/* UMacRandomSpi.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
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
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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
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or based on this library.  If you modify this library, you may extend
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package gnu.javax.crypto.jce.prng;

import gnu.java.security.Configuration;
import gnu.java.security.Registry;
import gnu.java.security.prng.LimitReachedException;
import gnu.javax.crypto.cipher.IBlockCipher;
import gnu.javax.crypto.prng.UMacGenerator;

import java.security.SecureRandomSpi;
import java.util.HashMap;
import java.util.Random;
import java.util.logging.Logger;

/**
 * An <em>Adapter</em> class around {@link UMacGenerator} to allow using this
 * algorithm as a JCE {@link java.security.SecureRandom}.
 */
public class UMacRandomSpi
    extends SecureRandomSpi
{
  private static final Logger log = Logger.getLogger(UMacRandomSpi.class.getName());
  /** Class-wide prng to generate random material for the underlying prng. */
  private static final UMacGenerator prng; // blank final
  static
    {
      prng = new UMacGenerator();
      resetLocalPRNG();
    }
  // error messages
  private static final String MSG = "Exception while setting up a "
                                    + Registry.UMAC_PRNG + " SPI: ";
  private static final String RETRY = "Retry...";
  /** Our underlying prng instance. */
  private UMacGenerator adaptee = new UMacGenerator();

  // default 0-arguments constructor

  private static void resetLocalPRNG()
  {
    HashMap attributes = new HashMap();
    attributes.put(UMacGenerator.CIPHER, Registry.AES_CIPHER);
    byte[] key = new byte[128 / 8]; // AES default key size
    Random rand = new Random(System.currentTimeMillis());
    rand.nextBytes(key);
    attributes.put(IBlockCipher.KEY_MATERIAL, key);
    int index = rand.nextInt() & 0xFF;
    attributes.put(UMacGenerator.INDEX, Integer.valueOf(index));
    prng.setup(attributes);
  }

  public byte[] engineGenerateSeed(int numBytes)
  {
    if (numBytes < 1)
      return new byte[0];
    byte[] result = new byte[numBytes];
    this.engineNextBytes(result);
    return result;
  }

  public void engineNextBytes(byte[] bytes)
  {
    if (! adaptee.isInitialised())
      this.engineSetSeed(new byte[0]);
    while (true)
      {
        try
          {
            adaptee.nextBytes(bytes, 0, bytes.length);
            break;
          }
        catch (LimitReachedException x)
          { // reseed the generator
            resetLocalPRNG();
          }
      }
  }

  public void engineSetSeed(byte[] seed)
  {
    // compute the total number of random bytes required to setup adaptee
    int materialLength = 0;
    materialLength += 16; // key material size
    materialLength++; // index size
    byte[] material = new byte[materialLength];
    // use as much as possible bytes from the seed
    int materialOffset = 0;
    int materialLeft = material.length;
    if (seed.length > 0)
      { // copy some bytes into key and update indices
        int lenToCopy = Math.min(materialLength, seed.length);
        System.arraycopy(seed, 0, material, 0, lenToCopy);
        materialOffset += lenToCopy;
        materialLeft -= lenToCopy;
      }
    if (materialOffset > 0) // generate the rest
      {
        while (true)
          {
            try
              {
                prng.nextBytes(material, materialOffset, materialLeft);
                break;
              }
            catch (IllegalStateException x) // should not happen
              {
                throw new InternalError(MSG + String.valueOf(x));
              }
            catch (LimitReachedException x)
              {
                if (Configuration.DEBUG)
                  {
                    log.fine(MSG + String.valueOf(x));
                    log.fine(RETRY);
                  }
              }
          }
      }
    // setup the underlying adaptee instance
    HashMap attributes = new HashMap();
    // use AES cipher with 128-bit block size
    attributes.put(UMacGenerator.CIPHER, Registry.AES_CIPHER);
    // specify the key
    byte[] key = new byte[16];
    System.arraycopy(material, 0, key, 0, 16);
    attributes.put(IBlockCipher.KEY_MATERIAL, key);
    // use a 1-byte index
    attributes.put(UMacGenerator.INDEX, Integer.valueOf(material[16] & 0xFF));
    adaptee.init(attributes);
  }
}