/* SSL3.java -- SSLv3 padding scheme.
   Copyright (C) 2004  Free Software Foundation, Inc.

This file is part of GNU Crypto.

GNU Crypto 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, or (at your option) any
later version.

GNU Crypto 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 for more details.

You should have received a copy of the GNU General Public License
along with GNU Crypto; see the file COPYING.  If not, write to the
Free Software Foundation, Inc., 51 Franklin Street, 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
combination.

As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
modules, and to copy and distribute the resulting executable under
terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
module.  An independent module is a module which is not derived from
or based on this library.  If you modify this library, you may extend
this exception to your version of the library, but you are not
obligated to do so.  If you do not wish to do so, delete this
exception statement from your version. */


package gnu.crypto.pad;

import gnu.crypto.util.PRNG;

/**
 * The padding scheme used by the Secure Sockets Layer, version 3. This
 * padding scheme is used in the block-ciphered struct, e.g.:
 *
 * <pre>
 * block-ciphered struct {
 *   opaque content[SSLCompressed.length];
 *   opaque MAC[CipherSpec.hash_size];
 *   uint8 padding[GenericBlockCipher.padding_length];
 *   uint8 padding_length;
 * } GenericBlockCipher;
 * </pre>
 *
 * <p>Where <i>padding_length</i> is <i>cipher_block_size</i> -
 * ((<i>SSLCompressed.length</i> + <i>CipherSpec.hash_size</i>)
 * % <i>cipher_block_size</i>) - 1. That is, the padding is enough bytes
 * to make the plaintext a multiple of the block size minus one, plus one
 * additional byte for the padding length. The padding can be any arbitrary
 * data.</p>
 */
public class SSL3 extends BasePad
{

  // Constructors.
  // -------------------------------------------------------------------------

  public SSL3()
  {
    super ("ssl3");
  }

  // Instance methods.
  // -------------------------------------------------------------------------

  public void setup()
  {
    if (blockSize <= 0 || blockSize > 255)
      throw new IllegalArgumentException ("invalid block size: " + blockSize);
  }

  public byte[] pad (final byte[] in, final int off, final int len)
  {
    int padlen = blockSize - (len % blockSize);
    byte[] pad = new byte[padlen];
    // FIXME this seems to hang during 'make check'.
//     PRNG.nextBytes (pad, 0, padlen - 1);
    pad[padlen - 1] = (byte) (padlen - 1);
    return pad;
  }

  public int unpad (final byte[] in, final int off, final int len)
    throws WrongPaddingException
  {
    int padlen = in[off+len-1] & 0xFF;
    if (padlen >= blockSize)
      throw new WrongPaddingException();
    return padlen + 1;
  }
}
