/* PKCS7.java -- 
 Copyright (C) 2001, 2002, 2006 Free Software Foundation, Inc.

 This file is a part of GNU Classpath.

 GNU Classpath is free software; you can redistribute it and/or modify
 it under the terms of the GNU General Public License as published by
 the Free Software Foundation; either version 2 of the License, or (at
 your option) any later version.

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 WITHOUT ANY WARRANTY; without even the implied warranty of
 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 General Public License for more details.

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 along with GNU Classpath; if not, write to the Free Software
 Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
 USA

 Linking this library statically or dynamically with other modules is
 making a combined work based on this library.  Thus, the terms and
 conditions of the GNU General Public License cover the whole
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 permission to link this library with independent modules to produce an
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package gnu.javax.crypto.pad;

import gnu.java.security.Configuration;
import gnu.java.security.Registry;
import gnu.java.security.util.Util;

import java.util.logging.Logger;

/**
 * The implementation of the PKCS7 padding algorithm.
 * <p>
 * This algorithm is described for 8-byte blocks in [RFC-1423] and extended to
 * block sizes of up to 256 bytes in [PKCS-7].
 * <p>
 * References:
 * <ol>
 * <li><a href="http://www.ietf.org/rfc/rfc1423.txt">RFC-1423</a>: Privacy
 * Enhancement for Internet Electronic Mail: Part III: Algorithms, Modes, and
 * Identifiers.</li>
 * <li><a href="http://www.ietf.org/">IETF</a>.</li>
 * <li><a href="http://www.rsasecurity.com/rsalabs/pkcs/pkcs-7/">[PKCS-7]</a>
 * PKCS #7: Cryptographic Message Syntax Standard - An RSA Laboratories
 * Technical Note.</li>
 * <li><a href="http://www.rsasecurity.com/">RSA Security</a>.</li>
 * </ol>
 */
public final class PKCS7
    extends BasePad
{
  private static final Logger log = Logger.getLogger(PKCS7.class.getName());

  /**
   * Trivial package-private constructor for use by the <i>Factory</i> class.
   * 
   * @see PadFactory
   */
  PKCS7()
  {
    super(Registry.PKCS7_PAD);
  }

  public void setup()
  {
    if (blockSize < 2 || blockSize > 256)
      throw new IllegalArgumentException();
  }

  public byte[] pad(byte[] in, int offset, int length)
  {
    int padLength = blockSize;
    if (length % blockSize != 0)
      padLength = blockSize - length % blockSize;
    byte[] result = new byte[padLength];
    for (int i = 0; i < padLength;)
      result[i++] = (byte) padLength;
    if (Configuration.DEBUG)
      log.fine("padding: 0x" + Util.toString(result));
    return result;
  }

  public int unpad(byte[] in, int offset, int length)
      throws WrongPaddingException
  {
    int limit = offset + length;
    int result = in[--limit] & 0xFF;
    for (int i = 0; i < result - 1; i++)
      if (result != (in[--limit] & 0xFF))
        throw new WrongPaddingException();
    if (Configuration.DEBUG)
      log.fine("padding length: " + result);
    return result;
  }
}