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Java > Open Source Codes > ch > ethz > ssh2 > crypto > cipher > CBCMode


1 package ch.ethz.ssh2.crypto.cipher;
2
3 /**
4  * CBCMode.
5  *
6  * @author Christian Plattner, plattner@inf.ethz.ch
7  * @version $Id: CBCMode.java,v 1.2 2005/12/05 17:13:27 cplattne Exp $
8  */
9 public class CBCMode implements BlockCipher
10 {
11     BlockCipher tc;
12     int blockSize;
13     boolean doEncrypt;
14
15     byte[] cbc_vector;
16     byte[] tmp_vector;
17
18     public void init(boolean forEncryption, byte[] key)
19     {
20     }
21     
22     public CBCMode(BlockCipher tc, byte[] iv, boolean doEncrypt)
23             throws IllegalArgumentException JavaDoc
24     {
25         this.tc = tc;
26         this.blockSize = tc.getBlockSize();
27         this.doEncrypt = doEncrypt;
28
29         if (this.blockSize != iv.length)
30             throw new IllegalArgumentException JavaDoc("IV must be " + blockSize
31                     + " bytes long! (currently " + iv.length + ")");
32
33         this.cbc_vector = new byte[blockSize];
34         this.tmp_vector = new byte[blockSize];
35         System.arraycopy(iv, 0, cbc_vector, 0, blockSize);
36     }
37
38     public int getBlockSize()
39     {
40         return blockSize;
41     }
42
43     private void encryptBlock(byte[] src, int srcoff, byte[] dst, int dstoff)
44     {
45         for (int i = 0; i < blockSize; i++)
46             cbc_vector[i] ^= src[srcoff + i];
47
48         tc.transformBlock(cbc_vector, 0, dst, dstoff);
49
50         System.arraycopy(dst, dstoff, cbc_vector, 0, blockSize);
51     }
52
53     private void decryptBlock(byte[] src, int srcoff, byte[] dst, int dstoff)
54     {
55         /* Assume the worst, src and dst are overlapping... */
56         
57         System.arraycopy(src, srcoff, tmp_vector, 0, blockSize);
58         
59         tc.transformBlock(src, srcoff, dst, dstoff);
60         
61         for (int i = 0; i < blockSize; i++)
62             dst[dstoff + i] ^= cbc_vector[i];
63
64         /* ...that is why we need a tmp buffer. */
65         
66         byte[] swap = cbc_vector;
67         cbc_vector = tmp_vector;
68         tmp_vector = swap;
69     }
70
71     public void transformBlock(byte[] src, int srcoff, byte[] dst, int dstoff)
72     {
73         if (doEncrypt)
74             encryptBlock(src, srcoff, dst, dstoff);
75         else
76             decryptBlock(src, srcoff, dst, dstoff);
77     }
78 }
79
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