Java example source code file (KeyGenerator.java)

This example Java source code file (KeyGenerator.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

i_none, i_params, i_random, i_size, instance, invalidalgorithmparameterexception, keygenerator, keygeneratorspi, nosuchalgorithmexception, object, provider, runtimeexception, securerandom, security, string, util

The KeyGenerator.java Java example source code

/*
 * Copyright (c) 1997, 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
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package javax.crypto;

import java.util.*;

import java.security.*;
import java.security.Provider.Service;
import java.security.spec.*;

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

/**
 * This class provides the functionality of a secret (symmetric) key generator.
 *
 * <p>Key generators are constructed using one of the getInstance
 * class methods of this class.
 *
 * <p>KeyGenerator objects are reusable, i.e., after a key has been
 * generated, the same KeyGenerator object can be re-used to generate further
 * keys.
 *
 * <p>There are two ways to generate a key: in an algorithm-independent
 * manner, and in an algorithm-specific manner.
 * The only difference between the two is the initialization of the object:
 *
 * <ul>
 * <li>Algorithm-Independent Initialization
 * <p>All key generators share the concepts of a keysize and a
 * <i>source of randomness.
 * There is an
 * {@link #init(int, java.security.SecureRandom) init}
 * method in this KeyGenerator class that takes these two universally
 * shared types of arguments. There is also one that takes just a
 * <code>keysize argument, and uses the SecureRandom implementation
 * of the highest-priority installed provider as the source of randomness
 * (or a system-provided source of randomness if none of the installed
 * providers supply a SecureRandom implementation), and one that takes just a
 * source of randomness.
 *
 * <p>Since no other parameters are specified when you call the above
 * algorithm-independent <code>init methods, it is up to the
 * provider what to do about the algorithm-specific parameters (if any) to be
 * associated with each of the keys.
 *
 * <li>Algorithm-Specific Initialization
 * <p>For situations where a set of algorithm-specific parameters already
 * exists, there are two
 * {@link #init(java.security.spec.AlgorithmParameterSpec) init}
 * methods that have an <code>AlgorithmParameterSpec
 * argument. One also has a <code>SecureRandom argument, while the
 * other uses the SecureRandom implementation
 * of the highest-priority installed provider as the source of randomness
 * (or a system-provided source of randomness if none of the installed
 * providers supply a SecureRandom implementation).
 * </ul>
 *
 * <p>In case the client does not explicitly initialize the KeyGenerator
 * (via a call to an <code>init method), each provider must
 * supply (and document) a default initialization.
 *
 * <p> Every implementation of the Java platform is required to support the
 * following standard <code>KeyGenerator algorithms with the keysizes in
 * parentheses:
 * <ul>
 * <li>AES (128)
 * <li>DES (56)
 * <li>DESede (168)
 * <li>HmacSHA1
 * <li>HmacSHA256
 * </ul>
 * These algorithms are described in the <a href=
 * "{@docRoot}/../technotes/guides/security/StandardNames.html#KeyGenerator">
 * KeyGenerator section</a> of the
 * Java Cryptography Architecture Standard Algorithm Name Documentation.
 * Consult the release documentation for your implementation to see if any
 * other algorithms are supported.
 *
 * @author Jan Luehe
 *
 * @see SecretKey
 * @since 1.4
 */

public class KeyGenerator {

    // see java.security.KeyPairGenerator for failover notes

    private final static int I_NONE   = 1;
    private final static int I_RANDOM = 2;
    private final static int I_PARAMS = 3;
    private final static int I_SIZE   = 4;

    // The provider
    private Provider provider;

    // The provider implementation (delegate)
    private volatile KeyGeneratorSpi spi;

    // The algorithm
    private final String algorithm;

    private final Object lock = new Object();

    private Iterator<Service> serviceIterator;

    private int initType;
    private int initKeySize;
    private AlgorithmParameterSpec initParams;
    private SecureRandom initRandom;

    /**
     * Creates a KeyGenerator object.
     *
     * @param keyGenSpi the delegate
     * @param provider the provider
     * @param algorithm the algorithm
     */
    protected KeyGenerator(KeyGeneratorSpi keyGenSpi, Provider provider,
                           String algorithm) {
        this.spi = keyGenSpi;
        this.provider = provider;
        this.algorithm = algorithm;
    }

    private KeyGenerator(String algorithm) throws NoSuchAlgorithmException {
        this.algorithm = algorithm;
        List<Service> list =
                GetInstance.getServices("KeyGenerator", algorithm);
        serviceIterator = list.iterator();
        initType = I_NONE;
        // fetch and instantiate initial spi
        if (nextSpi(null, false) == null) {
            throw new NoSuchAlgorithmException
                (algorithm + " KeyGenerator not available");
        }
    }

    /**
     * Returns the algorithm name of this <code>KeyGenerator object.
     *
     * <p>This is the same name that was specified in one of the
     * <code>getInstance calls that created this
     * <code>KeyGenerator object.
     *
     * @return the algorithm name of this <code>KeyGenerator object.
     */
    public final String getAlgorithm() {
        return this.algorithm;
    }

    /**
     * Returns a <code>KeyGenerator object that generates secret keys
     * for the specified algorithm.
     *
     * <p> This method traverses the list of registered security Providers,
     * starting with the most preferred Provider.
     * A new KeyGenerator object encapsulating the
     * KeyGeneratorSpi 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.
     *
     * @param algorithm the standard name of the requested key algorithm.
     * See the KeyGenerator section in the <a href=
     * "{@docRoot}/../technotes/guides/security/StandardNames.html#KeyGenerator">
     * Java Cryptography Architecture Standard Algorithm Name Documentation</a>
     * for information about standard algorithm names.
     *
     * @return the new <code>KeyGenerator object.
     *
     * @exception NullPointerException if the specified algorithm is null.
     *
     * @exception NoSuchAlgorithmException if no Provider supports a
     *          KeyGeneratorSpi implementation for the
     *          specified algorithm.
     *
     * @see java.security.Provider
     */
    public static final KeyGenerator getInstance(String algorithm)
            throws NoSuchAlgorithmException {
        return new KeyGenerator(algorithm);
    }

    /**
     * Returns a <code>KeyGenerator object that generates secret keys
     * for the specified algorithm.
     *
     * <p> A new KeyGenerator object encapsulating the
     * KeyGeneratorSpi 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 standard name of the requested key algorithm.
     * See the KeyGenerator section in the <a href=
     * "{@docRoot}/../technotes/guides/security/StandardNames.html#KeyGenerator">
     * Java Cryptography Architecture Standard Algorithm Name Documentation</a>
     * for information about standard algorithm names.
     *
     * @param provider the name of the provider.
     *
     * @return the new <code>KeyGenerator object.
     *
     * @exception NullPointerException if the specified algorithm is null.
     *
     * @exception NoSuchAlgorithmException if a KeyGeneratorSpi
     *          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 <code>provider
     *          is null or empty.
     *
     * @see java.security.Provider
     */
    public static final KeyGenerator getInstance(String algorithm,
            String provider) throws NoSuchAlgorithmException,
            NoSuchProviderException {
        Instance instance = JceSecurity.getInstance("KeyGenerator",
                KeyGeneratorSpi.class, algorithm, provider);
        return new KeyGenerator((KeyGeneratorSpi)instance.impl,
                instance.provider, algorithm);
    }

    /**
     * Returns a <code>KeyGenerator object that generates secret keys
     * for the specified algorithm.
     *
     * <p> A new KeyGenerator object encapsulating the
     * KeyGeneratorSpi implementation from the specified Provider
     * object is returned.  Note that the specified Provider object
     * does not have to be registered in the provider list.
     *
     * @param algorithm the standard name of the requested key algorithm.
     * See the KeyGenerator section in the <a href=
     * "{@docRoot}/../technotes/guides/security/StandardNames.html#KeyGenerator">
     * Java Cryptography Architecture Standard Algorithm Name Documentation</a>
     * for information about standard algorithm names.
     *
     * @param provider the provider.
     *
     * @return the new <code>KeyGenerator object.
     *
     * @exception NullPointerException if the specified algorithm is null.
     *
     * @exception NoSuchAlgorithmException if a KeyGeneratorSpi
     *          implementation for the specified algorithm is not available
     *          from the specified Provider object.
     *
     * @exception IllegalArgumentException if the <code>provider
     *          is null.
     *
     * @see java.security.Provider
     */
    public static final KeyGenerator getInstance(String algorithm,
            Provider provider) throws NoSuchAlgorithmException {
        Instance instance = JceSecurity.getInstance("KeyGenerator",
                KeyGeneratorSpi.class, algorithm, provider);
        return new KeyGenerator((KeyGeneratorSpi)instance.impl,
                instance.provider, algorithm);
    }

    /**
     * Returns the provider of this <code>KeyGenerator object.
     *
     * @return the provider of this <code>KeyGenerator object
     */
    public final Provider getProvider() {
        synchronized (lock) {
            disableFailover();
            return provider;
        }
    }

    /**
     * Update the active spi of this class and return the next
     * implementation for failover. If no more implemenations are
     * available, this method returns null. However, the active spi of
     * this class is never set to null.
     */
    private KeyGeneratorSpi nextSpi(KeyGeneratorSpi oldSpi,
            boolean reinit) {
        synchronized (lock) {
            // somebody else did a failover concurrently
            // try that spi now
            if ((oldSpi != null) && (oldSpi != spi)) {
                return spi;
            }
            if (serviceIterator == null) {
                return null;
            }
            while (serviceIterator.hasNext()) {
                Service s = serviceIterator.next();
                if (JceSecurity.canUseProvider(s.getProvider()) == false) {
                    continue;
                }
                try {
                    Object inst = s.newInstance(null);
                    // ignore non-spis
                    if (inst instanceof KeyGeneratorSpi == false) {
                        continue;
                    }
                    KeyGeneratorSpi spi = (KeyGeneratorSpi)inst;
                    if (reinit) {
                        if (initType == I_SIZE) {
                            spi.engineInit(initKeySize, initRandom);
                        } else if (initType == I_PARAMS) {
                            spi.engineInit(initParams, initRandom);
                        } else if (initType == I_RANDOM) {
                            spi.engineInit(initRandom);
                        } else if (initType != I_NONE) {
                            throw new AssertionError
                                ("KeyGenerator initType: " + initType);
                        }
                    }
                    provider = s.getProvider();
                    this.spi = spi;
                    return spi;
                } catch (Exception e) {
                    // ignore
                }
            }
            disableFailover();
            return null;
        }
    }

    void disableFailover() {
        serviceIterator = null;
        initType = 0;
        initParams = null;
        initRandom = null;
    }

    /**
     * Initializes this key generator.
     *
     * @param random the source of randomness for this generator
     */
    public final void init(SecureRandom random) {
        if (serviceIterator == null) {
            spi.engineInit(random);
            return;
        }
        RuntimeException failure = null;
        KeyGeneratorSpi mySpi = spi;
        do {
            try {
                mySpi.engineInit(random);
                initType = I_RANDOM;
                initKeySize = 0;
                initParams = null;
                initRandom = random;
                return;
            } catch (RuntimeException e) {
                if (failure == null) {
                    failure = e;
                }
                mySpi = nextSpi(mySpi, false);
            }
        } while (mySpi != null);
        throw failure;
    }

    /**
     * Initializes this key generator with the specified parameter set.
     *
     * <p> If this key generator requires any random bytes, it will get them
     * using the
     * {@link java.security.SecureRandom}
     * implementation of the highest-priority installed
     * provider as the source of randomness.
     * (If none of the installed providers supply an implementation of
     * SecureRandom, a system-provided source of randomness will be used.)
     *
     * @param params the key generation parameters
     *
     * @exception InvalidAlgorithmParameterException if the given parameters
     * are inappropriate for this key generator
     */
    public final void init(AlgorithmParameterSpec params)
        throws InvalidAlgorithmParameterException
    {
        init(params, JceSecurity.RANDOM);
    }

    /**
     * Initializes this key generator with the specified parameter
     * set and a user-provided source of randomness.
     *
     * @param params the key generation parameters
     * @param random the source of randomness for this key generator
     *
     * @exception InvalidAlgorithmParameterException if <code>params is
     * inappropriate for this key generator
     */
    public final void init(AlgorithmParameterSpec params, SecureRandom random)
        throws InvalidAlgorithmParameterException
    {
        if (serviceIterator == null) {
            spi.engineInit(params, random);
            return;
        }
        Exception failure = null;
        KeyGeneratorSpi mySpi = spi;
        do {
            try {
                mySpi.engineInit(params, random);
                initType = I_PARAMS;
                initKeySize = 0;
                initParams = params;
                initRandom = random;
                return;
            } catch (Exception e) {
                if (failure == null) {
                    failure = e;
                }
                mySpi = nextSpi(mySpi, false);
            }
        } while (mySpi != null);
        if (failure instanceof InvalidAlgorithmParameterException) {
            throw (InvalidAlgorithmParameterException)failure;
        }
        if (failure instanceof RuntimeException) {
            throw (RuntimeException)failure;
        }
        throw new InvalidAlgorithmParameterException("init() failed", failure);
    }

    /**
     * Initializes this key generator for a certain keysize.
     *
     * <p> If this key generator requires any random bytes, it will get them
     * using the
     * {@link java.security.SecureRandom}
     * implementation of the highest-priority installed
     * provider as the source of randomness.
     * (If none of the installed providers supply an implementation of
     * SecureRandom, a system-provided source of randomness will be used.)
     *
     * @param keysize the keysize. This is an algorithm-specific metric,
     * specified in number of bits.
     *
     * @exception InvalidParameterException if the keysize is wrong or not
     * supported.
     */
    public final void init(int keysize) {
        init(keysize, JceSecurity.RANDOM);
    }

    /**
     * Initializes this key generator for a certain keysize, using a
     * user-provided source of randomness.
     *
     * @param keysize the keysize. This is an algorithm-specific metric,
     * specified in number of bits.
     * @param random the source of randomness for this key generator
     *
     * @exception InvalidParameterException if the keysize is wrong or not
     * supported.
     */
    public final void init(int keysize, SecureRandom random) {
        if (serviceIterator == null) {
            spi.engineInit(keysize, random);
            return;
        }
        RuntimeException failure = null;
        KeyGeneratorSpi mySpi = spi;
        do {
            try {
                mySpi.engineInit(keysize, random);
                initType = I_SIZE;
                initKeySize = keysize;
                initParams = null;
                initRandom = random;
                return;
            } catch (RuntimeException e) {
                if (failure == null) {
                    failure = e;
                }
                mySpi = nextSpi(mySpi, false);
            }
        } while (mySpi != null);
        throw failure;
    }

    /**
     * Generates a secret key.
     *
     * @return the new key
     */
    public final SecretKey generateKey() {
        if (serviceIterator == null) {
            return spi.engineGenerateKey();
        }
        RuntimeException failure = null;
        KeyGeneratorSpi mySpi = spi;
        do {
            try {
                return mySpi.engineGenerateKey();
            } catch (RuntimeException e) {
                if (failure == null) {
                    failure = e;
                }
                mySpi = nextSpi(mySpi, true);
            }
        } while (mySpi != null);
        throw failure;
   }
}