diff --git a/ArcFormats/ArcFormats.csproj b/ArcFormats/ArcFormats.csproj
index b7178cc6..01a44441 100644
--- a/ArcFormats/ArcFormats.csproj
+++ b/ArcFormats/ArcFormats.csproj
@@ -777,6 +777,7 @@
     <Compile Include="BlackCyc\ArcVPK.cs" />
     <Compile Include="Unity\ArcASSET.cs" />
     <Compile Include="Unity\ArcBIN.cs" />
+    <Compile Include="Unity\ArcDSM.cs" />
     <Compile Include="Unity\ArcSpVM.cs" />
     <Compile Include="Unity\ArcUnityFS.cs" />
     <Compile Include="Unity\Asset.cs" />
diff --git a/ArcFormats/Unity/ArcDSM.cs b/ArcFormats/Unity/ArcDSM.cs
new file mode 100644
index 00000000..c8357219
--- /dev/null
+++ b/ArcFormats/Unity/ArcDSM.cs
@@ -0,0 +1,98 @@
+//! \file       ArcDSM.cs
+//! \date       2022 Apr 30
+//! \brief      Encrypted DSM script file as an archive.
+//
+// Copyright (C) 2022 by morkt
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to
+// deal in the Software without restriction, including without limitation the
+// rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
+// sell copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+// IN THE SOFTWARE.
+//
+
+using System;
+using System.Collections.Generic;
+using System.ComponentModel.Composition;
+using System.IO;
+using System.Security.Cryptography;
+using System.Text;
+
+namespace GameRes.Formats.Unity
+{
+    [Export(typeof(ArchiveFormat))]
+    public class DsmOpener : ArchiveFormat
+    {
+        public override string         Tag { get { return "DSM/UNITY"; } }
+        public override string Description { get { return "Unity engine encrypted script file"; } }
+        public override uint     Signature { get { return 0; } }
+        public override bool  IsHierarchic { get { return false; } }
+        public override bool      CanWrite { get { return false; } }
+
+        const string DefaultPassword = "pass";
+
+        public override ArcFile TryOpen (ArcView file)
+        {
+            if (!VFS.IsPathEqualsToFileName (file.Name, "data.dsm")
+                || (file.View.ReadUInt32 (0) & 0xFFFFFF) != 0xBFBBEF) // UTF-8 BOM
+                return null;
+
+            var dir = new List<Entry> {
+                new Entry {
+                    Name = "data.txt",
+                    Type = "script",
+                    Offset = 0,
+                    Size = (uint)file.MaxOffset / 4 * 3,
+                }
+            };
+            return new ArcFile (file, this, dir);
+        }
+
+        public override Stream OpenEntry (ArcFile arc, Entry entry)
+        {
+            using (var input = arc.File.CreateStream())
+            using (var reader = new StreamReader (input))
+            {
+                var sourceString = reader.ReadToEnd();
+                var text = DecryptString (sourceString, DefaultPassword);
+                return new BinMemoryStream (text, entry.Name);
+            }
+        }
+
+        static byte[] DecryptString (string sourceString, string password)
+        {
+            var rijndaelManaged = new RijndaelManaged();
+            byte[] key, iv;
+            GenerateKeyFromPassword (password, rijndaelManaged.KeySize, out key, rijndaelManaged.BlockSize, out iv);
+            rijndaelManaged.Key = key;
+            rijndaelManaged.IV = iv;
+            var array = Convert.FromBase64String (sourceString);
+            using (var cryptoTransform = rijndaelManaged.CreateDecryptor())
+            {
+                return cryptoTransform.TransformFinalBlock (array, 0, array.Length);
+            }
+        }
+
+        static readonly byte[] DefaultSalt = Encoding.UTF8.GetBytes("saltは必ず8バイト以上");
+
+        static void GenerateKeyFromPassword (string password, int keySize, out byte[] key, int blockSize, out byte[] iv)
+        {
+            var rfc2898DeriveBytes = new Rfc2898DeriveBytes (password, DefaultSalt);
+            rfc2898DeriveBytes.IterationCount = 1000;
+            key = rfc2898DeriveBytes.GetBytes (keySize / 8);
+            iv = rfc2898DeriveBytes.GetBytes (blockSize / 8);
+        }
+    }
+}