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//
// ARC4Managed.cs: Alleged RC4(tm) compatible symmetric stream cipher
// RC4 is a trademark of RSA Security
//
//
// 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.Globalization;
using System.Security.Cryptography;
namespace Mono.Security.Cryptography {
// References:
// a. Usenet 1994 - RC4 Algorithm revealed
// http://www.qrst.de/html/dsds/rc4.htm
public class ARC4Managed : RC4, ICryptoTransform {
private byte[] key;
private byte[] state;
private byte x;
private byte y;
private bool m_disposed;
public ARC4Managed () : base ()
{
state = new byte [256];
m_disposed = false;
}
~ARC4Managed ()
{
Dispose (true);
}
protected override void Dispose (bool disposing)
{
if (!m_disposed) {
x = 0;
y = 0;
if (key != null) {
Array.Clear (key, 0, key.Length);
key = null;
}
Array.Clear (state, 0, state.Length);
state = null;
GC.SuppressFinalize (this);
m_disposed = true;
}
}
public override byte[] Key {
get { return (byte[]) key.Clone (); }
set {
key = (byte[]) value.Clone ();
KeySetup (key);
}
}
public bool CanReuseTransform {
get { return false; }
}
public override ICryptoTransform CreateEncryptor (byte[] rgbKey, byte[] rgvIV)
{
Key = rgbKey;
return (ICryptoTransform) this;
}
public override ICryptoTransform CreateDecryptor (byte[] rgbKey, byte[] rgvIV)
{
Key = rgbKey;
return CreateEncryptor ();
}
public override void GenerateIV ()
{
// not used for a stream cipher
IV = new byte [0];
}
public override void GenerateKey ()
{
Key = KeyBuilder.Key (KeySizeValue >> 3);
}
public bool CanTransformMultipleBlocks {
get { return true; }
}
public int InputBlockSize {
get { return 1; }
}
public int OutputBlockSize {
get { return 1; }
}
private void KeySetup (byte[] key)
{
byte index1 = 0;
byte index2 = 0;
for (int counter = 0; counter < 256; counter++)
state [counter] = (byte) counter;
x = 0;
y = 0;
for (int counter = 0; counter < 256; counter++) {
index2 = (byte) (key [index1] + state [counter] + index2);
// swap byte
byte tmp = state [counter];
state [counter] = state [index2];
state [index2] = tmp;
index1 = (byte) ((index1 + 1) % key.Length);
}
}
private void CheckInput (byte[] inputBuffer, int inputOffset, int inputCount)
{
if (inputBuffer == null)
throw new ArgumentNullException ("inputBuffer");
if (inputOffset < 0)
throw new ArgumentOutOfRangeException ("inputOffset", "< 0");
if (inputCount < 0)
throw new ArgumentOutOfRangeException ("inputCount", "< 0");
// ordered to avoid possible integer overflow
if (inputOffset > inputBuffer.Length - inputCount)
throw new ArgumentException ("inputBuffer", Locale.GetText ("Overflow"));
}
public int TransformBlock (byte[] inputBuffer, int inputOffset, int inputCount, byte[] outputBuffer, int outputOffset)
{
CheckInput (inputBuffer, inputOffset, inputCount);
// check output parameters
if (outputBuffer == null)
throw new ArgumentNullException ("outputBuffer");
if (outputOffset < 0)
throw new ArgumentOutOfRangeException ("outputOffset", "< 0");
// ordered to avoid possible integer overflow
if (outputOffset > outputBuffer.Length - inputCount)
throw new ArgumentException ("outputBuffer", Locale.GetText ("Overflow"));
return InternalTransformBlock (inputBuffer, inputOffset, inputCount, outputBuffer, outputOffset);
}
private int InternalTransformBlock (byte[] inputBuffer, int inputOffset, int inputCount, byte[] outputBuffer, int outputOffset)
{
byte xorIndex;
for (int counter = 0; counter < inputCount; counter ++) {
x = (byte) (x + 1);
y = (byte) (state [x] + y);
// swap byte
byte tmp = state [x];
state [x] = state [y];
state [y] = tmp;
xorIndex = (byte) (state [x] + state [y]);
outputBuffer [outputOffset + counter] = (byte) (inputBuffer [inputOffset + counter] ^ state [xorIndex]);
}
return inputCount;
}
public byte[] TransformFinalBlock (byte[] inputBuffer, int inputOffset, int inputCount)
{
CheckInput (inputBuffer, inputOffset, inputCount);
byte[] output = new byte [inputCount];
InternalTransformBlock (inputBuffer, inputOffset, inputCount, output, 0);
return output;
}
}
}
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