Hash.java

/*
 * Copyright 2012 JBoss, by Red Hat, Inc
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.jboss.pitbull.internal.nio.websocket.impl.oio.internal.util;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.SecureRandom;

/**
 * @author Mike Brock
 */
public final class Hash
{
   private Hash()
   {
   }

   final static String secureRandomAlgorithm = "SHA1PRNG";
   final static String hashAlgorithm = "SHA1";
   private final static ThreadLocal<SecureRandom> random = new ThreadLocal<SecureRandom>();

   private static SecureRandom createRandom()
   {
      try
      {
         SecureRandom random = SecureRandom.getInstance(secureRandomAlgorithm);
         random.setSeed(SecureRandom.getInstance(secureRandomAlgorithm).generateSeed(64));
         return random;
      }
      catch (NoSuchAlgorithmException e)
      {
         throw new RuntimeException("runtime does not support secure random algorithm: " + secureRandomAlgorithm);
      }
   }

   private static SecureRandom getRandom()
   {
      SecureRandom r = random.get();
      if (r == null)
      {
         r = createRandom();
         random.set(r);
      }
      return r;
   }

   public static int nextInt(int max)
   {
      return getRandom().nextInt(max);
   }

   public static void getRandomBytes(byte[] bytes)
   {
      getRandom().nextBytes(bytes);
   }

   public static String newUniqueHash()
   {
      return nextSecureHash(hashAlgorithm, SecureRandom.getSeed(128));
   }

   private static String nextSecureHash(final String algorithm, final byte[] additionalSeed)
   {
      try
      {
         final MessageDigest md = MessageDigest.getInstance(algorithm);

         md.update(String.valueOf(System.nanoTime()).getBytes());

         if (additionalSeed != null)
         {
            md.update(additionalSeed);
         }

         byte[] randBytes = new byte[64];
         getRandom().nextBytes(randBytes);

         // 1,000 rounds.
         for (int i = 0; i < 1000; i++)
         {
            md.update(md.digest());
         }

         return hashToHexString(md.digest());
      }
      catch (Exception e)
      {
         throw new RuntimeException("failed to generate session id hash", e);
      }
   }

   private static String hashToHexString(byte[] hash)
   {
      final StringBuilder hexString = new StringBuilder(hash.length);
      for (byte mdbyte : hash)
      {
         hexString.append(Integer.toHexString(0xFF & mdbyte));
      }
      return hexString.toString();
   }

}