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1 package com.trilead.ssh2.crypto.cipher;
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2
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3 /**
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4 * CBCMode.
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5 *
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6 * @author Christian Plattner, plattner@trilead.com
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7 * @version $Id: CBCMode.java,v 1.1 2007/10/15 12:49:55 cplattne Exp $
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8 */
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9 public class CBCMode implements BlockCipher {
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10 BlockCipher tc;
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11 int blockSize;
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12 boolean doEncrypt;
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13
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14 byte[] cbc_vector;
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15 byte[] tmp_vector;
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16
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17 public void init(boolean forEncryption, byte[] key) {
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18 }
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19
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20 public CBCMode(BlockCipher tc, byte[] iv, boolean doEncrypt)
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21 throws IllegalArgumentException {
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22 this.tc = tc;
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23 this.blockSize = tc.getBlockSize();
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24 this.doEncrypt = doEncrypt;
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25
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26 if (this.blockSize != iv.length)
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27 throw new IllegalArgumentException("IV must be " + blockSize
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28 + " bytes long! (currently " + iv.length + ")");
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29
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30 this.cbc_vector = new byte[blockSize];
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31 this.tmp_vector = new byte[blockSize];
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32 System.arraycopy(iv, 0, cbc_vector, 0, blockSize);
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33 }
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34
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35 public int getBlockSize() {
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36 return blockSize;
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37 }
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38
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39 private void encryptBlock(byte[] src, int srcoff, byte[] dst, int dstoff) {
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40 for (int i = 0; i < blockSize; i++)
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41 cbc_vector[i] ^= src[srcoff + i];
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42
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43 tc.transformBlock(cbc_vector, 0, dst, dstoff);
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44 System.arraycopy(dst, dstoff, cbc_vector, 0, blockSize);
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45 }
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46
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47 private void decryptBlock(byte[] src, int srcoff, byte[] dst, int dstoff) {
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48 /* Assume the worst, src and dst are overlapping... */
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49 System.arraycopy(src, srcoff, tmp_vector, 0, blockSize);
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50 tc.transformBlock(src, srcoff, dst, dstoff);
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51
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52 for (int i = 0; i < blockSize; i++)
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53 dst[dstoff + i] ^= cbc_vector[i];
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54
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55 /* ...that is why we need a tmp buffer. */
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56 byte[] swap = cbc_vector;
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57 cbc_vector = tmp_vector;
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58 tmp_vector = swap;
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59 }
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60
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61 public void transformBlock(byte[] src, int srcoff, byte[] dst, int dstoff) {
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62 if (doEncrypt)
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63 encryptBlock(src, srcoff, dst, dstoff);
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64 else
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65 decryptBlock(src, srcoff, dst, dstoff);
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66 }
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67 }
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