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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).
   *
   * You should have received a copy of the GNU General Public License version
   * 2 along with this work; if not, write to the Free Software Foundation,
   * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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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 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> 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 KeySpec
   * @see java.security.spec.DSAPublicKeySpec
   * @see java.security.spec.X509EncodedKeySpec
   *
   * @since 1.2
   */
  
  public abstract class 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.
       *
       * @exception 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.
       *
       * @exception 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.
  
       * @exception 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.
       *
       * @exception InvalidKeyException if the given key cannot be processed
       * by this key factory.
       */
      protected abstract Key engineTranslateKey(Key key)
          throws InvalidKeyException;
  
  }
  