https://openjdk.java.net/ 
/*
 * Copyright (c) 1996, 2017, 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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 * questions.
 */

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 4086: Randomness Requirements for Security.

 Many SecureRandom implementations are in the form of a pseudo-random number generator (PRNG, also known as deterministic random bits generator or DRBG), which means they use a deterministic algorithm to produce a pseudo-random sequence from a random seed. Other implementations may produce true random numbers, and yet others may use a combination of both techniques. 
A caller obtains a SecureRandom instance via the no-argument constructor or one of the getInstance methods. For example: 
SecureRandom r1 = new SecureRandom();
SecureRandom r2 = SecureRandom.getInstance("NativePRNG");
SecureRandom r3 = SecureRandom.getInstance("DRBG",
        DrbgParameters.instantiation(128, RESEED_ONLY, null));




 The third statement above returns a SecureRandom object of the specific algorithm supporting the specific instantiate parameters. The implementation's effective instantiated parameters must match this minimum request but is not necessarily the same. For example, even if the request does not require a certain feature, the actual instantiation can provide the feature. An implementation may lazily instantiate a SecureRandom until it's actually used, but the effective instantiate parameters must be determined right after it's created and getParameters() should always return the same result unchanged. 
 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);




 A newly created PRNG SecureRandom object is not seeded (except if it is created by SecureRandom(byte[])). The first call to nextBytes will force it to seed itself from an implementation- specific entropy source. This self-seeding will not occur if setSeed was previously called. 
 A SecureRandom can be reseeded at any time by calling the reseed or setSeed method. The reseed method reads entropy input from its entropy source to reseed itself. The setSeed method requires the caller to provide the seed. 
 Please note that reseed may not be supported by all SecureRandom implementations. 
 Some SecureRandom implementations may accept a SecureRandomParameters parameter in its nextBytes(byte[], SecureRandomParameters) and reseed(SecureRandomParameters) methods to further control the behavior of the methods. 
 Note: Depending on the implementation, the generateSeed, reseed and nextBytes methods may block as entropy is being gathered, for example, if the entropy source is /dev/random on various Unix-like operating systems. 
 Thread safety 
 SecureRandom objects are safe for use by multiple concurrent threads. 
Author:Benjamin Renaud, Josh Bloch
See Also:
Implementation Requirements: A SecureRandom service provider can advertise that it is thread-safe by setting the service
provider attribute "ThreadSafe" to "true" when registering the provider. Otherwise, this class will instead synchronize access to the following methods of the SecureRandomSpi implementation: 
Since:1.1
/**
 * 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://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.140-2.pdf">
 * <i>FIPS 140-2, Security Requirements for Cryptographic Modules</i></a>,
 * section 4.9.1.
 * Additionally, {@code SecureRandom} must produce non-deterministic output.
 * Therefore any seed material passed to a {@code SecureRandom} object must be
 * unpredictable, and all {@code SecureRandom} output sequences must be
 * cryptographically strong, as described in
 * <a href="http://tools.ietf.org/html/rfc4086">
 * <i>RFC 4086: Randomness Requirements for Security</i></a>.
 *
 * <p> Many {@code SecureRandom} implementations are in the form of a
 * pseudo-random number generator (PRNG, also known as deterministic random
 * bits generator or DRBG), which means they use a deterministic algorithm
 * to produce a pseudo-random sequence from a random seed.
 * Other implementations may produce true random numbers,
 * and yet others may use a combination of both techniques.
 *
 * <p>A caller obtains a {@code SecureRandom} instance via the
 * no-argument constructor or one of the {@code getInstance} methods.
 * For example:
 *
 * <blockquote><pre>
 * SecureRandom r1 = new SecureRandom();
 * SecureRandom r2 = SecureRandom.getInstance("NativePRNG");
 * SecureRandom r3 = SecureRandom.getInstance("DRBG",
 *         DrbgParameters.instantiation(128, RESEED_ONLY, null));</pre>
 * </blockquote>
 *
 * <p> The third statement above returns a {@code SecureRandom} object of the
 * specific algorithm supporting the specific instantiate parameters. The
 * implementation's effective instantiated parameters must match this minimum
 * request but is not necessarily the same. For example, even if the request
 * does not require a certain feature, the actual instantiation can provide
 * the feature. An implementation may lazily instantiate a {@code SecureRandom}
 * until it's actually used, but the effective instantiate parameters must be
 * determined right after it's created and {@link #getParameters()} should
 * always return the same result unchanged.
 *
 * <p> Typical callers of {@code SecureRandom} invoke the following methods
 * to retrieve random bytes:
 *
 * <blockquote><pre>
 * SecureRandom random = new SecureRandom();
 * byte[] bytes = new byte[20];
 * random.nextBytes(bytes);</pre>
 * </blockquote>
 *
 * <p> Callers may also invoke the {@link #generateSeed} method
 * to generate a given number of seed bytes (to seed other random number
 * generators, for example):
 *
 * <blockquote><pre>
 * byte[] seed = random.generateSeed(20);</pre>
 * </blockquote>
 *
 * <p> A newly created PRNG {@code SecureRandom} object is not seeded (except
 * if it is created by {@link #SecureRandom(byte[])}). The first call to
 * {@code nextBytes} will force it to seed itself from an implementation-
 * specific entropy source. This self-seeding will not occur if {@code setSeed}
 * was previously called.
 *
 * <p> A {@code SecureRandom} can be reseeded at any time by calling the
 * {@code reseed} or {@code setSeed} method. The {@code reseed} method
 * reads entropy input from its entropy source to reseed itself.
 * The {@code setSeed} method requires the caller to provide the seed.
 *
 * <p> Please note that {@code reseed} may not be supported by all
 * {@code SecureRandom} implementations.
 *
 * <p> Some {@code SecureRandom} implementations may accept a
 * {@link SecureRandomParameters} parameter in its
 * {@link #nextBytes(byte[], SecureRandomParameters)} and
 * {@link #reseed(SecureRandomParameters)} methods to further
 * control the behavior of the methods.
 *
 * <p> Note: Depending on the implementation, the {@code generateSeed},
 * {@code reseed} and {@code nextBytes} methods may block as entropy is being
 * gathered, for example, if the entropy source is /dev/random on various
 * Unix-like operating systems.
 *
 * <h2> Thread safety </h2>
 * {@code SecureRandom} objects are safe for use by multiple concurrent threads.
 *
 * @implSpec
 * A {@code SecureRandom} service provider can advertise that it is thread-safe
 * by setting the <a href=
 * "{@docRoot}/../specs/security/standard-names.html#service-attributes">service
 * provider attribute</a> "ThreadSafe" to "true" when registering the provider.
 * Otherwise, this class will instead synchronize access to the following
 * methods of the {@code SecureRandomSpi} implementation:
 * <ul>
 * <li>{@link SecureRandomSpi#engineSetSeed(byte[])}
 * <li>{@link SecureRandomSpi#engineNextBytes(byte[])}
 * <li>{@link SecureRandomSpi#engineNextBytes(byte[], SecureRandomParameters)}
 * <li>{@link SecureRandomSpi#engineGenerateSeed(int)}
 * <li>{@link SecureRandomSpi#engineReseed(SecureRandomParameters)}
 * </ul>
 *
 * @see java.security.SecureRandomSpi
 * @see java.util.Random
 *
 * @author Benjamin Renaud
 * @author Josh Bloch
 * @since 1.1
 */

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;

    
Thread safety.

@serial
Since:9
/**
     * Thread safety.
     *
     * @serial
     * @since 9
     */
    private final boolean threadSafe;

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

    // Seed Generator
    private static volatile SecureRandom seedGenerator;

    
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 Security Standard Algorithm Names Specification
for information about standard RNG algorithm names.

/**
     * 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 {@code SecureRandom} object encapsulating the
     * {@code SecureRandomSpi} implementation from the first
     * Provider that supports a {@code 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 {@code SecureRandom} section in the <a href=
     * "{@docRoot}/../specs/security/standard-names.html#securerandom-number-generation-algorithms">
     * Java Security Standard Algorithm Names Specification</a>
     * for information about standard RNG algorithm names.
     */
    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);
        this.threadSafe = getThreadSafe();
    }

    private boolean getThreadSafe() {
        if (provider == null || algorithm == null) {
            return false;
        } else {
            return Boolean.parseBoolean(provider.getProperty(
                    "SecureRandom." + algorithm + " ThreadSafe", "false"));
        }
    }

    
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 Security Standard Algorithm Names Specification
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 {@code 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 {@code SecureRandom} object encapsulating the
     * {@code SecureRandomSpi} implementation from the first
     * Provider that supports a {@code 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 {@code SecureRandom} section in the <a href=
     * "{@docRoot}/../specs/security/standard-names.html#securerandom-number-generation-algorithms">
     * Java Security Standard Algorithm Names Specification</a>
     * for information about standard RNG algorithm names.
     *
     * @param seed the seed.
     */
    public SecureRandom(byte[] seed) {
        super(0);
        getDefaultPRNG(true, seed);
        this.threadSafe = getThreadSafe();
    }

    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 {@code SecureRandom} object.
     *
     * @param secureRandomSpi the {@code 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;
        this.threadSafe = getThreadSafe();

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

    private String getProviderName() {
        return (provider == null) ? "(no provider)" : 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. 
Params:
Throws:
See Also:
Implementation Note: The JDK Reference Implementation additionally uses the jdk.security.provider.preferred Security property to determine the preferred provider order for the specified algorithm. This may be different than the order of providers returned by Security.getProviders().
Returns:the new SecureRandom object
Since:1.2
/**
     * Returns a {@code 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 {@code SecureRandom} object encapsulating the
     * {@code 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.
     *
     * @implNote
     * The JDK Reference Implementation additionally uses the
     * {@code jdk.security.provider.preferred}
     * {@link Security#getProperty(String) Security} property to determine
     * the preferred provider order for the specified algorithm. This
     * may be different than the order of providers returned by
     * {@link Security#getProviders() Security.getProviders()}.
     *
     * @param algorithm the name of the RNG algorithm.
     * See the {@code SecureRandom} section in the <a href=
     * "{@docRoot}/../specs/security/standard-names.html#securerandom-number-generation-algorithms">
     * Java Security Standard Algorithm Names Specification</a>
     * for information about standard RNG algorithm names.
     *
     * @return the new {@code SecureRandom} object
     *
     * @throws NoSuchAlgorithmException if no {@code Provider} supports a
     *         {@code SecureRandomSpi} implementation for the
     *         specified algorithm
     *
     * @throws NullPointerException if {@code algorithm} is {@code null}
     *
     * @see Provider
     *
     * @since 1.2
     */
    public static SecureRandom getInstance(String algorithm)
            throws NoSuchAlgorithmException {
        Objects.requireNonNull(algorithm, "null algorithm name");
        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. 
Params:
Throws:
See Also:
Returns:the new SecureRandom object
Since:1.2
/**
     * Returns a {@code SecureRandom} object that implements the specified
     * Random Number Generator (RNG) algorithm.
     *
     * <p> A new {@code SecureRandom} object encapsulating the
     * {@code 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.
     *
     * @param algorithm the name of the RNG algorithm.
     * See the {@code SecureRandom} section in the <a href=
     * "{@docRoot}/../specs/security/standard-names.html#securerandom-number-generation-algorithms">
     * Java Security Standard Algorithm Names Specification</a>
     * for information about standard RNG algorithm names.
     *
     * @param provider the name of the provider.
     *
     * @return the new {@code SecureRandom} object
     *
     * @throws IllegalArgumentException if the provider name is {@code null}
     *         or empty
     *
     * @throws NoSuchAlgorithmException if a {@code SecureRandomSpi}
     *         implementation for the specified algorithm is not
     *         available from the specified provider
     *
     * @throws NoSuchProviderException if the specified provider is not
     *         registered in the security provider list
     *
     * @throws NullPointerException if {@code algorithm} is {@code null}
     *
     * @see Provider
     *
     * @since 1.2
     */
    public static SecureRandom getInstance(String algorithm, String provider)
            throws NoSuchAlgorithmException, NoSuchProviderException {
        Objects.requireNonNull(algorithm, "null algorithm name");
        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. 
Params:
Throws:
See Also:
Returns:the new SecureRandom object
Since:1.4
/**
     * Returns a {@code SecureRandom} object that implements the specified
     * Random Number Generator (RNG) algorithm.
     *
     * <p> A new {@code SecureRandom} object encapsulating the
     * {@code SecureRandomSpi} implementation from the specified {@code Provider}
     * object is returned.  Note that the specified {@code Provider} object
     * does not have to be registered in the provider list.
     *
     * @param algorithm the name of the RNG algorithm.
     * See the {@code SecureRandom} section in the <a href=
     * "{@docRoot}/../specs/security/standard-names.html#securerandom-number-generation-algorithms">
     * Java Security Standard Algorithm Names Specification</a>
     * for information about standard RNG algorithm names.
     *
     * @param provider the provider.
     *
     * @return the new {@code SecureRandom} object
     *
     * @throws IllegalArgumentException if the specified provider is
     *         {@code null}
     *
     * @throws NoSuchAlgorithmException if a {@code SecureRandomSpi}
     *         implementation for the specified algorithm is not available
     *         from the specified {@code Provider} object
     *
     * @throws NullPointerException if {@code algorithm} is {@code null}
     *
     * @see Provider
     *
     * @since 1.4
     */
    public static SecureRandom getInstance(String algorithm,
            Provider provider) throws NoSuchAlgorithmException {
        Objects.requireNonNull(algorithm, "null algorithm name");
        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 and supports the specified SecureRandomParameters request. 
 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 and the specified SecureRandomParameters is returned. 
 Note that the list of registered providers may be retrieved via the Security.getProviders() method. 
Params:
  • algorithm – the name of the RNG algorithm. See the SecureRandom section in the 
Java Security Standard Algorithm Names Specification
for information about standard RNG algorithm names.
  • params – the SecureRandomParameters the newly created SecureRandom object must support.
Throws:
See Also:
Implementation Note: The JDK Reference Implementation additionally uses the jdk.security.provider.preferred property to determine the preferred provider order for the specified algorithm. This may be different than the order of providers returned by Security.getProviders().
Returns:the new SecureRandom object
Since:9
/**
     * Returns a {@code SecureRandom} object that implements the specified
     * Random Number Generator (RNG) algorithm and supports the specified
     * {@code SecureRandomParameters} request.
     *
     * <p> This method traverses the list of registered security Providers,
     * starting with the most preferred Provider.
     * A new {@code SecureRandom} object encapsulating the
     * {@code SecureRandomSpi} implementation from the first
     * Provider that supports the specified algorithm and the specified
     * {@code SecureRandomParameters} is returned.
     *
     * <p> Note that the list of registered providers may be retrieved via
     * the {@link Security#getProviders() Security.getProviders()} method.
     *
     * @implNote
     * The JDK Reference Implementation additionally uses the
     * {@code jdk.security.provider.preferred} property to determine
     * the preferred provider order for the specified algorithm. This
     * may be different than the order of providers returned by
     * {@link Security#getProviders() Security.getProviders()}.
     *
     * @param algorithm the name of the RNG algorithm.
     * See the {@code SecureRandom} section in the <a href=
     * "{@docRoot}/../specs/security/standard-names.html#securerandom-number-generation-algorithms">
     * Java Security Standard Algorithm Names Specification</a>
     * for information about standard RNG algorithm names.
     *
     * @param params the {@code SecureRandomParameters}
     *               the newly created {@code SecureRandom} object must support.
     *
     * @return the new {@code SecureRandom} object
     *
     * @throws IllegalArgumentException if the specified params is
     *         {@code null}
     *
     * @throws NoSuchAlgorithmException if no Provider supports a
     *         {@code SecureRandomSpi} implementation for the specified
     *         algorithm and parameters
     *
     * @throws NullPointerException if {@code algorithm} is {@code null}
     *
     * @see Provider
     *
     * @since 9
     */
    public static SecureRandom getInstance(
            String algorithm, SecureRandomParameters params)
            throws NoSuchAlgorithmException {
        Objects.requireNonNull(algorithm, "null algorithm name");
        if (params == null) {
            throw new IllegalArgumentException("params cannot be null");
        }
        Instance instance = GetInstance.getInstance("SecureRandom",
                SecureRandomSpi.class, algorithm, params);
        return new SecureRandom((SecureRandomSpi)instance.impl,
                instance.provider, algorithm);
    }

    
Returns a SecureRandom object that implements the specified Random Number Generator (RNG) algorithm and supports the specified SecureRandomParameters request. 
 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. 
Params:
  • algorithm – the name of the RNG algorithm. See the SecureRandom section in the 
Java Security Standard Algorithm Names Specification
for information about standard RNG algorithm names.
  • params – the SecureRandomParameters the newly created SecureRandom object must support.
  • provider – the name of the provider.
Throws:
See Also:
Returns:the new SecureRandom object
Since:9
/**
     * Returns a {@code SecureRandom} object that implements the specified
     * Random Number Generator (RNG) algorithm and supports the specified
     * {@code SecureRandomParameters} request.
     *
     * <p> A new {@code SecureRandom} object encapsulating the
     * {@code 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.
     *
     * @param algorithm the name of the RNG algorithm.
     * See the {@code SecureRandom} section in the <a href=
     * "{@docRoot}/../specs/security/standard-names.html#securerandom-number-generation-algorithms">
     * Java Security Standard Algorithm Names Specification</a>
     * for information about standard RNG algorithm names.
     *
     * @param params the {@code SecureRandomParameters}
     *               the newly created {@code SecureRandom} object must support.
     *
     * @param provider the name of the provider.
     *
     * @return the new {@code SecureRandom} object
     *
     * @throws IllegalArgumentException if the provider name is {@code null}
     *         or empty, or params is {@code null}
     *
     * @throws NoSuchAlgorithmException if the specified provider does not
     *         support a {@code SecureRandomSpi} implementation for the
     *         specified algorithm and parameters
     *
     * @throws NoSuchProviderException if the specified provider is not
     *         registered in the security provider list
     *
     * @throws NullPointerException if {@code algorithm} is {@code null}
     *
     * @see Provider
     *
     * @since 9
     */
    public static SecureRandom getInstance(String algorithm,
            SecureRandomParameters params, String provider)
            throws NoSuchAlgorithmException, NoSuchProviderException {
        Objects.requireNonNull(algorithm, "null algorithm name");
        if (params == null) {
            throw new IllegalArgumentException("params cannot be null");
        }
        Instance instance = GetInstance.getInstance("SecureRandom",
                SecureRandomSpi.class, algorithm, params, provider);
        return new SecureRandom((SecureRandomSpi)instance.impl,
                instance.provider, algorithm);
    }

    
Returns a SecureRandom object that implements the specified Random Number Generator (RNG) algorithm and supports the specified SecureRandomParameters request. 
 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. 
Params:
  • algorithm – the name of the RNG algorithm. See the SecureRandom section in the 
Java Security Standard Algorithm Names Specification
for information about standard RNG algorithm names.
  • params – the SecureRandomParameters the newly created SecureRandom object must support.
  • provider – the provider.
Throws:
See Also:
Returns:the new SecureRandom object
Since:9
/**
     * Returns a {@code SecureRandom} object that implements the specified
     * Random Number Generator (RNG) algorithm and supports the specified
     * {@code SecureRandomParameters} request.
     *
     * <p> A new {@code SecureRandom} object encapsulating the
     * {@code SecureRandomSpi} implementation from the specified
     * {@code Provider} object is returned.  Note that the specified
     * {@code Provider} object does not have to be registered in the
     * provider list.
     *
     * @param algorithm the name of the RNG algorithm.
     * See the {@code SecureRandom} section in the <a href=
     * "{@docRoot}/../specs/security/standard-names.html#securerandom-number-generation-algorithms">
     * Java Security Standard Algorithm Names Specification</a>
     * for information about standard RNG algorithm names.
     *
     * @param params the {@code SecureRandomParameters}
     *               the newly created {@code SecureRandom} object must support.
     *
     * @param provider the provider.
     *
     * @return the new {@code SecureRandom} object
     *
     * @throws IllegalArgumentException if the specified provider or params
     *         is {@code null}
     *
     * @throws NoSuchAlgorithmException if the specified provider does not
     *         support a {@code SecureRandomSpi} implementation for the
     *         specified algorithm and parameters
     *
     * @throws NullPointerException if {@code algorithm} is {@code null}
     *
     * @see Provider
     *
     * @since 9
     */
    public static SecureRandom getInstance(String algorithm,
            SecureRandomParameters params, Provider provider)
            throws NoSuchAlgorithmException {
        Objects.requireNonNull(algorithm, "null algorithm name");
        if (params == null) {
            throw new IllegalArgumentException("params cannot be null");
        }
        Instance instance = GetInstance.getInstance("SecureRandom",
                SecureRandomSpi.class, algorithm, params, provider);
        return new SecureRandom((SecureRandomSpi)instance.impl,
                instance.provider, algorithm);
    }

    
Returns the SecureRandomSpi of this SecureRandom object. 
/**
     * Returns the {@code SecureRandomSpi} of this {@code 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 {@code SecureRandom} object.
     *
     * @return the provider of this {@code 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
     * {@code 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 Objects.toString(algorithm, "unknown");
    }

    
Returns a Human-readable string representation of this SecureRandom. 
Returns:the string representation
/**
     * Returns a Human-readable string representation of this
     * {@code SecureRandom}.
     *
     * @return the string representation
     */
    @Override
    public String toString() {
        return secureRandomSpi.toString();
    }

    
Returns the effective SecureRandomParameters for this SecureRandom instance. 
 The returned value can be different from the SecureRandomParameters object passed into a getInstance method, but it cannot change during the lifetime of this SecureRandom object. 
 A caller can use the returned value to find out what features this SecureRandom supports. 
See Also:
Returns:the effective SecureRandomParameters parameters, or null if no parameters were used.
Since:9
/**
     * Returns the effective {@link SecureRandomParameters} for this
     * {@code SecureRandom} instance.
     * <p>
     * The returned value can be different from the
     * {@code SecureRandomParameters} object passed into a {@code getInstance}
     * method, but it cannot change during the lifetime of this
     * {@code SecureRandom} object.
     * <p>
     * A caller can use the returned value to find out what features this
     * {@code SecureRandom} supports.
     *
     * @return the effective {@link SecureRandomParameters} parameters,
     * or {@code null} if no parameters were used.
     *
     * @since 9
     * @see SecureRandomSpi
     */
    public SecureRandomParameters getParameters() {
        return secureRandomSpi.engineGetParameters();
    }

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

 A PRNG SecureRandom will not seed itself automatically if setSeed is called before any nextBytes or reseed calls. The caller should make sure that the seed argument contains enough entropy for the security of this SecureRandom. 
Params:
  • seed – the seed.
See Also:
/**
     * Reseeds this random object with the given seed. The seed supplements,
     * rather than replaces, the existing seed. Thus, repeated calls are
     * guaranteed never to reduce randomness.
     * <p>
     * A PRNG {@code SecureRandom} will not seed itself automatically if
     * {@code setSeed} is called before any {@code nextBytes} or {@code reseed}
     * calls. The caller should make sure that the {@code seed} argument
     * contains enough entropy for the security of this {@code SecureRandom}.
     *
     * @param seed the seed.
     *
     * @see #getSeed
     */
    public void setSeed(byte[] seed) {
        if (threadSafe) {
            secureRandomSpi.engineSetSeed(seed);
        } else {
            synchronized (this) {
                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) {
            setSeed(longToByteArray(seed));
        }
    }

    
Generates a user-specified number of random bytes.

Params:
  • bytes – the array to be filled in with random bytes.
/**
     * Generates a user-specified number of random bytes.
     *
     * @param bytes the array to be filled in with random bytes.
     */
    @Override
    public void nextBytes(byte[] bytes) {
        if (threadSafe) {
            secureRandomSpi.engineNextBytes(bytes);
        } else {
            synchronized (this) {
                secureRandomSpi.engineNextBytes(bytes);
            }
        }
    }

    
Generates a user-specified number of random bytes with
additional parameters.

Params:
  • bytes – the array to be filled in with random bytes
  • params – additional parameters
Throws:
Since:9
/**
     * Generates a user-specified number of random bytes with
     * additional parameters.
     *
     * @param bytes the array to be filled in with random bytes
     * @param params additional parameters
     * @throws NullPointerException if {@code bytes} is null
     * @throws UnsupportedOperationException if the underlying provider
     *         implementation has not overridden this method
     * @throws IllegalArgumentException if {@code params} is {@code null},
     *         illegal or unsupported by this {@code SecureRandom}
     *
     * @since 9
     */
    public void nextBytes(byte[] bytes, SecureRandomParameters params) {
        if (params == null) {
            throw new IllegalArgumentException("params cannot be null");
        }
        if (threadSafe) {
            secureRandomSpi.engineNextBytes(
                    Objects.requireNonNull(bytes), params);
        } else {
            synchronized (this) {
                secureRandomSpi.engineNextBytes(
                        Objects.requireNonNull(bytes), params);
            }
        }
    }

    
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
    protected final 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.
Throws:
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 {@code 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.
     *
     * @throws IllegalArgumentException if {@code numBytes} is negative
     * @return the seed bytes.
     *
     * @see #setSeed
     */
    public static byte[] getSeed(int numBytes) {
        SecureRandom seedGen = seedGenerator;
        if (seedGen == null) {
            seedGen = new SecureRandom();
            seedGenerator = seedGen;
        }
        return seedGen.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.
Throws:
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.
     * @throws IllegalArgumentException if {@code numBytes} is negative
     * @return the seed bytes.
     */
    public byte[] generateSeed(int numBytes) {
        if (numBytes < 0) {
            throw new IllegalArgumentException("numBytes cannot be negative");
        }
        if (threadSafe) {
            return secureRandomSpi.engineGenerateSeed(numBytes);
        } else {
            synchronized (this) {
                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 {@code SecureRandom} implementation, or null if none of
     * the registered providers supplies a {@code 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<>() {
                @Override
                public String run() {
                    return Security.getProperty(
                        "securerandom.strongAlgorithms");
                }
            });

        if (property == null || property.isEmpty()) {
            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);
    }

    
Reseeds this SecureRandom with entropy input read from its entropy source. 
Throws:
Since:9
/**
     * Reseeds this {@code SecureRandom} with entropy input read from its
     * entropy source.
     *
     * @throws UnsupportedOperationException if the underlying provider
     *         implementation has not overridden this method.
     *
     * @since 9
     */
    public void reseed() {
        if (threadSafe) {
            secureRandomSpi.engineReseed(null);
        } else {
            synchronized (this) {
                secureRandomSpi.engineReseed(null);
            }
        }
    }

    
Reseeds this SecureRandom with entropy input read from its entropy source with additional parameters. 
 Note that entropy is obtained from an entropy source. While some data in params may contain entropy, its main usage is to provide diversity. 
Params:
  • params – extra parameters
Throws:
Since:9
/**
     * Reseeds this {@code SecureRandom} with entropy input read from its
     * entropy source with additional parameters.
     * <p>
     * Note that entropy is obtained from an entropy source. While
     * some data in {@code params} may contain entropy, its main usage is to
     * provide diversity.
     *
     * @param params extra parameters
     * @throws UnsupportedOperationException if the underlying provider
     *         implementation has not overridden this method.
     * @throws IllegalArgumentException if {@code params} is {@code null},
     *         illegal or unsupported by this {@code SecureRandom}
     *
     * @since 9
     */
    public void reseed(SecureRandomParameters params) {
        if (params == null) {
            throw new IllegalArgumentException("params cannot be null");
        }
        if (threadSafe) {
            secureRandomSpi.engineReseed(params);
        } else {
            synchronized (this) {
                secureRandomSpi.engineReseed(params);
            }
        }
    }

    // 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 {@code SecureRandom} class itself.
     */
    private byte[] randomBytes;
    
@serial
/**
     * @serial
     */
    private int randomBytesUsed;
    
@serial
/**
     * @serial
     */
    private long counter;
}