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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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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 keys (opaque
cryptographic keys of type Key) into key specifications
(transparent representations of the underlying key material), and vice
versa.
 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.
 Multiple compatible key specifications may exist for the same key.
For example, a DSA public key may be specified using
DSAPublicKeySpec or
X509EncodedKeySpec. A key factory can be used to translate
between compatible key specifications.
 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:
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);

Author:
Jan Luehe
See Also:
Key
PublicKey
PrivateKey
KeySpec
DSAPublicKeySpec
X509EncodedKeySpec
Since:
1.2/**
 * Key factories are used to convert <I>keys</I> (opaque
 * cryptographic keys of type <code>Key</code>) 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</code> or
 * <code>X509EncodedKeySpec</code>. 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>
 *
 * @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.
Params:
keyFacSpi – the delegate
provider – the provider
algorithm – the name of the algorithm
to associate with this KeyFactory/**
     * Creates a KeyFactory object.
     *
     * @param keyFacSpi the delegate
     * @param provider the provider
     * @param algorithm the name of the algorithm
     * to associate with this <tt>KeyFactory</tt>
     */
    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.
 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.
 Note that the list of registered providers may be retrieved via the Security.getProviders() method. 
Params:
algorithm – the name of the requested key algorithm.
See Appendix A in the 
Java Cryptography Architecture API Specification & Reference 
for information about standard algorithm names.
Throws:
NoSuchAlgorithmException – if no Provider supports a
         KeyFactorySpi implementation for the
         specified algorithm.
See Also:
Provider
Returns:
the new KeyFactory object./**
     * 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.
     *
     * @param algorithm the name of the requested key algorithm.
     * See Appendix A in the <a href=
     * "../../../technotes/guides/security/crypto/CryptoSpec.html#AppA">
     * Java Cryptography Architecture API Specification &amp; Reference </a>
     * for information about standard algorithm names.
     *
     * @return the new KeyFactory object.
     *
     * @exception NoSuchAlgorithmException if no Provider supports a
     *          KeyFactorySpi implementation for the
     *          specified algorithm.
     *
     * @see Provider
     */
    public static KeyFactory getInstance(String algorithm)
            throws NoSuchAlgorithmException {
        return new KeyFactory(algorithm);
    }

    
Returns a KeyFactory object that converts
public/private keys of the specified algorithm.
 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.
 Note that the list of registered providers may be retrieved via the Security.getProviders() method. 
Params:
algorithm – the name of the requested key algorithm.
See Appendix A in the 
Java Cryptography Architecture API Specification & Reference 
for information about standard algorithm names.
provider – the name of the provider.
Throws:
NoSuchAlgorithmException – if a KeyFactorySpi
         implementation for the specified algorithm is not
         available from the specified provider.
NoSuchProviderException – if the specified provider is not
         registered in the security provider list.
IllegalArgumentException – if the provider name is null
         or empty.
See Also:
Provider
Returns:
the new KeyFactory object./**
     * 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 Appendix A in the <a href=
     * "../../../technotes/guides/security/crypto/CryptoSpec.html#AppA">
     * Java Cryptography Architecture API Specification &amp; Reference </a>
     * for information about standard algorithm names.
     *
     * @param provider the name of the provider.
     *
     * @return the new KeyFactory object.
     *
     * @exception NoSuchAlgorithmException if a KeyFactorySpi
     *          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 provider name is null
     *          or empty.
     *
     * @see Provider
     */
    public static KeyFactory getInstance(String algorithm, String provider)
            throws NoSuchAlgorithmException, NoSuchProviderException {
        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.
 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.
Params:
algorithm – the name of the requested key algorithm.
See Appendix A in the 
Java Cryptography Architecture API Specification & Reference 
for information about standard algorithm names.
provider – the provider.
Throws:
NoSuchAlgorithmException – if a KeyFactorySpi
         implementation for the specified algorithm is not available
         from the specified Provider object.
IllegalArgumentException – if the specified provider is null.
See Also:
Provider
Returns:
the new KeyFactory object.
Since:
1.4/**
     * 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 Appendix A in the <a href=
     * "../../../technotes/guides/security/crypto/CryptoSpec.html#AppA">
     * Java Cryptography Architecture API Specification &amp; Reference </a>
     * for information about standard algorithm names.
     *
     * @param provider the provider.
     *
     * @return the new KeyFactory object.
     *
     * @exception NoSuchAlgorithmException if a KeyFactorySpi
     *          implementation for the specified algorithm is not available
     *          from the specified Provider object.
     *
     * @exception IllegalArgumentException if the specified provider is null.
     *
     * @see Provider
     *
     * @since 1.4
     */
    public static KeyFactory getInstance(String algorithm, Provider provider)
            throws NoSuchAlgorithmException {
        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.
Returns:
the provider of this key factory object/**
     * 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 KeyFactory.
Returns:
the name of the algorithm associated with this
KeyFactory/**
     * Gets the name of the algorithm
     * associated with this <tt>KeyFactory</tt>.
     *
     * @return the name of the algorithm associated with this
     * <tt>KeyFactory</tt>
     */
    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.
/**
     * 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).
Params:
keySpec – the specification (key material) of the public key.
Throws:
InvalidKeySpecException – if the given key specification
is inappropriate for this key factory to produce a public key.
Returns:
the public key./**
     * 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).
Params:
keySpec – the specification (key material) of the private key.
Throws:
InvalidKeySpecException – if the given key specification
is inappropriate for this key factory to produce a private key.
Returns:
the private key./**
     * 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.
keySpec identifies the specification class in which
the key material should be returned. It could, for example, be
DSAPublicKeySpec.class, to indicate that the
key material should be returned in an instance of the
DSAPublicKeySpec class.
Params:
key – the key.
keySpec – the specification class in which
the key material should be returned.
Throws:
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).
Returns:
the underlying key specification (key material) in an instance
of the requested specification class./**
     * Returns a specification (key material) of the given key object.
     * <code>keySpec</code> identifies the specification class in which
     * the key material should be returned. It could, for example, be
     * <code>DSAPublicKeySpec.class</code>, to indicate that the
     * key material should be returned in an instance of the
     * <code>DSAPublicKeySpec</code> class.
     *
     * @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.
Params:
key – the key whose provider is unknown or untrusted.
Throws:
InvalidKeyException – if the given key cannot be processed
by this key factory.
Returns:
the translated key./**
     * 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);
    }

}