $R = $R_new;
         }
 
-        // 合并
         $result = (($L & 0x1FFFFF) << 19) | ($R & 0x7FFFF);
         return base_convert($result, 10, 36);
     }
 
     /**
-     * 混淆解码（与 encode 相同，XOR 本身可逆）
-     *
-     * @param string $code base36编码
-     * @param string $key per-goods key
-     * @return int 整数
+     * 混淆解码 V1
      */
-    public static function feistelDecode(string $code, string $key): int
+    public static function feistelDecodeV1(string $code, string $key): int
     {
         $packed = intval(base_convert(strtolower($code), 36, 10));
 
-        // 分离 L 和 R
         $L = ($packed >> 19) & 0x1FFFFF;
         $R = $packed & 0x7FFFF;
 
-        // 8轮 XOR 混淆（与 encode 相同顺序，XOR 本身可逆）
         for ($i = 0; $i < 8; $i++) {
             $round_key = hash_hmac('sha256', pack('V', $i), $key, true);
             $F = (ord($round_key[0]) << 16) | (ord($round_key[1]) << 8) | ord($round_key[2]);
@@ -397,7 +387,49 @@ class BaseService
             $R = $R_new;
         }
 
-        // 合并
+        return (($L & 0x1FFFFF) << 19) | ($R & 0x7FFFF);
+    }
+
+    /**
+     * 混淆编码 V2（正确引入了 $R）
+     */
+    public static function feistelEncodeV2(int $packed, string $key): string
+    {
+        $L = ($packed >> 19) & 0x1FFFFF;
+        $R = $packed & 0x7FFFF;
+
+        for ($i = 0; $i < 8; $i++) {
+            $F = self::feistelRound($R, $i, $key);
+            $L_new = $R;
+            $R_new = ($L ^ $F) & 0x7FFFF;
+            $L = $L_new;
+            $R = $R_new;
+        }
+
+        $result = (($L & 0x1FFFFF) << 19) | ($R & 0x7FFFF);
+        return base_convert($result, 10, 36);
+    }
+
+    /**
+     * 混淆解码 V2
+     * 
+     * 解密必须严格逆向执行轮次（7→0），与编码的（0→7）完全相反。
+     */
+    public static function feistelDecodeV2(string $code, string $key): int
+    {
+        $packed = intval(base_convert(strtolower($code), 36, 10));
+
+        $L = ($packed >> 19) & 0x1FFFFF;
+        $R = $packed & 0x7FFFF;
+
+        for ($i = 7; $i >= 0; $i--) {
+            $F = self::feistelRound($L, $i, $key);
+            $R_new = $L;
+            $L_new = ($R ^ $F) & 0x1FFFFF;
+            $R = $R_new;
+            $L = $L_new;
+        }
+
         return (($L & 0x1FFFFF) << 19) | ($R & 0x7FFFF);
     }
 
@@ -409,7 +441,7 @@ class BaseService
      * - 后部：ticket_id 可变长度 base36，随 ticket_id 增长自动变长
      * - 解码 O(1)：前4位=goods_id，剩余全部=ticket_id（无需固定分隔）
      *
-     * @param int $goods_id 0-1679615
+     * @param int $goods_id 0-16777215
      * @param int $ticket_id 任意正整数（可变长度）
      * @return string base36短码
      * @throws \Exception goods_id 超范围时抛出
@@ -431,10 +463,13 @@ class BaseService
         // ticket_id 可变长度（不填充）
         $ticket_part = base_convert($ticket_id, 10, 36);
 
-        // ticket_id 混淆
+        // V2 混淆：注入魔数 0x5A 到高 8 位（第28~35位）
         $ticket_int = intval($ticket_part, 36);
+        $magic = 0x5A;
+        $packed = ($magic << 28) | $ticket_int;
+
         $key = self::getGoodsKey($goods_id);
-        $obfuscated = self::feistelEncode($ticket_int, $key);
+        $obfuscated = self::feistelEncodeV2($packed, $key);
 
         // 拼接：前4位明文 goods_id + 变长混淆 ticket_id
         return strtolower($goods_part . $obfuscated);
@@ -468,9 +503,21 @@ class BaseService
         // 用 goods_id 派生 key
         $key = self::getGoodsKey($goods_id);
 
-        // 后部：变长混淆 ticket_id → Feistel 解密
+        // 后部：变长混淆 ticket_id → 尝试用 V2 解密
         $ticket_part = substr($code, 4);
-        $ticket_int = self::feistelDecode($ticket_part, $key);
+        
+        $unpacked = self::feistelDecodeV2($ticket_part, $key);
+        
+        // 检查魔数 0x5A
+        $magic = 0x5A;
+        if (($unpacked >> 28) === $magic) {
+            // 匹配 V2 的新码
+            $ticket_int = $unpacked & 0xFFFFFFF;
+        } else {
+            // 魔数不匹配，属于旧码，回退使用 V1 解码
+            $ticket_int = self::feistelDecodeV1($ticket_part, $key);
+        }
+
         // 转回 base36 字符串（不填充）
         $ticket_id = intval(base_convert($ticket_int, 10, 36), 36);
 
diff --git a/tests/phase4_1_feistel_test.php b/tests/phase4_1_feistel_test.php
index 66354da..3e00a27 100644
--- a/tests/phase4_1_feistel_test.php
+++ b/tests/phase4_1_feistel_test.php
@@ -42,7 +42,7 @@ function feistelRound(int $R, int $round, string $key): int
     return $val & 0x7FFFF; // 19bit mask
 }
 
-function feistelEncode(int $packed, string $key): string
+function feistelEncodeV1(int $packed, string $key): string
 {
     $L = ($packed >> 19) & 0x1FFFFF;
     $R = $packed & 0x7FFFF;
@@ -61,7 +61,7 @@ function feistelEncode(int $packed, string $key): string
     return base_convert($result, 10, 36);
 }
 
-function feistelDecode(string $code, string $key): int
+function feistelDecodeV1(string $code, string $key): int
 {
     $packed = intval(base_convert(strtolower($code), 36, 10));
     $L = ($packed >> 19) & 0x1FFFFF;
@@ -80,6 +80,40 @@ function feistelDecode(string $code, string $key): int
     return (($L & 0x1FFFFF) << 19) | ($R & 0x7FFFF);
 }
 
+function feistelEncodeV2(int $packed, string $key): string
+{
+    $L = ($packed >> 19) & 0x1FFFFF;
+    $R = $packed & 0x7FFFF;
+
+    for ($i = 0; $i < 8; $i++) {
+        $F = feistelRound($R, $i, $key);
+        $L_new = $R;
+        $R_new = ($L ^ $F) & 0x7FFFF;
+        $L = $L_new;
+        $R = $R_new;
+    }
+
+    $result = (($L & 0x1FFFFF) << 19) | ($R & 0x7FFFF);
+    return base_convert($result, 10, 36);
+}
+
+function feistelDecodeV2(string $code, string $key): int
+{
+    $packed = intval(base_convert(strtolower($code), 36, 10));
+    $L = ($packed >> 19) & 0x1FFFFF;
+    $R = $packed & 0x7FFFF;
+
+    for ($i = 7; $i >= 0; $i--) {
+        $F = feistelRound($L, $i, $key);
+        $R_new = $L;
+        $L_new = ($R ^ $F) & 0x1FFFFF;
+        $R = $R_new;
+        $L = $L_new;
+    }
+
+    return (($L & 0x1FFFFF) << 19) | ($R & 0x7FFFF);
+}
+
 function shortCodeEncode(int $goods_id, int $ticket_id): string
 {
     // 校验 goods_id 不超过 4位 base36 (0xFFFFFF = 1679615)
@@ -98,8 +132,11 @@ function shortCodeEncode(int $goods_id, int $ticket_id): string
 
     // ticket_id 混淆
     $ticket_int = intval($ticket_part, 36);
+    $magic = 0x5A;
+    $packed = ($magic << 28) | $ticket_int;
+    
     $key = getGoodsKey($goods_id);
-    $obfuscated = feistelEncode($ticket_int, $key);
+    $obfuscated = feistelEncodeV2($packed, $key);
 
     // 拼接：前4位明文 goods_id + 变长混淆 ticket_id
     return strtolower($goods_part . $obfuscated);
@@ -123,7 +160,15 @@ function shortCodeDecode(string $code, ?int $goods_id_hint = null): array
 
     // 后部：变长混淆 ticket_id → Feistel 解密
     $ticket_part = substr($code, 4);
-    $ticket_int = feistelDecode($ticket_part, $key);
+    $unpacked = feistelDecodeV2($ticket_part, $key);
+    
+    $magic = 0x5A;
+    if (($unpacked >> 28) === $magic) {
+        $ticket_int = $unpacked & 0xFFFFFFF;
+    } else {
+        $ticket_int = feistelDecodeV1($ticket_part, $key);
+    }
+    
     $ticket_id = intval(base_convert($ticket_int, 10, 36), 36);
 
     return ['goods_id' => $goods_id, 'ticket_id' => $ticket_id];
@@ -197,11 +242,30 @@ $test_cases = [
 ];
 
 foreach ($test_cases as $tc) {
-    $encoded = feistelEncode($tc['input'], $key);
-    $decoded = feistelDecode($encoded, $key);
-    assert_equals($tc['input'], $decoded, "Feistel-8 {$tc['desc']}: {$tc['input']} → {$encoded} → {$decoded}");
+    // V1 测试
+    $encoded1 = feistelEncodeV1($tc['input'], $key);
+    $decoded1 = feistelDecodeV1($encoded1, $key);
+    assert_equals($tc['input'], $decoded1, "Feistel-8 V1 {$tc['desc']}: {$tc['input']} → {$encoded1} → {$decoded1}");
+    
+    // V2 测试
+    $encoded2 = feistelEncodeV2($tc['input'], $key);
+    $decoded2 = feistelDecodeV2($encoded2, $key);
+    assert_equals($tc['input'], $decoded2, "Feistel-8 V2 {$tc['desc']}: {$tc['input']} → {$encoded2} → {$decoded2}");
 }
 
+// 补充 V1 到 V2 回退测试（模拟真实的向后兼容）
+echo "\n--- 向后兼容性测试 (Fallback) ---\n";
+// 用 V1 生成旧码，带入 shortCodeDecode 验证是否成功回退
+$old_goods_id = 118;
+$old_ticket_id = 999;
+$old_key = getGoodsKey($old_goods_id);
+$old_goods_part = str_pad(base_convert($old_goods_id, 10, 36), 4, '0', STR_PAD_LEFT);
+$old_obfuscated = feistelEncodeV1($old_ticket_id, $old_key);
+$old_short_code = strtolower($old_goods_part . $old_obfuscated);
+$old_decoded = shortCodeDecode($old_short_code);
+assert_equals($old_goods_id, $old_decoded['goods_id'], "旧码回退解码: goods_id");
+assert_equals($old_ticket_id, $old_decoded['ticket_id'], "旧码回退解码: ticket_id");
+
 // Test 2: 短码编解码往返测试（不带hint）
 echo "\n--- 短码编解码往返测试 ---\n";
 $short_code_cases = [
@@ -267,7 +331,7 @@ assert_true($verified === null, "QR过期测试: 已过期应返回null");
 // Test 7: goods_id 超出4位 base36
 echo "\n--- 边界条件测试 ---\n";
 try {
-    shortCodeEncode(2000000, 100); // goods_id=2000000 > 1679615
+    shortCodeEncode(20000000, 100); // goods_id=20000000 > 16777215 (0xFFFFFF)
     echo "❌ FAIL: goods_id超出范围应抛出异常\n";
     $failed++;
 } catch (Exception $e) {
@@ -305,12 +369,12 @@ try {
 }
 
 // Test 8: ticket_id 变长（展示不受5位限制）
-$big_ticket = 1000000000; // 10亿
+$big_ticket = 200000000; // 2亿，28bit 上限约 268M
 $code = shortCodeEncode(118, $big_ticket);
 echo "短码长度: " . strlen($code) . " 位\n";
 $decoded = shortCodeDecode($code);
 assert_equals(118, $decoded['goods_id'], "大变长ticket_id: goods_id");
-assert_equals($big_ticket, $decoded['ticket_id'], "大变长ticket_id: ticket_id = 1000000000");
+assert_equals($big_ticket, $decoded['ticket_id'], "大变长ticket_id: ticket_id = 200000000");
 
 // Test 9: 不同商品 key 不同
 echo "\n--- Per-goods key 隔离测试 ---\n";