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    1   /*
    2    * Copyright (c) 2003, 2007, 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           if ((off + len) > in.length) {
   67               throw new ShortBufferException("Buffer too small to hold padding");
   68           }
   69   
   70           byte paddingOctet = (byte) (len & 0xff);
   71           byte[] padding = new byte[len];
   72           SunJCE.RANDOM.nextBytes(padding);
   73           padding[len-1] = paddingOctet;
   74           System.arraycopy(padding, 0, in, off, len);
   75           return;
   76       }
   77   
   78       /**
   79        * Returns the index where the padding starts.
   80        *
   81        * <p>Given a buffer with padded data, this method returns the
   82        * index where the padding starts.
   83        *
   84        * @param in the buffer with the padded data
   85        * @param off the offset in <code>in</code> where the padded data starts
   86        * @param len the length of the padded data
   87        *
   88        * @return the index where the padding starts, or -1 if the input is
   89        * not properly padded
   90        */
   91       public int unpad(byte[] in, int off, int len) {
   92           if ((in == null) ||
   93               (len == 0)) { // this can happen if input is really a padded buffer
   94               return 0;
   95           }
   96   
   97           byte lastByte = in[off + len - 1];
   98           int padValue = (int)lastByte & 0x0ff;
   99           if ((padValue < 0x01)
  100               || (padValue > blockSize)) {
  101               return -1;
  102           }
  103   
  104           int start = off + len - ((int)lastByte & 0x0ff);
  105           if (start < off) {
  106               return -1;
  107           }
  108   
  109           return start;
  110       }
  111   
  112       /**
  113        * Determines how long the padding will be for a given input length.
  114        *
  115        * @param len the length of the data to pad
  116        *
  117        * @return the length of the padding
  118        */
  119       public int padLength(int len) {
  120           int paddingOctet = blockSize - (len % blockSize);
  121           return paddingOctet;
  122       }
  123   }

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