RC4Engine
using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Utilities;
using System;
namespace Org.BouncyCastle.Crypto.Engines
{
public class RC4Engine : IStreamCipher
{
private static readonly int STATE_LENGTH = 256;
private byte[] engineState;
private int x;
private int y;
private byte[] workingKey;
public virtual string AlgorithmName => "RC4";
public virtual void Init(bool forEncryption, ICipherParameters parameters)
{
KeyParameter keyParameter = parameters as KeyParameter;
if (keyParameter != null) {
workingKey = keyParameter.GetKey();
SetKey(workingKey);
return;
}
throw new ArgumentException("invalid parameter passed to RC4 init - " + Platform.GetTypeName(parameters));
}
public virtual byte ReturnByte(byte input)
{
x = ((x + 1) & 255);
y = ((engineState[x] + y) & 255);
byte b = engineState[x];
engineState[x] = engineState[y];
engineState[y] = b;
return (byte)(input ^ engineState[(engineState[x] + engineState[y]) & 255]);
}
public virtual void ProcessBytes(byte[] input, int inOff, int length, byte[] output, int outOff)
{
Check.DataLength(input, inOff, length, "input buffer too short");
Check.OutputLength(output, outOff, length, "output buffer too short");
for (int i = 0; i < length; i++) {
x = ((x + 1) & 255);
y = ((engineState[x] + y) & 255);
byte b = engineState[x];
byte b2 = engineState[y];
engineState[x] = b2;
engineState[y] = b;
output[i + outOff] = (byte)(input[i + inOff] ^ engineState[(b + b2) & 255]);
}
}
public virtual void Reset()
{
SetKey(workingKey);
}
private void SetKey(byte[] keyBytes)
{
workingKey = keyBytes;
x = 0;
y = 0;
if (engineState == null)
engineState = new byte[STATE_LENGTH];
for (int i = 0; i < STATE_LENGTH; i++) {
engineState[i] = (byte)i;
}
int num = 0;
int num2 = 0;
for (int j = 0; j < STATE_LENGTH; j++) {
num2 = (((keyBytes[num] & 255) + engineState[j] + num2) & 255);
byte b = engineState[j];
engineState[j] = engineState[num2];
engineState[num2] = b;
num = (num + 1) % keyBytes.Length;
}
}
}
}