1/*
2 * Copyright (c) 2006-2011 Christian Plattner. All rights reserved.
3 * Please refer to the LICENSE.txt for licensing details.
4 */
5package 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 */
13public 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