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1
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2 package com.trilead.ssh2.crypto.cipher;
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3
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4 /**
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5 * This is CTR mode as described in draft-ietf-secsh-newmodes-XY.txt
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6 *
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7 * @author Christian Plattner, plattner@trilead.com
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8 * @version $Id: CTRMode.java,v 1.1 2007/10/15 12:49:55 cplattne Exp $
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9 */
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10 public class CTRMode implements BlockCipher {
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11 byte[] X;
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12 byte[] Xenc;
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13
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14 BlockCipher bc;
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15 int blockSize;
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16 boolean doEncrypt;
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17
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18 int count = 0;
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19
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20 public void init(boolean forEncryption, byte[] key) {
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21 }
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22
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23 public CTRMode(BlockCipher tc, byte[] iv, boolean doEnc) throws IllegalArgumentException {
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24 bc = tc;
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25 blockSize = bc.getBlockSize();
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26 doEncrypt = doEnc;
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27
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28 if (blockSize != iv.length)
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29 throw new IllegalArgumentException("IV must be " + blockSize + " bytes long! (currently " + iv.length + ")");
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30
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31 X = new byte[blockSize];
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32 Xenc = new byte[blockSize];
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33 System.arraycopy(iv, 0, X, 0, blockSize);
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34 }
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35
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36 public final int getBlockSize() {
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37 return blockSize;
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38 }
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39
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40 public final void transformBlock(byte[] src, int srcoff, byte[] dst, int dstoff) {
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41 bc.transformBlock(X, 0, Xenc, 0);
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42
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43 for (int i = 0; i < blockSize; i++) {
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44 dst[dstoff + i] = (byte)(src[srcoff + i] ^ Xenc[i]);
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45 }
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46
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47 for (int i = (blockSize - 1); i >= 0; i--) {
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48 X[i]++;
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49
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50 if (X[i] != 0)
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51 break;
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52 }
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53 }
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54 }
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