1package org.bouncycastle.crypto.modes;
2
3import org.bouncycastle.crypto.BlockCipher;
4import org.bouncycastle.crypto.CipherParameters;
5import org.bouncycastle.crypto.DataLengthException;
6import org.bouncycastle.crypto.params.ParametersWithIV;
7
8/**
9 * Implements the Segmented Integer Counter (SIC) mode on top of a simple
10 * block cipher. This mode is also known as CTR mode.
11 */
12public class SICBlockCipher
13    implements BlockCipher
14{
15    private final BlockCipher     cipher;
16    private final int             blockSize;
17
18    private byte[]          IV;
19    private byte[]          counter;
20    private byte[]          counterOut;
21
22
23    /**
24     * Basic constructor.
25     *
26     * @param c the block cipher to be used.
27     */
28    public SICBlockCipher(BlockCipher c)
29    {
30        this.cipher = c;
31        this.blockSize = cipher.getBlockSize();
32        this.IV = new byte[blockSize];
33        this.counter = new byte[blockSize];
34        this.counterOut = new byte[blockSize];
35    }
36
37
38    /**
39     * return the underlying block cipher that we are wrapping.
40     *
41     * @return the underlying block cipher that we are wrapping.
42     */
43    public BlockCipher getUnderlyingCipher()
44    {
45        return cipher;
46    }
47
48
49    public void init(
50        boolean             forEncryption, //ignored by this CTR mode
51        CipherParameters    params)
52        throws IllegalArgumentException
53    {
54        if (params instanceof ParametersWithIV)
55        {
56          ParametersWithIV ivParam = (ParametersWithIV)params;
57          byte[]           iv      = ivParam.getIV();
58          System.arraycopy(iv, 0, IV, 0, IV.length);
59
60          reset();
61
62          // if null it's an IV changed only.
63          if (ivParam.getParameters() != null)
64          {
65            cipher.init(true, ivParam.getParameters());
66          }
67        }
68        else
69        {
70            throw new IllegalArgumentException("SIC mode requires ParametersWithIV");
71        }
72    }
73
74    public String getAlgorithmName()
75    {
76        return cipher.getAlgorithmName() + "/SIC";
77    }
78
79    public int getBlockSize()
80    {
81        return cipher.getBlockSize();
82    }
83
84
85    public int processBlock(byte[] in, int inOff, byte[] out, int outOff)
86          throws DataLengthException, IllegalStateException
87    {
88        cipher.processBlock(counter, 0, counterOut, 0);
89
90        //
91        // XOR the counterOut with the plaintext producing the cipher text
92        //
93        for (int i = 0; i < counterOut.length; i++)
94        {
95          out[outOff + i] = (byte)(counterOut[i] ^ in[inOff + i]);
96        }
97
98        // increment counter by 1.
99        for (int i = counter.length - 1; i >= 0 && ++counter[i] == 0; i--)
100        {
101            ; // do nothing - pre-increment and test for 0 in counter does the job.
102        }
103
104        return counter.length;
105    }
106
107
108    public void reset()
109    {
110        System.arraycopy(IV, 0, counter, 0, counter.length);
111        cipher.reset();
112    }
113}
114