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 * 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).
 *
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 * 2 along with this work; if not, write to the Free Software Foundation,
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 *
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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}/../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.
 *
 * @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.
 *
 * @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 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.
 *
 * @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");
 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}/../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.
 *
 * @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 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}/../specs/security/standard-names.html#keyagreement-algorithms">
 * Java Security Standard Algorithm Names Specification</a>
 * for information about standard algorithm names.
 *
 * @param provider the provider.
 *
 * @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 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()) == 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: " +
 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
 * 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);
 }

 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 or not this is the last
 * phase of this key agreement.
 *
 * @return the (intermediate) key resulting from this phase, or 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
 *
 * @return the shared secret key
 *
 * @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 available
 * @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)
 */
 public final SecretKey generateSecret(String algorithm)
 throws IllegalStateException, NoSuchAlgorithmException,
 InvalidKeyException
 {
 chooseFirstProvider();
 return spi.engineGenerateSecret(algorithm);
 }
}