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annotate src/ch/ethz/ssh2/crypto/cipher/CTRMode.java @ 386:e481699db6b1

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author Carl Byington <carl@five-ten-sg.com>
date Wed, 06 Aug 2014 11:50:10 -0700
parents 071eccdff8ea
children
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1 /*
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2 * Copyright (c) 2006-2011 Christian Plattner. All rights reserved.
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3 * Please refer to the LICENSE.txt for licensing details.
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4 */
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5 package ch.ethz.ssh2.crypto.cipher;
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6
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7 /**
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8 * This is CTR mode as described in draft-ietf-secsh-newmodes-XY.txt
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9 *
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10 * @author Christian Plattner
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11 * @version 2.50, 03/15/10
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12 */
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13 public class CTRMode implements BlockCipher {
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14 byte[] X;
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15 byte[] Xenc;
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17 BlockCipher bc;
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18 int blockSize;
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19 boolean doEncrypt;
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21 int count = 0;
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22
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23 public void init(boolean forEncryption, byte[] key) {
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24 }
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26 public CTRMode(BlockCipher tc, byte[] iv, boolean doEnc) throws IllegalArgumentException {
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27 bc = tc;
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28 blockSize = bc.getBlockSize();
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29 doEncrypt = doEnc;
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31 if (blockSize != iv.length)
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32 throw new IllegalArgumentException("IV must be " + blockSize + " bytes long! (currently " + iv.length + ")");
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34 X = new byte[blockSize];
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35 Xenc = new byte[blockSize];
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36 System.arraycopy(iv, 0, X, 0, blockSize);
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37 }
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39 public final int getBlockSize() {
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40 return blockSize;
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41 }
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42
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43 public final void transformBlock(byte[] src, int srcoff, byte[] dst, int dstoff) {
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44 bc.transformBlock(X, 0, Xenc, 0);
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45
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46 for (int i = 0; i < blockSize; i++) {
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47 dst[dstoff + i] = (byte)(src[srcoff + i] ^ Xenc[i]);
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48 }
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50 for (int i = (blockSize - 1); i >= 0; i--) {
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51 X[i]++;
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53 if (X[i] != 0)
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54 break;
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55 }
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56 }
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57 }