/* ICMRandomSpi.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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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
making a combined work based on this library.  Thus, the terms and
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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
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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.ICMGenerator;

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

/**
 * An <em>Adapter</em> class around {@link ICMGenerator} to allow using this
 * algorithm as a JCE {@link java.security.SecureRandom}.
 */
public class ICMRandomSpi
    extends SecureRandomSpi
{
  private static final Logger log = Logger.getLogger(ICMRandomSpi.class.getName());
  /** Class-wide prng to generate random material for the underlying prng. */
  private static final ICMGenerator prng; // blank final
  static
    {
      prng = new ICMGenerator();
      resetLocalPRNG();
    }

  // error messages
  private static final String MSG = "Exception while setting up an "
                                    + Registry.ICM_PRNG + " SPI: ";
  private static final String RETRY = "Retry...";
  private static final String LIMIT_REACHED_MSG = "Limit reached: ";
  private static final String RESEED = "Re-seed...";
  /** Our underlying prng instance. */
  private ICMGenerator adaptee = new ICMGenerator();

  // default 0-arguments constructor

  private static void resetLocalPRNG()
  {
    if (Configuration.DEBUG)
      log.entering(ICMRandomSpi.class.getName(), "resetLocalPRNG");
    HashMap attributes = new HashMap();
    attributes.put(ICMGenerator.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 aesBlockSize = 128 / 8; // AES block size in bytes
    byte[] offset = new byte[aesBlockSize];
    rand.nextBytes(offset);
    attributes.put(ICMGenerator.OFFSET, offset);
    int ndxLen = 0; // the segment length
    // choose a random value between 1 and aesBlockSize / 2
    int limit = aesBlockSize / 2;
    while (ndxLen < 1 || ndxLen > limit)
      ndxLen = rand.nextInt(limit + 1);
    attributes.put(ICMGenerator.SEGMENT_INDEX_LENGTH, Integer.valueOf(ndxLen));
    byte[] index = new byte[ndxLen];
    rand.nextBytes(index);
    attributes.put(ICMGenerator.SEGMENT_INDEX, new BigInteger(1, index));
    prng.setup(attributes);
    if (Configuration.DEBUG)
      log.exiting(ICMRandomSpi.class.getName(), "resetLocalPRNG");
  }

  public byte[] engineGenerateSeed(int numBytes)
  {
    if (Configuration.DEBUG)
      log.entering(this.getClass().getName(), "engineGenerateSeed");
    if (numBytes < 1)
      {
        if (Configuration.DEBUG)
          log.exiting(this.getClass().getName(), "engineGenerateSeed");
        return new byte[0];
      }
    byte[] result = new byte[numBytes];
    this.engineNextBytes(result);
    if (Configuration.DEBUG)
      log.exiting(this.getClass().getName(), "engineGenerateSeed");
    return result;
  }

  public void engineNextBytes(byte[] bytes)
  {
    if (Configuration.DEBUG)
      log.entering(this.getClass().getName(), "engineNextBytes");
    if (! adaptee.isInitialised())
      this.engineSetSeed(new byte[0]);
    while (true)
      {
        try
          {
            adaptee.nextBytes(bytes, 0, bytes.length);
            break;
          }
        catch (LimitReachedException x)
          { // reseed the generator
            if (Configuration.DEBUG)
              {
                log.fine(LIMIT_REACHED_MSG + String.valueOf(x));
                log.fine(RESEED);
              }
            resetLocalPRNG();
          }
      }
    if (Configuration.DEBUG)
      log.exiting(this.getClass().getName(), "engineNextBytes");
  }

  public void engineSetSeed(byte[] seed)
  {
    if (Configuration.DEBUG)
      log.entering(this.getClass().getName(), "engineSetSeed");
    // compute the total number of random bytes required to setup adaptee
    int materialLength = 0;
    materialLength += 16; // key material size
    materialLength += 16; // offset size
    materialLength += 8; // index size == half of an AES block
    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(ICMGenerator.CIPHER, Registry.AES_CIPHER);
    // use an index the size of quarter of an AES block
    attributes.put(ICMGenerator.SEGMENT_INDEX_LENGTH, Integer.valueOf(4));
    // specify the key
    byte[] key = new byte[16];
    System.arraycopy(material, 0, key, 0, 16);
    attributes.put(IBlockCipher.KEY_MATERIAL, key);
    // specify the offset
    byte[] offset = new byte[16];
    System.arraycopy(material, 16, offset, 0, 16);
    attributes.put(ICMGenerator.OFFSET, offset);
    // specify the index
    byte[] index = new byte[8];
    System.arraycopy(material, 32, index, 0, 8);
    attributes.put(ICMGenerator.SEGMENT_INDEX, new BigInteger(1, index));
    adaptee.init(attributes);
    if (Configuration.DEBUG)
      log.exiting(this.getClass().getName(), "engineSetSeed");
  }
}