/* UMacGenerator.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
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General Public License for more details.

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Linking this library statically or dynamically with other modules is
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package gnu.javax.crypto.prng;

import gnu.java.security.Registry;
import gnu.java.security.prng.BasePRNG;
import gnu.java.security.prng.LimitReachedException;
import gnu.javax.crypto.cipher.CipherFactory;
import gnu.javax.crypto.cipher.IBlockCipher;

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.security.InvalidKeyException;

/**
 * <i>KDF</i>s (Key Derivation Functions) are used to stretch user-supplied key
 * material to specific size(s) required by high level cryptographic primitives.
 * Described in the <A
 * HREF="http://www.ietf.org/internet-drafts/draft-krovetz-umac-01.txt">UMAC</A>
 * paper, this function basically operates an underlying <em>symmetric key block
 * cipher</em> instance in output feedback mode (OFB), as a <b>strong</b>
 * pseudo-random number generator.
 * <p>
 * <code>UMacGenerator</code> requires an <em>index</em> parameter
 * (initialisation parameter <code>gnu.crypto.prng.umac.kdf.index</code> taken
 * to be an instance of {@link Integer} with a value between <code>0</code> and
 * <code>255</code>). Using the same key, but different indices, generates
 * different pseudorandom outputs.
 * <p>
 * This implementation generalises the definition of the
 * <code>UmacGenerator</code> algorithm to allow for other than the AES
 * symetric key block cipher algorithm (initialisation parameter
 * <code>gnu.crypto.prng.umac.cipher.name</code> taken to be an instance of
 * {@link String}). If such a parameter is not defined/included in the
 * initialisation <code>Map</code>, then the "Rijndael" algorithm is used.
 * Furthermore, if the initialisation parameter
 * <code>gnu.crypto.cipher.block.size</code> (taken to be a instance of
 * {@link Integer}) is missing or undefined in the initialisation
 * <code>Map</code>, then the cipher's <em>default</em> block size is used.
 * <p>
 * <b>NOTE</b>: Rijndael is used as the default symmetric key block cipher
 * algorithm because, with its default block and key sizes, it is the AES. Yet
 * being Rijndael, the algorithm offers more versatile block and key sizes which
 * may prove to be useful for generating "longer" key streams.
 * <p>
 * References:
 * <ol>
 * <li><a href="http://www.ietf.org/internet-drafts/draft-krovetz-umac-01.txt">
 * UMAC</a>: Message Authentication Code using Universal Hashing.<br>
 * T. Krovetz, J. Black, S. Halevi, A. Hevia, H. Krawczyk, and P. Rogaway.</li>
 * </ol>
 */
public class UMacGenerator
    extends BasePRNG
    implements Cloneable
{
  /**
   * Property name of the KDF <code>index</code> value to use in this
   * instance. The value is taken to be an {@link Integer} less than
   * <code>256</code>.
   */
  public static final String INDEX = "gnu.crypto.prng.umac.index";
  /** The name of the underlying symmetric key block cipher algorithm. */
  public static final String CIPHER = "gnu.crypto.prng.umac.cipher.name";
  /** The generator's underlying block cipher. */
  private IBlockCipher cipher;

  /** Trivial 0-arguments constructor. */
  public UMacGenerator()
  {
    super(Registry.UMAC_PRNG);
  }

  public void setup(Map attributes)
  {
    boolean newCipher = true;
    String cipherName = (String) attributes.get(CIPHER);
    if (cipherName == null)
      if (cipher == null) // happy birthday
        cipher = CipherFactory.getInstance(Registry.RIJNDAEL_CIPHER);
      else // we already have one. use it as is
        newCipher = false;
    else
      cipher = CipherFactory.getInstance(cipherName);
    // find out what block size we should use it in
    int cipherBlockSize = 0;
    Integer bs = (Integer) attributes.get(IBlockCipher.CIPHER_BLOCK_SIZE);
    if (bs != null)
      cipherBlockSize = bs.intValue();
    else
      {
        if (newCipher) // assume we'll use its default block size
          cipherBlockSize = cipher.defaultBlockSize();
        // else use as is
      }
    // get the key material
    byte[] key = (byte[]) attributes.get(IBlockCipher.KEY_MATERIAL);
    if (key == null)
      throw new IllegalArgumentException(IBlockCipher.KEY_MATERIAL);

    int keyLength = key.length;
    // ensure that keyLength is valid for the chosen underlying cipher
    boolean ok = false;
    for (Iterator it = cipher.keySizes(); it.hasNext();)
      {
        ok = (keyLength == ((Integer) it.next()).intValue());
        if (ok)
          break;
      }
    if (! ok)
      throw new IllegalArgumentException("key length");
    // ensure that remaining params make sense
    int index = -1;
    Integer i = (Integer) attributes.get(INDEX);
    if (i != null)
      {
        index = i.intValue();
        if (index < 0 || index > 255)
          throw new IllegalArgumentException(INDEX);
      }
    // now initialise the underlying cipher
    Map map = new HashMap();
    if (cipherBlockSize != 0) // only needed if new or changed
      map.put(IBlockCipher.CIPHER_BLOCK_SIZE, Integer.valueOf(cipherBlockSize));
    map.put(IBlockCipher.KEY_MATERIAL, key);
    try
      {
        cipher.init(map);
      }
    catch (InvalidKeyException x)
      {
        throw new IllegalArgumentException(IBlockCipher.KEY_MATERIAL);
      }
    buffer = new byte[cipher.currentBlockSize()];
    buffer[cipher.currentBlockSize() - 1] = (byte) index;
    try
      {
        fillBlock();
      }
    catch (LimitReachedException impossible)
      {
      }
  }

  public void fillBlock() throws LimitReachedException
  {
    cipher.encryptBlock(buffer, 0, buffer, 0);
  }
}