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package org.bouncycastle.crypto.modes;
import org.bouncycastle.crypto.BlockCipher;
import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.DataLengthException;
import org.bouncycastle.crypto.params.ParametersWithIV;
/**
* Implements the Segmented Integer Counter (SIC) mode on top of a simple
* block cipher. This mode is also known as CTR mode.
*/
public class SICBlockCipher
implements BlockCipher
{
private final BlockCipher cipher;
private final int blockSize;
private byte[] IV;
private byte[] counter;
private byte[] counterOut;
/**
* Basic constructor.
*
* @param c the block cipher to be used.
*/
public SICBlockCipher(BlockCipher c)
{
this.cipher = c;
this.blockSize = cipher.getBlockSize();
this.IV = new byte[blockSize];
this.counter = new byte[blockSize];
this.counterOut = new byte[blockSize];
}
/**
* return the underlying block cipher that we are wrapping.
*
* @return the underlying block cipher that we are wrapping.
*/
public BlockCipher getUnderlyingCipher()
{
return cipher;
}
public void init(
boolean forEncryption, //ignored by this CTR mode
CipherParameters params)
throws IllegalArgumentException
{
if (params instanceof ParametersWithIV)
{
ParametersWithIV ivParam = (ParametersWithIV)params;
byte[] iv = ivParam.getIV();
System.arraycopy(iv, 0, IV, 0, IV.length);
reset();
// if null it's an IV changed only.
if (ivParam.getParameters() != null)
{
cipher.init(true, ivParam.getParameters());
}
}
else
{
throw new IllegalArgumentException("SIC mode requires ParametersWithIV");
}
}
public String getAlgorithmName()
{
return cipher.getAlgorithmName() + "/SIC";
}
public int getBlockSize()
{
return cipher.getBlockSize();
}
public int processBlock(byte[] in, int inOff, byte[] out, int outOff)
throws DataLengthException, IllegalStateException
{
cipher.processBlock(counter, 0, counterOut, 0);
//
// XOR the counterOut with the plaintext producing the cipher text
//
for (int i = 0; i < counterOut.length; i++)
{
out[outOff + i] = (byte)(counterOut[i] ^ in[inOff + i]);
}
// increment counter by 1.
for (int i = counter.length - 1; i >= 0 && ++counter[i] == 0; i--)
{
; // do nothing - pre-increment and test for 0 in counter does the job.
}
return counter.length;
}
public void reset()
{
System.arraycopy(IV, 0, counter, 0, counter.length);
cipher.reset();
}
}
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