/* AlgorithmParameterGenerator.java --- Algorithm Parameter Generator
   Copyright (C) 1999, 2003 Free Software Foundation, Inc.

This file is part of GNU Classpath.

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package java.security;

import java.security.spec.AlgorithmParameterSpec;

import gnu.java.security.Engine;

/**
 * <p>The <code>AlgorithmParameterGenerator</code> class is used to generate a
 * set of parameters to be used with a certain algorithm. Parameter generators
 * are constructed using the <code>getInstance()</code> factory methods (static
 * methods that return instances of a given class).</p>
 *
 * <p>The object that will generate the parameters can be initialized in two
 * different ways: in an algorithm-independent manner, or in an
 * algorithm-specific manner:</p>
 *
 * <ul>
 *  <li>The algorithm-independent approach uses the fact that all parameter
 *  generators share the concept of a <i>"size"</i> and a <i>source of
 *  randomness</i>. The measure of <i>size</i> is universally shared by all
 *  algorithm parameters, though it is interpreted differently for different
 *  algorithms. For example, in the case of parameters for the <i>DSA</i>
 *  algorithm, <i>"size"</i> corresponds to the size of the prime modulus (in
 *  bits). When using this approach, algorithm-specific parameter generation
 *  values - if any - default to some standard values, unless they can be
 *  derived from the specified size.</li>
 *  <li>The other approach initializes a parameter generator object using
 *  algorithm-specific semantics, which are represented by a set of
 *  algorithm-specific parameter generation values. To generate Diffie-Hellman
 *  system parameters, for example, the parameter generation values usually
 *  consist of the size of the prime modulus and the size of the random
 *  exponent, both specified in number of bits.</li>
 * <ul>
 *
 * <p>In case the client does not explicitly initialize the
 * <code>AlgorithmParameterGenerator</code> (via a call to an <code>init()</code>
 * method), each provider must supply (and document) a default initialization.
 * For example, the <b>GNU</b> provider uses a default modulus prime size of
 * <code>1024</code> bits for the generation of <i>DSA</i> parameters.
 *
 * @author Mark Benvenuto
 * @since 1.2
 * @see AlgorithmParameters
 * @see AlgorithmParameterSpec
 */
public class AlgorithmParameterGenerator
{
  /** Service name for algorithm parameter generators. */
  private static final String ALGORITHM_PARAMETER_GENERATOR =
    "AlgorithmParameterGenerator";

  private AlgorithmParameterGeneratorSpi paramGenSpi;
  private Provider provider;
  private String algorithm;

  /**
   * Creates an <code>AlgorithmParameterGenerator</code> object.
   *
   * @param paramGenSpi the delegate.
   * @param provider the provider.
   * @param algorithm the algorithm.
   */
  protected AlgorithmParameterGenerator(AlgorithmParameterGeneratorSpi
					paramGenSpi, Provider provider,
					String algorithm)
  {
    this.paramGenSpi = paramGenSpi;
    this.provider = provider;
    this.algorithm = algorithm;
  }

  /**
   * Returns the standard name of the algorithm this parameter generator is
   * associated with.
   *
   * @return the string name of the algorithm.
   */
  public final String getAlgorithm()
  {
    return algorithm;
  }

  /**
   * Generates an <code>AlgorithmParameterGenerator</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>AlgorithmParameterGenerator</code> containing that implementation
   * is returned. If the algorithm is not available in the default package,
   * other packages are searched.
   *
   * @param algorithm the string name of the algorithm this parameter generator
   * is associated with.
   * @return the new <code>AlgorithmParameterGenerator</code> object.
   * @throws NoSuchAlgorithmException if the algorithm is not available in the
   * environment.
   */
  public static AlgorithmParameterGenerator 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 ignored) {}

    throw new NoSuchAlgorithmException(algorithm);
  }

  /**
   * Generates an <code>AlgorithmParameterGenerator</code> object for the
   * requested algorithm, as supplied from the specified provider, if such a
   * parameter generator is available from the provider.
   *
   * @param algorithm the string name of the algorithm.
   * @param provider the string name of the provider.
   * @return the new <code>AlgorithmParameterGenerator</code> object.
   * @throws NoSuchAlgorithmException if the <code>algorithm</code> is not
   * available from the <code>provider</code>.
   * @throws NoSuchProviderException if the <code>provider</code> is not
   * available in the environment.
   * @throws IllegalArgumentException if the <code>provider</code> name is
   * <code>null</code> or empty.
   * @see Provider
   */
  public static AlgorithmParameterGenerator getInstance(String algorithm,
							String provider)
    throws NoSuchAlgorithmException, NoSuchProviderException
  {
    if (provider == null || provider.length() == 0)
      throw new IllegalArgumentException("Illegal provider");

    Provider p = Security.getProvider(provider);
    if (p == null)
      throw new NoSuchProviderException();

    return getInstance(algorithm, p);
  }

  /**
   * Generates an AlgorithmParameterGenerator object for the requested
   * algorithm, as supplied from the specified provider, if such a parameter
   * generator is available from the provider. Note: the <code>provider</code>
   * doesn't have to be registered.
   *
   * @param algorithm the string name of the algorithm.
   * @param provider the provider.
   * @return the new AlgorithmParameterGenerator object.
   * @throws NoSuchAlgorithmException if the algorithm is not available from
   * the provider.
   * @throws IllegalArgumentException if the provider is null.
   * @since 1.4
   * @see Provider
   */
  public static AlgorithmParameterGenerator getInstance(String algorithm,
                                                        Provider provider)
    throws NoSuchAlgorithmException
  {
    if (provider == null)
      throw new IllegalArgumentException("Illegal provider");

    try
      {
	return new AlgorithmParameterGenerator(
	  (AlgorithmParameterGeneratorSpi) Engine.getInstance(
	    ALGORITHM_PARAMETER_GENERATOR, algorithm, provider),
	  provider, algorithm);
      }
    catch (java.lang.reflect.InvocationTargetException ite)
      {
	throw new NoSuchAlgorithmException(algorithm);
      }
    catch (ClassCastException cce)
      {
	throw new NoSuchAlgorithmException(algorithm);
      }
  }

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

  /**
   * Initializes this parameter generator for a certain <i>size</i>. To create
   * the parameters, the {@link SecureRandom} implementation of the
   * highest-priority installed provider is used 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 size the size (number of bits).
   */
  public final void init(int size)
  {
    init(size, new SecureRandom());
  }

  /**
   * Initializes this parameter generator for a certain size and source of
   * randomness.
   *
   * @param size the size (number of bits).
   * @param random the source of randomness.
   */
  public final void init(int size, SecureRandom random)
  {
    paramGenSpi.engineInit(size, random);
  }

  /**
   * Initializes this parameter generator with a set of algorithm-specific
   * parameter generation values. To generate the parameters, the {@link
   * SecureRandom} implementation of the highest-priority installed provider is
   * used 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 genParamSpec the set of algorithm-specific parameter generation
   * values.
   * @throws InvalidAlgorithmParameterException if the given parameter
   * generation values are inappropriate for this parameter generator.
   */
  public final void init(AlgorithmParameterSpec genParamSpec)
    throws InvalidAlgorithmParameterException
  {
    init(genParamSpec, new SecureRandom());
  }

  /**
   * Initializes this parameter generator with a set of algorithm-specific
   * parameter generation values.
   *
   * @param genParamSpec the set of algorithm-specific parameter generation
   * values.
   * @param random the source of randomness.
   * @throws InvalidAlgorithmParameterException if the given parameter
   * generation values are inappropriate for this parameter generator.
   */
  public final void init(AlgorithmParameterSpec genParamSpec,
                         SecureRandom random)
    throws InvalidAlgorithmParameterException
  {
    paramGenSpi.engineInit(genParamSpec, random);
  }

  /**
   * Generates the parameters.
   *
   * @return the new {@link AlgorithmParameters} object.
   */
  public final AlgorithmParameters generateParameters()
  {
    return paramGenSpi.engineGenerateParameters();
  }
}