From b713a010312cc5356b49e9e2c92007336e4f5ab2 Mon Sep 17 00:00:00 2001
From: morkt <muvluv.ru@gmail.com>
Date: Wed, 27 Sep 2017 15:42:53 +0400
Subject: [PATCH] (XP3): added optional AES decryption.

---
 ArcFormats/KiriKiri/ArcXP3.cs | 82 +++++++++++++++++++++++++++++++++++
 1 file changed, 82 insertions(+)

diff --git a/ArcFormats/KiriKiri/ArcXP3.cs b/ArcFormats/KiriKiri/ArcXP3.cs
index fcf08e06..cb59d513 100644
--- a/ArcFormats/KiriKiri/ArcXP3.cs
+++ b/ArcFormats/KiriKiri/ArcXP3.cs
@@ -354,6 +354,10 @@ NextEntry:
                 // assume no scripts are compressed using LZ4, return decompressed stream right away
                 return DecompressLz4 (xp3_entry, header, input);
             }
+            else if (0xA590D7FD == header.ToUInt32 (0)) // cZLIB magic
+            {
+                return DecompressCz (xp3_entry, header, input);
+            }
 
             if (0xFE == header[0] && 0xFE == header[1] && header[2] < 3 && 0xFF == header[3] && 0xFE == header[4])
                 return DecryptScript (header[2], input, xp3_entry.UnpackedSize);
@@ -389,6 +393,84 @@ NextEntry:
             return new Lz4Stream (input, info);
         }
 
+        Stream DecompressCz (Xp3Entry entry, byte[] src_header, Stream input)
+        {
+            var header = new byte[15];
+            Buffer.BlockCopy (src_header, 0, header, 0, Math.Min (header.Length, src_header.Length));
+            if (header.Length > src_header.Length)
+                input.Read (header, src_header.Length, header.Length - src_header.Length);
+            header[4] ^= 0x11;
+            header[5] ^= 0x7F;
+            header[6] ^= 0x9A;
+            byte key = header[4];
+            int unpacked_size = CzDecryptInt (header, 7, key);
+            int packed_size = CzDecryptInt (header, 11, key);
+            var data = new byte[packed_size];
+            input.Read (data, 0, packed_size);
+            input.Dispose();
+            data = CzDecryptData (data);
+            input = new BinMemoryStream (data);
+            if ('C' == header[4])
+                input = new ZLibStream (input, CompressionMode.Decompress);
+            return input;
+        }
+
+        static int CzDecryptInt (byte[] data, int offset, byte key)
+        {
+            for (int i = 0; i < 4; ++i)
+            {
+                data[offset+i] ^= (byte)(key ^ CzHeaderKey[i]);
+            }
+            return data.ToInt32 (offset);
+        }
+
+        static byte[] CzDecryptData (byte[] data)
+        {
+            int padded_size = data.Length - 5;
+            int original_size = padded_size - (data[padded_size+1] ^ data[padded_size]);
+            uint iv_seed = data.ToUInt32 (padded_size+1) ^ 0xBFBFBFBFu;
+            using (var aes = Aes.Create())
+            {
+                aes.Mode = CipherMode.CBC;
+                aes.Padding = PaddingMode.Zeros;
+                aes.Key = CzDefaultKey;
+                aes.IV = CzCreateIV (iv_seed);
+                using (var enc = new MemoryStream (data, 0, padded_size))
+                using (var dec = new InputCryptoStream (enc, aes.CreateDecryptor()))
+                {
+                    var original = new byte[original_size];
+                    dec.Read (original, 0, original_size);
+                    return original;
+                }
+            }
+        }
+
+        static byte[] CzCreateIV (uint seed)
+        {
+            var state = new uint[4];
+            state[0] = 123456789; // field_0
+            state[1] = 972436830; // field_4
+            state[2] = 524018621; // field_8
+            state[3] = seed;      // field_C
+            var iv = new byte[16];
+            for (int i = 0; i < 16; ++i)
+            {
+                uint a = state[3];
+                uint b = state[0] ^ (state[0] << 11);
+                state[0] = state[1];
+                state[1] = state[2];
+                state[2] = a;
+                state[3] = b ^ a ^ ((b ^ (a >> 11)) >> 8);
+                iv[i] = (byte)state[3];
+            }
+            return iv;
+        }
+
+        static readonly byte[] CzHeaderKey = { 0x9D, 0x1D, 0x9A, 0xF2 };
+        static readonly byte[] CzDefaultKey = {
+            0x91, 0x10, 0xFC, 0x75, 0x45, 0x8F, 0xB5, 0xE6, 0xFE, 0xAC, 0xBA, 0x44, 0x76, 0x58, 0xC2, 0x1A
+        };
+
         Stream DecryptScript (int enc_type, Stream input, uint unpacked_size)
         {
             using (var reader = new BinaryReader (input, Encoding.Unicode, true))