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package org.spongycastle.crypto.engines;
import org.spongycastle.crypto.CipherParameters;
import org.spongycastle.crypto.DataLengthException;
import org.spongycastle.crypto.OutputLengthException;
import org.spongycastle.crypto.StreamCipher;
import org.spongycastle.crypto.params.KeyParameter;
public class RC4Engine implements StreamCipher
{
private final static int STATE_LENGTH = 256;
/*
* variables to hold the state of the RC4 engine
* during encryption and decryption
*/
private byte[] engineState = null;
private int x = 0;
private int y = 0;
private byte[] workingKey = null;
/**
* initialise a RC4 cipher.
*
* @param forEncryption whether or not we are for encryption.
* @param params the parameters required to set up the cipher.
* @exception IllegalArgumentException if the params argument is
* inappropriate.
*/
public void init(
boolean forEncryption,
CipherParameters params
)
{
if (params instanceof KeyParameter)
{
/*
* RC4 encryption and decryption is completely
* symmetrical, so the 'forEncryption' is
* irrelevant.
*/
workingKey = ((KeyParameter)params).getKey();
setKey(workingKey);
return;
}
throw new IllegalArgumentException("invalid parameter passed to RC4 init - " + params.getClass().getName());
}
public String getAlgorithmName()
{
return "RC4";
}
public byte returnByte(byte in)
{
x = (x + 1) & 0xff;
y = (engineState[x] + y) & 0xff;
// swap
byte tmp = engineState[x];
engineState[x] = engineState[y];
engineState[y] = tmp;
// xor
return (byte)(in ^ engineState[(engineState[x] + engineState[y]) & 0xff]);
}
public void processBytes(
byte[] in,
int inOff,
int len,
byte[] out,
int outOff)
{
if ((inOff + len) > in.length)
{
throw new DataLengthException("input buffer too short");
}
if ((outOff + len) > out.length)
{
throw new OutputLengthException("output buffer too short");
}
for (int i = 0; i < len ; i++)
{
x = (x + 1) & 0xff;
y = (engineState[x] + y) & 0xff;
// swap
byte tmp = engineState[x];
engineState[x] = engineState[y];
engineState[y] = tmp;
// xor
out[i+outOff] = (byte)(in[i + inOff]
^ engineState[(engineState[x] + engineState[y]) & 0xff]);
}
}
public void reset()
{
setKey(workingKey);
}
// Private implementation
private void setKey(byte[] keyBytes)
{
workingKey = keyBytes;
// System.out.println("the key length is ; "+ workingKey.length);
x = 0;
y = 0;
if (engineState == null)
{
engineState = new byte[STATE_LENGTH];
}
// reset the state of the engine
for (int i=0; i < STATE_LENGTH; i++)
{
engineState[i] = (byte)i;
}
int i1 = 0;
int i2 = 0;
for (int i=0; i < STATE_LENGTH; i++)
{
i2 = ((keyBytes[i1] & 0xff) + engineState[i] + i2) & 0xff;
// do the byte-swap inline
byte tmp = engineState[i];
engineState[i] = engineState[i2];
engineState[i2] = tmp;
i1 = (i1+1) % keyBytes.length;
}
}
}
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