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/* KDF.java --

   Copyright (C) 2003, 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.

GNU Classpath 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 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

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.javax.crypto.sasl.srp;

import gnu.java.security.Registry;

import gnu.java.security.prng.LimitReachedException;

import gnu.java.security.util.PRNG;

import gnu.javax.crypto.cipher.IBlockCipher;

import gnu.javax.crypto.prng.UMacGenerator;

import java.util.HashMap;

/**

 * The SASL-SRP KDF implementation, which is also used, depending on how it was

 * instantiated, as a secure Pseudo Random Number Generator.

 */

public class KDF

{

  private static final int AES_BLOCK_SIZE = 16; // default block size for AES

  private static final int AES_KEY_SIZE = 16; // default key size for the AES

  private static final byte[] buffer = new byte[1];

  /** Our default source of randomness. */

  private static final PRNG prng = PRNG.getInstance();

  /** The underlying UMAC Generator instance. */

  private UMacGenerator umac = null;

  /**

   * Constructs an instance of the <code>KDF</code> initialised with the

   * designated shared secret bytes.

   *

   * @param keyMaterial the SASL SRP shared secret (K) bytes.

   */

  private KDF(final byte[] keyMaterial, final int ndx)

  {

    super();

    final HashMap map = new HashMap();

    map.put(UMacGenerator.CIPHER, Registry.AES_CIPHER);

    map.put(UMacGenerator.INDEX, Integer.valueOf(ndx));

    map.put(IBlockCipher.CIPHER_BLOCK_SIZE, Integer.valueOf(AES_BLOCK_SIZE));

    final byte[] key = new byte[AES_KEY_SIZE];

    System.arraycopy(keyMaterial, 0, key, 0, AES_KEY_SIZE);

    map.put(IBlockCipher.KEY_MATERIAL, key);

    umac = new UMacGenerator();

    umac.init(map);

  }

  /**

   * A Factory mehod that returns an instance of a <code>KDF</code> based on

   * supplied seed data.

   *

   * @param K the SASL SRP shared secret for a <code>KDF</code> to be used for

   *          <i>CALG</i> and <i>IALG</i> setup. <code>null</code> otherwise.

   * @return an instance of a <code>KDF</code>.

   */

  static final KDF getInstance(final byte[] K)

  {

    int ndx = -1;

    final byte[] keyMaterial;

    if (K != null)

      {

        keyMaterial = K;

        ndx = 0;

      }

    else

      {

        keyMaterial = new byte[AES_BLOCK_SIZE];

        while (ndx < 1 || ndx > 255)

          ndx = (byte) nextByte();

      }

    return new KDF(keyMaterial, ndx);

  }

  private static synchronized final int nextByte()

  {

    prng.nextBytes(buffer);

    return (buffer[0] & 0xFF);

  }

  /**

   * Returns a designated number of bytes suitable for use in the SASL SRP

   * mechanism.

   *

   * @param length the number of bytes needed.

   * @return a byte array containing the generated/selected bytes.

   */

  public synchronized byte[] derive(final int length)

  {

    final byte[] result = new byte[length];

    try

      {

        umac.nextBytes(result, 0, length);

      }

    catch (IllegalStateException x) // should not happen

      {

        x.printStackTrace(System.err);

      }

    catch (LimitReachedException x) // idem

      {

        x.printStackTrace(System.err);

      }

    return result;

  }

}