1 /*
   2  * Copyright (c) 2003, 2017, Oracle and/or its affiliates. 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.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * 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 W3 XML ENC standard.
  32  *
  33  * @author Valerie Peng
  34  *
  35  *
  36  * @see Padding
  37  */
  38 final class ISO10126Padding implements Padding {
  39 
  40     private int blockSize;
  41 
  42     ISO10126Padding(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         int idx = Math.addExact(off, len);
  67         if (idx > in.length) {
  68             throw new ShortBufferException("Buffer too small to hold padding");
  69         }
  70 
  71         byte paddingOctet = (byte) (len & 0xff);
  72         byte[] padding = new byte[len - 1];
  73         SunJCE.getRandom().nextBytes(padding);
  74         System.arraycopy(padding, 0, in, off, len - 1);
  75         in[idx - 1] = paddingOctet;
  76         return;
  77     }
  78 
  79     /**
  80      * Returns the index where the padding starts.
  81      *
  82      * <p>Given a buffer with padded data, this method returns the
  83      * index where the padding starts.
  84      *
  85      * @param in the buffer with the padded data
  86      * @param off the offset in <code>in</code> where the padded data starts
  87      * @param len the length of the padded data
  88      *
  89      * @return the index where the padding starts, or -1 if the input is
  90      * not properly padded
  91      */
  92     public int unpad(byte[] in, int off, int len) {
  93         if ((in == null) ||
  94             (len == 0)) { // this can happen if input is really a padded buffer
  95             return 0;
  96         }
  97 
  98         int idx = Math.addExact(off, len);
  99         byte lastByte = in[idx - 1];
 100         int padValue = (int)lastByte & 0x0ff;
 101         if ((padValue < 0x01)
 102             || (padValue > blockSize)) {
 103             return -1;
 104         }
 105 
 106         int start = idx - padValue;
 107         if (start < off) {
 108             return -1;
 109         }
 110 
 111         return start;
 112     }
 113 
 114     /**
 115      * Determines how long the padding will be for a given input length.
 116      *
 117      * @param len the length of the data to pad
 118      *
 119      * @return the length of the padding
 120      */
 121     public int padLength(int len) {
 122         int paddingOctet = blockSize - (len % blockSize);
 123         return paddingOctet;
 124     }
 125 }