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package java.security;

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

/**
 * This class defines the <i>Service Provider Interface</i> (<b>SPI</b>)
 * for the {@code KeyFactory} class.
 * All the abstract methods in this class must be implemented by each
 * cryptographic service provider who wishes to supply the implementation
 * of a key factory for a particular algorithm.
 *
 * <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.
 *
 * <P> Key factories are bidirectional. 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> A provider should document all the key specifications supported by its
 * key factory.
 *
 * @author Jan Luehe
 *
 *
 * @see KeyFactory
 * @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 abstract class KeyFactorySpi {

    /**
     * Constructor for subclasses to call.
     */
    public KeyFactorySpi() {}

    /**
     * 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.
     *
     * @throws    InvalidKeySpecException if the given key specification
     * is inappropriate for this key factory to produce a public key.
     */
    protected abstract PublicKey engineGeneratePublic(KeySpec keySpec)
        throws InvalidKeySpecException;

    /**
     * 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.
     *
     * @throws    InvalidKeySpecException if the given key specification
     * is inappropriate for this key factory to produce a private key.
     */
    protected abstract PrivateKey engineGeneratePrivate(KeySpec keySpec)
        throws InvalidKeySpecException;

    /**
     * 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.
     *
     * @throws    InvalidKeySpecException if the requested key specification is
     * inappropriate for the given key, or the given key cannot be dealt with
     * (e.g., the given key has an unrecognized format).
     */
    protected abstract <T extends KeySpec>
        T engineGetKeySpec(Key key, Class<T> keySpec)
        throws InvalidKeySpecException;

    /**
     * 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.
     *
     * @throws    InvalidKeyException if the given key cannot be processed
     * by this key factory.
     */
    protected abstract Key engineTranslateKey(Key key)
        throws InvalidKeyException;

}
