J. Duke | 319a3b9 | 2007-12-01 00:00:00 +0000 | [diff] [blame^] | 1 | /* |
| 2 | * Copyright 1997-2007 Sun Microsystems, Inc. All Rights Reserved. |
| 3 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| 4 | * |
| 5 | * This code is free software; you can redistribute it and/or modify it |
| 6 | * under the terms of the GNU General Public License version 2 only, as |
| 7 | * published by the Free Software Foundation. Sun designates this |
| 8 | * particular file as subject to the "Classpath" exception as provided |
| 9 | * by Sun in the LICENSE file that accompanied this code. |
| 10 | * |
| 11 | * This code is distributed in the hope that it will be useful, but WITHOUT |
| 12 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| 13 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| 14 | * version 2 for more details (a copy is included in the LICENSE file that |
| 15 | * accompanied this code). |
| 16 | * |
| 17 | * You should have received a copy of the GNU General Public License version |
| 18 | * 2 along with this work; if not, write to the Free Software Foundation, |
| 19 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| 20 | * |
| 21 | * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
| 22 | * CA 95054 USA or visit www.sun.com if you need additional information or |
| 23 | * have any questions. |
| 24 | */ |
| 25 | |
| 26 | package com.sun.crypto.provider; |
| 27 | |
| 28 | import javax.crypto.ShortBufferException; |
| 29 | |
| 30 | /** |
| 31 | * This class implements padding as specified in the PKCS#5 standard. |
| 32 | * |
| 33 | * @author Gigi Ankeny |
| 34 | * |
| 35 | * |
| 36 | * @see Padding |
| 37 | */ |
| 38 | final class PKCS5Padding implements Padding { |
| 39 | |
| 40 | private int blockSize; |
| 41 | |
| 42 | PKCS5Padding(int blockSize) { |
| 43 | this.blockSize = blockSize; |
| 44 | } |
| 45 | |
| 46 | /** |
| 47 | * Adds the given number of padding bytes to the data input. |
| 48 | * The value of the padding bytes is determined |
| 49 | * by the specific padding mechanism that implements this |
| 50 | * interface. |
| 51 | * |
| 52 | * @param in the input buffer with the data to pad |
| 53 | * @param off the offset in <code>in</code> where the padding bytes |
| 54 | * are appended |
| 55 | * @param len the number of padding bytes to add |
| 56 | * |
| 57 | * @exception ShortBufferException if <code>in</code> is too small to hold |
| 58 | * the padding bytes |
| 59 | */ |
| 60 | public void padWithLen(byte[] in, int off, int len) |
| 61 | throws ShortBufferException |
| 62 | { |
| 63 | if (in == null) |
| 64 | return; |
| 65 | |
| 66 | if ((off + len) > in.length) { |
| 67 | throw new ShortBufferException("Buffer too small to hold padding"); |
| 68 | } |
| 69 | |
| 70 | byte paddingOctet = (byte) (len & 0xff); |
| 71 | for (int i = 0; i < len; i++) { |
| 72 | in[i + off] = paddingOctet; |
| 73 | } |
| 74 | return; |
| 75 | } |
| 76 | |
| 77 | /** |
| 78 | * Returns the index where the padding starts. |
| 79 | * |
| 80 | * <p>Given a buffer with padded data, this method returns the |
| 81 | * index where the padding starts. |
| 82 | * |
| 83 | * @param in the buffer with the padded data |
| 84 | * @param off the offset in <code>in</code> where the padded data starts |
| 85 | * @param len the length of the padded data |
| 86 | * |
| 87 | * @return the index where the padding starts, or -1 if the input is |
| 88 | * not properly padded |
| 89 | */ |
| 90 | public int unpad(byte[] in, int off, int len) { |
| 91 | if ((in == null) || |
| 92 | (len == 0)) { // this can happen if input is really a padded buffer |
| 93 | return 0; |
| 94 | } |
| 95 | |
| 96 | byte lastByte = in[off + len - 1]; |
| 97 | int padValue = (int)lastByte & 0x0ff; |
| 98 | if ((padValue < 0x01) |
| 99 | || (padValue > blockSize)) { |
| 100 | return -1; |
| 101 | } |
| 102 | |
| 103 | int start = off + len - ((int)lastByte & 0x0ff); |
| 104 | if (start < off) { |
| 105 | return -1; |
| 106 | } |
| 107 | |
| 108 | for (int i = 0; i < ((int)lastByte & 0x0ff); i++) { |
| 109 | if (in[start+i] != lastByte) { |
| 110 | return -1; |
| 111 | } |
| 112 | } |
| 113 | |
| 114 | return start; |
| 115 | } |
| 116 | |
| 117 | /** |
| 118 | * Determines how long the padding will be for a given input length. |
| 119 | * |
| 120 | * @param len the length of the data to pad |
| 121 | * |
| 122 | * @return the length of the padding |
| 123 | */ |
| 124 | public int padLength(int len) { |
| 125 | int paddingOctet = blockSize - (len % blockSize); |
| 126 | return paddingOctet; |
| 127 | } |
| 128 | } |