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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.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

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 * 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

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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.util.Debug;

import sun.security.jca.*;

import sun.security.jca.GetInstance.Instance;

/**

 * This class provides the functionality of a key agreement (or key

 * exchange) protocol.

 * <p>

 * The keys involved in establishing a shared secret are created by one of the

 * key generators ({@code KeyPairGenerator} or

 * {@code KeyGenerator}), a {@code KeyFactory}, or as a result from

 * an intermediate phase of the key agreement protocol.

 *

 * <p> For each of the correspondents in the key exchange, {@code doPhase}

 * needs to be called. For example, if this key exchange is with one other

 * party, {@code doPhase} needs to be called once, with the

 * {@code lastPhase} flag set to {@code true}.

 * If this key exchange is

 * with two other parties, {@code doPhase} needs to be called twice,

 * the first time setting the {@code lastPhase} flag to

 * {@code false}, and the second time setting it to {@code true}.

 * There may be any number of parties involved in a key exchange.

 *

 * <p> Every implementation of the Java platform is required to support the

 * following standard {@code KeyAgreement} algorithm:

 * <ul>

 * <li>{@code DiffieHellman}</li>

 * </ul>

 * This algorithm is described in the <a href=

 * "{@docRoot}/../technotes/guides/security/StandardNames.html#KeyAgreement">

 * KeyAgreement 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 KeyGenerator

 * @see SecretKey

 * @since 1.4

 */

public class KeyAgreement {

    private static final Debug debug =

                        Debug.getInstance("jca", "KeyAgreement");

    private static final Debug pdebug =

                        Debug.getInstance("provider", "Provider");

    private static final boolean skipDebug =

        Debug.isOn("engine=") && !Debug.isOn("keyagreement");

    // The provider

    private Provider provider;

    // The provider implementation (delegate)

    private KeyAgreementSpi spi;

    // The name of the key agreement algorithm.

    private final String algorithm;

    // next service to try in provider selection

    // null once provider is selected

    private Service firstService;

    // remaining services to try in provider selection

    // null once provider is selected

    private Iterator<Service> serviceIterator;

    private final Object lock;

    /**

     * Creates a KeyAgreement object.

     *

     * @param keyAgreeSpi the delegate

     * @param provider the provider

     * @param algorithm the algorithm

     */

    protected KeyAgreement(KeyAgreementSpi keyAgreeSpi, Provider provider,

                           String algorithm) {

        this.spi = keyAgreeSpi;

        this.provider = provider;

        this.algorithm = algorithm;

        lock = null;

    }

    private KeyAgreement(Service s, Iterator<Service> t, String algorithm) {

        firstService = s;

        serviceIterator = t;

        this.algorithm = algorithm;

        lock = new Object();

    }

    /**

     * Returns the algorithm name of this {@code KeyAgreement} object.

     *

     * <p>This is the same name that was specified in one of the

     * {@code getInstance} calls that created this

     * {@code KeyAgreement} object.

     *

     * @return the algorithm name of this {@code KeyAgreement} object.

     */

    public final String getAlgorithm() {

        return this.algorithm;

    }

    /**

     * Returns a {@code KeyAgreement} object that implements the

     * specified key agreement algorithm.

     *

     * <p> This method traverses the list of registered security Providers,

     * starting with the most preferred Provider.

     * A new KeyAgreement object encapsulating the

     * KeyAgreementSpi 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 agreement

     * algorithm.

     * See the KeyAgreement section in the <a href=

     * "{@docRoot}/../technotes/guides/security/StandardNames.html#KeyAgreement">

     * Java Cryptography Architecture Standard Algorithm Name Documentation</a>

     * for information about standard algorithm names.

     *

     * @return the new {@code KeyAgreement} object.

     *

     * @exception NullPointerException if the specified algorithm

     *          is null.

     *

     * @exception NoSuchAlgorithmException if no Provider supports a

     *          KeyAgreementSpi implementation for the

     *          specified algorithm.

     *

     * @see java.security.Provider

     */

    public static final KeyAgreement getInstance(String algorithm)

            throws NoSuchAlgorithmException {

        List<Service> services =

                GetInstance.getServices("KeyAgreement", algorithm);

        // make sure there is at least one service from a signed provider

        Iterator<Service> t = services.iterator();

        while (t.hasNext()) {

            Service s = t.next();

            if (JceSecurity.canUseProvider(s.getProvider()) == false) {

                continue;

            }

            return new KeyAgreement(s, t, algorithm);

        }

        throw new NoSuchAlgorithmException

                                ("Algorithm " + algorithm + " not available");

    }

    /**

     * Returns a {@code KeyAgreement} object that implements the

     * specified key agreement algorithm.

     *

     * <p> A new KeyAgreement object encapsulating the

     * KeyAgreementSpi 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 agreement

     * algorithm.

     * See the KeyAgreement section in the <a href=

     * "{@docRoot}/../technotes/guides/security/StandardNames.html#KeyAgreement">

     * 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 KeyAgreement} object.

     *

     * @exception NullPointerException if the specified algorithm

     *          is null.

     *

     * @exception NoSuchAlgorithmException if a KeyAgreementSpi

     *          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 KeyAgreement getInstance(String algorithm,

            String provider) throws NoSuchAlgorithmException,

            NoSuchProviderException {

        Instance instance = JceSecurity.getInstance

                ("KeyAgreement", KeyAgreementSpi.class, algorithm, provider);

        return new KeyAgreement((KeyAgreementSpi)instance.impl,

                instance.provider, algorithm);

    }

    /**

     * Returns a {@code KeyAgreement} object that implements the

     * specified key agreement algorithm.

     *

     * <p> A new KeyAgreement object encapsulating the

     * KeyAgreementSpi 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 agreement

     * algorithm.

     * See the KeyAgreement section in the <a href=

     * "{@docRoot}/../technotes/guides/security/StandardNames.html#KeyAgreement">

     * Java Cryptography Architecture Standard Algorithm Name Documentation</a>

     * for information about standard algorithm names.

     *

     * @param provider the provider.

     *

     * @return the new {@code KeyAgreement} object.

     *

     * @exception NullPointerException if the specified algorithm

     *          is null.

     *

     * @exception NoSuchAlgorithmException if a KeyAgreementSpi

     *          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 KeyAgreement getInstance(String algorithm,

            Provider provider) throws NoSuchAlgorithmException {

        Instance instance = JceSecurity.getInstance

                ("KeyAgreement", KeyAgreementSpi.class, algorithm, provider);

        return new KeyAgreement((KeyAgreementSpi)instance.impl,

                instance.provider, algorithm);

    }

    // max number of debug warnings to print from chooseFirstProvider()

    private static int warnCount = 10;

    /**

     * Choose the Spi from the first provider available. Used if

     * delayed provider selection is not possible because init()

     * is not the first method called.

     */

    void chooseFirstProvider() {

        if (spi != null) {

            return;

        }

        synchronized (lock) {

            if (spi != null) {

                return;

            }

            if (debug != null) {

                int w = --warnCount;

                if (w >= 0) {

                    debug.println("KeyAgreement.init() not first method "

                        + "called, disabling delayed provider selection");

                    if (w == 0) {

                        debug.println("Further warnings of this type will "

                            + "be suppressed");

                    }

                    new Exception("Call trace").printStackTrace();

                }

            }

            Exception lastException = null;

            while ((firstService != null) || serviceIterator.hasNext()) {

                Service s;

                if (firstService != null) {

                    s = firstService;

                    firstService = null;

                } else {

                    s = serviceIterator.next();

                }

                if (JceSecurity.canUseProvider(s.getProvider()) == false) {

                    continue;

                }

                try {

                    Object obj = s.newInstance(null);

                    if (obj instanceof KeyAgreementSpi == false) {

                        continue;

                    }

                    spi = (KeyAgreementSpi)obj;

                    provider = s.getProvider();

                    // not needed any more

                    firstService = null;

                    serviceIterator = null;

                    return;

                } catch (Exception e) {

                    lastException = e;

                }

            }

            ProviderException e = new ProviderException

                    ("Could not construct KeyAgreementSpi instance");

            if (lastException != null) {

                e.initCause(lastException);

            }

            throw e;

        }

    }

    private static final int I_NO_PARAMS = 1;

    private static final int I_PARAMS    = 2;

    private void implInit(KeyAgreementSpi spi, int type, Key key,

            AlgorithmParameterSpec params, SecureRandom random)

            throws InvalidKeyException, InvalidAlgorithmParameterException {

        if (type == I_NO_PARAMS) {

            spi.engineInit(key, random);

        } else { // I_PARAMS

            spi.engineInit(key, params, random);

        }

    }

    private void chooseProvider(int initType, Key key,

            AlgorithmParameterSpec params, SecureRandom random)

            throws InvalidKeyException, InvalidAlgorithmParameterException {

        synchronized (lock) {

            if (spi != null) {

                implInit(spi, initType, key, params, random);

                return;

            }

            Exception lastException = null;

            while ((firstService != null) || serviceIterator.hasNext()) {

                Service s;

                if (firstService != null) {

                    s = firstService;

                    firstService = null;

                } else {

                    s = serviceIterator.next();

                }

                // if provider says it does not support this key, ignore it

                if (s.supportsParameter(key) == false) {

                    continue;

                }

                if (JceSecurity.canUseProvider(s.getProvider()) == false) {

                    continue;

                }

                try {

                    KeyAgreementSpi spi = (KeyAgreementSpi)s.newInstance(null);

                    implInit(spi, initType, key, params, random);

                    provider = s.getProvider();

                    this.spi = spi;

                    firstService = null;

                    serviceIterator = null;

                    return;

                } catch (Exception e) {

                    // NoSuchAlgorithmException from newInstance()

                    // InvalidKeyException from init()

                    // RuntimeException (ProviderException) from init()

                    if (lastException == null) {

                        lastException = e;

                    }

                }

            }

            // no working provider found, fail

            if (lastException instanceof InvalidKeyException) {

                throw (InvalidKeyException)lastException;

            }

            if (lastException instanceof InvalidAlgorithmParameterException) {

                throw (InvalidAlgorithmParameterException)lastException;

            }

            if (lastException instanceof RuntimeException) {

                throw (RuntimeException)lastException;

            }

            String kName = (key != null) ? key.getClass().getName() : "(null)";

            throw new InvalidKeyException

                ("No installed provider supports this key: "

                + kName, lastException);

        }

    }

    /**

     * Returns the provider of this {@code KeyAgreement} object.

     *

     * @return the provider of this {@code KeyAgreement} object

     */

    public final Provider getProvider() {

        chooseFirstProvider();

        return this.provider;

    }

    /**

     * Initializes this key agreement with the given key, which is required to

     * contain all the algorithm parameters required for this key agreement.

     *

     * <p> If this key agreement 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 key the party's private information. For example, in the case

     * of the Diffie-Hellman key agreement, this would be the party's own

     * Diffie-Hellman private key.

     *

     * @exception InvalidKeyException if the given key is

     * inappropriate for this key agreement, e.g., is of the wrong type or

     * has an incompatible algorithm type.

     */

    public final void init(Key key) throws InvalidKeyException {

        init(key, JceSecurity.RANDOM);

    }

    /**

     * Initializes this key agreement with the given key and source of

     * randomness. The given key is required to contain all the algorithm

     * parameters required for this key agreement.

     *

     * <p> If the key agreement algorithm requires random bytes, it gets them

     * from the given source of randomness, {@code random}.

     * However, if the underlying

     * algorithm implementation does not require any random bytes,

     * {@code random} is ignored.

     *

     * @param key the party's private information. For example, in the case

     * of the Diffie-Hellman key agreement, this would be the party's own

     * Diffie-Hellman private key.

     * @param random the source of randomness

     *

     * @exception InvalidKeyException if the given key is

     * inappropriate for this key agreement, e.g., is of the wrong type or

     * has an incompatible algorithm type.

     */

    public final void init(Key key, SecureRandom random)

            throws InvalidKeyException {

        if (spi != null) {

            spi.engineInit(key, random);

        } else {

            try {

                chooseProvider(I_NO_PARAMS, key, null, random);

            } catch (InvalidAlgorithmParameterException e) {

                // should never occur

                throw new InvalidKeyException(e);

            }

        }

        if (!skipDebug && pdebug != null) {

            pdebug.println("KeyAgreement." + algorithm + " algorithm from: " +

                this.provider.getName());

        }

    }

    /**

     * Initializes this key agreement with the given key and set of

     * algorithm parameters.

     *

     * <p> If this key agreement 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 key the party's private information. For example, in the case

     * of the Diffie-Hellman key agreement, this would be the party's own

     * Diffie-Hellman private key.

     * @param params the key agreement parameters

     *

     * @exception InvalidKeyException if the given key is

     * inappropriate for this key agreement, e.g., is of the wrong type or

     * has an incompatible algorithm type.

     * @exception InvalidAlgorithmParameterException if the given parameters

     * are inappropriate for this key agreement.

     */

    public final void init(Key key, AlgorithmParameterSpec params)

        throws InvalidKeyException, InvalidAlgorithmParameterException

    {

        init(key, params, JceSecurity.RANDOM);

    }