randomdataimpl.java

Apache的common math数学软件包

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.apache.commons.math.random;

import java.io.Serializable;
import java.security.MessageDigest;
import java.security.SecureRandom;
import java.security.NoSuchAlgorithmException;
import java.security.NoSuchProviderException;
import java.util.Collection;

/**
 * Implements the {@link RandomData} interface using a {@link RandomGenerator}
 * instance to generate non-secure data and a 
 * {@link java.security.SecureRandom} instance to provide data for the
 * <code>nextSecureXxx</code> methods.  If no <code>RandomGenerator</code>
 * is provided in the constructor, the default is to use a generator based on
 * {@link java.util.Random}.   To plug in a different implementation, 
 * either implement <code>RandomGenerator</code> directly or extend
 * {@link AbstractRandomGenerator}.
 * <p>
 * Supports reseeding the underlying pseudo-random number generator (PRNG). 
 * The <code>SecurityProvider</code> and <code>Algorithm</code>
 * used by the <code>SecureRandom</code> instance can also be reset.</p>
 * <p>
 * For details on the default PRNGs, see {@link java.util.Random} and
 * {@link java.security.SecureRandom}.</p>
 * <p>
 * <strong>Usage Notes</strong>: <ul>
 * <li>
 * Instance variables are used to maintain <code>RandomGenerator</code> and
 * <code>SecureRandom</code> instances used in data generation. Therefore,
 * to generate a random sequence of values or strings, you should use just
 * <strong>one</strong> <code>RandomDataImpl</code> instance repeatedly.</li>
 * <li>
 * The "secure" methods are *much* slower.  These should be used only when a
 * cryptographically secure random sequence is required.  A secure random
 * sequence is a sequence of pseudo-random values which, in addition to being
 * well-dispersed (so no subsequence of values is an any more likely than other
 * subsequence of the the same length), also has the additional property that
 * knowledge of values generated up to any point in the sequence does not make
 * it any easier to predict subsequent values.</li>
 * <li>
 * When a new <code>RandomDataImpl</code> is created, the underlying random
 * number generators are <strong>not</strong> intialized.  If you do not
 * explicitly seed the default non-secure generator, it is seeded with the current time
 * in milliseconds on first use.  The same holds for the secure generator.  
 * If you provide a <code>RandomGenerator</code> to the constructor, however,
 * this generator is not reseeded by the constructor nor is it reseeded on
 * first use. </li>
 * <li>
 * The <code>reSeed</code> and <code>reSeedSecure</code> methods delegate
 * to the corresponding methods on the underlying <code>RandomGenerator</code>
 * and<code>SecureRandom</code> instances.  Therefore, 
 * <code>reSeed(long)</code> fully resets the initial state of the non-secure
 * random number generator (so that reseeding with a specific value always
 * results in the same subsequent random sequence); whereas reSeedSecure(long)
 * does <strong>not</strong> reinitialize the secure random number generator
 * (so secure sequences started with calls to reseedSecure(long) won't be
 * identical).</li>
 * <li>
 * This implementation is not synchronized.
 * </ul></p>
 *
 * @version $Revision: 615734 $ $Date: 2008-01-27 23:10:03 -0700 (Sun, 27 Jan 2008) $
 */
public class RandomDataImpl implements RandomData, Serializable {

    /** Serializable version identifier */
    private static final long serialVersionUID = -626730818244969716L;

    /** underlying random number generator */
    private RandomGenerator rand = null;

    /** underlying secure random number generator */
    private SecureRandom secRand = null;

    /**
     * Construct a RandomDataImpl.
     */
    public RandomDataImpl() {
    }
    
    /**
     * Construct a RandomDataImpl using the supplied {@link RandomGenerator}
     * as the source of (non-secure) random data.
     * 
     * @param rand  the source of (non-secure) random data
     * @since 1.1
     */
    public RandomDataImpl(RandomGenerator rand) {
        super();
        this.rand = rand;
    }

    /**
     * {@inheritDoc}<p>
     * <strong>Algorithm Description:</strong> hex strings are generated
     * using a 2-step process. <ol>
     * <li>
     * len/2+1 binary bytes are generated using the underlying Random</li>
     * <li>
     * Each binary byte is translated into 2 hex digits</li></ol></p>
     * 
     * @param len the desired string length.
     * @return the random string.
     */
    public String nextHexString(int len) {
        if (len <= 0) {
            throw new IllegalArgumentException("length must be positive");
        }

        //Get a random number generator
        RandomGenerator ran = getRan();

        //Initialize output buffer
        StringBuffer outBuffer = new StringBuffer();

        //Get int(len/2)+1 random bytes
        byte[] randomBytes = new byte[(len / 2) + 1];
        ran.nextBytes(randomBytes);

        //Convert each byte to 2 hex digits
        for (int i = 0; i < randomBytes.length; i++) {
            Integer c = new Integer(randomBytes[i]);

            /* Add 128 to byte value to make interval 0-255 before
             * doing hex conversion.
             * This guarantees <= 2 hex digits from toHexString()
             * toHexString would otherwise add 2^32 to negative arguments.
             */
             String hex = Integer.toHexString(c.intValue() + 128);

             // Make sure we add 2 hex digits for each byte
             if (hex.length() == 1)  {
                 hex = "0" + hex;
             }
             outBuffer.append(hex);
        }
        return outBuffer.toString().substring(0, len);
    }

    /**
     * Generate a random int value uniformly distributed between
     * <code>lower</code> and <code>upper</code>, inclusive.
     * 
     * @param lower the lower bound.
     * @param upper the upper bound.
     * @return the random integer.
     */
    public int nextInt(int lower, int upper) {
        if (lower >= upper) {
            throw new IllegalArgumentException
                ("upper bound must be > lower bound");
        }
        RandomGenerator rand = getRan();
        double r = rand.nextDouble();
        return (int)((r * upper) + ((1.0 - r) * lower) + r);
    }

    /**
     * Generate a random long value uniformly distributed between
     * <code>lower</code> and <code>upper</code>, inclusive.
     * 
     * @param lower the lower bound.
     * @param upper the upper bound.
     * @return the random integer.
     */
    public long nextLong(long lower, long upper) {
        if (lower >= upper) {
            throw new IllegalArgumentException
                ("upper bound must be > lower bound");
        }
        RandomGenerator rand = getRan();
        double r = rand.nextDouble();
        return (long)((r * upper) + ((1.0 - r) * lower) + r);
    }

     /**
     * {@inheritDoc}<p>
     * <strong>Algorithm Description:</strong> hex strings are generated in
     * 40-byte segments using a 3-step process. <ol>
     * <li>
     * 20 random bytes are generated using the underlying
     * <code>SecureRandom</code>.</li>
     * <li>
     * SHA-1 hash is applied to yield a 20-byte binary digest.</li>
     * <li>
     * Each byte of the binary digest is converted to 2 hex digits.</li></ol>
     * </p>
     *
     * @param len the length of the generated string
     * @return the random string
     */
    public String nextSecureHexString(int len) {
        if (len <= 0) {
            throw new IllegalArgumentException("length must be positive");
        }

       // Get SecureRandom and setup Digest provider
       SecureRandom secRan = getSecRan();
       MessageDigest alg = null;
       try {
            alg = MessageDigest.getInstance("SHA-1");
       } catch (NoSuchAlgorithmException ex) {
           return null; // gulp FIXME? -- this *should* never fail.
       }
       alg.reset();

       //Compute number of iterations required (40 bytes each)
       int numIter = (len / 40) + 1;

       StringBuffer outBuffer = new StringBuffer();
       for (int iter = 1; iter < numIter + 1; iter++) {
            byte[] randomBytes = new byte[40];
            secRan.nextBytes(randomBytes);
            alg.update(randomBytes);

            //Compute hash -- will create 20-byte binary hash
            byte hash[] = alg.digest();

            //Loop over the hash, converting each byte to 2 hex digits
            for (int i = 0; i < hash.length; i++) {
                Integer c = new Integer(hash[i]);

                /* Add 128 to byte value to make interval 0-255
                 * This guarantees <= 2 hex digits from toHexString()
                 * toHexString would otherwise add 2^32 to negative
                 * arguments
                 */
                String hex = Integer.toHexString(c.intValue() + 128);

               //Keep strings uniform length -- guarantees 40 bytes
                if (hex.length() == 1) {
                    hex = "0" + hex;
                }
               outBuffer.append(hex);
            }
        }
        return outBuffer.toString().substring(0, len);
    }

    /**
     * Generate a random int value uniformly distributed between
     * <code>lower</code> and <code>upper</code>, inclusive.  This algorithm
     * uses a secure random number generator.
     * 
     * @param lower the lower bound.
     * @param upper the upper bound.
     * @return the random integer.
     */
    public int nextSecureInt(int lower, int upper) {
          if (lower >= upper) {
              throw new IllegalArgumentException
                ("lower bound must be < upper bound");
          }
          SecureRandom sec = getSecRan();
          return lower + (int) (sec.nextDouble() * (upper - lower + 1));
    }

    /**
     * Generate a random long value uniformly distributed between
     * <code>lower</code> and <code>upper</code>, inclusive.  This algorithm
     * uses a secure random number generator.
     * 
     * @param lower the lower bound.
     * @param upper the upper bound.
     * @return the random integer.
     */
    public long nextSecureLong(long lower, long upper) {
        if (lower >= upper) {
            throw new IllegalArgumentException
            ("lower bound must be < upper bound");
        }
        SecureRandom sec = getSecRan();
        return lower + (long) (sec.nextDouble() * (upper - lower + 1));
    }

    /**
     * {@inheritDoc}
     * <p>
     * <strong>Algorithm Description</strong>:
     * Uses simulation of a Poisson process using Uniform deviates, as
     * described
     * <a href="http://irmi.epfl.ch/cmos/Pmmi/interactive/rng7.htm">
     * here.</a></p>
     * <p>
     * The Poisson process (and hence value returned) is bounded by