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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * 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.
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 * 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).
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 * 2 along with this work; if not, write to the Free Software Foundation,
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 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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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;
import sun.security.util.Debug;

/**
 * This class provides the functionality of a secret (symmetric) key generator.
 *
 * <p>Key generators are constructed using one of the {@code 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><b>Algorithm-Independent Initialization</b>
 * <p>All key generators share the concepts of a <i>keysize</i> and a
 * <i>source of randomness</i>.
 * 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><b>Algorithm-Specific Initialization</b>
 * <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.
 * See the Keysize Restriction sections of the
 * {@extLink security_guide_jdk_providers JDK Providers}
 * document for information on the KeyGenerator defaults used by
 * JDK providers.
 * However, note that defaults may vary across different providers.
 * Additionally, the default value for a provider may change in a future
 * version. Therefore, it is recommended to explicitly initialize the
 * KeyGenerator instead of relying on provider-specific defaults.
 *
 * <p> Every implementation of the Java platform is required to support the
 * following standard {@code KeyGenerator} algorithms with the keysizes in
 * parentheses:
 * <ul>
 * <li>{@code AES} (128)</li>
 * <li>{@code DES} (56)</li>
 * <li>{@code DESede} (168)</li>
 * <li>{@code HmacSHA1}</li>
 * <li>{@code HmacSHA256}</li>
 * </ul>
 * These algorithms are described in the <a href=
 * "{@docRoot}/../specs/security/standard-names.html#keygenerator-algorithms">
 * KeyGenerator section</a> of the
 * Java Security Standard Algorithm Names Specification.
 * 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 {

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

    // see java.security.KeyPairGenerator for failover notes

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

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

    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");
        }

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

    private String getProviderName() {
        return (provider == null) ? "(no provider)" : provider.getName();
    }

    /**
     * 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.
     *
     * @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 standard name of the requested key algorithm.
     * See the KeyGenerator section in the <a href=
     * "{@docRoot}/../specs/security/standard-names.html#keygenerator-algorithms">
     * Java Security Standard Algorithm Names Specification</a>
     * for information about standard algorithm names.
     *
     * @return the new {@code KeyGenerator} object
     *
     * @throws NoSuchAlgorithmException if no {@code Provider} supports a
     *         {@code KeyGeneratorSpi} implementation for the
     *         specified algorithm
     *
     * @throws NullPointerException if {@code algorithm} is {@code null}
     *
     * @see java.security.Provider
     */
    public static final KeyGenerator getInstance(String algorithm)
            throws NoSuchAlgorithmException {
        Objects.requireNonNull(algorithm, "null algorithm name");
        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}/../specs/security/standard-names.html#keygenerator-algorithms">
     * Java Security Standard Algorithm Names Specification</a>
     * for information about standard algorithm names.
     *
     * @param provider the name of the provider.
     *
     * @return the new {@code KeyGenerator} object
     *
     * @throws IllegalArgumentException if the {@code provider}
     *         is {@code null} or empty
     *
     * @throws NoSuchAlgorithmException if a {@code KeyGeneratorSpi}
     *         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 java.security.Provider
     */
    public static final KeyGenerator getInstance(String algorithm,
            String provider) throws NoSuchAlgorithmException,
            NoSuchProviderException {
        Objects.requireNonNull(algorithm, "null algorithm name");
        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}/../specs/security/standard-names.html#keygenerator-algorithms">
     * Java Security Standard Algorithm Names Specification</a>
     * for information about standard algorithm names.
     *
     * @param provider the provider.
     *
     * @return the new {@code KeyGenerator} object
     *
     * @throws IllegalArgumentException if the {@code provider}
     *         is {@code null}
     *
     * @throws NoSuchAlgorithmException if a {@code KeyGeneratorSpi}
     *         implementation for the specified algorithm is not available
     *         from the specified {@code Provider} object
     *
     * @throws NullPointerException if {@code algorithm} is {@code null}
     *
     * @see java.security.Provider
     */
    public static final KeyGenerator getInstance(String algorithm,
            Provider provider) throws NoSuchAlgorithmException {
        Objects.requireNonNull(algorithm, "null algorithm name");
        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 implementations 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;
   }
}