/*
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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*/
package com.sun.crypto.provider;
import javax.crypto.ShortBufferException;
/**
* This class implements padding as specified in the PKCS#5 standard.
*
* @author Gigi Ankeny
*
*
* @see Padding
*/
final class PKCS5Padding implements Padding {
private int blockSize;
PKCS5Padding(int blockSize) {
this.blockSize = blockSize;
}
/**
* Adds the given number of padding bytes to the data input.
* The value of the padding bytes is determined
* by the specific padding mechanism that implements this
* interface.
*
* @param in the input buffer with the data to pad
* @param off the offset in <code>in</code> where the padding bytes
* are appended
* @param len the number of padding bytes to add
*
* @exception ShortBufferException if <code>in</code> is too small to hold
* the padding bytes
*/
public void padWithLen(byte[] in, int off, int len)
throws ShortBufferException
{
if (in == null)
return;
if ((off + len) > in.length) {
throw new ShortBufferException("Buffer too small to hold padding");
}
byte paddingOctet = (byte) (len & 0xff);
for (int i = 0; i < len; i++) {
in[i + off] = paddingOctet;
}
return;
}
/**
* Returns the index where the padding starts.
*
* <p>Given a buffer with padded data, this method returns the
* index where the padding starts.
*
* @param in the buffer with the padded data
* @param off the offset in <code>in</code> where the padded data starts
* @param len the length of the padded data
*
* @return the index where the padding starts, or -1 if the input is
* not properly padded
*/
public int unpad(byte[] in, int off, int len) {
if ((in == null) ||
(len == 0)) { // this can happen if input is really a padded buffer
return 0;
}
byte lastByte = in[off + len - 1];
int padValue = (int)lastByte & 0x0ff;
if ((padValue < 0x01)
|| (padValue > blockSize)) {
return -1;
}
int start = off + len - ((int)lastByte & 0x0ff);
if (start < off) {
return -1;
}
for (int i = 0; i < ((int)lastByte & 0x0ff); i++) {
if (in[start+i] != lastByte) {
return -1;
}
}
return start;
}
/**
* Determines how long the padding will be for a given input length.
*
* @param len the length of the data to pad
*
* @return the length of the padding
*/
public int padLength(int len) {
int paddingOctet = blockSize - (len % blockSize);
return paddingOctet;
}
}