/* AESKeyWrapSpi.java -- Common AES Key Wrapping Algorithm methods
   Copyright (C) 2006 Free Software Foundation, Inc.

This file is 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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package gnu.javax.crypto.jce.cipher;

/**
 * Base abstract class to group common AES Key Wrapping Algorithm Adapter
 * methods.
 */
abstract class AESKeyWrapSpi
    extends KeyWrappingAlgorithmAdapter
{
  protected AESKeyWrapSpi(String name, int keySize, String supportedMode)
  {
    super(name, 16, keySize, supportedMode);
  }

  /**
   * AES Key Wrapping algorithms operate on an 8-byte block; a block half the
   * size of the AES block itself.
   * <p>
   * In wrapping, the number of 8-byte output blocks is ALWAYS one block longer
   * than the input.
   * 
   * @param inputLength the size of the plain text.
   * @return the size in bytes of <code>n + 1</code> 8-byte blocks where
   * <code>n</code> is the smallest number of 8-byte blocks that contain the
   * designated number of input bytes.
   */
  protected int getOutputSizeForWrap(int inputLength)
  {
    int n = (inputLength + 7) / 8;
    return 8 * (n + 1);
  }

  /**
   * AES Key Wrapping algorithms operate on an 8-byte block; a block half the
   * size of the AES block itself.
   * <p>
   * In unwrapping, the number of 8-byte output blocks is ALWAYS one block
   * shorter than the input.
   * 
   * @param inputLength the size of the cipher text.
   * @return the size in bytes of <code>n - 1</code> 8-byte blocks where
   * <code>n</code> is the smallest number of 8-byte blocks that contain the
   * designated number of input bytes.
   */
  protected int getOutputSizeForUnwrap(int inputLength)
  {
    int n = (inputLength + 7) / 8;
    return 8 * (n - 1);
  }
}