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      1 /*
      2  * Copyright (c) 2006-2011 Christian Plattner. All rights reserved.
      3  * Please refer to the LICENSE.txt for licensing details.
      4  */
      5 package ch.ethz.ssh2.crypto.cipher;
      6 
      7 /**
      8  * This is CTR mode as described in draft-ietf-secsh-newmodes-XY.txt
      9  *
     10  * @author Christian Plattner
     11  * @version 2.50, 03/15/10
     12  */
     13 public class CTRMode implements BlockCipher
     14 {
     15 	byte[] X;
     16 	byte[] Xenc;
     17 
     18 	BlockCipher bc;
     19 	int blockSize;
     20 	boolean doEncrypt;
     21 
     22 	int count = 0;
     23 
     24 	public void init(boolean forEncryption, byte[] key)
     25 	{
     26 	}
     27 
     28 	public CTRMode(BlockCipher tc, byte[] iv, boolean doEnc) throws IllegalArgumentException
     29 	{
     30 		bc = tc;
     31 		blockSize = bc.getBlockSize();
     32 		doEncrypt = doEnc;
     33 
     34 		if (blockSize != iv.length)
     35 			throw new IllegalArgumentException("IV must be " + blockSize + " bytes long! (currently " + iv.length + ")");
     36 
     37 		X = new byte[blockSize];
     38 		Xenc = new byte[blockSize];
     39 
     40 		System.arraycopy(iv, 0, X, 0, blockSize);
     41 	}
     42 
     43 	public final int getBlockSize()
     44 	{
     45 		return blockSize;
     46 	}
     47 
     48 	public final void transformBlock(byte[] src, int srcoff, byte[] dst, int dstoff)
     49 	{
     50 		bc.transformBlock(X, 0, Xenc, 0);
     51 
     52 		for (int i = 0; i < blockSize; i++)
     53 		{
     54 			dst[dstoff + i] = (byte) (src[srcoff + i] ^ Xenc[i]);
     55 		}
     56 
     57 		for (int i = (blockSize - 1); i >= 0; i--)
     58 		{
     59 			X[i]++;
     60 			if (X[i] != 0)
     61 				break;
     62 
     63 		}
     64 	}
     65 }
     66