(EAGLS): auto-detect CG archive encryption scheme.

ArcFormats/Eagls/ArcEAGLS.cs

@@ -2,7 +2,7 @@
 //! \date       Fri May 15 02:52:04 2015
 //! \brief      EAGLS system resource archives.
 //
-// Copyright (C) 2015 by morkt
+// Copyright (C) 2015-2016 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
@@ -27,6 +27,7 @@ using System;
 using System.Collections.Generic;
 using System.ComponentModel.Composition;
 using System.IO;
+using System.Linq;
 using GameRes.Utility;
 
 namespace GameRes.Formats.Eagls
@@ -45,8 +46,11 @@ namespace GameRes.Formats.Eagls
             Extensions = new string[] { "pak" };
         }
 
-        static readonly string IndexKey = "1qaz2wsx3edc4rfv5tgb6yhn7ujm8ik,9ol.0p;/-@:^[]";
+        internal static readonly string IndexKey = "1qaz2wsx3edc4rfv5tgb6yhn7ujm8ik,9ol.0p;/-@:^[]";
-        static readonly string Key = "EAGLS_SYSTEM";
+        internal static readonly string Key = "EAGLS_SYSTEM";
+
+        // FIXME not thread-safe
+        CRuntimeRandomGenerator m_rng = new CRuntimeRandomGenerator();
 
         public override ArcFile TryOpen (ArcView file)
         {
@@ -94,45 +98,31 @@ namespace GameRes.Formats.Eagls
             }
             if (0 == dir.Count)
                 return null;
+            if (dir[0].Name.EndsWith (".gr", StringComparison.InvariantCultureIgnoreCase)) // CG archive
+                return new CgArchive (file, this, dir);
+            else
                 return new ArcFile (file, this, dir);
         }
 
         public override Stream OpenEntry (ArcFile arc, Entry entry)
         {
-            if (entry.Name.EndsWith (".gr", StringComparison.InvariantCultureIgnoreCase))
+            var cg_arc = arc as CgArchive;
-                return DecryptGr (arc, entry);
+            if (null != cg_arc)
+                return cg_arc.DecryptEntry (entry);
             if (entry.Name.EndsWith (".dat", StringComparison.InvariantCultureIgnoreCase))
                 return DecryptDat (arc, entry);
             return arc.File.CreateStream (entry.Offset, entry.Size);
         }
 
-        Stream DecryptGr (ArcFile arc, Entry entry)
-        {
-            var input = new byte[entry.Size];
-            arc.File.View.Read (entry.Offset, input, 0, entry.Size);
-            int seed = 0x75bd924 ^ input[input.Length-1];
-            int limit = Math.Min (input.Length-1, 0x174b);
-            for (int i = 0; i < limit; ++i)
-            {
-                seed = LRand (seed);
-                int index = (int)(seed * 4.656612875245797e-10 * 256);
-                input[i] ^= (byte)Key[index % Key.Length];
-            }
-            return new MemoryStream (input);
-        }
-
         Stream DecryptDat (ArcFile arc, Entry entry)
         {
-            byte[] input = new byte[entry.Size];
+            byte[] input = arc.File.View.ReadBytes (entry.Offset, entry.Size);
-            arc.File.View.Read (entry.Offset, input, 0, entry.Size);
             int text_offset = 3600;
             int text_length = (int)(entry.Size - text_offset - 2);
-            int seed = (sbyte)input[input.Length-1];
+            m_rng.SRand ((sbyte)input[input.Length-1]);
             for (int i = 0; i < text_length; i += 2)
             {
-                seed = seed * 0x343FD + 0x269EC3;
+                input[text_offset + i] ^= (byte)Key[m_rng.Rand() % Key.Length];
-                int index = (int)(((uint)seed >> 16) & 0x7fff);
-                input[text_offset + i] ^= (byte)Key[index % Key.Length];
             }
             return new MemoryStream (input);
         }
@@ -144,15 +134,13 @@ namespace GameRes.Formats.Eagls
             using (var view = idx.CreateViewAccessor (0, (uint)idx.MaxOffset))
             unsafe
             {
-                uint seed = view.ReadUInt32 (idx_size);
+                m_rng.SRand (view.ReadInt32 (idx_size));
                 byte* ptr = view.GetPointer (0);
                 try
                 {
                     for (int i = 0; i < idx_size; ++i)
                     {
-                        seed = seed * 0x343FD + 0x269EC3;
+                        output[i] = (byte)(ptr[i] ^ IndexKey[m_rng.Rand() % IndexKey.Length]);
-                        int index = (int)(seed >> 16) & 0x7FFF;
-                        output[i] = (byte)(ptr[i] ^ IndexKey[index % IndexKey.Length]);
                     }
                     return output;
                 }
@@ -162,17 +150,97 @@ namespace GameRes.Formats.Eagls
                 }
             }
         }
+    }
 
-        int LRand (int seed)
+    internal interface IRandomGenerator
     {
+        void SRand (int seed);
+        int Rand ();
+    }
+
+    internal class CRuntimeRandomGenerator : IRandomGenerator
+    {
+        uint m_seed;
+
+        public void SRand (int seed)
+        {
+            m_seed = (uint)seed;
+        }
+
+        public int Rand ()
+        {
+            m_seed = m_seed * 214013u + 2531011u;
+            return (int)(m_seed >> 16) & 0x7FFF;
+        }
+    }
+
+    internal class LehmerRandomGenerator : IRandomGenerator
+    {
+        int m_seed;
+
         const int A = 48271;
         const int Q = 44488;
         const int R = 3399;
         const int M = 2147483647;
-            seed = A * (seed % Q) - R * (seed / Q);
+
-            if (seed < 0)
+        public void SRand (int seed)
-                seed += M;
+        {
-            return seed;
+            m_seed = seed ^ 123459876;
+        }
+
+        public int Rand ()
+        {
+            m_seed = A * (m_seed % Q) - R * (m_seed / Q);
+            if (m_seed < 0)
+                m_seed += M;
+            return (int)(m_seed * 4.656612875245797e-10 * 256);
+        }
+    }
+
+    internal class CgArchive : ArcFile
+    {
+        IRandomGenerator    m_rng;
+
+        public CgArchive (ArcView arc, ArchiveFormat impl, ICollection<Entry> dir)
+            : base (arc, impl, dir)
+        {
+            m_rng = DetectEncryptionScheme();
+        }
+
+        IRandomGenerator DetectEncryptionScheme ()
+        {
+            var first_entry = Dir.First();
+            int signature = (File.View.ReadInt32 (first_entry.Offset) >> 8) & 0xFFFF;
+            byte seed = File.View.ReadByte (first_entry.Offset+first_entry.Size-1);
+            IRandomGenerator[] rng_list = {
+                new LehmerRandomGenerator(),
+                new CRuntimeRandomGenerator(),
+            };
+            foreach (var rng in rng_list)
+            {
+                rng.SRand (seed);
+                rng.Rand(); // skip LZSS control byte
+                int test = signature;
+                test ^= PakOpener.Key[rng.Rand() % PakOpener.Key.Length];
+                test ^= PakOpener.Key[rng.Rand() % PakOpener.Key.Length] << 8;
+                // FIXME
+                // as key is rather short, this detection could produce false results sometimes
+                if (0x4D42 == test) // 'BM'
+                    return rng;
+            }
+            throw new UnknownEncryptionScheme();
+        }
+
+        public Stream DecryptEntry (Entry entry)
+        {
+            var input = File.View.ReadBytes (entry.Offset, entry.Size);
+            m_rng.SRand (input[input.Length-1]);
+            int limit = Math.Min (input.Length-1, 0x174b);
+            for (int i = 0; i < limit; ++i)
+            {
+                input[i] ^= (byte)PakOpener.Key[m_rng.Rand() % PakOpener.Key.Length];
+            }
+            return new MemoryStream (input);
         }
     }
 }

supported.html

@@ -328,6 +328,7 @@ Warusa<br/>
 <tr class="odd"><td>*.mgd<br/>*.mgs</td><td><tt>MGD</tt><br/><tt>MGS</tt></td><td>No</td><td rowspan="2">MEGU</td><td rowspan="2">Seduce</tr>
 <tr class="odd"><td>*.agc</td><td><tt>AGd</tt></td><td>No</td></tr>
 <tr><td>*.pak+*.idx</td><td>-</td><td>No</td><td rowspan="2">EAGLS</td><td rowspan="2">
+Futago Hinyuu x 3<br/>
 Oppai Baka<br/>
 Mainichi Shabutte Ii Desu ka?<br/>
 Senpai - Oppai - Kako ni Modori Pai<br/>