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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.jca.*;

import sun.security.jca.GetInstance.Instance;

/**

 * This class represents a factory for secret keys.

 *

 * <P> 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.

 * Secret key factories operate only on secret (symmetric) keys.

 *

 * <P> Key factories are bi-directional, i.e., they allow 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> Application developers should refer to their provider's documentation

 * to find out which key specifications are supported by the

 * {@link #generateSecret(java.security.spec.KeySpec) generateSecret} and

 * {@link #getKeySpec(javax.crypto.SecretKey, java.lang.Class) getKeySpec}

 * methods.

 * For example, the DES secret-key factory supplied by the "SunJCE" provider

 * supports {@code DESKeySpec} as a transparent representation of DES

 * keys, and that provider's secret-key factory for Triple DES keys supports

 * {@code DESedeKeySpec} as a transparent representation of Triple DES

 * keys.

 *

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

 * following standard {@code SecretKeyFactory} algorithms:

 * <ul>

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

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

 * </ul>

 * These algorithms are described in the <a href=

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

 * SecretKeyFactory 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 SecretKey

 * @see javax.crypto.spec.DESKeySpec

 * @see javax.crypto.spec.DESedeKeySpec

 * @see javax.crypto.spec.PBEKeySpec

 * @since 1.4

 */

public class SecretKeyFactory {

    // The provider

    private Provider provider;

    // The algorithm associated with this factory

    private final String algorithm;

    // The provider implementation (delegate)

    private volatile SecretKeyFactorySpi 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 SecretKeyFactory object.

     *

     * @param keyFacSpi the delegate

     * @param provider the provider

     * @param algorithm the secret-key algorithm

     */

    protected SecretKeyFactory(SecretKeyFactorySpi keyFacSpi,

                               Provider provider, String algorithm) {

        this.spi = keyFacSpi;

        this.provider = provider;

        this.algorithm = algorithm;

    }

    private SecretKeyFactory(String algorithm) throws NoSuchAlgorithmException {

        this.algorithm = algorithm;

        List<Service> list =

                GetInstance.getServices("SecretKeyFactory", algorithm);

        serviceIterator = list.iterator();

        // fetch and instantiate initial spi

        if (nextSpi(null) == null) {

            throw new NoSuchAlgorithmException

                (algorithm + " SecretKeyFactory not available");

        }

    }

    /**

     * Returns a {@code SecretKeyFactory} object that converts

     * secret keys of the specified algorithm.

     *

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

     * starting with the most preferred Provider.

     * A new SecretKeyFactory object encapsulating the

     * SecretKeyFactorySpi 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 secret-key

     * algorithm.

     * See the SecretKeyFactory section in the <a href=

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

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

     * for information about standard algorithm names.

     *

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

     *

     * @exception NullPointerException if the specified algorithm

     *          is null.

     *

     * @exception NoSuchAlgorithmException if no Provider supports a

     *          SecretKeyFactorySpi implementation for the

     *          specified algorithm.

     *

     * @see java.security.Provider

     */

    public static final SecretKeyFactory getInstance(String algorithm)

            throws NoSuchAlgorithmException {

        return new SecretKeyFactory(algorithm);

    }

    /**

     * Returns a {@code SecretKeyFactory} object that converts

     * secret keys of the specified algorithm.

     *

     * <p> A new SecretKeyFactory object encapsulating the

     * SecretKeyFactorySpi 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 secret-key

     * algorithm.

     * See the SecretKeyFactory section in the <a href=

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

     * 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 SecretKeyFactory} object.

     *

     * @exception NoSuchAlgorithmException if a SecretKeyFactorySpi

     *          implementation for the specified algorithm is not

     *          available from the specified provider.

     *

     * @exception NullPointerException if the specified algorithm

     *          is null.

     *

     * @throws 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 SecretKeyFactory getInstance(String algorithm,

            String provider) throws NoSuchAlgorithmException,

            NoSuchProviderException {

        Instance instance = JceSecurity.getInstance("SecretKeyFactory",

                SecretKeyFactorySpi.class, algorithm, provider);

        return new SecretKeyFactory((SecretKeyFactorySpi)instance.impl,

                instance.provider, algorithm);

    }

    /**

     * Returns a {@code SecretKeyFactory} object that converts

     * secret keys of the specified algorithm.

     *

     * <p> A new SecretKeyFactory object encapsulating the

     * SecretKeyFactorySpi 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 secret-key

     * algorithm.

     * See the SecretKeyFactory section in the <a href=

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

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

     * for information about standard algorithm names.

     *

     * @param provider the provider.

     *

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

     *

     * @exception NullPointerException if the specified algorithm

     * is null.

     *

     * @exception NoSuchAlgorithmException if a SecretKeyFactorySpi

     *          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 SecretKeyFactory getInstance(String algorithm,

            Provider provider) throws NoSuchAlgorithmException {

        Instance instance = JceSecurity.getInstance("SecretKeyFactory",

                SecretKeyFactorySpi.class, algorithm, provider);

        return new SecretKeyFactory((SecretKeyFactorySpi)instance.impl,

                instance.provider, algorithm);

    }

    /**

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

     *

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

     */

    public final Provider getProvider() {

        synchronized (lock) {

            // disable further failover after this call

            serviceIterator = null;

            return provider;

        }

    }

    /**

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

     *

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

     * {@code getInstance} calls that created this

     * {@code SecretKeyFactory} object.

     *

     * @return the algorithm name of this {@code SecretKeyFactory}

     * object.

     */

    public final String getAlgorithm() {

        return this.algorithm;

    }

    /**

     * Update the active spi 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 SecretKeyFactorySpi nextSpi(SecretKeyFactorySpi 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();

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

                    continue;

                }

                try {

                    Object obj = s.newInstance(null);

                    if (obj instanceof SecretKeyFactorySpi == false) {

                        continue;

                    }

                    SecretKeyFactorySpi spi = (SecretKeyFactorySpi)obj;

                    provider = s.getProvider();

                    this.spi = spi;

                    return spi;

                } catch (NoSuchAlgorithmException e) {

                    // ignore

                }

            }

            serviceIterator = null;

            return null;

        }

    }

    /**

     * Generates a {@code SecretKey} object from the provided key

     * specification (key material).

     *

     * @param keySpec the specification (key material) of the secret key

     *

     * @return the secret key

     *

     * @exception InvalidKeySpecException if the given key specification

     * is inappropriate for this secret-key factory to produce a secret key.

     */

    public final SecretKey generateSecret(KeySpec keySpec)

            throws InvalidKeySpecException {

        if (serviceIterator == null) {

            return spi.engineGenerateSecret(keySpec);

        }

        Exception failure = null;

        SecretKeyFactorySpi mySpi = spi;

        do {

            try {

                return mySpi.engineGenerateSecret(keySpec);

            } catch (Exception e) {

                if (failure == null) {

                    failure = e;

                }

                mySpi = nextSpi(mySpi);

            }

        } while (mySpi != null);

        if (failure instanceof InvalidKeySpecException) {

            throw (InvalidKeySpecException)failure;

        }

        throw new InvalidKeySpecException

                ("Could not generate secret key", failure);

    }

    /**

     * Returns a specification (key material) of the given key object

     * in the requested format.

     *

     * @param key the key

     * @param keySpec the requested format in which the key material shall be

     * returned

     *

     * @return the underlying key specification (key material) in the

     * requested format

     *

     * @exception InvalidKeySpecException if the requested key specification is

     * inappropriate for the given key (e.g., the algorithms associated with

     * {@code key} and {@code keySpec} do not match, or

     * {@code key} references a key on a cryptographic hardware device

     * whereas {@code keySpec} is the specification of a software-based

     * key), or the given key cannot be dealt with

     * (e.g., the given key has an algorithm or format not supported by this

     * secret-key factory).

     */

    public final KeySpec getKeySpec(SecretKey key, Class<?> keySpec)

            throws InvalidKeySpecException {

        if (serviceIterator == null) {

            return spi.engineGetKeySpec(key, keySpec);

        }

        Exception failure = null;

        SecretKeyFactorySpi 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 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 secret-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 secret-key factory.

     */

    public final SecretKey translateKey(SecretKey key)

            throws InvalidKeyException {

        if (serviceIterator == null) {

            return spi.engineTranslateKey(key);

        }

        Exception failure = null;

        SecretKeyFactorySpi 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 InvalidKeyException) {

            throw (InvalidKeyException)failure;

        }

        throw new InvalidKeyException

                ("Could not translate key", failure);

    }

}