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annotate src/ch/ethz/ssh2/crypto/cipher/CBCMode.java @ 273:91a31873c42a ganymed

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start conversion from trilead to ganymed
author Carl Byington <carl@five-ten-sg.com>
date Fri, 18 Jul 2014 11:21:46 -0700
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children 071eccdff8ea
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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 * CBCMode.
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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 CBCMode implements BlockCipher
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14 {
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15 BlockCipher tc;
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16 int blockSize;
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17 boolean doEncrypt;
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18
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19 byte[] cbc_vector;
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20 byte[] tmp_vector;
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21
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22 public void init(boolean forEncryption, byte[] key)
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23 {
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24 }
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25
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26 public CBCMode(BlockCipher tc, byte[] iv, boolean doEncrypt)
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27 throws IllegalArgumentException
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28 {
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29 this.tc = tc;
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30 this.blockSize = tc.getBlockSize();
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31 this.doEncrypt = doEncrypt;
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32
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33 if (this.blockSize != iv.length)
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34 throw new IllegalArgumentException("IV must be " + blockSize
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35 + " bytes long! (currently " + iv.length + ")");
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36
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37 this.cbc_vector = new byte[blockSize];
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38 this.tmp_vector = new byte[blockSize];
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39 System.arraycopy(iv, 0, cbc_vector, 0, blockSize);
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40 }
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41
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42 public int getBlockSize()
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43 {
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44 return blockSize;
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45 }
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46
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47 private void encryptBlock(byte[] src, int srcoff, byte[] dst, int dstoff)
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48 {
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49 for (int i = 0; i < blockSize; i++)
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50 cbc_vector[i] ^= src[srcoff + i];
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51
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52 tc.transformBlock(cbc_vector, 0, dst, dstoff);
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53
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54 System.arraycopy(dst, dstoff, cbc_vector, 0, blockSize);
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55 }
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56
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57 private void decryptBlock(byte[] src, int srcoff, byte[] dst, int dstoff)
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58 {
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59 /* Assume the worst, src and dst are overlapping... */
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60
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61 System.arraycopy(src, srcoff, tmp_vector, 0, blockSize);
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62
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63 tc.transformBlock(src, srcoff, dst, dstoff);
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64
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65 for (int i = 0; i < blockSize; i++)
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66 dst[dstoff + i] ^= cbc_vector[i];
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67
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68 /* ...that is why we need a tmp buffer. */
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69
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70 byte[] swap = cbc_vector;
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71 cbc_vector = tmp_vector;
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72 tmp_vector = swap;
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73 }
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74
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75 public void transformBlock(byte[] src, int srcoff, byte[] dst, int dstoff)
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76 {
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77 if (doEncrypt)
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78 encryptBlock(src, srcoff, dst, dstoff);
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79 else
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80 decryptBlock(src, srcoff, dst, dstoff);
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81 }
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82 }