https://openjdk.java.net/ 
/*
 * Copyright (c) 1996, 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code 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
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 */

package java.security;

import java.util.*;
import java.util.regex.*;

import java.security.Provider.Service;

import sun.security.jca.*;
import sun.security.jca.GetInstance.Instance;
import sun.security.util.Debug;


This class provides a cryptographically strong random number
generator (RNG).

A cryptographically strong random number
minimally complies with the statistical random number generator tests
specified in 
FIPS 140-2, Security Requirements for Cryptographic Modules,
section 4.9.1.
Additionally, SecureRandom must produce non-deterministic output.
Therefore any seed material passed to a SecureRandom object must be
unpredictable, and all SecureRandom output sequences must be
cryptographically strong, as described in

RFC 1750: Randomness Recommendations for Security.

A caller obtains a SecureRandom instance via the no-argument constructor or one of the getInstance methods: 
     SecureRandom random = new SecureRandom();



 Many SecureRandom implementations are in the form of a pseudo-random
number generator (PRNG), which means they use a deterministic algorithm
to produce a pseudo-random sequence from a true random seed.
Other implementations may produce true random numbers,
and yet others may use a combination of both techniques.

 Typical callers of SecureRandom invoke the following methods
to retrieve random bytes:

     SecureRandom random = new SecureRandom();
     byte bytes[] = new byte[20];
     random.nextBytes(bytes);



 Callers may also invoke the generateSeed method to generate a given number of seed bytes (to seed other random number generators, for example): 
     byte seed[] = random.generateSeed(20);

 Note: Depending on the implementation, the generateSeed and nextBytes methods may block as entropy is being gathered, for example, if they need to read from /dev/random on various Unix-like operating systems. 
Author:Benjamin Renaud, Josh Bloch
See Also:
/**
 * This class provides a cryptographically strong random number
 * generator (RNG).
 *
 * <p>A cryptographically strong random number
 * minimally complies with the statistical random number generator tests
 * specified in <a href="http://csrc.nist.gov/cryptval/140-2.htm">
 * <i>FIPS 140-2, Security Requirements for Cryptographic Modules</i></a>,
 * section 4.9.1.
 * Additionally, SecureRandom must produce non-deterministic output.
 * Therefore any seed material passed to a SecureRandom object must be
 * unpredictable, and all SecureRandom output sequences must be
 * cryptographically strong, as described in
 * <a href="http://www.ietf.org/rfc/rfc1750.txt">
 * <i>RFC 1750: Randomness Recommendations for Security</i></a>.
 *
 * <p>A caller obtains a SecureRandom instance via the
 * no-argument constructor or one of the {@code getInstance} methods:
 *
 * <pre>
 *      SecureRandom random = new SecureRandom();
 * </pre>
 *
 * <p> Many SecureRandom implementations are in the form of a pseudo-random
 * number generator (PRNG), which means they use a deterministic algorithm
 * to produce a pseudo-random sequence from a true random seed.
 * Other implementations may produce true random numbers,
 * and yet others may use a combination of both techniques.
 *
 * <p> Typical callers of SecureRandom invoke the following methods
 * to retrieve random bytes:
 *
 * <pre>
 *      SecureRandom random = new SecureRandom();
 *      byte bytes[] = new byte[20];
 *      random.nextBytes(bytes);
 * </pre>
 *
 * <p> Callers may also invoke the {@code generateSeed} method
 * to generate a given number of seed bytes (to seed other random number
 * generators, for example):
 * <pre>
 *      byte seed[] = random.generateSeed(20);
 * </pre>
 *
 * Note: Depending on the implementation, the {@code generateSeed} and
 * {@code nextBytes} methods may block as entropy is being gathered,
 * for example, if they need to read from /dev/random on various Unix-like
 * operating systems.
 *
 * @see java.security.SecureRandomSpi
 * @see java.util.Random
 *
 * @author Benjamin Renaud
 * @author Josh Bloch
 */

public class SecureRandom extends java.util.Random {

    private static final Debug pdebug =
                        Debug.getInstance("provider", "Provider");
    private static final boolean skipDebug =
        Debug.isOn("engine=") && !Debug.isOn("securerandom");

    
The provider.

@serial
Since:1.2
/**
     * The provider.
     *
     * @serial
     * @since 1.2
     */
    private Provider provider = null;

    
The provider implementation.

@serial
Since:1.2
/**
     * The provider implementation.
     *
     * @serial
     * @since 1.2
     */
    private SecureRandomSpi secureRandomSpi = null;

    /*
     * The algorithm name of null if unknown.
     *
     * @serial
     * @since 1.5
     */
    private String algorithm;

    // Seed Generator
    private static volatile SecureRandom seedGenerator = null;

    
Constructs a secure random number generator (RNG) implementing the
default random number algorithm.

 This constructor traverses the list of registered security Providers,
starting with the most preferred Provider.
A new SecureRandom object encapsulating the
SecureRandomSpi implementation from the first
Provider that supports a SecureRandom (RNG) algorithm is returned.
If none of the Providers support a RNG algorithm,
then an implementation-specific default is returned.

 Note that the list of registered providers may be retrieved via the Security.getProviders() method. 
 See the SecureRandom section in the 
Java Cryptography Architecture Standard Algorithm Name Documentation
for information about standard RNG algorithm names.

 The returned SecureRandom object has not been seeded. To seed the returned object, call the setSeed method. If setSeed is not called, the first call to nextBytes will force the SecureRandom object to seed itself. This self-seeding will not occur if setSeed was previously called. 
/**
     * Constructs a secure random number generator (RNG) implementing the
     * default random number algorithm.
     *
     * <p> This constructor traverses the list of registered security Providers,
     * starting with the most preferred Provider.
     * A new SecureRandom object encapsulating the
     * SecureRandomSpi implementation from the first
     * Provider that supports a SecureRandom (RNG) algorithm is returned.
     * If none of the Providers support a RNG algorithm,
     * then an implementation-specific default is returned.
     *
     * <p> Note that the list of registered providers may be retrieved via
     * the {@link Security#getProviders() Security.getProviders()} method.
     *
     * <p> See the SecureRandom section in the <a href=
     * "{@docRoot}/../technotes/guides/security/StandardNames.html#SecureRandom">
     * Java Cryptography Architecture Standard Algorithm Name Documentation</a>
     * for information about standard RNG algorithm names.
     *
     * <p> The returned SecureRandom object has not been seeded.  To seed the
     * returned object, call the {@code setSeed} method.
     * If {@code setSeed} is not called, the first call to
     * {@code nextBytes} will force the SecureRandom object to seed itself.
     * This self-seeding will not occur if {@code setSeed} was
     * previously called.
     */
    public SecureRandom() {
        /*
         * This call to our superclass constructor will result in a call
         * to our own {@code setSeed} method, which will return
         * immediately when it is passed zero.
         */
        super(0);
        getDefaultPRNG(false, null);
    }

    
Constructs a secure random number generator (RNG) implementing the
default random number algorithm.
The SecureRandom instance is seeded with the specified seed bytes.

 This constructor traverses the list of registered security Providers,
starting with the most preferred Provider.
A new SecureRandom object encapsulating the
SecureRandomSpi implementation from the first
Provider that supports a SecureRandom (RNG) algorithm is returned.
If none of the Providers support a RNG algorithm,
then an implementation-specific default is returned.

 Note that the list of registered providers may be retrieved via the Security.getProviders() method. 
 See the SecureRandom section in the 
Java Cryptography Architecture Standard Algorithm Name Documentation
for information about standard RNG algorithm names.

Params:
  • seed – the seed.
/**
     * Constructs a secure random number generator (RNG) implementing the
     * default random number algorithm.
     * The SecureRandom instance is seeded with the specified seed bytes.
     *
     * <p> This constructor traverses the list of registered security Providers,
     * starting with the most preferred Provider.
     * A new SecureRandom object encapsulating the
     * SecureRandomSpi implementation from the first
     * Provider that supports a SecureRandom (RNG) algorithm is returned.
     * If none of the Providers support a RNG algorithm,
     * then an implementation-specific default is returned.
     *
     * <p> Note that the list of registered providers may be retrieved via
     * the {@link Security#getProviders() Security.getProviders()} method.
     *
     * <p> See the SecureRandom section in the <a href=
     * "{@docRoot}/../technotes/guides/security/StandardNames.html#SecureRandom">
     * Java Cryptography Architecture Standard Algorithm Name Documentation</a>
     * for information about standard RNG algorithm names.
     *
     * @param seed the seed.
     */
    public SecureRandom(byte seed[]) {
        super(0);
        getDefaultPRNG(true, seed);
    }

    private void getDefaultPRNG(boolean setSeed, byte[] seed) {
        String prng = getPrngAlgorithm();
        if (prng == null) {
            // bummer, get the SUN implementation
            prng = "SHA1PRNG";
            this.secureRandomSpi = new sun.security.provider.SecureRandom();
            this.provider = Providers.getSunProvider();
            if (setSeed) {
                this.secureRandomSpi.engineSetSeed(seed);
            }
        } else {
            try {
                SecureRandom random = SecureRandom.getInstance(prng);
                this.secureRandomSpi = random.getSecureRandomSpi();
                this.provider = random.getProvider();
                if (setSeed) {
                    this.secureRandomSpi.engineSetSeed(seed);
                }
            } catch (NoSuchAlgorithmException nsae) {
                // never happens, because we made sure the algorithm exists
                throw new RuntimeException(nsae);
            }
        }
        // JDK 1.1 based implementations subclass SecureRandom instead of
        // SecureRandomSpi. They will also go through this code path because
        // they must call a SecureRandom constructor as it is their superclass.
        // If we are dealing with such an implementation, do not set the
        // algorithm value as it would be inaccurate.
        if (getClass() == SecureRandom.class) {
            this.algorithm = prng;
        }
    }

    
Creates a SecureRandom object.

Params:
  • secureRandomSpi – the SecureRandom implementation.
  • provider – the provider.
/**
     * Creates a SecureRandom object.
     *
     * @param secureRandomSpi the SecureRandom implementation.
     * @param provider the provider.
     */
    protected SecureRandom(SecureRandomSpi secureRandomSpi,
                           Provider provider) {
        this(secureRandomSpi, provider, null);
    }

    private SecureRandom(SecureRandomSpi secureRandomSpi, Provider provider,
            String algorithm) {
        super(0);
        this.secureRandomSpi = secureRandomSpi;
        this.provider = provider;
        this.algorithm = algorithm;

        if (!skipDebug && pdebug != null) {
            pdebug.println("SecureRandom." + algorithm +
                " algorithm from: " + this.provider.getName());
        }
    }

    
Returns a SecureRandom object that implements the specified
Random Number Generator (RNG) algorithm.

 This method traverses the list of registered security Providers,
starting with the most preferred Provider.
A new SecureRandom object encapsulating the
SecureRandomSpi implementation from the first
Provider that supports the specified algorithm is returned.

 Note that the list of registered providers may be retrieved via the Security.getProviders() method. 
 The returned SecureRandom object has not been seeded. To seed the returned object, call the setSeed method. If setSeed is not called, the first call to nextBytes will force the SecureRandom object to seed itself. This self-seeding will not occur if setSeed was previously called. 
Params:
Throws:
See Also:
Returns:the new SecureRandom object.
Since:1.2
/**
     * Returns a SecureRandom object that implements the specified
     * Random Number Generator (RNG) algorithm.
     *
     * <p> This method traverses the list of registered security Providers,
     * starting with the most preferred Provider.
     * A new SecureRandom object encapsulating the
     * SecureRandomSpi implementation from the first
     * Provider that supports the specified algorithm is returned.
     *
     * <p> Note that the list of registered providers may be retrieved via
     * the {@link Security#getProviders() Security.getProviders()} method.
     *
     * <p> The returned SecureRandom object has not been seeded.  To seed the
     * returned object, call the {@code setSeed} method.
     * If {@code setSeed} is not called, the first call to
     * {@code nextBytes} will force the SecureRandom object to seed itself.
     * This self-seeding will not occur if {@code setSeed} was
     * previously called.
     *
     * @param algorithm the name of the RNG algorithm.
     * See the SecureRandom section in the <a href=
     * "{@docRoot}/../technotes/guides/security/StandardNames.html#SecureRandom">
     * Java Cryptography Architecture Standard Algorithm Name Documentation</a>
     * for information about standard RNG algorithm names.
     *
     * @return the new SecureRandom object.
     *
     * @exception NoSuchAlgorithmException if no Provider supports a
     *          SecureRandomSpi implementation for the
     *          specified algorithm.
     *
     * @see Provider
     *
     * @since 1.2
     */
    public static SecureRandom getInstance(String algorithm)
            throws NoSuchAlgorithmException {
        Instance instance = GetInstance.getInstance("SecureRandom",
            SecureRandomSpi.class, algorithm);
        return new SecureRandom((SecureRandomSpi)instance.impl,
            instance.provider, algorithm);
    }

    
Returns a SecureRandom object that implements the specified
Random Number Generator (RNG) algorithm.

 A new SecureRandom object encapsulating the
SecureRandomSpi implementation from the specified provider
is returned.  The specified provider must be registered
in the security provider list.

 Note that the list of registered providers may be retrieved via the Security.getProviders() method. 
 The returned SecureRandom object has not been seeded. To seed the returned object, call the setSeed method. If setSeed is not called, the first call to nextBytes will force the SecureRandom object to seed itself. This self-seeding will not occur if setSeed was previously called. 
Params:
Throws:
See Also:
Returns:the new SecureRandom object.
Since:1.2
/**
     * Returns a SecureRandom object that implements the specified
     * Random Number Generator (RNG) algorithm.
     *
     * <p> A new SecureRandom object encapsulating the
     * SecureRandomSpi implementation from the specified provider
     * is returned.  The specified provider must be registered
     * in the security provider list.
     *
     * <p> Note that the list of registered providers may be retrieved via
     * the {@link Security#getProviders() Security.getProviders()} method.
     *
     * <p> The returned SecureRandom object has not been seeded.  To seed the
     * returned object, call the {@code setSeed} method.
     * If {@code setSeed} is not called, the first call to
     * {@code nextBytes} will force the SecureRandom object to seed itself.
     * This self-seeding will not occur if {@code setSeed} was
     * previously called.
     *
     * @param algorithm the name of the RNG algorithm.
     * See the SecureRandom section in the <a href=
     * "{@docRoot}/../technotes/guides/security/StandardNames.html#SecureRandom">
     * Java Cryptography Architecture Standard Algorithm Name Documentation</a>
     * for information about standard RNG algorithm names.
     *
     * @param provider the name of the provider.
     *
     * @return the new SecureRandom object.
     *
     * @exception NoSuchAlgorithmException if a SecureRandomSpi
     *          implementation for the specified algorithm is not
     *          available from the specified provider.
     *
     * @exception NoSuchProviderException if the specified provider is not
     *          registered in the security provider list.
     *
     * @exception IllegalArgumentException if the provider name is null
     *          or empty.
     *
     * @see Provider
     *
     * @since 1.2
     */
    public static SecureRandom getInstance(String algorithm, String provider)
            throws NoSuchAlgorithmException, NoSuchProviderException {
        Instance instance = GetInstance.getInstance("SecureRandom",
            SecureRandomSpi.class, algorithm, provider);
        return new SecureRandom((SecureRandomSpi)instance.impl,
            instance.provider, algorithm);
    }

    
Returns a SecureRandom object that implements the specified
Random Number Generator (RNG) algorithm.

 A new SecureRandom object encapsulating the
SecureRandomSpi implementation from the specified Provider
object is returned.  Note that the specified Provider object
does not have to be registered in the provider list.

 The returned SecureRandom object has not been seeded. To seed the returned object, call the setSeed method. If setSeed is not called, the first call to nextBytes will force the SecureRandom object to seed itself. This self-seeding will not occur if setSeed was previously called. 
Params:
Throws:
See Also:
Returns:the new SecureRandom object.
Since:1.4
/**
     * Returns a SecureRandom object that implements the specified
     * Random Number Generator (RNG) algorithm.
     *
     * <p> A new SecureRandom object encapsulating the
     * SecureRandomSpi implementation from the specified Provider
     * object is returned.  Note that the specified Provider object
     * does not have to be registered in the provider list.
     *
     * <p> The returned SecureRandom object has not been seeded.  To seed the
     * returned object, call the {@code setSeed} method.
     * If {@code setSeed} is not called, the first call to
     * {@code nextBytes} will force the SecureRandom object to seed itself.
     * This self-seeding will not occur if {@code setSeed} was
     * previously called.
     *
     * @param algorithm the name of the RNG algorithm.
     * See the SecureRandom section in the <a href=
     * "{@docRoot}/../technotes/guides/security/StandardNames.html#SecureRandom">
     * Java Cryptography Architecture Standard Algorithm Name Documentation</a>
     * for information about standard RNG algorithm names.
     *
     * @param provider the provider.
     *
     * @return the new SecureRandom object.
     *
     * @exception NoSuchAlgorithmException if a SecureRandomSpi
     *          implementation for the specified algorithm is not available
     *          from the specified Provider object.
     *
     * @exception IllegalArgumentException if the specified provider is null.
     *
     * @see Provider
     *
     * @since 1.4
     */
    public static SecureRandom getInstance(String algorithm,
            Provider provider) throws NoSuchAlgorithmException {
        Instance instance = GetInstance.getInstance("SecureRandom",
            SecureRandomSpi.class, algorithm, provider);
        return new SecureRandom((SecureRandomSpi)instance.impl,
            instance.provider, algorithm);
    }

    
Returns the SecureRandomSpi of this SecureRandom object.

/**
     * Returns the SecureRandomSpi of this SecureRandom object.
     */
    SecureRandomSpi getSecureRandomSpi() {
        return secureRandomSpi;
    }

    
Returns the provider of this SecureRandom object.

Returns:the provider of this SecureRandom object.
/**
     * Returns the provider of this SecureRandom object.
     *
     * @return the provider of this SecureRandom object.
     */
    public final Provider getProvider() {
        return provider;
    }

    
Returns the name of the algorithm implemented by this SecureRandom
object.

Returns:the name of the algorithm or unknown if the algorithm name cannot be determined.
Since:1.5
/**
     * Returns the name of the algorithm implemented by this SecureRandom
     * object.
     *
     * @return the name of the algorithm or {@code unknown}
     *          if the algorithm name cannot be determined.
     * @since 1.5
     */
    public String getAlgorithm() {
        return (algorithm != null) ? algorithm : "unknown";
    }

    
Reseeds this random object. The given seed supplements, rather than
replaces, the existing seed. Thus, repeated calls are guaranteed
never to reduce randomness.

Params:
  • seed – the seed.
See Also:
/**
     * Reseeds this random object. The given seed supplements, rather than
     * replaces, the existing seed. Thus, repeated calls are guaranteed
     * never to reduce randomness.
     *
     * @param seed the seed.
     *
     * @see #getSeed
     */
    synchronized public void setSeed(byte[] seed) {
        secureRandomSpi.engineSetSeed(seed);
    }

    
Reseeds this random object, using the eight bytes contained in the given long seed. The given seed supplements, rather than replaces, the existing seed. Thus, repeated calls are guaranteed never to reduce randomness. 
This method is defined for compatibility with java.util.Random. 
Params:
  • seed – the seed.
See Also:
/**
     * Reseeds this random object, using the eight bytes contained
     * in the given {@code long seed}. The given seed supplements,
     * rather than replaces, the existing seed. Thus, repeated calls
     * are guaranteed never to reduce randomness.
     *
     * <p>This method is defined for compatibility with
     * {@code java.util.Random}.
     *
     * @param seed the seed.
     *
     * @see #getSeed
     */
    @Override
    public void setSeed(long seed) {
        /*
         * Ignore call from super constructor (as well as any other calls
         * unfortunate enough to be passing 0).  It's critical that we
         * ignore call from superclass constructor, as digest has not
         * yet been initialized at that point.
         */
        if (seed != 0) {
            secureRandomSpi.engineSetSeed(longToByteArray(seed));
        }
    }

    
Generates a user-specified number of random bytes.

 If a call to setSeed had not occurred previously, the first call to this method forces this SecureRandom object to seed itself. This self-seeding will not occur if setSeed was previously called. 
Params:
  • bytes – the array to be filled in with random bytes.
/**
     * Generates a user-specified number of random bytes.
     *
     * <p> If a call to {@code setSeed} had not occurred previously,
     * the first call to this method forces this SecureRandom object
     * to seed itself.  This self-seeding will not occur if
     * {@code setSeed} was previously called.
     *
     * @param bytes the array to be filled in with random bytes.
     */
    @Override
    public void nextBytes(byte[] bytes) {
        secureRandomSpi.engineNextBytes(bytes);
    }

    
Generates an integer containing the user-specified number of pseudo-random bits (right justified, with leading zeros). This method overrides a java.util.Random method, and serves to provide a source of random bits to all of the methods inherited from that class (for example, nextInt, nextLong, and nextFloat). 
Params:
  • numBits – number of pseudo-random bits to be generated, where 0 <= numBits <= 32.
Returns:an int containing the user-specified number of pseudo-random bits (right justified, with leading zeros).
/**
     * Generates an integer containing the user-specified number of
     * pseudo-random bits (right justified, with leading zeros).  This
     * method overrides a {@code java.util.Random} method, and serves
     * to provide a source of random bits to all of the methods inherited
     * from that class (for example, {@code nextInt},
     * {@code nextLong}, and {@code nextFloat}).
     *
     * @param numBits number of pseudo-random bits to be generated, where
     * {@code 0 <= numBits <= 32}.
     *
     * @return an {@code int} containing the user-specified number
     * of pseudo-random bits (right justified, with leading zeros).
     */
    @Override
    final protected int next(int numBits) {
        int numBytes = (numBits+7)/8;
        byte b[] = new byte[numBytes];
        int next = 0;

        nextBytes(b);
        for (int i = 0; i < numBytes; i++) {
            next = (next << 8) + (b[i] & 0xFF);
        }

        return next >>> (numBytes*8 - numBits);
    }

    
Returns the given number of seed bytes, computed using the seed
generation algorithm that this class uses to seed itself.  This
call may be used to seed other random number generators.

This method is only included for backwards compatibility. The caller is encouraged to use one of the alternative getInstance methods to obtain a SecureRandom object, and then call the generateSeed method to obtain seed bytes from that object. 
Params:
  • numBytes – the number of seed bytes to generate.
See Also:
Returns:the seed bytes.
/**
     * Returns the given number of seed bytes, computed using the seed
     * generation algorithm that this class uses to seed itself.  This
     * call may be used to seed other random number generators.
     *
     * <p>This method is only included for backwards compatibility.
     * The caller is encouraged to use one of the alternative
     * {@code getInstance} methods to obtain a SecureRandom object, and
     * then call the {@code generateSeed} method to obtain seed bytes
     * from that object.
     *
     * @param numBytes the number of seed bytes to generate.
     *
     * @return the seed bytes.
     *
     * @see #setSeed
     */
    public static byte[] getSeed(int numBytes) {
        if (seedGenerator == null) {
            seedGenerator = new SecureRandom();
        }
        return seedGenerator.generateSeed(numBytes);
    }

    
Returns the given number of seed bytes, computed using the seed
generation algorithm that this class uses to seed itself.  This
call may be used to seed other random number generators.

Params:
  • numBytes – the number of seed bytes to generate.
Returns:the seed bytes.
/**
     * Returns the given number of seed bytes, computed using the seed
     * generation algorithm that this class uses to seed itself.  This
     * call may be used to seed other random number generators.
     *
     * @param numBytes the number of seed bytes to generate.
     *
     * @return the seed bytes.
     */
    public byte[] generateSeed(int numBytes) {
        return secureRandomSpi.engineGenerateSeed(numBytes);
    }

    
Helper function to convert a long into a byte array (least significant
byte first).

/**
     * Helper function to convert a long into a byte array (least significant
     * byte first).
     */
    private static byte[] longToByteArray(long l) {
        byte[] retVal = new byte[8];

        for (int i = 0; i < 8; i++) {
            retVal[i] = (byte) l;
            l >>= 8;
        }

        return retVal;
    }

    
Gets a default PRNG algorithm by looking through all registered
providers. Returns the first PRNG algorithm of the first provider that
has registered a SecureRandom implementation, or null if none of the
registered providers supplies a SecureRandom implementation.

/**
     * Gets a default PRNG algorithm by looking through all registered
     * providers. Returns the first PRNG algorithm of the first provider that
     * has registered a SecureRandom implementation, or null if none of the
     * registered providers supplies a SecureRandom implementation.
     */
    private static String getPrngAlgorithm() {
        for (Provider p : Providers.getProviderList().providers()) {
            for (Service s : p.getServices()) {
                if (s.getType().equals("SecureRandom")) {
                    return s.getAlgorithm();
                }
            }
        }
        return null;
    }

    /*
     * Lazily initialize since Pattern.compile() is heavy.
     * Effective Java (2nd Edition), Item 71.
     */
    private static final class StrongPatternHolder {
        /*
         * Entries are alg:prov separated by ,
         * Allow for prepended/appended whitespace between entries.
         *
         * Capture groups:
         *     1 - alg
         *     2 - :prov (optional)
         *     3 - prov (optional)
         *     4 - ,nextEntry (optional)
         *     5 - nextEntry (optional)
         */
        private static Pattern pattern =
            Pattern.compile(
                "\\s*([\\S&&[^:,]]*)(\\:([\\S&&[^,]]*))?\\s*(\\,(.*))?");
    }

    
Returns a SecureRandom object that was selected by using the algorithms/providers specified in the 
securerandom.strongAlgorithms Security property. 
 Some situations require strong random values, such as when creating high-value/long-lived secrets like RSA public/private keys. To help guide applications in selecting a suitable strong SecureRandom implementation, Java distributions include a list of known strong SecureRandom implementations in the securerandom.strongAlgorithms Security property. 
 Every implementation of the Java platform is required to support at least one strong SecureRandom implementation. 
Throws:
See Also:
Returns:a strong SecureRandom implementation as indicated by the securerandom.strongAlgorithms Security property
Since:1.8
/**
     * Returns a {@code SecureRandom} object that was selected by using
     * the algorithms/providers specified in the {@code
     * securerandom.strongAlgorithms} {@link Security} property.
     * <p>
     * Some situations require strong random values, such as when
     * creating high-value/long-lived secrets like RSA public/private
     * keys.  To help guide applications in selecting a suitable strong
     * {@code SecureRandom} implementation, Java distributions
     * include a list of known strong {@code SecureRandom}
     * implementations in the {@code securerandom.strongAlgorithms}
     * Security property.
     * <p>
     * Every implementation of the Java platform is required to
     * support at least one strong {@code SecureRandom} implementation.
     *
     * @return a strong {@code SecureRandom} implementation as indicated
     * by the {@code securerandom.strongAlgorithms} Security property
     *
     * @throws NoSuchAlgorithmException if no algorithm is available
     *
     * @see Security#getProperty(String)
     *
     * @since 1.8
     */
    public static SecureRandom getInstanceStrong()
            throws NoSuchAlgorithmException {

        String property = AccessController.doPrivileged(
            new PrivilegedAction<String>() {
                @Override
                public String run() {
                    return Security.getProperty(
                        "securerandom.strongAlgorithms");
                }
            });

        if ((property == null) || (property.length() == 0)) {
            throw new NoSuchAlgorithmException(
                "Null/empty securerandom.strongAlgorithms Security Property");
        }

        String remainder = property;
        while (remainder != null) {
            Matcher m;
            if ((m = StrongPatternHolder.pattern.matcher(
                    remainder)).matches()) {

                String alg = m.group(1);
                String prov = m.group(3);

                try {
                    if (prov == null) {
                        return SecureRandom.getInstance(alg);
                    } else {
                        return SecureRandom.getInstance(alg, prov);
                    }
                } catch (NoSuchAlgorithmException |
                        NoSuchProviderException e) {
                }
                remainder = m.group(5);
            } else {
                remainder = null;
            }
        }

        throw new NoSuchAlgorithmException(
            "No strong SecureRandom impls available: " + property);
    }

    // Declare serialVersionUID to be compatible with JDK1.1
    static final long serialVersionUID = 4940670005562187L;

    // Retain unused values serialized from JDK1.1
    
@serial
/**
     * @serial
     */
    private byte[] state;
    
@serial
/**
     * @serial
     */
    private MessageDigest digest = null;
    
@serial
We know that the MessageDigest class does not implement
java.io.Serializable.  However, since this field is no longer
used, it will always be NULL and won't affect the serialization
of the SecureRandom class itself.
/**
     * @serial
     *
     * We know that the MessageDigest class does not implement
     * java.io.Serializable.  However, since this field is no longer
     * used, it will always be NULL and won't affect the serialization
     * of the SecureRandom class itself.
     */
    private byte[] randomBytes;
    
@serial
/**
     * @serial
     */
    private int randomBytesUsed;
    
@serial
/**
     * @serial
     */
    private long counter;
}