/* TLS1.java -- TLSv1 padding scheme.
   Copyright (C) 2004, 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
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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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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
USA

Linking this library statically or dynamically with other modules is
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permission to link this library with independent modules to produce an
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independent module, the terms and conditions of the license of that
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package gnu.javax.crypto.pad;

/**
 * The padding scheme used by the Transport Layer Security protocol, version 1.
 * This padding scheme is used in the block-ciphered struct, e.g.:
 * <pre>
 *  block-ciphered struct {
 *    opaque content[TLSCompressed.length];
 *    opaque MAC[CipherSpec.hash_size];
 *    uint8 padding[GenericBlockCipher.padding_length];
 *    uint8 padding_length;
 *  } GenericBlockCipher;
 * </pre>
 * <p>
 * Where <i>padding_length</i> is any multiple of <i>cipher_block_size</i> -
 * ((<i>SSLCompressed.length</i> + <i>CipherSpec.hash_size</i>) %
 * <i>cipher_block_size</i>) - 1 that is less than 255. Every byte of the
 * padding must be equal to <i>padding_length</i>. That is, the end of the
 * plaintext is <i>n</i> + 1 copies of the unsigned byte <i>n</i>.
 */
public class TLS1
    extends BasePad
{
  public TLS1()
  {
    super("tls1");
  }

  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];
    for (int i = 0; i < padlen; i++)
      pad[i] = (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;
    for (int i = off + (len - padlen - 1); i < off + len - 1; i++)
      if ((in[i] & 0xFF) != padlen)
        throw new WrongPaddingException();
    return padlen + 1;
  }
}