diff --git a/ArcFormats/ArcFormats.csproj b/ArcFormats/ArcFormats.csproj
index a50676a4..b91bda4f 100644
--- a/ArcFormats/ArcFormats.csproj
+++ b/ArcFormats/ArcFormats.csproj
@@ -204,6 +204,7 @@
     <Compile Include="Primel\ImageGBC.cs" />
     <Compile Include="Primel\RC6.cs" />
     <Compile Include="Primel\SHA256.cs" />
+    <Compile Include="RC4.cs" />
     <Compile Include="RealLive\ArcG00.cs" />
     <Compile Include="RealLive\ArcOVK.cs" />
     <Compile Include="RealLive\AudioNWA.cs" />
diff --git a/ArcFormats/Dogenzaka/ImageRSA.cs b/ArcFormats/Dogenzaka/ImageRSA.cs
index 3d77635a..4ce37333 100644
--- a/ArcFormats/Dogenzaka/ImageRSA.cs
+++ b/ArcFormats/Dogenzaka/ImageRSA.cs
@@ -29,6 +29,7 @@ using System.IO;
 using System.Linq;
 using System.Security.Cryptography;
 using System.Text;
+using GameRes.Cryptography;
 
 namespace GameRes.Formats.Dogenzaka
 {
@@ -89,72 +90,4 @@ namespace GameRes.Formats.Dogenzaka
             throw new NotImplementedException ("Rc4PngFormat.Write not implemented");
         }
     }
-
-    public sealed class Rc4Transform : ICryptoTransform
-    {
-        private const int StateLength = 256;
-        private const int BlockSize = 256;
-        private byte[]	m_state = new byte[StateLength];
-        private int		x;
-        private int		y;
-        private byte[]  m_key;
-
-        public bool          CanReuseTransform { get { return false; } }
-        public bool CanTransformMultipleBlocks { get { return true; } }
-        public int              InputBlockSize { get { return BlockSize; } }
-        public int             OutputBlockSize { get { return BlockSize; } }
-
-        public Rc4Transform (byte[] key)
-        {
-            m_key = key;
-            x = 0;
-            y = 0;
-
-            for (int i = 0; i < StateLength; ++i)
-            {
-                m_state[i] = (byte)i;
-            }
-
-            int i1 = 0;
-            int i2 = 0;
-
-            for (int i = 0; i < StateLength; ++i)
-            {
-                i2 = ((m_key[i1] & 0xFF) + m_state[i] + i2) & 0xFF;
-                byte t = m_state[i];
-                m_state[i] = m_state[i2];
-                m_state[i2] = t;
-                i1 = (i1+1) % m_key.Length;
-            }
-        }
-
-        public int TransformBlock (byte[] inBuf, int inOffset, int inCount,
-                                   byte[] outBuf, int outOffset)
-        {
-            for (int i = 0; i < inCount; i++)
-            {
-                x = (x + 1) & 0xFF;
-                y = (m_state[x] + y) & 0xFF;
-
-                byte t = m_state[x];
-                m_state[x] = m_state[y];
-                m_state[y] = t;
-
-                outBuf[i+outOffset] = (byte)(inBuf[i + inOffset] ^ m_state[(m_state[x] + m_state[y]) & 0xFF]);
-            }
-            return inCount;
-        }
-
-        public byte[] TransformFinalBlock (byte[] inBuf, int inOffset, int inCount)
-        {
-            byte[] output = new byte[inCount];
-            TransformBlock (inBuf, inOffset, inCount, output, 0);
-            return output;
-        }
-
-        public void Dispose ()
-        {
-            GC.SuppressFinalize (this);
-        }
-    }
 }
diff --git a/ArcFormats/RC4.cs b/ArcFormats/RC4.cs
new file mode 100644
index 00000000..d713e0da
--- /dev/null
+++ b/ArcFormats/RC4.cs
@@ -0,0 +1,86 @@
+//! \file       RC4.cs
+//! \date       Sat Oct 08 00:38:00 2016
+//! \brief      RC4 encryption algorithm implementation.
+//
+
+using System.Security.Cryptography;
+
+namespace GameRes.Cryptography
+{
+    public sealed class Rc4Transform : ICryptoTransform
+    {
+        private const int StateLength = 256;
+        private const int BlockSize = 1;
+        private byte[]	m_state;
+        private int		m_x;
+        private int		m_y;
+
+        public bool          CanReuseTransform { get { return false; } }
+        public bool CanTransformMultipleBlocks { get { return true; } }
+        public int              InputBlockSize { get { return BlockSize; } }
+        public int             OutputBlockSize { get { return BlockSize; } }
+
+        public byte[]                    State { get { return m_state; } }
+
+        public Rc4Transform (byte[] key)
+        {
+            m_x = 0;
+            m_y = 0;
+
+            m_state = new byte[StateLength];
+            for (int i = 0; i < StateLength; ++i)
+            {
+                m_state[i] = (byte)i;
+            }
+
+            int s = 0;
+            for (int i = 0; i < StateLength; ++i)
+            {
+                s = (key[i % key.Length] + m_state[i] + s) & 0xFF;
+                byte t = m_state[i];
+                m_state[i] = m_state[s];
+                m_state[s] = t;
+            }
+        }
+
+        public byte NextByte ()
+        {
+            m_x = (m_x + 1) & 0xFF;
+            byte a = m_state[m_x];
+            m_y = (m_y + a) & 0xFF;
+            byte b = m_state[m_y];
+            m_state[m_x] = b;
+            m_state[m_y] = a;
+            return m_state[(a + b) & 0xFF];
+        }
+
+        public byte[] GenerateBlock (int length)
+        {
+            var block = new byte[length];
+            for (int i = 0; i < block.Length; ++i)
+                block[i] = NextByte();
+            return block;
+        }
+
+        public int TransformBlock (byte[] inBuf, int inOffset, int inCount, byte[] outBuf, int outOffset)
+        {
+            for (int i = 0; i < inCount; i++)
+            {
+                outBuf[i+outOffset] = (byte)(inBuf[i + inOffset] ^ NextByte());
+            }
+            return inCount;
+        }
+
+        public byte[] TransformFinalBlock (byte[] inBuf, int inOffset, int inCount)
+        {
+            byte[] output = new byte[inCount];
+            TransformBlock (inBuf, inOffset, inCount, output, 0);
+            return output;
+        }
+
+        public void Dispose ()
+        {
+            System.GC.SuppressFinalize (this);
+        }
+    }
+}