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//! \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);
}
}
}