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package java.security;

import java.util.*;

import java.security.Provider.Service;
import java.security.spec.KeySpec;
import java.security.spec.InvalidKeySpecException;

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

/**
 * Key factories are used to convert <I>keys</I> (opaque
 * cryptographic keys of type {@code Key}) into <I>key specifications</I>
 * (transparent representations of the underlying key material), and vice
 * versa.
 *
 * <P> Key factories are bi-directional. That is, they allow you to build an
 * opaque key object from a given key specification (key material), or to
 * retrieve the underlying key material of a key object in a suitable format.
 *
 * <P> Multiple compatible key specifications may exist for the same key.
 * For example, a DSA public key may be specified using
 * {@code DSAPublicKeySpec} or
 * {@code X509EncodedKeySpec}. A key factory can be used to translate
 * between compatible key specifications.
 *
 * <P> The following is an example of how to use a key factory in order to
 * instantiate a DSA public key from its encoding.
 * Assume Alice has received a digital signature from Bob.
 * Bob also sent her his public key (in encoded format) to verify
 * his signature. Alice then performs the following actions:
 *
 * <pre>
 * X509EncodedKeySpec bobPubKeySpec = new X509EncodedKeySpec(bobEncodedPubKey);
 * KeyFactory keyFactory = KeyFactory.getInstance("DSA");
 * PublicKey bobPubKey = keyFactory.generatePublic(bobPubKeySpec);
 * Signature sig = Signature.getInstance("DSA");
 * sig.initVerify(bobPubKey);
 * sig.update(data);
 * sig.verify(signature);
 * </pre>
 *
 * <p> Every implementation of the Java platform is required to support the
 * following standard {@code KeyFactory} algorithms:
 * <ul>
 * <li>{@code DiffieHellman}</li>
 * <li>{@code DSA}</li>
 * <li>{@code RSA}</li>
 * </ul>
 * These algorithms are described in the <a href=
 * "{@docRoot}/../specs/security/standard-names.html#keyfactory-algorithms">
 * KeyFactory 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 Key
 * @see PublicKey
 * @see PrivateKey
 * @see java.security.spec.KeySpec
 * @see java.security.spec.DSAPublicKeySpec
 * @see java.security.spec.X509EncodedKeySpec
 *
 * @since 1.2
 */

public class KeyFactory {

 private static final Debug debug =
 Debug.getInstance("jca", "KeyFactory");

 // The algorithm associated with this key factory
 private final String algorithm;

 // The provider
 private Provider provider;

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

 // lock for mutex during provider selection
 private final Object lock = new Object();

 // remaining services to try in provider selection
 // null once provider is selected
 private Iterator<Service> serviceIterator;

 /**
 * Creates a KeyFactory object.
 *
 * @param keyFacSpi the delegate
 * @param provider the provider
 * @param algorithm the name of the algorithm
 * to associate with this {@code KeyFactory}
 */
 protected KeyFactory(KeyFactorySpi keyFacSpi, Provider provider,
 String algorithm) {
 this.spi = keyFacSpi;
 this.provider = provider;
 this.algorithm = algorithm;
 }

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

 /**
 * Returns a KeyFactory object that converts
 * public/private keys of the specified algorithm.
 *
 * <p> This method traverses the list of registered security Providers,
 * starting with the most preferred Provider.
 * A new KeyFactory object encapsulating the
 * KeyFactorySpi 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 name of the requested key algorithm.
 * See the KeyFactory section in the <a href=
 * "{@docRoot}/../specs/security/standard-names.html#keyfactory-algorithms">
 * Java Security Standard Algorithm Names Specification</a>
 * for information about standard algorithm names.
 *
 * @return the new {@code KeyFactory} object
 *
 * @throws NoSuchAlgorithmException if no {@code Provider} supports a
 * {@code KeyFactorySpi} implementation for the
 * specified algorithm
 *
 * @throws NullPointerException if {@code algorithm} is {@code null}
 *
 * @see Provider
 */
 public static KeyFactory getInstance(String algorithm)
 throws NoSuchAlgorithmException {
 Objects.requireNonNull(algorithm, "null algorithm name");
 return new KeyFactory(algorithm);
 }

 /**
 * Returns a KeyFactory object that converts
 * public/private keys of the specified algorithm.
 *
 * <p> A new KeyFactory object encapsulating the
 * KeyFactorySpi 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 name of the requested key algorithm.
 * See the KeyFactory section in the <a href=
 * "{@docRoot}/../specs/security/standard-names.html#keyfactory-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 KeyFactory} object
 *
 * @throws IllegalArgumentException if the provider name is {@code null}
 * or empty
 *
 * @throws NoSuchAlgorithmException if a {@code KeyFactorySpi}
 * 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 Provider
 */
 public static KeyFactory getInstance(String algorithm, String provider)
 throws NoSuchAlgorithmException, NoSuchProviderException {
 Objects.requireNonNull(algorithm, "null algorithm name");
 Instance instance = GetInstance.getInstance("KeyFactory",
 KeyFactorySpi.class, algorithm, provider);
 return new KeyFactory((KeyFactorySpi)instance.impl,
 instance.provider, algorithm);
 }

 /**
 * Returns a KeyFactory object that converts
 * public/private keys of the specified algorithm.
 *
 * <p> A new KeyFactory object encapsulating the
 * KeyFactorySpi 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 name of the requested key algorithm.
 * See the KeyFactory section in the <a href=
 * "{@docRoot}/../specs/security/standard-names.html#keyfactory-algorithms">
 * Java Security Standard Algorithm Names Specification</a>
 * for information about standard algorithm names.
 *
 * @param provider the provider.
 *
 * @return the new {@code KeyFactory} object
 *
 * @throws IllegalArgumentException if the specified provider is
 * {@code null}
 *
 * @throws NoSuchAlgorithmException if a {@code KeyFactorySpi}
 * implementation for the specified algorithm is not available
 * from the specified {@code Provider} object
 *
 * @throws NullPointerException if {@code algorithm} is {@code null}
 *
 * @see Provider
 *
 * @since 1.4
 */
 public static KeyFactory getInstance(String algorithm, Provider provider)
 throws NoSuchAlgorithmException {
 Objects.requireNonNull(algorithm, "null algorithm name");
 Instance instance = GetInstance.getInstance("KeyFactory",
 KeyFactorySpi.class, algorithm, provider);
 return new KeyFactory((KeyFactorySpi)instance.impl,
 instance.provider, algorithm);
 }

 /**
 * Returns the provider of this key factory object.
 *
 * @return the provider of this key factory object
 */
 public final Provider getProvider() {
 synchronized (lock) {
 // disable further failover after this call
 serviceIterator = null;
 return provider;
 }
 }

 /**
 * Gets the name of the algorithm
 * associated with this {@code KeyFactory}.
 *
 * @return the name of the algorithm associated with this
 * {@code KeyFactory}
 */
 public final String getAlgorithm() {
 return this.algorithm;
 }

 /**
 * Update the active KeyFactorySpi of this class and return the next
 * implementation for failover. If no more implemenations are
 * available, this method returns null. However, the active spi of
 * this class is never set to null.
 */
 private KeyFactorySpi nextSpi(KeyFactorySpi oldSpi) {
 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();
 try {
 Object obj = s.newInstance(null);
 if (obj instanceof KeyFactorySpi == false) {
 continue;
 }
 KeyFactorySpi spi = (KeyFactorySpi)obj;
 provider = s.getProvider();
 this.spi = spi;
 return spi;
 } catch (NoSuchAlgorithmException e) {
 // ignore
 }
 }
 serviceIterator = null;
 return null;
 }
 }

 /**
 * Generates a public key object from the provided key specification
 * (key material).
 *
 * @param keySpec the specification (key material) of the public key.
 *
 * @return the public key.
 *
 * @exception InvalidKeySpecException if the given key specification
 * is inappropriate for this key factory to produce a public key.
 */
 public final PublicKey generatePublic(KeySpec keySpec)
 throws InvalidKeySpecException {
 if (serviceIterator == null) {
 return spi.engineGeneratePublic(keySpec);
 }
 Exception failure = null;
 KeyFactorySpi mySpi = spi;
 do {
 try {
 return mySpi.engineGeneratePublic(keySpec);
 } catch (Exception e) {
 if (failure == null) {
 failure = e;
 }
 mySpi = nextSpi(mySpi);
 }
 } while (mySpi != null);
 if (failure instanceof RuntimeException) {
 throw (RuntimeException)failure;
 }
 if (failure instanceof InvalidKeySpecException) {
 throw (InvalidKeySpecException)failure;
 }
 throw new InvalidKeySpecException
 ("Could not generate public key", failure);
 }

 /**
 * Generates a private key object from the provided key specification
 * (key material).
 *
 * @param keySpec the specification (key material) of the private key.
 *
 * @return the private key.
 *
 * @exception InvalidKeySpecException if the given key specification
 * is inappropriate for this key factory to produce a private key.
 */
 public final PrivateKey generatePrivate(KeySpec keySpec)
 throws InvalidKeySpecException {
 if (serviceIterator == null) {
 return spi.engineGeneratePrivate(keySpec);
 }
 Exception failure = null;
 KeyFactorySpi mySpi = spi;
 do {
 try {
 return mySpi.engineGeneratePrivate(keySpec);
 } catch (Exception e) {
 if (failure == null) {
 failure = e;
 }
 mySpi = nextSpi(mySpi);
 }
 } while (mySpi != null);
 if (failure instanceof RuntimeException) {
 throw (RuntimeException)failure;
 }
 if (failure instanceof InvalidKeySpecException) {
 throw (InvalidKeySpecException)failure;
 }
 throw new InvalidKeySpecException
 ("Could not generate private key", failure);
 }

 /**
 * Returns a specification (key material) of the given key object.
 * {@code keySpec} identifies the specification class in which
 * the key material should be returned. It could, for example, be
 * {@code DSAPublicKeySpec.class}, to indicate that the
 * key material should be returned in an instance of the
 * {@code DSAPublicKeySpec} class.
 *
 * @param <T> the type of the key specification to be returned
 *
 * @param key the key.
 *
 * @param keySpec the specification class in which
 * the key material should be returned.
 *
 * @return the underlying key specification (key material) in an instance
 * of the requested specification class.
 *
 * @exception InvalidKeySpecException if the requested key specification is
 * inappropriate for the given key, or the given key cannot be processed
 * (e.g., the given key has an unrecognized algorithm or format).
 */
 public final <T extends KeySpec> T getKeySpec(Key key, Class<T> keySpec)
 throws InvalidKeySpecException {
 if (serviceIterator == null) {
 return spi.engineGetKeySpec(key, keySpec);
 }
 Exception failure = null;
 KeyFactorySpi mySpi = spi;
 do {
 try {
 return mySpi.engineGetKeySpec(key, keySpec);
 } catch (Exception e) {
 if (failure == null) {
 failure = e;
 }
 mySpi = nextSpi(mySpi);
 }
 } while (mySpi != null);
 if (failure instanceof RuntimeException) {
 throw (RuntimeException)failure;
 }
 if (failure instanceof InvalidKeySpecException) {
 throw (InvalidKeySpecException)failure;
 }
 throw new InvalidKeySpecException
 ("Could not get key spec", failure);
 }

 /**
 * Translates a key object, whose provider may be unknown or potentially
 * untrusted, into a corresponding key object of this key factory.
 *
 * @param key the key whose provider is unknown or untrusted.
 *
 * @return the translated key.
 *
 * @exception InvalidKeyException if the given key cannot be processed
 * by this key factory.
 */
 public final Key translateKey(Key key) throws InvalidKeyException {
 if (serviceIterator == null) {
 return spi.engineTranslateKey(key);
 }
 Exception failure = null;
 KeyFactorySpi mySpi = spi;
 do {
 try {
 return mySpi.engineTranslateKey(key);
 } catch (Exception e) {
 if (failure == null) {
 failure = e;
 }
 mySpi = nextSpi(mySpi);
 }
 } while (mySpi != null);
 if (failure instanceof RuntimeException) {
 throw (RuntimeException)failure;
 }
 if (failure instanceof InvalidKeyException) {
 throw (InvalidKeyException)failure;
 }
 throw new InvalidKeyException
 ("Could not translate key", failure);
 }

}