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package com.trilead.ssh2.crypto.cipher;
/**
* This is CTR mode as described in draft-ietf-secsh-newmodes-XY.txt
*
* @author Christian Plattner, plattner@trilead.com
* @version $Id: CTRMode.java,v 1.1 2007/10/15 12:49:55 cplattne Exp $
*/
public class CTRMode implements BlockCipher
{
byte[] X;
byte[] Xenc;
BlockCipher bc;
int blockSize;
boolean doEncrypt;
int count = 0;
public void init(boolean forEncryption, byte[] key)
{
}
public CTRMode(BlockCipher tc, byte[] iv, boolean doEnc) throws IllegalArgumentException
{
bc = tc;
blockSize = bc.getBlockSize();
doEncrypt = doEnc;
if (blockSize != iv.length)
throw new IllegalArgumentException("IV must be " + blockSize + " bytes long! (currently " + iv.length + ")");
X = new byte[blockSize];
Xenc = new byte[blockSize];
System.arraycopy(iv, 0, X, 0, blockSize);
}
public final int getBlockSize()
{
return blockSize;
}
public final void transformBlock(byte[] src, int srcoff, byte[] dst, int dstoff)
{
bc.transformBlock(X, 0, Xenc, 0);
for (int i = 0; i < blockSize; i++)
{
dst[dstoff + i] = (byte) (src[srcoff + i] ^ Xenc[i]);
}
for (int i = (blockSize - 1); i >= 0; i--)
{
X[i]++;
if (X[i] != 0)
break;
}
}
}
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