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 * Copyright (c) 1997, 2025, 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,
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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.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.  However,
 * support for key exchanges with more than two parties is implementation
 * specific or as specified by the standard key agreement algorithm.
 *
 * <p> Every implementation of the Java platform is required to support the
 * following standard {@code KeyAgreement} algorithms. For the "ECDH"
 * algorithm, implementations must support the curves in parentheses.
 * <ul>
 * <li>{@code DiffieHellman}</li>
 * <li>{@code ECDH} (secp256r1, secp384r1)</li>
 * <li>{@code X25519}</li>
 * </ul>
 * These algorithms are described in the <a href=
 * "{@docRoot}/../specs/security/standard-names.html#keyagreement-algorithms">
 * KeyAgreement 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.
 *
 * @spec security/standard-names.html Java Security Standard Algorithm Names
 * @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 {@code 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 {@code KeyAgreement} object encapsulating the
     * {@code 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.
     *
     * @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 from the order of providers returned by
     * {@link Security#getProviders() Security.getProviders()}.
     *
     * @param algorithm the standard name of the requested key agreement
     * algorithm.
     * See the KeyAgreement section in the <a href=
     * "{@docRoot}/../specs/security/standard-names.html#keyagreement-algorithms">
     * Java Security Standard Algorithm Names Specification</a>
     * for information about standard algorithm names.
     *
     * @spec security/standard-names.html Java Security Standard Algorithm Names
     * @return the new {@code KeyAgreement} object
     *
     * @throws NoSuchAlgorithmException if no {@code Provider} supports a
     *         {@code KeyAgreementSpi} implementation for the
     *         specified algorithm
     *
     * @throws NullPointerException if {@code algorithm} is {@code null}
     *
     * @see java.security.Provider
     */
    public static final KeyAgreement getInstance(String algorithm)
            throws NoSuchAlgorithmException {
        Objects.requireNonNull(algorithm, "null algorithm name");
        // make sure there is at least one service from a signed provider
        Iterator<Service> t = GetInstance.getServices("KeyAgreement", algorithm);
        while (t.hasNext()) {
            Service s = t.next();
            if (!JceSecurity.canUseProvider(s.getProvider())) {
                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 {@code KeyAgreement} object encapsulating the
     * {@code 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}/../specs/security/standard-names.html#keyagreement-algorithms">
     * Java Security Standard Algorithm Names Specification</a>
     * for information about standard algorithm names.
     *
     * @param provider the name of the provider.
     *
     * @spec security/standard-names.html Java Security Standard Algorithm Names
     * @return the new {@code KeyAgreement} object
     *
     * @throws IllegalArgumentException if the {@code provider}
     *         is {@code null} or empty
     *
     * @throws NoSuchAlgorithmException if a {@code KeyAgreementSpi}
     *         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 KeyAgreement getInstance(String algorithm,
            String provider) throws NoSuchAlgorithmException,
            NoSuchProviderException {
        Objects.requireNonNull(algorithm, "null algorithm name");
        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 {@code KeyAgreement} object encapsulating the
     * {@code KeyAgreementSpi} implementation from the specified
     * provider is returned.  Note that the specified provider
     * 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}/../specs/security/standard-names.html#keyagreement-algorithms">
     * Java Security Standard Algorithm Names Specification</a>
     * for information about standard algorithm names.
     *
     * @param provider the provider.
     *
     * @spec security/standard-names.html Java Security Standard Algorithm Names
     * @return the new {@code KeyAgreement} object
     *
     * @throws IllegalArgumentException if the {@code provider}
     *         is {@code null}
     *
     * @throws NoSuchAlgorithmException if a {@code KeyAgreementSpi}
     *         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 KeyAgreement getInstance(String algorithm,
            Provider provider) throws NoSuchAlgorithmException {
        Objects.requireNonNull(algorithm, "null algorithm name");
        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())) {
                    continue;
                }
                try {
                    Object obj = s.newInstance(null);
                    if (!(obj instanceof KeyAgreementSpi)) {
                        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)) {
                    continue;
                }
                if (!JceSecurity.canUseProvider(s.getProvider())) {
                    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
     * {@code 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, JCAUtil.getDefSecureRandom());
    }

    /**
     * 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: " +
                getProviderName());
        }
    }

    /**
     * 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
     * {@code 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, JCAUtil.getDefSecureRandom());
    }

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

    /**
     * Initializes this key agreement with the given key, set of
     * algorithm parameters, and source of randomness.
     *
     * @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
     * @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.
     * @exception InvalidAlgorithmParameterException if the given parameters
     * are inappropriate for this key agreement.
     */
    public final void init(Key key, AlgorithmParameterSpec params,
                           SecureRandom random)
        throws InvalidKeyException, InvalidAlgorithmParameterException
    {
        if (spi != null) {
            spi.engineInit(key, params, random);
        } else {
            chooseProvider(I_PARAMS, key, params, random);
        }

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

    /**
     * Executes the next phase of this key agreement with the given
     * key that was received from one of the other parties involved in this key
     * agreement.
     *
     * @param key the key for this phase. For example, in the case of
     * Diffie-Hellman between 2 parties, this would be the other party's
     * Diffie-Hellman public key.
     * @param lastPhase flag which indicates whether this is the last
     * phase of this key agreement.
     *
     * @return the (intermediate) key resulting from this phase, or {@code null}
     * if this phase does not yield a key
     *
     * @exception InvalidKeyException if the given key is inappropriate for
     * this phase.
     * @exception IllegalStateException if this key agreement has not been
     * initialized.
     */
    public final Key doPhase(Key key, boolean lastPhase)
        throws InvalidKeyException, IllegalStateException
    {
        chooseFirstProvider();
        return spi.engineDoPhase(key, lastPhase);
    }

    /**
     * Generates the shared secret and returns it in a new buffer.
     *
     * <p>This method resets this {@code KeyAgreement} object to the state that
     * it was in after the most recent call to one of the {@code init} methods.
     * After a call to {@code generateSecret}, the object can be reused for
     * further key agreement operations by calling {@code doPhase} to supply
     * new keys, and then calling {@code generateSecret} to produce a new
     * secret. In this case, the private information and algorithm parameters
     * supplied to {@code init} will be used for multiple key agreement
     * operations. The {@code init} method can be called after
     * {@code generateSecret} to change the private information used in
     * subsequent operations.
     *
     * @return the new buffer with the shared secret
     *
     * @exception IllegalStateException if this key agreement has not been
     * initialized or if {@code doPhase} has not been called to supply the
     * keys for all parties in the agreement
     */
    public final byte[] generateSecret() throws IllegalStateException {
        chooseFirstProvider();
        return spi.engineGenerateSecret();
    }

    /**
     * Generates the shared secret, and places it into the buffer
     * {@code sharedSecret}, beginning at {@code offset} inclusive.
     *
     * <p>If the {@code sharedSecret} buffer is too small to hold the
     * result, a {@code ShortBufferException} is thrown.
     * In this case, this call should be repeated with a larger output buffer.
     *
     * <p>This method resets this {@code KeyAgreement} object to the state that
     * it was in after the most recent call to one of the {@code init} methods.
     * After a call to {@code generateSecret}, the object can be reused for
     * further key agreement operations by calling {@code doPhase} to supply
     * new keys, and then calling {@code generateSecret} to produce a new
     * secret. In this case, the private information and algorithm parameters
     * supplied to {@code init} will be used for multiple key agreement
     * operations. The {@code init} method can be called after
     * {@code generateSecret} to change the private information used in
     * subsequent operations.
     *
     * @param sharedSecret the buffer for the shared secret
     * @param offset the offset in {@code sharedSecret} where the
     * shared secret will be stored
     *
     * @return the number of bytes placed into {@code sharedSecret}
     *
     * @exception IllegalStateException if this key agreement has not been
     * initialized or if {@code doPhase} has not been called to supply the
     * keys for all parties in the agreement
     * @exception ShortBufferException if the given output buffer is too small
     * to hold the secret
     */
    public final int generateSecret(byte[] sharedSecret, int offset)
        throws IllegalStateException, ShortBufferException
    {
        chooseFirstProvider();
        return spi.engineGenerateSecret(sharedSecret, offset);
    }

    /**
     * Creates the shared secret and returns it as a {@code SecretKey}
     * object of the specified algorithm.
     *
     * <p>This method resets this {@code KeyAgreement} object to the state that
     * it was in after the most recent call to one of the {@code init} methods.
     * After a call to {@code generateSecret}, the object can be reused for
     * further key agreement operations by calling {@code doPhase} to supply
     * new keys, and then calling {@code generateSecret} to produce a new
     * secret. In this case, the private information and algorithm parameters
     * supplied to {@code init} will be used for multiple key agreement
     * operations. The {@code init} method can be called after
     * {@code generateSecret} to change the private information used in
     * subsequent operations.
     *
     * @param algorithm the requested secret key algorithm. This is different
     *      from the {@code KeyAgreement} algorithm provided to the
     *      {@code getInstance} method. See the SecretKey Algorithms section in the
     *      <a href="{@docRoot}/../specs/security/standard-names.html#secretkey-algorithms">
     *      Java Security Standard Algorithm Names Specification</a>
     *      for information about standard secret key algorithm names.
     *      Specify "Generic" if the output will be used as the input keying
     *      material of a key derivation function (KDF).
     *
     * @return the shared secret key. The length of the key material
     *      may be adjusted to be compatible with the specified algorithm,
     *      regardless of whether the key is extractable. If {@code algorithm}
     *      is specified as "Generic" and it is supported by the implementation,
     *      the full shared secret is returned.
     *
     * @exception IllegalStateException if this key agreement has not been
     * initialized or if {@code doPhase} has not been called to supply the
     * keys for all parties in the agreement
     * @exception NoSuchAlgorithmException if the specified secret key
     * algorithm is not supported
     * @exception InvalidKeyException if the shared secret key material cannot
     * be used to generate a secret key of the specified algorithm (e.g.,
     * the key material is too short)
     * @spec security/standard-names.html Java Security Standard Algorithm Names
     */
    public final SecretKey generateSecret(String algorithm)
        throws IllegalStateException, NoSuchAlgorithmException,
            InvalidKeyException
    {
        chooseFirstProvider();
        return spi.engineGenerateSecret(algorithm);
    }
}