PKCS7Padding.java revision e6bf3e8dfa2804891a82075cb469b736321b4827 
1package org.bouncycastle.crypto.paddings;
2
3import java.security.SecureRandom;
4
5import org.bouncycastle.crypto.InvalidCipherTextException;
6
7/**
8 * A padder that adds PKCS7/PKCS5 padding to a block.
9 */
10public class PKCS7Padding
11    implements BlockCipherPadding
12{
13    /**
14     * Initialise the padder.
15     *
16     * @param random - a SecureRandom if available.
17     */
18    public void init(SecureRandom random)
19        throws IllegalArgumentException
20    {
21        // nothing to do.
22    }
23
24    /**
25     * Return the name of the algorithm the padder implements.
26     *
27     * @return the name of the algorithm the padder implements.
28     */
29    public String getPaddingName()
30    {
31        return "PKCS7";
32    }
33
34    /**
35     * add the pad bytes to the passed in block, returning the
36     * number of bytes added.
37     */
38    public int addPadding(
39        byte[]  in,
40        int     inOff)
41    {
42        byte code = (byte)(in.length - inOff);
43
44        while (inOff < in.length)
45        {
46            in[inOff] = code;
47            inOff++;
48        }
49
50        return code;
51    }
52
53    /**
54     * return the number of pad bytes present in the block.
55     */
56    public int padCount(byte[] in)
57        throws InvalidCipherTextException
58    {
59        int count = in[in.length - 1] & 0xff;
60
61        if (count > in.length || count == 0)
62        {
63            throw new InvalidCipherTextException("pad block corrupted");
64        }
65
66        for (int i = 1; i <= count; i++)
67        {
68            if (in[in.length - i] != count)
69            {
70                throw new InvalidCipherTextException("pad block corrupted");
71            }
72        }
73
74        return count;
75    }
76}
77