KeyPairGenerator.java

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

This file is part of GNU Classpath.

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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.
   * @see Provider
   */
  public static KeyPairGenerator getInstance(String algorithm, String provider)
    throws NoSuchAlgorithmException, NoSuchProviderException
  {
    Provider p = Security.getProvider(provider);
    if (p == null)
      throw new NoSuchProviderException(provider);

    return getInstance(algorithm, p);
  }

  /**
   * 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. Note: the provider doesn't have to be
   * registered.
   *
   * @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 provider.
   * @return the new <code>KeyPairGenerator</code> object.
   * @throws NoSuchAlgorithmException if the <code>algorithm</code> is not
   * available from the <code>provider</code>.
   * @throws IllegalArgumentException if the <code>provider</code> is
   * <code>null</code>.
   * @since 1.4
   * @see Provider
   */
  public static KeyPairGenerator getInstance(String algorithm, 
					     Provider provider)
    throws NoSuchAlgorithmException
  {
    if (provider == null)
      throw new IllegalArgumentException("Illegal provider");

    Object o = null;
    try
      {
        o = Engine.getInstance(KEY_PAIR_GENERATOR, algorithm, provider);
      }
    catch (java.lang.reflect.InvocationTargetException ite)
      {
	throw new NoSuchAlgorithmException(algorithm);
      }

    KeyPairGenerator result = null;
    if (o instanceof KeyPairGeneratorSpi)
      {
	result = new DummyKeyPairGenerator((KeyPairGeneratorSpi) o, algorithm);
      }
    else if (o instanceof KeyPairGenerator)
      {
        result = (KeyPairGenerator) o;
        result.algorithm = algorithm;
      }
    result.provider = provider;
    return result;
  }

  /**
   * Returns the provider of this key pair generator object.
   *
   * @return the provider of this key pair generator object.
   */
  public final Provider getProvider()
  {
    return provider;
  }

  /**
   * Initializes the key pair generator for a certain keysize using a default
   * parameter set and 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.)
   *
   * @param keysize the keysize. This is an algorithm-specific metric, such as
   * modulus length, specified in number of bits.
   * @throws InvalidParameterException if the keysize is not supported by this
   * <code>KeyPairGenerator</code> object.
   */
  public void initialize(int keysize)
  {
    initialize(keysize, new SecureRandom());
  }

  /**
   * Initializes the key pair generator for a certain keysize with the given
   * source of randomness (and a default parameter set).
   *
   * @param keysize the keysize. This is an algorithm-specific metric, such as
   * modulus length, specified in number of bits.
   * @param random the source of randomness.
   * @throws InvalidParameterException if the <code>keysize</code> is not
   * supported by this <code>KeyPairGenerator</code> object.
   * @since 1.2
   */
  public void initialize(int keysize, SecureRandom random)
  {
    initialize(keysize, random);
  }

  /**
   * <p>Initializes the key pair generator using the specified parameter set and
   * 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.)</p>
   *
   * <p>This concrete method has been added to this previously-defined abstract
   * class. This method calls the
   * {@link KeyPairGeneratorSpi#initialize(AlgorithmParameterSpec, SecureRandom)}
   * initialize method, passing it <code>params</code> and a source of
   * randomness (obtained from the highest-priority installed provider or
   * system-provided if none of the installed providers supply one). That
   * initialize method always throws an {@link UnsupportedOperationException}
   * if it is not overridden by the provider.</p>
   *
   * @param params the parameter set used to generate the keys.
   * @throws InvalidAlgorithmParameterException if the given parameters are
   * inappropriate for this key pair generator.
   * @since 1.2
   */
  public void initialize(AlgorithmParameterSpec params)
    throws InvalidAlgorithmParameterException
  {
    initialize(params, new SecureRandom());
  }

  /**
   * <p>Initializes the key pair generator with the given parameter set and
   * source of randomness.</p>
   *
   * <p>This concrete method has been added to this previously-defined abstract
   * class. This method calls the
   * {@link KeyPairGeneratorSpi#initialize(AlgorithmParameterSpec, SecureRandom)}
   * initialize method, passing it <code>params</code> and <code>random</code>.
   * That initialize method always throws an {@link UnsupportedOperationException}
   * if it is not overridden by the provider.</p>
   *
   * @param params the parameter set used to generate the keys.
   * @param random the source of randomness.
   * @throws InvalidAlgorithmParameterException if the given parameters are
   * inappropriate for this key pair generator.
   * @since 1.2
   */
  public void initialize(AlgorithmParameterSpec params, SecureRandom random)
    throws InvalidAlgorithmParameterException
  {
    super.initialize(params, random);
  }

  /**
   * <p>Generates a key pair.</p>
   *
   * <p>If this <code>KeyPairGenerator</code> has not been initialized
   * explicitly, provider-specific defaults will be used for the size and other
   * (algorithm-specific) values of the generated keys.</p>
   *
   * <p>This will generate a new key pair every time it is called.</p>
   *
   * <p>This method is functionally equivalent to {@link #generateKeyPair()}.</p>
   *
   * @return the generated key pair.
   * @since 1.2
   */
  public final KeyPair genKeyPair()
  {
    try
      {
        return getInstance("DSA", "GNU").generateKeyPair();
      }
    catch (Exception e)
      {
        System.err.println("genKeyPair failed: " + e);
        e.printStackTrace();
        return null;
      }
  }

  /**
   * <p>Generates a key pair.</p>
   *
   * <p>If this <code>KeyPairGenerator</code> has not been initialized
   * explicitly, provider-specific defaults will be used for the size and other
   * (algorithm-specific) values of the generated keys.</p>
   *
   * <p>This will generate a new key pair every time it is called.</p>
   *
   * <p>This method is functionally equivalent to {@link #genKeyPair()}.</p>
   *
   * @return the generated key pair.
   */
  public KeyPair generateKeyPair()
  {
    return genKeyPair();
  }
}