keypairgenerator.java

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/* KeyPairGenerator.java --- Key Pair Generator Class
   Copyright (C) 1999, 2002, 2003, 2004, 2005  Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

GNU Classpath 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 for more details.

You should have received a copy of the GNU General Public License
along with GNU Classpath; see the file COPYING.  If not, write to the
Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02110-1301 USA.

Linking this library statically or dynamically with other modules is
making a combined work based on this library.  Thus, the terms and
conditions of the GNU General Public License cover the whole
combination.

As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent
modules, and to copy and distribute the resulting executable under
terms of your choice, provided that you also meet, for each linked
independent module, the terms and conditions of the license of that
module.  An independent module is a module which is not derived from
or based on this library.  If you modify this library, you may extend
this exception to your version of the library, but you are not
obligated to do so.  If you do not wish to do so, delete this
exception statement from your version. */


package java.security;

import gnu.java.security.Engine;

import java.security.spec.AlgorithmParameterSpec;

/**
 * <p>The <code>KeyPairGenerator</code> class is used to generate pairs of
 * public and private keys. Key pair generators are constructed using the
 * <code>getInstance()</code> factory methods (static methods that return
 * instances of a given class).</p>
 *
 * <p>A Key pair generator for a particular algorithm creates a public/private
 * key pair that can be used with this algorithm. It also associates
 * algorithm-specific parameters with each of the generated keys.</p>
 *
 * <p>There are two ways to generate a key pair: in an algorithm-independent
 * manner, and in an algorithm-specific manner. The only difference between the
 * two is the initialization of the object:</p>
 *
 * <ul>
 * <li><b>Algorithm-Independent Initialization</b><br/>
 *     All key pair generators share the concepts of a <i>keysize</i> and a
 *     <i>source of randomness</i>. The <i>keysize</i> is interpreted differently
 *     for different algorithms (e.g., in the case of the <i>DSA</i> algorithm,
 *     the <i>keysize</i> corresponds to the length of the modulus). There is an
 *     <code>initialize()</code> method in this <code>KeyPairGenerator</code>
 *     class that takes these two universally shared types of arguments. There
 *     is also one that takes just a <i>keysize</i> argument, and uses the
 *     {@link SecureRandom} implementation of the highest-priority installed
 *     provider as the <i>source of randomness</i>. (If none of the installed
 *     providers supply an implementation of {@link SecureRandom}, a
 *     system-provided source of randomness is used.)
 *
 *     <p>Since no other parameters are specified when you call the above
 *     algorithm-independent initialize methods, it is up to the provider what
 *     to do about the algorithm-specific parameters (if any) to be associated
 *     with each of the keys.</p>
 *
 *     <p>If the algorithm is the <i>DSA</i> algorithm, and the <i>keysize</i>
 *     (modulus size) is <code>512</code>, <code>768</code>, or <code>1024</code>,
 *     then the <b>GNU</b> provider uses a set of precomputed values for the
 *     <code>p</code>, <code>q</code>, and <code>g</code> parameters. If the
 *     <i>modulus size</i> is not one of the above values, the <b>GNU</b>
 *     provider creates a new set of parameters. Other providers might have
 *     precomputed parameter sets for more than just the three modulus sizes
 *     mentioned above. Still others might not have a list of precomputed
 *     parameters at all and instead always create new parameter sets.</p></li>
 * <li><b>Algorithm-Specific Initialization</b><br/>
 *     For situations where a set of algorithm-specific parameters already
 *     exists (e.g., so-called <i>community parameters</i> in <i>DSA</i>), there
 *     are two initialize methods that have an {@link AlgorithmParameterSpec}
 *     argument. One also has a {@link SecureRandom} argument, while the the
 *     other uses the {@link SecureRandom} implementation of the highest-priority
 *     installed provider as the source of randomness. (If none of the installed
 *     providers supply an implementation of {@link SecureRandom}, a
 *     system-provided source of randomness is used.)</li>
 * </ul>
 *
 * <p>In case the client does not explicitly initialize the
 * <code>KeyPairGenerator</code> (via a call to an initialize method), each
 * provider must supply (and document) a default initialization. For example,
 * the <b>GNU</b> provider uses a default modulus size (keysize) of
 * <code>1024</code> bits.</p>
 *
 * <p>Note that this class is abstract and extends from {@link
 * KeyPairGeneratorSpi} for historical reasons. Application developers should
 * only take notice of the methods defined in this <code>KeyPairGenerator</code>
 * class; all the methods in the superclass are intended for cryptographic
 * service providers who wish to supply their own implementations of key pair
 * generators.</p>
 *
 * @see Signature
 * @see KeyPair
 * @see AlgorithmParameterSpec
 * @author Mark Benvenuto
 * @author Casey Marshall
 */
public abstract class KeyPairGenerator extends KeyPairGeneratorSpi
{
  /** The service name for key pair generators. */
  private static final String KEY_PAIR_GENERATOR = "KeyPairGenerator";

  Provider provider;
  private String algorithm;

  /**
   * Creates a <code>KeyPairGenerator</code> object for the specified 
   * algorithm.
   *
   * @param algorithm the standard string name of the algorithm. 
   * See Appendix A in the Java Cryptography Architecture API 
   * Specification &amp; Reference for information about standard 
   * algorithm names.
   */
  protected KeyPairGenerator(String algorithm)
  {
    this.algorithm = algorithm;
    this.provider = null;
  }

  /**
   * Returns the standard name of the algorithm for this key pair generator.
   * See Appendix A in the Java Cryptography Architecture API Specification
   * &amp; Reference for information about standard algorithm names.
   *
   * @return the standard string name of the algorithm.
   */
  public String getAlgorithm()
  {
    return algorithm;
  }

  /**
   * Generates a <code>KeyPairGenerator</code> object that implements the
   * specified digest algorithm. If the default provider package provides an
   * implementation of the requested digest algorithm, an instance of
   * <code>KeyPairGenerator</code> containing that implementation is returned.
   * If the algorithm is not available in the default package, other packages
   * are searched.
   *
   * @param algorithm the standard string name of the algorithm. See Appendix A
   * in the Java Cryptography Architecture API Specification &amp; Reference for
   * information about standard algorithm names.
   * @return the new <code>KeyPairGenerator</code> object.
   * @throws NoSuchAlgorithmException if the algorithm is not available in the
   * environment.
   */
  public static KeyPairGenerator getInstance(String algorithm)
    throws NoSuchAlgorithmException
  {
    Provider[] p = Security.getProviders();
    for (int i = 0; i < p.length; i++)
      {
        try
          {
            return getInstance(algorithm, p[i]);
	  }
	catch (NoSuchAlgorithmException e)
	  {
	    // Ignored.
	  }
      }

    throw new NoSuchAlgorithmException(algorithm);
  }

  /**
   * Generates a <code>KeyPairGenerator</code> object implementing the 
   * specified algorithm, as supplied from the specified provider, if 
   * such an algorithm is available from the provider.
   *
   * @param algorithm the standard string name of the algorithm. See 
   * Appendix A in the Java Cryptography Architecture API Specification 
   * &amp; Reference for information about standard algorithm names.
   * @param provider the string name of the provider.
   * @return the new <code>KeyPairGenerator</code> object.
   * @throws NoSuchAlgorithmException if the algorithm is not available 
   * from the provider.
   * @throws NoSuchProviderException if the provider is not available in the
   * environment.
   * @throws IllegalArgumentException if the provider name is <code>null</code>
   * or empty.